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Progress in Computational Fluid Dynamics, An International Journal

Progress in Computational Fluid Dynamics, An International Journal (PCFD)

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Progress in Computational Fluid Dynamics, An International Journal (35 papers in press)

Regular Issues

  • Wake interaction studies of flow past tandem circular cylinders for different diameter and gap ratios   Order a copy of this article
    by R. Rajita Shenoi, Neeraj Paul Manelil, Thirumalachari Sundararajan, Shaligram Tiwari 
    Abstract: Three-dimensional computations are carried out to study the flow past tandem stationary cylinders at moderate Reynolds number (Re = 2000). Wake structures are analyzed with the help of instantaneous vorticity contours and hydrodynamic characteristics are reported using drag and lift coefficient plots. Effects of diameter ratio and gap ratio on wake structure as well as its dynamic characteristics are presented. Cross recurrence analysis is performed to study the coupled interactions between cylinder wakes. In particular, conditions for the in-phase synchronization, out-of-phase coupling or non-synchronous coupling of the wakes behind the tandem cylinders are identified. Qualitative results obtained from cross recurrencernplots are quantified using parameters such as recurrence rate, determinism and averaged diagonal length. These results give deep insight into wake synchronizations between the cylinders. In-phase or out-of-phase wake oscillations can lead to catastrophic structural failures and predicting such conditions can be a useful design tool.
    Keywords: Tandem circular cylinders; diameter ratio; inter-cylinder spacing; dynamic wake characteristics; recurrence plots; synchronization.

  • Coupled natural convection and radiation in a cubic cavity filled with an air - H_2O mixture in the presence of a heated obstacle   Order a copy of this article
    by Xuan Bach NGUYEN, Didier SAURY, Denis LEMONNIER 
    Abstract: Natural convection in a cubical cavity with a hot obstacle located on its floor is investigated. The inner fluid is a semi transparent mixture of dry air and water vapor, which creates a coupled convective and radiative transport within the fluid. The conservation equations are solved by a finite volume method and the radiative transfer equation by using the discrete ordinates method. The radiative properties of the mixture are accounted for by a spectral line weighted sum of gray gases model associated to the rank correlated approach. It was observed that the volume radiation has a strong influence on the thermal and dynamic fields. The nearly vertical stratification of the temperature field around the plume is broken. Radiation also accelerates the boundary layers near the lateral surfaces and the ceiling and the floor of the enclosure. The total heat transfer is decreased due to both the reduction in convective process near the vertical walls and the attenuation by radiation.
    Keywords: Heat transfer; Convection; Radiation; Numerical method.
    DOI: 10.1504/PCFD.2021.10042895
     
  • Solid Rocket Motor Interior Ballistics Fluid-Solid Interaction Simulation Using Level Set Method for 2D Grains   Order a copy of this article
    by Hossam Alqaleiby, Aly Hashem, Mohamed Tosson, Amr Guaily 
    Abstract: The flow inside a solid rocket motor is considered taking into account the fluid-solid interaction between the combustion gases and the burning grain surface. An unsteady flow model is presented for the flow variables while the time-dependent burning surface is captured using the level set method. Then a hybrid model is presented by coupling the flow model with the interface capturing technique. The proposed hybrid model is successfully tested against previously published experimental and numerical data. The use of the level set method enables the flow model to consider complex grain shapes like the star shapes. The proposed hybrid model is used to produce the pressure-time curves for cross-shaped grain and a star grain with five points.
    Keywords: Fluid-solid interaction; Level set method; Finite element method; Internal ballistics.

  • CFD based Optimization of Base Pressure Behavior on Suddenly Expanded Flows at Supersonic Mach numbers   Order a copy of this article
    by Jaimon Dennis Quadros, Sher Afghan Khan, Prashanth T. 
    Abstract: In this work, a suddenly expanded flow process is modeled for determining base pressure characteristics. The base pressure developed in a suddenly expanded flow process majorly depends on the pertinent selection of Mach number (M), nozzle pressure ratio (NPR), area ratio (AR), and length to diameter ratio (L/D). Numerical analysis of the flow process was carried out using the computational fluid dynamics (CFD) technique. The input-output test cases for CFD analysis were developed as per two statistical methods, namely central composite design (CCD) and Box-Behnken design (BBD). The CFD results were validated by experiments that were conducted by using a nozzle and expanded duct. The input-output relationship obtained from the BBD was found to be statistically adequate and yielded better prediction accuracy. The BBD response model was used for generating data that trained the recurrent and backpropagation neural networks. The recurrent neural network outperformed both the backpropagation neural network and Box-Behnken design. Furthermore, to assess the right range of conditions for maximizing base pressure, the genetic algorithm (GA), desirability function approach (DFA), and particle swarm optimization (PSO) techniques were implemented. The performance of PSO and GA techniques was found to be better, as they carried out search operations in many directions at multi-dimensional space simultaneously. All the models and optimization techniques were compared, and final comments are drawn.
    Keywords: base pressure; CFD; Response surface methodology (RSM); neural networks; optimization.

