# Forthcoming articles

Progress in Computational Fluid Dynamics, An International Journal

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 Progress in Computational Fluid Dynamics, An International Journal (47 papers in press)  Regular Issues  Effect of grooved cooling passage near the trailing edge region for HP stage gas turbine blade -A numerical investigation   by Chandrakant R. Kini, Satish Shenoy B, N. Yagnesh Sharma Abstract: Gas turbines have become one of the most important prime movers especially in aircraft propulsion, land-based power generation, and industrial applications. Cooling of gas turbine blades is a major consideration because HP stage blades are subjected to high temperature working conditions. Several methods have been suggested in the past for the cooling of HP stage blades. The main objective of the present work is to study the effect of grooved cooling passages with different geometric shapes for the groove. This method of cooling is specifically useful for cooling the blades near the trailing edge region. In an earlier work by the present authors optimized helicoidal cooling duct geometry with circular cross section was proposed and same technique has been incorporated in the present work for augmented cooling of the leading edge region. The analysis is carried out for different types of groove configuration to assess their cooling performance in terms of their cooling efficiency. The major finding of this work is that the cooling duct provided with buttress shaped grooves results in better cooling of the HP stage gas turbine blade. Keywords: numerical analysis; helicoidal duct; trailing edge; buttress shaped grooves.DOI: 10.1504/PCFD.2016.10001208  A further study of inverted hydrodynamic drafting for flow past two flexible filaments in tandem arrangement   by Fangfang Xie, Jian Deng Abstract: Two tandem filaments in a uniform flow are simulated by using a penalty immersed boundary method. First, we investigate two identical filaments, duplicating the inverted drafting". We then fix the structural parameters of the leader while vary that of the follower in $k_{b2}$ and $rho_{s2}$. It is found as the follower is stiffer or lighter than the leader, the follower flaps in larger amplitude than the leader. While the drag force acting on the follower is lower than that of the leader, which is in conflict with the so-called inverted drafting". However, if we compare the dynamics of the follower to that of an isolated filament with the same structural properties, the inverted drafting" holds again. Furthermore, we investigate the characteristic of energy transfer between filaments and their surrounding fluid. The correlation parameter $C_{lv}$ indicates the follower extracts more energy than the leader except for the cases with $rho_{s2}leq 0.2$. Keywords: Fluid-structure interaction; Flexible filaments; Hydrodynamic drafting.DOI: 10.1504/PCFD.2016.10001218  Material point method and smoothed particle hydrodynamics simulations of fluid flow problems: a comparative study   by Zheng Sun, Haiqiao Li, Yong Gan, Hantao Liu, Zhilong Huang, Lisha He Abstract: The material point method (MPM) and the smoothed particle hydrodynamics (SPH) are two commonly used particle-based methods for solving large-deformation problems. Especially, the SPH has been widely applied to fluid dynamics problems, while the MPM performance in fluid dynamics simulations has rarely been investigated. In this study, the capabilities of the MPM and the SPH in simulating fluid dynamics problems have been quantitatively examined and compared through three example problems, i.e., Poiseuille and Couette flows and water dam break flows. Both numerical methods could yield the results in good agreements with the theoretical and experimental results. Without requiring neighbor search and additional boundary particles, the MPM exhibits significantly higher computational efficiency as compared with the SPH. The comparisons also demonstrate that the MPM has higher accuracy and faster convergence than the SPH. It is shown that the MPM could be a promising alternative to the SPH for the fluid dynamics simulations. Future work for the improvement of the MPM in fluid dynamics modeling is discussed. Keywords: material point method; smoothed particle hydrodynamics; fluid flow problems; particle methods; computational fluid dynamics; Poiseuille flow; Couette flow; dam break flow.DOI: 10.1504/PCFD.2016.10001222  Fluid Flow and Heat transfer Characteristics within a Rectangular Microchannel Array of Different Manifold Shapes Modelization and Optimization Using CFD and Response Surface Methodology   by Krishna Kant, Satyender Singh, Prashant Dhiman Abstract: Different manifold shapes of microchannel device are investigated for the pressure drop characteristics under the effect of varying microchannel depth, width and spacing. The response surface methodology is applied to optimize the operating conditions of different microchannel systems. Four operating parameters, the channel width, depth, spacing and the inlet Reynolds number are considered in this study. The individual effects of these operating parameters and the combined effects of multiple operating conditions on pressure drop characteristics are examined using CFD. The semi-elliptical manifold shapes results the high level of fluid flow uniformity within microchannels and lower pressure drop. The maximum percentage reduction in the pressure drop across the microchannel device is 70%, obtained for semi-elliptical manifold shape as compared to other. The heat transfer analysis is also carried out in the extent of the study. Keywords: Microchannels; Pressure Drop; Fluid Flow; Channels; Heat transfer.DOI: 10.1504/PCFD.2016.10001422  Turbulence Model Verification and Validation in an Open Source Environment   by Daniel Wei, Seymour M.J. Spence, Ahsan Kareem Abstract: In this paper, the verification of two Low-Reynolds-Number turbulence models in an open source environment is reported. The two models are the Spalart-Allmaras model without the ft2 term and the k-\omega SST model using vorticity in production estimation. Grid convergence is achieved in all verification cases, while reasonable agreements with other codes are found. The two turbulence models are also validated through comparison with some well-known validation cases, the results of which show good agreement with experimental data. The differences between the results obtained from incompressible and compressible codes are also discussed. The impact of wall distance estimation on the performance of turbulence modeling is also evaluated through grid convergence studies.Within the realm of search algorithms for wall distance estimation, a three-level search approach is found to be necessary in order to achieve correct and converged results, especially for skewed meshes. It is shown, through a 2D bump flow grid convergence study, that the use of a one-level search approach can not only lead to a maximum friction coefficient deviation of 3.8%, but also cause an inconsistent convergence