  • On the use of adaptive relaxation times in lattice Boltzmann methods   Order a copy of this article
    by Simon Marié 
    Abstract: The lattice Boltzmann collision model with multiple relaxation times is modified to make the relaxation rates dependent on the shear stress. With these adaptive relaxation times, the optimal choice made by the theoretical development of MRT does not hold anymore. However, it is shown that the numerical properties of the collision model remains close to the MRT model. In particular, it is shown that the adaptive model recover the BGK properties in terms of acoustical dissipation but keeps the numerical stability of MRT when shear stress becomes high. Then the adaptive model is studied in terms of stability and accuracy on the Taylor-Green vortex case, and the acoustic properties are tested on the sound radiated by a square cylinder.
    Keywords: Lattice Boltzmann method; multiple relaxation times; Adaptive relaxationrntimes; Taylor Green Vortex; aerodynamic sound.

  • Experimental and Numerical Investigation of Co-Axial Rotor Interaction to Thrust   Order a copy of this article
    by Ahmet Soydan, Hurkan Sahin, Baris Bicer, Sebnem Sariozkan, Mehmet Sahin 
    Abstract: The experimental and numerical computational investigation of co-axial rotor performance has been increased over the past decade in order to understand complex interactions in coaxial-rotor flows to improve design of unmanned-aerial vehicles. Nevertheless, the issues related rotor aerodynamic performance, wake interactions, etc. are not well understood. In the current work, aerodynamic interactions in co-axial rotor have been investigated with both experimental and numerical methods in hover flight by varying tip diameters, rpm, axial distance etc. In order to calculate the co-axial thrust efficiency, in-house test bench has been created. On the numerical side, the three-dimensional unsteady Navier-Stokes equation is solved using a pressure based, segregated, compressible and time-accurate solver of OpenFOAM. A sliding mesh interface procedure is utilized to link rotating regions and SST k-$omega$ model is employed for the turbulence modelling. The computational results indicate relatively good agreement with in-house experimental data.
    Keywords: Multi-rotor; Coaxial rotor; OpenFOAM; RANS; Sliding mesh; Hover flight.
    DOI: 10.1504/PCFD.2021.10045801
     
  • Numerical Study of Characteristics of Confined Diffusion Flames of Synthetic Gases in Coflow and Inverse Coflow Configurations   Order a copy of this article
    by Mohd. Ibrahim, S. Muthu Kumaran, Vasudevan Raghavan 
    Abstract: Comprehensive numerical predictions of diffusion flame characteristics of practical synthetic gas (syngas) fuels in coflow (CDF) and inverse coflow (IDF) configurations with stoichiometric amount of coflow air have been compared. A numerical model with variable thermo-physical properties, multi-component diffusion, Soret diffusion, detailed chemical kinetics mechanism and an optically thin radiation model has been used. Effect of hydrogen content in fuel, which controls the reactivity, on flame characteristics has been revealed systematically. Higher peak flame temperature is observed in IDF than in CDF. However, its radially averaged temperature peak is lower in IDF than that in CDF within the flame zone. Higher rate of radial oxygen transport is seen in IDF, resulting in lesser flame radius. Combustion efficiency is higher in IDF than in CDF, for syngas fuels with intermediate reactivity. Understanding the characteristics of these flames will lead to better design of multi-slot burners using mixture of syngas fuels.
    Keywords: Synthetic gas; hydrogen content; inverse coflow diffusion flames; detailed chemical kinetics; multi-component diffusion; flame structure; numerical model; combustion efficiency; thermo-physical properties; optically-thin radiation model.

  • Numerical prediction of solid-liquid slurry flows and derivation of simulation-based correlations for local solid concentration   Order a copy of this article
    by Manoj Kumar Gopaliya, Deo Raj Kaushal 
    Abstract: This paper presents correlations for predicting local solid concentration for pseudo-homogeneous and mildly heterogeneous solid-liquid slurry flows through horizontal pipelines using curve fitting techniques applied on exhaustive simulation data. These data are obtained using a duly validated Eulerian multiphase model whose applicability is ascertained for the slurry flow cases under consideration. The ranges of geometric and working input parameters of solid-liquid slurry flow analyzed during the present research work are quite comprehensive and wide which increases the applicability realm of the derived correlations.
    Keywords: Local solid concentration; Slurry flows; Simulation; CFD.

  • Thermal non-equilibrium simulation of diffuse and constricted anode attachments of a high intensity transferred arc   Order a copy of this article
    by Chong Niu, Jin-Yue Geng, Su-Rong Sun, Yan Shen, Tao Zhu, Hai-Xing Wang 
    Abstract: The arc attachment modes on anode of a high intensity argon arc with water-cooled constrictor are numerically investigated by a two-temperature model. An inelastic electron energy loss factor, representing the energy loss due to non-equilibrium chemical kinetic processes, is introduced to the electron energy equation. Two different attachment modes, i.e., diffuse and constricted anode attachments, are obtained based on the experimental conditions. Results for both anode attachment modes indicate that the temperature discrepancy between electrons and heavy particles is very pronounced in the arc fringes and in the regions close to the anode. By comparing the axial and radial Lorentz forces between the diffuse and constricted anode attachments, it is found that the larger axial and radial Lorentz forces in a constricted anode attachment are the main cause for the formation and maintenance of anode jet. The effects of inelastic electron energy loss on different anode attachment modes are discussed and the results indicate that it is very important to consider the chemical non-equilibrium processes in an appropriate way for predicting arc attachment modes on anode reasonably.
    Keywords: Constricted anode attachment; diffuse anode attachment; inelastic electron energy.
    DOI: 10.1504/PCFD.2021.10045639
     
  • Effect of the Injector Flow Field on the Performance of a Model Scramjet Combustor   Order a copy of this article
    by Sagarika Iyyer, Viswanathan Babu 
    Abstract: The effect of injector flow field on the jet-freestream interaction and the mixingrnperformance, is investigated. Numerical simulations of the supersonic injection of hydrogenrnthrough a supersonic, diamond-shaped, wall mounted injector as well as an equivalent circularrninjector, into a Mach 2.4 supersonic crossflow in a model scramjet combustor have been carriedrnout. Two equivalence ratios, namely, ?=0.3 and 0.5, which result in pure scram mode of operation,rnare considered. Oil flow images and Schlieren images overlaid with contours of hydrogen massrnfraction are used to demonstrate that the fuel penetrates higher with the diamond injector and thatrnthe fuel issues out of a part of the injector only on account of the jet being over-expanded. Thernhigher penetration leads to better near-field mixing but the mixing slows down in the far field. Therncircular injector exhibits more lateral spreading as a result of flow separation ahead of the injector.rnAlthough the penetration and the near-field mixing are less, mixing continues farther downstreamrnresulting in almost the same level as that of the diamond injector. Fuel plume outline, contours ofrnlocal equivalence ratio and local mixing efficiency are used to obtain insights into the spreadingrnand the mixing of the fuel.
    Keywords: scramjet; supersonic combustion; simulations; injection; mixing.

  • Analysis Of Three-Dimensional Cavitating Flow Over Different Cavitators Using Boundary Element Method   Order a copy of this article
    by Ramin Fadaei Roodi, Mahmoud Pasandidehfard 
    Abstract: The most essential component in the cavitation flow is the pressure distribution on the streamline. Hydrodynamic forces, which are essential in projectile design, could be achieved through the simulation of cavitation flow and demonstration of the pressure distribution. In present paper, the three-dimensional boundary element method (BEM) is employed to simulate the partial cavitation (? = 0.1 - 0.5) around projectiles with different cavitators. Based on the assumption of potential flow and using integral expression of Green\'s theory and an iterative algorithm, the three-dimensional flow around the projectiles is simulated. To each surface boundary mesh element dipole and source potential components have been specified. The assessment of the effect of quadratic element size on both cavitation cloud shape and pressure distribution is investigated for spherical and conical cavitators with different head angles. It has been observed that in Boundary Element Method, using small element size is not generally a reasonable procedure to achieve better results. However, comparing with the experimental data a relation for the element size based on the cavitator shape and cavitation number variables is proposed. Further, the BEM predictions obtained by these relations have been evaluated by comparing them with the numerical simulation results using ANSYS Fluent software. It is obtained that using BEM and employing specific quadratic elements proposed in this paper, satisfactory values for the cavity dimensions and pressure distributions can be found in just a few minutes.
    Keywords: 3D boundary element method; BEM; conical; spherical; cavitator; partial cavitation; element size; pressure distribution; cavity length.

  • Optimization of Francis turbine draft tube using response surface model   Order a copy of this article
    by Ali Abbas, Arun Kumar 
    Abstract: The draft tube design of low and medium head hydraulic turbines plays an important role in determining the efficiency and power output. Proposed Francis draft tube geometry was optimized with two different optimization goals i.e. (a) rehabilitation and (b) a new design. Using design of experiment approach, 81 design points were generated for both cases separately and response surface methodology was used for optimization. Two objective functions the i.e. pressure recovery (Cp) and loss factor (?) were considered in optimization process. Multi objective genetic algorithm coupled with RSM was adapted to optimize the proposed draft tube geometry for achieving the desired optimization goal. For case 1, optimum values of Cp and ? value were found as 0.8290 and 0.1158 respectively. Value of pressure recovery was enhanced 7.0% at best efficiency point. For case 2, optimum value of Cp was found as out 0.851 which is 10.0% higher compared with performance of existing draft tube.
    Keywords: Francis turbine; Draft tube; CFD; Response surface methodology; Design of experiment; Multi objective genetic algorithm;.

  • Value of blade number in centrifugal flow pumps in both turbine and pump mode through experimental and numerical means   Order a copy of this article
    by Yang Sun-Sheng, Fang Tian, Wang Tao, Punit Singh 
    Abstract: The hydraulic significance of blade number of pump impellers is experimentally and numerically investigated in turbine mode and pump mode respectively for three different specific speeds and validated using the classical theoretical approach of streamline shape (angular momentum of fluid) and loss gradient. The results indicate that for both pump and turbine mode operation, the effect of streamline shape is dominating over the change in hydraulic loss with increase in blade number. The frictional component of losses for blade passage using an existing empirical model is compared with computational results. While the flow line shapes markedly improved, yet the losses could not be reduced. The study finds an optimum number of blades different for turbine (more blades) and pump (fewer blades) operation. It recommends systematic adaption of increased blade number particularly for pump as turbine users.
    Keywords: Centrifugal pump; pump as turbine; blade number; angular momentum; streamline; hydraulic losses; Euler velocity vectors.