behavior. Keywords: CFD; Verification and Validation; OpenFOAM; RANS.DOI: 10.1504/PCFD.2016.10001448  Application of a Parallel Solver to the LES Modeling of Turbulent Buoyant Flows with Heat Transfer   by Ilyas Yilmaz, Hasan Saygin, Lars Davidson Abstract: An existing fully implicit, non-dissipative Direct Numerical Simulation (DNS) algorithm is reformulated to utilize the sub-grid scale (SGS) models in Large Eddy Simulation (LES). The Favre-filtered equations with low-Mach number scaling are derived. The Wall-Adapting Local Eddy-Viscosity (WALE) is used as SGS model. A fully parallel, finite volume solver is developed based on the resulting LES algorithm using PETSc library and applied to buoyancy- and thermally-driven transitional/turbulent flows in Rayleigh-Taylor instability and turbulent Rayleigh-B'{e}nard convection. Results verify that the proposed low-Mach number LES approach, which is physically more accurate than pure incompressible methods for flows with variable properties, perfectly captures the evolution and complex physics of turbulent buoyant flows with or without heat transfer by taking the e ffects of density and viscosity changes into account without the Oberbeck-Boussinesq (OB) assumption even at large temperature diff erences with uniform accuracy and efficiency. Keywords: LES; low-Mach; Variable-density; WALE; Rayleigh-B'{e}nard convection; Rayleigh-Taylor instability.DOI: 10.1504/PCFD.2016.10001451  Natural convection analysis through a radiatively participating media within a rectangular enclosure   by Fadhila Hajji, Akram Mazgar, Khouloud Jarray, Faycal Ben Nejma Abstract: A computational approach for the modeling of combined gas radiation and laminar natural convection heat transfer within a rectangular enclosure is presented. One wall among the others is maintained at a constant higher temperature (Th) while the others are of a constant lower temperature (Tc). The discrete-ordinate method (DOM) through S12 directions is applied to resolve the radiative transport equation (RTE) while the statistical narrow band correlated-k (SNBCK) model is adopted to provide gas radiative properties. The effect of radiative contribution, the enclosure tilt angle, the boundary and geometry conditions are presented. Special attention is given to the effect scales of these parameters on the average Nusselt numbers. The results show that radiative effect remarkably contributes to the acceleration of the vortexes, improving heat exchanges at walls. Keywords: natural convection; thermal radiation; non-gray gas; SNBCK; rectangular enclosure.DOI: 10.1504/PCFD.2016.10001455  ANN-GA OPTIMISATION OF RECTANGULAR FIN ARRAY WITH CLOSED TOP PLATE UNDER FORCED CONVECTION   by Pragadeesh M, Shanmughasundaram M, Balachandar C, Venkatesan Muniyandi Abstract: Heat fins play an important role in removing undesired heat generated in many electronic applications. Heat Fins are extended surfaces which are provided to enhance heat transfer. Quite a number of studies have been done on conventional open top rectangular fins. However there is a necessity to increase heat transfer rate for particular fin geometry with geometric constraints. In the present study, experiments are done in a standard heat sink with open top and closed top rectangular fins. The numerical model of rectangular fins with closed top plate under forced convection conditions is validated with the experimental results. Studies are done using commercial CFD code ANSYS FLUENT Keywords: Closed Top fins; Artificial Neural Network; Genetic Algorithm; Optimisation; Numerical.DOI: 10.1504/PCFD.2016.10001456  Large-Eddy Simulation of a Jet in Cross flow Using Local Mesh Refinement   by Thorsten Stoesser, Mehtap Cevheri Abstract: A numerical simulation of a fully developed turbulent round jet issuing normally into a laminar crossflow is performed using the method of large-eddy simulation (LES). The jet-to-crossflow-velocity ratio is 3.3 and the Reynolds number, based on crossflow bulk velocity, is Re=2100. In order to be able to employ LES efficiently for such multi-scale problems, the code utilises a local mesh refinement (LMR) algorithm and employs a multigrid method to solve the unsteady, incompressible Navier-Stokes equations on a Cartesian grid with staggered variable arrangement. The accuracy of several LMR implementations is assessed first for the Taylor-Green vortex problem. Second order accuracy of the LES-LMR code is achieved when ghost cell pressures are computed through an approximate projection method and velocities are computed using quadratic interpolation with a mass conservation condition. Three different LMR strategies for a jet in crossflow are then setup in order to assess the predictive capabilities of the method. The results of the three simulated cases are validated against similar LES and experimental data and excellent agreement with experimental data is found for medium and fine LMR grids, while the coarse LMR grid suffers from overprediction of the jet centerline speed. This study demonstrates the effectiveness and potential of LMR used for large-eddy simulations of complex high-Re flows. Keywords: Jet in Crossflow; Local Mesh Refinement; Large-eddy simulation; LES; LMR.DOI: 10.1504/PCFD.2016.10001458  Three-Dimensional ALE-FEM Method for Fluid Flow in Domains with Moving Boundaries Part II: Accuracy and Convergence   by David Carrington, Juan Heinrich Abstract: An Arbitrary Lagrangian-Eulerian numerical method for the numerical simulations of fluid flow in three-dimensional time dependent domains that uses a fixed computational mesh locally fitted to the position of the moving interfaces, developed in the first part of this work, is examined from the point of view of its accuracy and convergence properties. During the simulations, the elements adjacent to the moving interfaces continuously change shape to fit the moving interfaces; very small elements or very large aspect ratio elements may be generated to correctly describe the position and shape of the moving interfaces. These elements are then used in conjunction with the rest of the mesh elements in the calculations. The question of how the deformation and changes in the mesh affect the accuracy of the results is examined through local truncation error analysis and numerical simulations. A two dimensional flow between two plates separating at a prescribed speed, for which an analytical solution is available for both the flow and pressure fields, is used to verify and illustrate the results. In three dimensions there is a similar solution for flow between two circular disks; however, this solution is only available for the flow field and the case of viscous Stokes flow; it is also used to show accuracy and convergence properties of the velocity field. It is determined that the accuracy of the calculations is not adversely affected by the continuous deformation and the changes in the elements, and it is shown that the convergence rate of the method is of second order. In particular, the behavior of the local error next to the moving interfaces exhibits the same accuracy as in the rest of the computational domain. Keywords: Arbitrary Lagrangian-Eulerian finite element method; time dependent domain; fixed mesh formulation; three-dimensional flow simulations; error analysis moving mesh. Three Dimensional Simulation of Transom Stern Flow at Various Froude Numbers and Trim Angles   by Parviz Ghadimi, Mohammad A. Feizi Chekab, Abbas Dashtimanesh, Seyed Hamid R. Mirhosseini Abstract: Numerical simulation of transom stern flow has proven to be an interesting topic, but a complicated task in the hydrodynamic field of research. In this paper, a three dimensional numerical simulation is presented using Ansys-CFX to survey the free surface flow, downstream of the transom stern. To this end, Finite volume method coupled with volume of fluid is utilized and k-ε turbulent model is applied. The numerical solutions are validated by comparing the findings against the results of empirical formula available in the literature. In order to conduct a parametric study, four different Froude numbers, four trim angles, and two deadrise angles are considered and the effect of each of these parameters is studied. Keywords: Transom Stern; Three Dimensional Simulation; Parametric Study; Ansys-CFX; Free Surface Modeling.DOI: 10.1504/PCFD.2016.10001459  Analytical benchmark solution for Stokes flow with variable viscosity in spherical sublayerby Igor Popov, Ilya Makev, Irina Blinova Abstract: . Keywords: . Explicit Staggered grid scheme for rotating shallow water equations on geostrophic flowsby Putu Harry Gunawan, Sri Redjeki Pudjaprasetya Abstract: . Keywords: . Three-Dimensional ALE-FEM Method for Fluid Flow in Domains with Moving Boundaries Part I: Algorithm Description   by David Carrington, Juan Heinrich Abstract: A three-dimensional finite element method for the numerical simulations of fluid flow in domains containing moving rigid objects or boundaries is developed. The method falls into the general category of Arbitrary-Lagrangian-Eulerian Finite Element methods; it is based on a fixed mesh that is locally fitted at the moving interfaces and recovers its original shape once the moving interfaces go past the elements. The moving interfaces are defined by independent sets of marker points so that the global mesh is not affected by the interfaces motion and the possibility of mesh entanglement is eliminated. The result is an efficient and fully robust formulation for multi-physics simulations on domains of complex geometry with moving boundaries or devises also of complex geometry that is never in danger of the mesh becoming unsuitable due to its continuous deformation, thus eliminating the need for repeated re-meshing and interpolation. The boundary conditions on the interfaces are of Dirichlet type and are imposed exactly, and the total domain volume is always calculated exactly thus automatically satisfying the geometric conservation law. This work supports the internal combustion engines simulator KIVA developed at Los Alamos National Laboratories; in this paper only the interface moving aspect is addressed, and this is done in the context of simple laminar incompressible flows. A validation is presented via a problem with an analytical solution for the flow field that shows second order accuracy, and the models capabilities are illustrated through application in realistic geometrical settings that prove it to be extremely efficient and show the robustness and flexibility of the technique to perform simulations involving moving boundaries undergoing large displacements in a three-dimensional domain. Keywords: Arbitrary Lagrangian-Eulerian finite element method; time dependent domain; fixed mesh formulation; three-dimensional flow simulations.DOI: 10.1504/PCFD.2016.10001470  Experimental and numerical investigation on a liquid jet impinging on a vertical superhydrophobic surface: spreading and reflection   by Ali Kibar Abstract: In this study, the flow characteristics of an impinging circular liquid jet on a superhydrophobic surface are examined both experimentally and numerically. A Computational Fluid Dynamics (CFD) program was used for comparison in terms of experimental results, and data from the literature was used to reveal phenomena related to the spreading and reflection of a liquid jet from a superhydrophobic surface. A piece of Brassica oleracea leaf with an apparent contact angle of 160 Keywords: liquid jet; CFD; superhydrophobic; reflection jet; Volume-of-Fluid (VOF) method.DOI: 10.1504/PCFD.2017.10004671  Numerical Investigation of Slug Characteristics in a Horizontal Air/Water and Air/Oil Pipe Flow   by Abdalellah O. Mohmmed, Mohammad S. Nasif, Hussain H. Al-Kayiem Abstract: In the present work, the transition from stratified flow to slug flow regime for air-water and air-oil two-phase flow was simulated and analysed numerically. The simulation was carried out by numerically solving a three dimensional (3D) implicit unsteady Volume of Fluid model (VOF). Typical slug characteristics, such as slug length, slug translational velocity, and slug frequency were determined. The numerical results were validated by comparison with experimental results and a reasonable agreement with an error less than 8.7% was achieved. Moreover, the results from the proposed model were compared to the results obtained from three empirical correlations for the two-phase slug flow and it demonstrated a good agreement. The simulation results demonstrated that for the same boundary conditions, the characteristics in terms of slug initiation and slug growth were strongly affected by the fluid properties. The simulation results also show that for air-oil flow, the pressure drop, slug translational velocity, and slug frequency values were less than in air-water flow by 2.9%, 14.3%, and 7.9%, respectively. Keywords: CFD; Numerical Simulation; Slug Flow; Slug Characteristics; Volume of Fluid.DOI: 10.1504/PCFD.2017.10006061  The Numerical Analysis of a Large Diameter Spherical Valve   by Shidong Li, Zhiyong Wu Abstract: Abstract: Due to low losses in pressure, a large flow coefficient, being lightweight and having good sealing performance, the spherical valve is widely used in hydropower plants. The hydraulic performance of a spherical valve is significant in ensuring that hydropower plants work efficiently, steadily, and above all, safely. However, it is almost impossible to conduct live experimental studies on a larger-sized spherical valve in the laboratory. In this paper, the hydraulic performance of a spherical valve with a diameter of 1100 mm was numerically studied. Three-dimensional numerical simulations were conducted with the commercial software ANSYS-CFX Keywords: Large diameter spherical valve • Computational Fluid Dynamics • Flow coefficient • Flow patterns. Numerical insight into multisize particulate flow field through rotating channel   by Pankaj Kumar Gupta Abstract: Detailed insight into dense multisize particulate flow field in a straight channel subject to spanwise system rotation is presented for the first time. Mathematical modelling employs