  • CFD modeling of the flow in zero-secondary flow ejectors: a sensitivity analysis to numerical parameters   Order a copy of this article
    by Ala Bouhanguel, Valérie Lepiller, Philippe Desevaux 
    Abstract: This paper proposes a sensitivity study of various CFD simulation parameters conducted in the case of a 2D axisymmetric ejector operating without induced flow. The influence of numerical parameters (solver, discretization scheme, mesh and turbulence model) is investigated by comparing the various CFD results obtained (pressure, velocity, Mach number, mass flow rate) with each other. The influence of the turbulence model is closely examined by comparing CFD results with velocity measurements obtained by Particle Image Velocimetry.rnRules to be respected to achieve correct CFD simulation of the flow in supersonic ejectors are proposed. The use of the pressure-based coupled solver associated with the SST k-omega turbulence model is recommended. The terms of energy and pressure can be solved using 1st order discretization while the other equations (momentum, turbulent quantities) require 2nd order discretization to correctly predict the supersonic flow with shocks.rn
    Keywords: Ejector; Supersonic flow; CFD; Turbulence model; Discretization scheme.

  • Two-phase modeling of the nanofluid mixed convection in a porous open cavity   Order a copy of this article
    by Hadi Shaker, Majid Abbasalizadeh, Shahram Khalilarya, Saber Yekani Motlagh 
    Abstract: The aim of the current work is to study the mixed convection of Fe3O4-water magnetic nanofluid in a heated porous open cavity. Buongiornos two-phase model is utilized to consider the Brownian and thermophoresis of nanoparticles in the carrier fluid. Using the Darcy-Brinkman and Boussinesq approximations, the governing equations are solved by the finite volume technique, numerically. Numerical computations are performed for various Richardson numbers (Ri=0.01, 0.1, 1 and 10), Reynolds numbers (Re=10, 100, 300 and 600), volume fraction of nanoparticle (?=0 and 0.06), Porosity (?=0.5, 0.8 and 1) and Darcy numbers (0.0002 Keywords: Mixed convection; magnetic nanofluid; Buongiorno’s two-phase model; Porous Open cavity; Darcy-Brinkman.

  • AIRFLOW CHARACTERISTICS IN DIFFERENTLY ELEVATED SCHNEIDERIAN MEMBRANES: A COMPUTATIONAL FLUID DYNAMICS ANALYSIS   Order a copy of this article
    by Abdulsamet Kundakcioglu, Erman Aslan, Mustafa Ayhan, Metin Berk Kasapoglu 
    Abstract: Distributions of air flow velocities and streamline are modelled numerically at different anatomical levels of sinus lifting surgery in Schnederian membrane models with various degrees of elevation. Three different elevated Schnederian membrane topography models are used which are control group (Case 0), symmetrically dome-shaped (Case 1), partially elevated model (Case 2) and plane model (Case 3). Three different volumetric flow rates which are 30l/min, 15l/min and 7.5l/minaret used. The inspiration and expiration are modelled numerically. In numerical analysis, computational fluid dynamic techniques are used. Incompressible flow and time independent assumptions are used. Airflow flow behaviors are discussed for different elevated Schnederian membrane topography, volumetric volume rates and for expiration and inspiration.
    Keywords: Sinus Lifting; Airflow; Computational Fluid Analysis; Schneiderian membrane; Flow velocity.
    DOI: 10.1504/PCFD.2021.10045586
     
  • Computational Investigation and Parametric Design of High Speed Evacuated Tube Transportation   Order a copy of this article
    by Arnav De, Sanket Sanjay Nangarea, Sreeja Sadasivan, Senthil Kumar Arumugam, Bibin John, Zhang Yaoping 
    Abstract: Evacuated Tube Transportation is a path-breaking technology that can potentially supplant the current transportation technologies by offering high-speed transportation with maximum efficiency. Different scenarios were considered in which the train was simulated to be travelling at subsonic, transonic, and supersonic speeds at a fixed blockage ratio. It is found that no shockwaves are formed in the subsonic range, but they start forming at the rear end of the train from Mach number 0.8 onwards. From Mach 2, shockwaves start forming at the front end, along the length of the train as well as the rear end of the train. Further, multi-objective optimization was conducted to evaluate the best combination of various influential factors. One of the salient conclusions of the present study is that the train with the oblique front end, elliptical rear end along with 1000 Pa tube pressure gives the best combination, resulting in minimum drag.
    Keywords: Design of Experiments; Evacuated Tube Transportation; Mach Number; Aerodynamic Drag; Shockwave.