Eulerian-Eulerian (continuum-mechanical) approach accounting for the broad particle size distribution that is common place in industrial slurries. Numerical formulation utilizes Galerkin FEM using Q1Q0 elements. Besides counter-intuitive observations in velocity flow field, the effects of varying system rotation rates and flow Reynolds number indicate interesting interplay between turbulence, Coriolis force and centrifugal force on the dense solid-liquid flow field. Keywords: Rotating channel; multisize particulate flow; Coriolis acceleration; system rotation; solid-liquid flow; GFEM. Towards the simulation of supercooling and convection in Phase change materials using a thermal lattice Boltzmann method   by HASSANE NAJI, Alissar Yehya Abstract: The use of phase-change materials (PCM) in building materials is becoming increasingly popular in the building sector. However, the presence of certain phenomena such as convection and supercooling may affect the fusion times and, consequently, the design of PCMs. Supercooling can have a noteworthy impact on the system performance. Moreover, convection alters the shape of the phase-front and should also be taken into account. Thereby, we propose here a thermal lattice Boltzmann model (TLBM) to simulate the phase-change problem with convection and supercooling. The numerical findings show that convection and supercooling phenomena are successfully taken into consideration. In addition, where appropriate, supercooling results exhibit a delay for the propagation of the solid-liquid interface. This proves that consideration of such a phenomenon in numerical modeling remains paramount for better design of PCM design. Keywords: Thermal lattice Boltzmann Method; Phase change materials; Supercooling; Melting; Nucleation; Convection. Flow Behavior and Drag Coefficients of Spherical Bubbles in Surfactant-laden Carreau Model Fluids   by Nanda Kishore Abstract: The flow and drag phenomena of contaminated spherical bubbles in columns filled with surfactant-laden Carreau model fluids is numerically investigated using a computational fluid dynamics based commercial solver, COMSOL Multiphysics 4.3b. The effect of contaminants is incorporated in the solver by the use of the spherical stagnant cap model. The numerical solver is thoroughly benchmarked through extensive validation with the existing literature results. Further new simulations are performed over wide range of the conditions as the Reynolds number (Re) varying in the range of (0 100), the power law index (n) ranging between (0.2 0.8), the Carreau number (Λ) varying in the range of (1 100) and the degree of contamination (α) ranging between (0 180 Keywords: Bubble; Contamination; Carreau model fluid; Stagnant cap; Drag; Carreau number.DOI: 10.1504/PCFD.2017.10005402  Numerical simulation of mixing vanes on flow and heat transfer characteristics in 5   by Li-Xin Yang, Meng-Jun Zhou Abstract: Single-phase heat transfer characteristics in a pressurized water reactor (PWR) fuel assembly are important. Many investigations have studied flow features in a 5 Keywords: CFD; Mixing Vane; Flow; Heat transfer. Influence of turbulence RANS models on heat transfer coefficients and stress distribution during thermal-FSI analysis of power turbine guide vane of helicopter turbine engine PZL-10W taking into account convergence of heat flux   by Kamil Banas, Janusz Badur Abstract: In this work we present thermal-FSI analysis of a power turbine guide vane of turbine helicopter engine PZL-10W. Firstly CFD conjugate heat transfer analyses were carried out, then stress analyses were performed with boundary conditions obtained via CFD analyses. Influence of turbulence RANS models on heat transfer coefficients and stress distribution were investigated in detail . We used eddy-viscosity SST and γ Reθ SST transition models and two second closure: RSM and WJ-BSL-EARSM. In addition, effect of mass flow rate of rotor disc cooling fluid on stress distribution was examined. Moreover, we discuss heat flux convergence in vane on temperature and stress distribution. In order to model a material effort the Burzynski parabolic model was implemented. Keywords: thermal-FSI; conjugate heat transfer; thermal stresses; turbine guide vane; Burzynski stresses; influence of RANS on stresses; convergence of heat flux. Numerical simulations of fin and tube air cooler and heat and mass transfer in cold storage   by Kamil Smierciew, Miroslawa Kolodziejczyk, Jerzy Gagan, Dariusz Jozef Butrymowicz Abstract: Fin-and-tube heat exchangers are extensively used in refrigeration systems applied to cold storage. Performance of the heat exchanger strongly affects the efficiency of refrigeration systems. Prediction of temperature, humidity, as well as velocity distribution in cold storage chamber requires accurate prediction of the finned air cooler operation. The operation of the air cooler unit is usually taken into account by the investigators, but with very simplified geometry and physics. Results of numerical modelling of cold storage chamber equipped with the fin-and-tube air cooler are presented in the paper. Porous media conditions were applied for the analysed heat exchanger modelling. The numerical results were evaluated on the basis of the experimental data. Good agreement between numerical and experimental results was achieved. Keywords: fin-and-tube; heat exchanger; CFD; porous media; cold storage; heat transfer modelling. Numerical study of thermal stratification in hot water storage tank   by Robert Smusz Abstract: Thermal stratified storage tanks are an effective tool to improve the efficiency of solar thermal systems. Stratification improves the overall performance of the systems by increasing the efficiency of solar collectors. Modelling of thermal stratification in storage tanks is an important topic for the optimization of storage tanks in thermal systems. This paper presents the results of numerical calculations of temperature and velocity fields in the domestic hot water storage tank equipped with three helical-shaped heating coils and cylindrical- shaped stratification device during the heating process. A 2D-axisimmetric computational fluid dynamic (CFD) model was performed. The results of the simulations were used to analyse the flow characteristics and the thermal stratification development during the charging process of the storage tank. The standard kepsilon turbulence model with full buoyancy effects and default turbulent constants were used for the analysis. Numerical simulations were compared with experimental results obtained on test stand with the model of hot water storage tank. Results of the comparison indicate the suitability of the applied numerical model. Keywords: numerical simulations; thermal stratification; storage tank. Numerical analysis of the oscillation frequency of the shock wave and the evaporation level on the Mach disc in the IMP PAN nozzle   by Sebastian Kornet, Janusz Badur Abstract: In the present paper we have focused on the phenomena occurring in the supersonic part of the de Laval nozzle, characterized by oscillation of the shock wave in the steam flow. The effect of the shock oscillation was observed by using the Tӧpler optical system in the IMP PAN experiment carried out on a symmetrical planar de Laval nozzle. Having observed the shock fluctuation in the wet steam flow, according to Puzyrewskis observations, we analysed the oscillation frequency in the IMP PAN nozzle depending on the pressure conditions. Additionally we analysed the evaporation level of condensate droplets during passage through the Mach disc depending on the inlet conditions. The model of a single continuum Wet Stem model with a special microstructure growing up during phase transitions was validated on an experiment carried out by Dykas et al. in 2013 on the half arc nozzle. The present work includes simulations results of oscillation frequency of the shock wave and the evaporation level of the liquid phase on the Mach disc. Keywords: shock wave; de Laval nozzle; Mach disc; lambda-foot; wet steam; evaporation level. Investigation of thermal interactions between the exhaust jet and airplane skin in small aircrafts   by P. Lapka, M. Seredynski, P. Furmanski Abstract: An advanced numerical model of the exhaust jet and its thermal interaction with the aircraft body (fuselage, wings and flaps) was developed in this paper and then applied for investigations of two aircraft prototypes in different configurations. Both airplanes were equipped with new turboprop engines. Therefore their new exhaust systems should be carefully analysed. The first of the investigated airplanes in the tractor configuration with one engine located in the fuselage (TR1) had the exhaust outlets below the nacelle. The second one was also in the tractor configuration with two engines located on the wings (TR2) and had the exhaust outlets on the rear part of the nacelles. The aim of the performed analyses was to check if the exhaust systems were properly designed and streams of hot exhaust gases would not contribute to airplane cover softening or even melting for the most adverse flight conditions. Keywords: exhaust jet; heat and fluid flow; numerical analysis; small aircraft; thermal radiation. A Numerical Study of Rayleigh-Taylor Instability for Various Atwood Numbers Using ISPH Method   by Mehmet Tildiz, Nima Tofighi, Amin Rahmat Abstract: In this paper, the wall bounded single-mode Rayleigh Taylor Instability (RTI) for a two-phase immiscible fluid system in a con ned domain is investigated numerically for various Atwood numbers. Governing equations are discretized using the Smoothed Particle Hydrodynamics (SPH) method. A robust numerical scheme is used to simulate the RTI phenomenon and in order to model the fluid-flow in the vicinity of the interface, transport parameters such as density and viscosity are smoothed using color function. The surface tension force is coupled to the momentum equation using Continuum Surface Force (CSF) model. It is shown that in general the RTI evolves in three distinct stages, namely linear stability, mushroom-head formation and long-term evolution. The growth rate in the rst stage, i.e. the linear instability, shows good agreement with the analytical solution in the literature. The qualitative and quantitative results of second and third stages are introduced and relevant discussions are made. Keywords: Smoothed Particle Hydrodynamics; Multi-Phase Flow; Interfacial Flow; Rayleigh-Taylor Instability; Atwood number. Adjoint method based inverse design of transonic compressor cascade with boundary layer control   by B. Ziegler Abstract: Gradient based methods for inverse design and optimisation are powerful tools for CFD based aerodynamic design. For problems characterised by large number of design variables, the computational effort of gradient based optimisation can be however prohibitively high. In this work, a numerical approach for which the number of design variables has insignificant effect on computational effort is used. Adjoint approach is a suitable methodology for handling inverse design or optimisation of complex geometries with single objective functional. In this work inverse design of 2D transonic compressor cascade with target pressure distribution chosen for later use of active boundary layer control is presented. High aerodynamic loading inviscid design is performed and then adapted for viscous flow with steady tangential blowing boundary layer control and investigated with RANS analysis. Keywords: inverse design; transonic flows; adjoint method; turbomachinery; boundary layer control. 3D Numerical Calculations of Tangent Leakages in Scroll Compressor During Unsteady Process   by Jozef Rak, Slawomir Pietrowicz, Zbigniew Gnutek Abstract: A continuous increase in computing power brought progress in a scroll compressor modelling. The early, simplified, models now can be supplemented with a significantly more detailed spatial CFD models. These models require a high resolution meshes due to the characteristics of the positive displacement machines. The working chambers geometries are evolving in time due to the vanes movement. For that reason a moving boundary conditions have to be applied to the numerical model. This entails it necessary to use a mesh deformation and to modify the solved equations so they are correct in the changing reference system. In order to remain a high mesh quality a procedurernfor remeshing also has to be introduced. In return the solution gives a better insight into the process compared to the simplified models. In the paper a numerical spatial scroll compressor model with a mesh generation procedure is presented. The calculations were performed for different values of the radial clearances between scroll wraps. The clearance causes a leakage between higher and lower pressure chambers and affect their mass and energy balance. A comparison between the numerical and an analytical solution was used as a benchmark for the results Keywords: scroll compressor; mesh generation; CFD; moving boundary; radial clearance.DOI: 10.1504/PCFD.2017.10007945  Towards Reduction of Computational Cost for Large-Scale Combustion Modeling with a Multi-Regional Concept   by Feichi Zhang, Thorsten Zirwes, Peter Habisreuther, Henning Bockhorn Abstract: Objective of the work is to validate the feasibility and the performance gain of a multi-regional approach, which has the potential to improve computing performance significantly for large-scale modelling of combustion processes. The basic idea is to solve the non-reactive, less CPU-intensive domain within the burner and the much more CPU-intensive domain with the flame downstream, separately. For the fresh gas flow within the nozzle, only the fundamental Navier-Stokes equations are solved, whereas complex combustion models accounting for the combustion reactions are switched on after the fresh mixture has left the burner exit. The methodology has been implemented into the OpenFOAM code and applied to a large eddy simulation of a turbulent, premixed methane/air flame. The multi-zonal simulation has shown a very good agreement with