  • Investigation on the 1 kW Francis Turbine Elbow Type Draft Tube Performance by Numerical and Optimization Approach   Order a copy of this article
    by Sathish Kalidas, Ramamoorthi Rangasamy, Venkatesh Seenivasan 
    Abstract: In this study, the performance of a 1-kW Francis turbine elbow-type draft tube is examined. Three geometric factors related to the draft tube, namely, the hose length, diffuser length, and exit diameter of the draft tube, are considered for improving the pressure recovery factor. The Taguchi method is applied to derive a regression equation related to these three parameters. The geometric factors of the draft tube are altered using a genetic algorithm (GA). The optimized draft tube is fabricated for the experimental investigation. The results indicate that using the optimized draft tube increases the overall efficiency. Moreover, it leads to an increase in the pressure recovery factor from 0.75 to 0.88. The pressure, velocity, and kinetic energy flow fields were obtained using computational fluid dynamics (CFD) simulation. The shear stress transport k-? model is applied for CFD simulation. The computed pressure recovery factor obtained from the CFD analysis is compared with that obtained from the experimental results. An acceptable range of accuracy is obtained in this study.
    Keywords: Elbow draft tube; Pressure recovery factor; Francis turbine; Overall efficiency; Velocity of flow; Kinetic energy.

  • Unsteady Aerodynamic Performance of SD7062 Airfoil at High Reynolds Number   Order a copy of this article
    by Berkan Anilir, Dilek Funda Kurtulus 
    Abstract: Aerodynamic performance of SD7062 airfoil in two-dimensional unsteady flows at high Reynolds number (Re?5
    Keywords: unsteady flow; high Reynolds number; computational fluid dynamics; SD7062; vortex shedding; laminar separation bubble.

  • Numerical simulation and optimization of CFB boiler furnace with air staged low NOx combustion   Order a copy of this article
    by Shun Sheng Xu, Dong Gang Yu, Fu Lian Yao, Kong Yao Wang 
    Abstract: Due to the introduction of new ultra-low emission regulations, circulating fluidized bed boilers are facing severe challenges in China. In this paper, the whole air staged combustion model in the furnace of a 300 MW circulating fluidized bed boiler was established and simulated by FLUENT, The simulation results were verified by experimental adopted. The effects of primary and secondary air distribution ratio, upper and lower secondary air distribution ratio, and secondary air incidence angle on NOx emission concentration at furnace outlet were studied through the simulation. The results showed that the NO emission concentration can be greatly reduced by applying air staged combustion technology in CFB Boiler and optimizing the operation parameters. Under the conditions studied in this paper, the NO emission concentration decreased from 142.97mg/m
    Keywords: CFB; Numerical simulation; Grading combustion; Low NOX combustion; Ratio of primary and secondary air distribution; Secondary air inlet Angle; Ratio of upper and lower secondary air.

  • Analysis of Interface Instabilities of Separated Gas-Liquid Two Phase Flows with Conservative Two Fluid Model   Order a copy of this article
    by Iman Abbaspour, Vahid Shokri 
    Abstract: A numerical study is conducted in order to simulate separated two-phase flows of gas-liquid with conservative two-fluid model. Firstly, different numerical methods are examined to investigate the flow characteristics and stability of governing equations through the shock flow problem. For this, the shock-capturing method is developed to an algorithm scripted in Fortran; and the Force method is selected for the models used in this work due to the higher accuracy. For validation of the simulations, the results of instability range are compared to the calculations using the classic Kelvin-Helmholtz instability equation. The wave growth was examined in separated two-phase flow in a horizontal pipe and were compared with the results of the previously published articles. The results show that the instability of the interface is dependent on the range of velocity differences. If relative velocity overpasses the allowed range, interface will be unstable over time. The obtained instability range of this research covers the classic kelvin-Helmholtz instability equation for the long wavelength with small amplitude. Results reveal that when the wavelengths are reduced, KelvinHelmholtz instability range is not consistent and wavelength affects on instability and kelvin-Helmholtz instability range is over predicted. This study presents a modified numerical method that improved the consistency with the analytical solution in comparison with other prior researchers codes.
    Keywords: Two-phase flow; Two-fluid model; Numerical simulation; Conservative two-fluid model.

  • Effect of aspect ratio of semitransparent window on interaction of the collimated beam with natural convection: Part I   Order a copy of this article
    by G. Chanakya, Pradeep Kumar 
    Abstract: The effect of the semitransparent window's aspect ratio on the interaction of the collimated beam with natural convection has been investigated numerically. The cavity is convectively heated from the bottom with a heat transfer coefficient of 50 W/m^2K and free stream temperature 305K. A semitransparent window is created on the left wall and isothermal conditions (T=296K) is applied on the semitransparent, left and right vertical walls, wherein adiabatic conditions are applied on the upper wall of the cavity. The combination of geometrical parameters of the semitransparent window, i.e., height ratio (hr) and window width ratio (wr) and Planck numbers of the medium has been considered for the present work. The other parameters like, flow parameter (Ra=10^5), fluid parameter (Pr=0.71), thermal parameter: conduction-radiation parameter (N=1.5), Irradiation (G=1000 W/m^2), angle of incidence (phi=135^0) and geometrical parameter of the geometry (Ar=1) and the wall conditions have been kept constant. A collimated beam is irradiated on the semitransparent window at an azimuthal angle (phi) 135^0. The dynamics of two vortices inside the cavity change considerably by combinations of semitransparent window's aspect ratio and Planck number (Pl) of the medium. The left vortex breaks into two parts and remains confined in upper and lower left corners for some combination of aspect ratios and Planck numbers of the medium. The thermal plume flickers depending on the situation of dynamics of two vortices inside the cavity. The localized heating of the fluid happens mostly for the large height ratio of the semitransparent window. The conduction, radiation and total Nusselt numbers are also greatly affected by the semitransparent window's aspect ratio and the Planck number of the medium.
    Keywords: Semitransparent wall; Natural convection; Collimated beam irradiation; Symmetrical cooling; Aspect ratio;.
    DOI: 10.1504/PCFD.2021.10045438
     