results obtained from the conventional single-regional. The multi-regional modelling, however, has been proved to be considerably faster than the single-zonal computation. Keywords: OpenFOAM; large eddy simulation; LES; multi-regional simulation; turbulent combustion; high performance computing; HPC. Numerical analysis of sloshing impact in horizontally excited prismatic tanks   by Hyunjong Kim, Yoon-Hwan Choi, Yeon-Won Lee Abstract: This paper reports the sloshing loads and visual analysis in a prismatic tank under violent sloshing conditions. The Volume of Fluid (VOF) method is used to perform multi-phase analysis of sloshing phenomena. The prismatic shape is an important parameter to estimate safety against sloshing effects. Horizontal motion is considered for periodic excitation motions. Six cases are used for simulating the sloshing loads. The results show the occurrence of the Bagnold and Wagner type impact pressure loads due to violent sloshing. This study also discusses the variable pressure loads when the upper and lower chamfered shapes are changed. Also, the effects of chamfered shapes and sloshing load distributions in the prismatic tank are visualized in this paper. Keywords: sloshing; prismatic tank; computational fluid dynamics. Numerical Investigation of flow and heat transfer from a block placed in a cavity subject to different inlet conditions   by Selvaraj Kumar Rakesh, Parthasarathy Rajesh Kanna, Jan Taler, Paweł Oclon, Dawid Taler, Ranish Sudhakaran Sudhakaran, G. Ramesh Abstract: Numerical simulation is carried out for laminar incompressible fluid flow over a solid block placed in a cavity for different positions of the inlet with a fixed Aspect ratio (AR) of 1 for the cavity. The square block is placed inside the geometric center of square cavity and maintained at a fixed higher temperature. The simulation is carried out for different positions of the inlet and results reported in terms of streamline contour, velocity profile, Nusselt number distribution. The governing equations are solved by finite volume based commercial Fluent software. The simulation of the fluid flow is carried out with Reynolds number equal to 100. The diagonal vortices formed normal to inlet and exit. The peak Nusselt number occurred at top solid wall and average Nusselt number increases when Reynolds number is increased. Keywords: CFD; block in a cavity; inlet flow; Nusselt number. Benchmarking the material point method for interaction problems between the free surface flow and elastic structure   by Zheng Sun Abstract: Numerical simulation of fluid structure interaction (FSI) problems is a significant and interesting field in computational fluid dynamics (CFD). The material point method (MPM), a relatively novel particle-based method, is extended and benchmarked for simulating interactions between the free surface flow and elastic structure. In the MPM method, both the fluid and structure media are described by Lagrangian particles and the unified governing equations are solved in the Eulerian background mesh and the no-slip boundary condition between the fluid and structure can be satisfied automatically, which imply that the MPM method would be a promising scheme for FSI problems. Three validated test cases are presented. The first one is oil flow in a sloshing tank interacting with an elastic bar, and the second test case is water dam-break flow through an elastic gate, and the last one is water dam-break flow past an elastic obstacle. The results obtained by the MPM method are in good agreement with published experimental results and other numerical simulations, which confirm that the MPM method is a promising and effective numerical algorithm for FSI problems involving the free surface flow. Keywords: fluid structure interaction (FSI); free surface flow; material point method (MPM); computational fluid dynamics (CFD); monolithic approach; sloshing; dam break. Modelling of vortex breakdown and calculation of large scale kinetic energy on a slender delta wing using URANS and Reynolds-stress modelling   by Zinon Vlahostergios, Dimitrios Komnos, Kyros Yakinthos Abstract: A computational study regarding the accurate modelling of the unsteady flow over a slender delta-wing and the vortex breakdown (VB) identification by adopting a Reynolds-stress turbulence model is presented. The VB is identified by the pressure distributions, the stagnation point inside the vortex core and the vorticity development over the delta-wing. Additionally, the whole range of the unsteady flow field kinetic energy, which is divided into two regions, is calculated. The first region is related to the modelled turbulent small scales and the second to the resolved large scales, which are produced due to the VB. The distributions of the small-scale, the large-scale and the total kinetic energy along the vortex core are presented, providing information regarding their development during VB. The results show that the adoption of URANS with an advanced/sophisticated turbulence model, is able to identify and describe with consistency the VB onset and its development over a slender delta-wing. Keywords: Delta wing; Vortex breakdown; URANS; Large/small scales; Reynolds-stress model. Lattice Boltzmann simulation of the cubic magnetoconvection with coupled Revised Matrix (RM)-Multiple Relaxation Time (MRT) model   by Mohamed Hamdi, Souheil Elalimi, Sassi Ben Nasrallah Abstract: Lattice Boltzmann Method (LBM) with Revised Matrix RM-D3Q19 coupled with Multiple Relaxation Time MRT-D3Q7 model is proposed for the first time to study the effect of external magnetic fields on heat transfer in a cubical cavity subjected to horizontal temperature difference. Heat transfer and flow patterns are predicted for fluid with low Prandtl number ranging from 0.05 to 0.15 and a range of Rayleigh number between 103 and 106, the Hartmann number up to 60 while the inclination angle of the magnetic field about the horizontal is between 0 Keywords: LBM; RM-D3Q19; MRT-D3Q7; cubic; magnetoconvection; inclination angle. Development of a model for unsteady conjugate heat transfer simulations   by Stefan Voigt, Berthold Noll, Manfred Aigner Abstract: Recent developments in CFD simulations go towards higher accuracy by using time-resolved simulations instead of steady RANS simulations and adding solid structures to the simulation instead of assuming constant wall temperatures or heat fluxes at wall boundaries. This makes the simulations very expensive. Another problem in near-wall heat transfer is the often used assumption of a constant turbulent Prandtl number Prt, which is not correct for many flow configurations.rnThe present work therefore focusses on the development of a methodology for accelerated unsteady CHT simulations. Furthermore the implementation of a near-wall heat transfer model that does not rely on a constant Prt was evaluated. The models are implemented in ANSYS CFX.rnThe validation of the turbulent heat transfer model shows improved agreement with experimental results compared to a constant Prt approach. The improved unsteady