  • Numerical Analysis of Geometry and Operating Conditions in Combined Honeycomb and Inclined Labyrinth Sealing Elements   Order a copy of this article
    by Ibrahim Zengin, Beytullah Erdo?an 
    Abstract: Leakage flows occurring during operating conditions within the gas turbine engine system significantly affect the turbine efficiency. It is a significant issue to control and predict the leakage flow. This study covered the labyrinth seal with inclined tooth form and honeycomb seal used together. The combined seal provides more efficient leakage flow reduction than seal designs available in the literature. The study also focused on the five different parameters affecting the leakage flow, which are clearance size (Cr=0.254-0.508-1.016 mm), honeycomb cell size (Lcell=0.793-1.590-3.175 mm), pressure ratio (pi=1.5-2.0-2.5-3.0), rotor speed (Vr=0-100-200-400 m/s), and tooth inclination angle (theta=90
    Keywords: Sealing elements; Honeycomb seal; Inclined labyrinth tooth; Sealing CFD.

  • Numerical simulation of transient flow with column separation using the Lattice Boltzmann method   Order a copy of this article
    by Kai Wu, Yujie Feng, Ying Xu 
    Abstract: This paper proposes a numerical solution to simulate the transient flow with column separation in pipelines using Lattice Boltzmann Method (LBM). Combination of LBM and the discrete vapor cavity model (DVCM), the governing equations and boundary conditions are analyzed and derived for numerical simulation.The experiments and acctual projects were adopted to verify and examine the new solution. The results show that the computational grid of LBM-DVCM is unrelated to the wave speed, so the computational resources and time are significantly reduced. Besides, compared to the method of characteristics (MOC-DVCM), LBM-DVCM avoids the virtual pressure peak during the transient flow. Finally, LBM-DVCM can simulate the process of transient flow both quickly and accurately. It is excepted that the development of this method will be useful for the practical pipeline numerical experimentation and efficient prediction.
    Keywords: discrete vapor cavity model; Lattice-Boltzmann method; water hammer with column separation; water supply systems.

  • Wake patterns and mode switching at low Reynolds numbers   Order a copy of this article
    by Nabih Naeem, Mahmoud Fouda, Mertcan Güney, Dilek Funda Kurtulus 
    Abstract: Instantaneous wake structures behind a 2% thick NACA 0002 symmetric airfoil are numerically studied in 2D at six different angles of attack for Reynolds numbers ranging from 100 to 3000. Classification of the flow patterns based on vortex structure is discussed. An in-depth study of the various flow modes of vortex dynamics in the wake of the airfoil is presented, considering the amplitude spectrum of the lift coefficient and Poincar
    Keywords: mode switching; Reynolds-based bifurcations; wake patterns; symmetric airfoil; NACA 0002; CFD; two dimensional flow; Kurtulus modes.

  • Study of gravitational sedimentation of multiple permeable particles using Immersed Boundary(IB) method   Order a copy of this article
    by Sudeshna Ghosh, Kashish Chhabra, Deepika Sharma 
    Abstract: This researchs goal is to study two particle systems interaction in two-dimensionalrnframework for the cases where the interacting particles are either permeable orrnimpermeable in nature. The numerical technique implemented to solve this problem isrnImmersed boundary(IB) method. Scenarios studied here are: Case 1 and Case 2 considersrninteracting particles with same and different permeabilities (k) respectively. Case 3,rnstudies the interaction between an impermeable and permeable particle. The resultsrnobtained indicates that the permeability value of the particle plays a vital role to therninteracting dynamics between the particles. In the end, we compared our computedrnresults of settling velocities of particles with existing analytical expressions.
    Keywords: IB method; sedimentation; fluid-structure interaction; permeable; DKT; settling velocityrn.
    DOI: 10.1504/PCFD.2022.10046096
     
  • Modeling and simulation of ash accumulation in SP boiler of decomposition kiln   Order a copy of this article
    by Shunsheng Xu, Chong Shen, Kongyao Wang, Fulian Yao, Jiazhen He 
    Abstract: Abstract: In this paper, the problem of ash accumulation in the superheater of a suspension preheater (SP) waste heat boiler is studied. A comprehensive ash accumulation growth model, including deposition and removal process, is established and verified by experimental results. According to the established model, the effects of flue gas velocity, ash concentration and tube shape on the ash accumulation are studied. The ash growth prediction model based on the initial simulation value fitting is proposed and used in the research of ash prediction. The results show that the ash growth prediction model can predict the ash accumulation better; the ash accumulation rate increases with the flue gas velocity and the ash concentration, and the ash accumulation time constant decreases; the maximum ash accumulation decreases negatively with the flue gas velocity but is little affected by the ash concentration ; the performance of the oval tube to reduce the ash accumulation is better than that of the round tube; when the oval tube layout angle is 45 degrees, the effect is best, and the comprehensive evaluation effect on the heat transfer and resistance is the best.
    Keywords: Keywords: SP waste heat boiler; ash accumulation; the simulation; accumulation of ash growth forecast; oval tube layout angle.