CHT methodology gives the same accuracy of the results as the implicit unsteady CHT model with less computational time. Keywords: CFD; Conjugate Heat Transfer; Unsteady CHT simulation; turbulent heat transfer modelling. Gasifying Agents Type At Lower Temperature Effect On Bubbling Fluidized Bed Gasification For Low Rank Coal   by Kamariah Md Isa, Kahar Osman, Nik Rosli Abdullah, Nor Fadzilah Othman, Mohd Norhakem Hamid Abstract: Oxygen and steam as gasifying agents are preferred for gasification process compared to air due to the production of higher heating value of syngas and lower contents of diluents. Lower operating temperature is required for Low Rank Coal (LRC) gasification process. This is because, carbon conversion will occur faster with high reactivity of LRC. Ash agglomeration formation is also prevented at lower operating temperature. Hydrodynamics of bubbling fluidization and gasification process are expected to be affected with different gasifying agents and operating temperature. Computational Fluid Dynamics (CFD) method was used to select suitable superficial velocity for Bubbling Fluidized Bed (BFB) simulation and explore the effects of different gasifying agents at a lower operating temperature. The model was validated with theoretical values and superficial velocities of 3 to 4 times the minimum velocity (3∼4Umf) were selected due to its best uniform bubbling fluidization. Different gasifying agents will produce different bubbling patterns which relates to the density and viscosity of the gasifying agents. Many and faster moving bubbles were produced when using oxygen and air at 1073K while no changes is detected when using steam. This concludes that air and oxygen as gasifying agents give higher effect to the bubbling hydrodynamics compared to selection of steam as gasifying agent. Keywords: Computational Fluid Dynamics; Bubbling Fluidized Bed Gasifier; Low Rank Coal Gasification; Gasifying Agent. Flow simulation over a triangular labyrinth side weir in a rectangular channel   by Ali Naghi Ziaei, Neda Nikou, Ali Beyhaghi, Fatemeh Attarzadeh, Saeed Reza Khodashenas Abstract: Labyrinth side weirs are used as regulator outlets in river diversion structures‎, ‎water conveyance systems and sewer networks‎. ‎Herein‎, ‎the flow around triangular labyrinth side weir with three different included angles (θ= 45‎, ‎60 and 90 Keywords: Numerical Modeling‎; ‎Boundary Condition‎s; ‎Discharge Coefficient‎; ‎Flow Pattern. FILM COOLING EFFECTIVENESS PREDICTIONS IN THE REGION OF THE BLADE-ENDWALL JUNCTION CORNER WITH INJECTION ASSISTED BY THE RECIRCULATING VORTEX FLOW   by Kypros Milidonis, Demos Georgiou Abstract: The region around the blade leading edge - endwall junction in Inlet Guide Vanes (IGV) of gas turbines presents one of the most difficult hot spots to be cooled within the blade passage, largely due to the presence of strong three dimensional flows which displace the coolant away from the region before it can provide adequate cooling. The present study investigates via RANS-based simulation the film cooling effectiveness of a novel slot injection in which the coolant is ejected in such a way that its cooling effectiveness is assisted by the presence of the local three dimensional flows (especially the horseshoe vortex) that dominate the junction area. The computational predictions indicate that the proposed injection geometry provides a very effective cooling method for addressing the high heat transfer rate around the problematic region. The predicted three-dimensional flow topology and the associated endwall heat transfer are presented and discussed in order to elucidate the physical mechanisms that lead to the successful film cooling effectiveness of the proposed injection slot. Keywords: Blade-endwall junction flows; horseshoe vortex; endwall film cooling; Turbomachinery; three-dimensional flows. CONTROL OF SELF-SUSTAINED OSCILLATIONS OF A THREE-DIMENSIONAL WATER JET IN A SLENDER CHANNEL   by AMINA MATAOUI, NORA BENSIDER, MOHAMED Aksouh Abstract: This work focuses on control of an oscillatory jet submerged in a thin parallelepipedic cavity of small thickness/width ratio (W/b=0.16), by means of two opposite injections arranged at the same height, on the thinnest sidewalls of the cavity, perpendicular and above its exit. In many engineering applications, this type of control is required when the characteristics of the main jet (Reynolds number, nozzle size) are set and not controllable. The objective of this work is about control of the jet deviation toward the thinner sidewall and its oscillations frequency, according the flow rate of the two lateral injections. Unsteady, three-dimensional problem is solved by finite volume method using URANS modeling. The validation confirms that second order model predicts more accurately this flow configuration than first order models. A parametric study is conducted according the flow rates ratios ( Keywords: Submerged jet; Self-sustained Oscillations; Turbulence; Thin cavity; thrust vectoring; Coanda effect. Numerical study of capillary driven flow in square micro-channel by Lattice Boltzmann Method.   by Mohamed El Amine Ben Amara, Patrick Perré, Abdolreza Kharaghani, Sassi Ben Nasrallah Abstract: This paper presents an investigation into capillary rise dynamics in a vertical square microchannel based on the lattice Boltzmann method with the Shan-Chen multiphase model. Several different numerical test problems are carried out to validate the model and to provide parameter information, which is then used to simulate the wetting fluid rise in a square tube. The numerical simulation results depict fast flow and accumulation of liquid in the capillary corners. The dynamics of the liquid penetration into a square capillary is also illustrated, which reveals the occurrence of oscillations at the initial time before the liquid reaches a stable regime. Furthermore, the streamlines inside the square capillary as well as the density profiles are obtained by the numerical simulations. The results show the existence of recirculation zones in the cross section and in the inlet region of the micro-channel. The dynamic contact angle was clearly observed via the numerical simulations. Finally, the dynamics of capillary rise were also studied for the micro-channel in which a thin vertical plate was integrated. Keywords: Capillary rise; Lattice Boltzmann Method; Shan-Chen model; corner liquid films. Application of different k-e turbulence models on combustion process modelling in small-scale pellet stoves for household heating   by Zagorka Brat, Nebojša Manić, Dragoslava Stojiljković, Marta Trninić Abstract: Constant demand for development and construction improvement of small-scale pellet stoves and boilers (nominal power up to 50 kWth) for household heating leads to conclusion that appropriate upgrading should be done on that field. Optimization of stove construction should be performed based on results of experimental tests, as well as results of numerical analysis and mathematical modelling of combustion process. This is