  • Optimization of crescent-shaped block upstream of the cylindrical hole to enhance film cooling effectiveness using CFD method and genetic algorithm   Order a copy of this article
    by Pengfei Zhang, Chao Zhang, Zhan Wang 
    Abstract: This study numerically investigated the optimal geometry of the crescent-shaped upstream block for the typical cylindrical inclined film-cooling hole to improve the cooling performance. The maximum area-averaged cooling effectiveness is pursued using the genetic algorithm combined with the CFD method at two blowing ratios of 0.5 and 1.5. Compared with the reference block, two optimized models obtained under the two blowing ratios increased the area-averaged cooling effectiveness by 127.8% at a blowing ratio of 0.5 and 16.6% at a blowing ratio of 1.5, respectively. The enhancement in the cooling performance mainly results from the improvement in the streamwise coolant coverage and the lateral coolant coverage at blowing ratios of 0.5 and 1.5, respectively.
    Keywords: gas turbine; film cooling; crescent-shaped block; cooling effectiveness; optimization.

  • A successful microblowing strategy for airfoils   Order a copy of this article
    by Aideal Zohary, Waqar Asrar, Mohammed Aldheeb 
    Abstract: This paper presents a successful microblowing technique (MBT) strategy for airfoils in subsonic flows, reducing both components of drag. Critical pressure distribution points on the airfoil are identified acting to aid in the airfoil selection process and prior determination of the blowing region. It effectively addresses the alteration of pressure distribution and hence the pressure drag caused by microblowing. Evidence through numerical simulation on a S1223 airfoil resulted in an improvement to its lift-to-drag ratio by 30% with a relatively strong blowing fraction of 5% when operating at 2
    Keywords: Active Flow Control; Microblowing Technique; Airfoil; RANS; UAV.

  • Calculation of the Development Length of Spanwise Rotating Three-Dimensional Laminar Channel Flow   Order a copy of this article
    by Manoochehr Barimani, Mehran Khaki Jamei, Morteza Abbasi 
    Abstract: The study aims to simulate Newtonian laminar fluid flow developments in a three-dimensional channel and a rotating frame of reference. Due to the complex solution of governing equations in the entrance region, as well as the non-neglectable effect of Coriolis and centrifugal pseudo-forces, the main objective of this study is to investigate a correlation for calculating the entrance region length in a spanwise rotating channel. OpenFOAM was used to simulate Reynolds numbers (Re) ranging from 10 to 80, angular velocity (?) ranging from 0 to 0.5, and three distinct channel aspect ratios (AR). A fitted point-fit curve was then generated by using the MATLAB curve fitting toolbox. Using the curve equation, the length of the entrance region is calculated as a function of Re, AR, and Dh (dimensionless hydraulic diameter). We conclude that increasing ? results in an increase in entrance region length, which increases threefold for a constant Reynolds number when ? increases from 0 to 0.5. Increasing Re, on the other hand, has the same effect. As Re is increased for a given value of ?, the length of the entrance region is increased by 15 to 35%. Moreover, when ? varies between 0 and 0.5 and Re varies between 10 and 80, the pressure drop ranges from 25 to 40%.
    Keywords: Angular velocity; Coriolis; Entrance region; OpenFOAM; Rotating channel.

  • Numerical Investigation on the Aerodynamics of High-Lift and Bird-like Low Reynolds Number Airfoils   Order a copy of this article
    by Smail Boughou, Ashraf Omar, Omer Ali Elsayed, Mohamed Aldheeb 
    Abstract: The current study numerically investigated the accuracy of turbulent models in predicting the aerodynamic performance of man-made, bird-like high-lift low Reynolds number airfoils. S1223, Seagull, and two Merganser airfoils were the main airfoils considered for analysis. The research included both 2D and 3D simulations. Spalart-Almaras (SA), Shear Stress Transport (SST), SST K-?, and SST ?-Re? models were used for 2D simulation whereas SST was used for 3D simulation. The numerical solution was verified against Xfoil and the experimental data for airfoils such as S1223 and FX63-137. The study results revealed that fully turbulent models failed in the accurate prediction of critical physical phenomena of the flow, owing to high unsteadiness near stall conditions. SST ?-Re?t model demonstrated better flow prediction abilities. The airfoils of all the three tested birds showed similar stalling behavior. In terms of drag coefficient, Seagull airfoil exhibited a favourable response in terms of increase in the angle of attack than Merganser airfoil.
    Keywords: low Reynolds number flow; Transition modelling; Laminar separation bubble; Bird-aerodynamics.