compulsory, because stove construction shall comply with demands for energy and environmental characteristics defined in appropriate quality standards. Besides, stove should operate with pellets of different quality, produced from various biomass raw materials. Considering that numerical analysis is less time consuming process than experimental tests, nowadays it is more often used for development and improvement of combustion appliance construction. As the turbulence modelling is one of the key parts in the eligible numerical analysis, the aim of the research presented in this paper is to define the influence of different k-e turbulence models and their application on defined CFD mathematical model of combustion process in small-scale pellet stove for household heating. Keywords: small-scale pellet stove; turbulence model; combustion; CFD. Modelling of Friction Stir Welding Processes with a Coupled Immersed Boundary- / Volume of Fluid-Approach   by Uwe Janoske, Markus Burger, Tobias Geiger Abstract: Friction stir welding (FSW) is an alternative to conventional joining processes for aluminium. Due to the process temperature which is below the liquidus temperature of the material, numerous problems can be avoided compared to conventional techniques. The modelling of the process was subject of different numerical approaches in the past. In this work, the FSW shall be modelled by an immersed boundary method capable of describing arbitrary movements of the tool. The materials which have to be joint are modelled by different phases in a volume of fluid method (VOF). Using this approach, the intermixing of the phases, the temperatures in the materials as well as the acting forces on the tool can be obtained. The focus in this paper is on the evaluation of the temperature distribution in FSW. Treating each material as a separate phase makes this model suitable for joining different materials. Keywords: CFD; Friction Stir Welding (FSW); Volume of Fluid (VOF); Immersed Boundary (IB). Computational and Experimental Study of Swirl Flow within SI Engine with Modified Shrouded Intake Valve   by Bidesh Roy, Rahul Dev Misra, Krishna Murari Pandey, Abhijit Sinha, Bachu Deb Abstract: Swirling flow can be used in a spark-ignition engine to increase turbulence intensity of the working fluid in the engine by using a shrouded intake valve. However, on using shrouded intake valve, a greater restriction to the incoming fluid is offered. In this backdrop, a computational and experimental study of swirl flow within the spark-ignition engine with a modified shrouded intake valve has been carried out, and the same is then compared with 100o, 120o and 180o shrouded intake valves. The results show that the fluid flow patterns generated by the intake valves within the engine cylinder are similar in nature. The engine with the modified shrouded intake valve generates a substantial amount of swirl with comparatively lesser restriction to the incoming fluid. Whereas, the engine using other types of intake valves, either generates higher swirl ratio with lower mean flow coefficient or lower swirl ratio with higher mean flow coefficient. Keywords: CFD; Mean flow coefficient; Modified shrouded intake valve; Spark ignition engine; Steady flow test; Swirl ratio. COMPUTATIONAL INVESTIGATION OF HEAT TRANSFER ENHANCEMENT BY ALTERNATING INCLINED RIBS IN TUBULAR HEAT EXCHANGER   by Suvanjan Bhattacharyya, H. Chattopadhyay, A.C. Benim Abstract: This paper encapsulates the results of a numerical investigation of heat transfer and fluid flow characteristics for the flow of an incompressible medium with constant properties through an axis-symmetric isothermal circular tube with alternating inclined ribs. Simulations are conducted for laminar, transitional, and turbulent flow regimes, for Reynolds numbers ranging from 200 to 15,000. As turbulence model, the transitional Shear Stress Transport model is employed. The problem is investigated for four rib angle of attack values, namely for 15 Keywords: Forced Convection; Heat Transfer Enhancement; Inclined Ribs; Transitional Turbulence; CFD. By-pass transition control with a DBD plasma actuator model coupled with a laminar kinetic energy turbulence model   by Zinon Vlahostergios, Pavlos Kaparos, Kyros Yakinthos Abstract: The effect of a DBD plasma actuator on the by-pass boundary layer transition control is numerically investigated. A two-equation DBD plasma actuator model is coupled with a three-equation eddy-viscosity turbulence model, which adopts the laminar kinetic energy concept. The investigated test-cases concern zero and variable freestream pressure gradient transitional flows on a flat plate with a sharp leading edge, which belong to the ERCOFTAC experimental database. The experimental data describe the transition characteristics with no plasma actuation and hence, they are used to assess the turbulence model behavior and as a reference point in order to quantify the coupling effect of the plasma actuator model with the laminar kinetic energy concept. The investigation is focused on the effect of the varying plasma actuator voltage on transitional and turbulent boundary layer characteristics, such as the Reynolds-stresses, the turbulent dissipation and the laminar kinetic energy distributions. The results show that with the DBD actuator activated, the turbulent quantities are suppressed, the transition onset location moves downstream and a boundary layer transition delay is observed. Keywords: plasma actuator; by-pass transition control; laminar kinetic energy; plasma and turbulence interaction. Computational Investigation of the Velocity and Temperature Fields in Corrugated Heat Exchanger Channels using RANS based Turbulence Models with Experimental Validationby Imdat Taymaz, Erman Aslan, Yasar Islamoglu, Mardiros Engin, Ilkay Colpan, Gokhan Karabas, Guven Ozcelik Abstract: The characteristics of convective heat transfer and friction factor for a periodic corrugated channel extensively used in compact heat exchangers have been investigated numerically. In numerical study Finite Volume Method (FVM) was used. Four different Reynolds Averaged Navier-Stokes (RANS) based turbulent models, namely the realizable k-ε, k-ω, Shear Stress Transport (SST) and transition SST models are used and compared with each other within RANS formulation. Experimental results which are get from previous study used for validation the numerical results. Studies were conducted for air flow conditions where contact angle is 30°. The Reynolds number is varied from 2000 to 11000, while keeping the Prandtl number constant at 0.70. Nusselt number, Colburn factor, friction factor, and goodness factor against Reynolds number have been studied. The effects of the corrugation geometry and minimum channel height have been discussed. The best agreement with the experimental data is provided by the SST model, whereas the least accurate results are obtained by the realizable k-ε model. Keywords: corrugated channel; convective heat transfer; friction factor; finite volume method; FVM; RANS based turbulence models