  • Two Dimensional Numerical Simulations of a Free-Falling Liquid Gallium Droplet in Quiescent Water   Order a copy of this article
    by Khellil Sefiane, Mohamad Sofwan Bin Mohamad, Rachid Bennacer 
    Abstract: In this study a Lattice Boltzman (LBM) approach is used to simulate free falling drops of liquid metal Gallium into a quiescent water column. The numerical simulations aimed at reproducing experimental observations of the deformations of the Gallium drops and its solutions during the fall. The developed code is first tested against literature for rising bubbles, which showed good agreement. The previously performed experimental investigations allowed the study of a falling liquid Gallium into a column of water to validate the simulations. Parameters such as size of the droplets and viscosity ratios are investigated in the simulations. Deformation mechanisms are explored by studying the instantaneous velocity and pressure field around the drop. A comparison between the numerical simulations and the experimental data showed a good agreement.
    Keywords: Drop fall; LBM; drag; simulations.

  • Numerical Investigation of Parietal Pressure Distribution on NACA0012 Wing Controlled by Micro-cylindrical Rod Arranged in Tandem   Order a copy of this article
    by Abderrahim LARABI, Michaël PEREIRA, Florent Ravelet, Tarik Azzam, Hamid Oualli, Laiche Menfoukh, Farid Bakir 
    Abstract: The aim of this study is to investigate the influence of disturbed freestream flow by a small cylinder on the laminar separated boundary layer over NACA0012 wing operating at a Reynolds number of Rec = 4.45x10^5. Detailed parametric investigations for the rod are performed using numerical simulations coupled with transition sensitive closure model (gamma-Re{theta, t}) seeking for the optimal passive control parameters. Firstly,the use of such steady RANS model has been successfully accurate in capturing the separation induced transition on the baseline wing suction surface. Secondly, the rod location was scaled according to the formation length of vortices behind the micro-cylinder for which the aerodynamic loads are very sensitive. The effects of three rod diameter ratios (d/c = 0.67%, 1.33% and 2%) on the laminar separation bubble and aerodynamic performances were examined. It was observed that the qualitative analysis of the flow structures revealed the mechanisms of the control device for the aerofoil performance improvements in which the rod wake exerted considerable effects on LSB size, pressure coeffcient and flow streamlines. Particularly, it contributes to eliminate the boundary layer separation with pronounced decrease of 75% by energizing the shear layer over a signi cant extent, resulting in a mean drag dropping of 73% at 12
    Keywords: Laminar separated flow; SST transition model; Passive flow control; Bodie's wake interaction; Laminar separation Bubble; Drag reduction; Lift enhancement.

  • Effect of the numerical dissipation and resolution on large-eddy simulation of turbulent square duct flow   Order a copy of this article
    by Amin Rasam, Zeinab Pouransari, Mohammad Reza Zangeneh 
    Abstract: Performance of large-eddy simulation (LES) in the presence of numerical dissipation due to the Rhie--Chow interpolation is assessed for the prediction of turbulent flow in a square duct. A wide range of resolutions and bulk Reynolds numbers $Re_b=2500$ and $5693$ are investigated. A second-order colocated finite-volume solver with the dynamic Smagorinsky (DS) subgrid-scale (SGS) model is employed. To distinguish between the role of the numerical and SGS dissipations, LESs without an SGS model are also performed. LESs without the Rhie--Chow interpolation did not experience numerical instabilities. Use of the Rhie--Chow interpolation, however, increased the error in the wall shear stress and enstrophy predictions, which were more pronounced at coarse resolutions. Significant mis-predictions in Reynolds stress and its anisotropy were also observed at coarse resolutions, which were improved, to some extent, by omitting the Rhie--Chow interpolation. Convergence behavior of important flow statistics, towards the DNS, were also assessed and resolution requirements were explored.
    Keywords: Large-eddy simulation; Rhie--Chow interpolation; turbulent duct flow; resolution requirements.

  • Thermodynamic Analysis of Riga Plate Effect on Nanofluid Flow in Porous Medium with Non-Linearly Varying Permeability
    by Lalrinpuia Tlau, Surender Ontela 
    Abstract: A comprehensive study of a copper-water nanofluid flowing through a porous medium embedded in an inclined channel is presented in the current article. The permeability of the porous medium is assumed to vary exponentially across the width of the channel. Navier slip at the channel walls is taken into account while the walls are also convectively heated, albeit asymmetrically. The lower wall of the channel is assumed to be made of a Riga plate, a new type of electro-magnetic plate made of electrodes and magnets, inducing a plate parallel Lorentz force. Appropriate transformations are applied to the governing equations such that they are non-dimensionalized. The obtained equations are then solved using the homotopy analysis method. For a reduced form of the governing equations, analytical solutions are obtained which are similar to previously presented results. Graphical presentations are discussed for various flow parameters. The impact of the classical Hartman number on the flow is seen to be very significant and can play a pivotal role in reduction of entropy and skin friction. The flow scheme presented in the present article are presented for the first time in literature.
    Keywords: Entropy; Inclined channel; Nanofluid; Variable permeability; Riga plate