Progress in Computational Fluid Dynamics, An International Journal (38 papers in press)
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.
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.
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.
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.
A new approach to solve mixture Multi-phase Flow model using Time Splitting Projection Method
by Farhang Behrangi, Mohammad Ali Banihashemi, Masoud Montazeri Namin, Asghar Bohluly
Abstract: This paper was aimed at introducing a new approach to numerical simulation of two-phase flows by solving the mixture model equations. In this approach, an effective numerical algorithm was developed based on the time splitting projection method to solve the mixture model equations for an incompressible two-phase flow. The mixture model contained a set of momentum equations for the mixture phase, a mixture continuity equation, a second phase continuity equation, and the algebraic equation for the relative velocity. In this study, a new technique was developed to solve the mixture continuity equation based on the time splitting projection method. One of the advantages of the mixture model is that, in addition to determining the velocities of each phase, it solves only one set of momentum equations and calculates the velocity differences between the phases by solving the relative velocity equation. Accordingly, an extended finite volume vertical two-dimensional numerical model was used to determine the pressure distribution, velocity field, and volume fraction of each phase at each time step. The model has been used in various tests to simulate unsteady flow problems. Comparison between numerical results, analytical solutions and experimental data demonstrated a satisfactory performance.
Keywords: time splitting; projection method; mixture model; multi-phase flow; slip velocity; computational fluid dynamics; phase interpenetrate; numerical methods; numerical modelling;numerical solution.
EXPERIMENTAL STUDIES OF THE THERMAL FLOWMETER AND ITS ANALYTICAL AND NUMERICAL ANALYSIS
by Artur Cebula
Abstract: The paper presents an analytical and numerical model of a thermal flow meter. The temperature distribution along the thermal flow meter is presented. Results show a very good conformity between numerical and analytical model. Besides the calculation, experimental results are presented, where the duct wall temperature was measured. The author performed a test to measure temperature of duct wall surface. The dependency of mass flow rate in terms of the duct surface temperature difference m = f(ΔT) was developed. Obtained results represent a strong background for further research and investigation of the thermal flow meter and its application for measuring the flow rate of liquids.
Keywords: thermal flow meter; heat transfer; conjugated heat transfer; CFD; measurements.
Numerical study on the engine room cooling performance of a medium size excavator
by HyungRak Kim, Young Min Seo, Man Yeong Ha, JaeSeok Lee, Pan Young Kim
Abstract: The temperatures at the inlet and outlet of the heat exchanger located inside an engine room are an important design variable which has much effect on the engine room cooling performance of a vehicle and heavy machinery. This study carried out the numerical simulation to investigate three-dimensional thermal and flow characteristics inside the engine room and also to predict the temperatures at the inlet and outlet of the heat exchanger located inside of the engine room that can evaluate the engine room cooling performance of a medium size excavator. The effects of the change in distance between the fan located inside the engine room and heat exchanger, the shroud tip clearance to the fan, and the fan immersion depths of box type shroud and bell mouth type shroud on three-dimensional thermal flow inside the engine room and cooling performance are presented in this paper.
Keywords: Heat exchanger; Cooling performance; Excavator; CFD.
Airfoil Noise Reduction Using Boundary Layer Control
by Li Dawei
Abstract: The flow field and sound radiation of a three component high lift configuration in free-flight is investigated through computational fluid dynamics simulations in conjunction with a Ffowcs Williams-Hawkings acoustics solver. The boundary layer blow and suction control method on the inner slat surface has been used to suppress the broadband noise generated by the high lift configuration. By the comparison of instantaneous and time averaged results, the boundary layer control can effectively stabilize the shear layer that originates from the leading edge of the slat by removing the secondary separation flow on the inner slat surface. When the suitable boundary layer blow control parameters have been chosen, the computation results show the fluctuating of the velocity and pressure, turbulence kinetic energy, vorticity and Lamb vector in the slat cove are suppressed by the boundary layer control. The strong reduction of noise level in far-field and the steadiness of flow field in the slat cove demonstrate that the boundary layer control method is an effective way to control the noise of the high lift configuration.
Keywords: CFD,TKE; Blow and Suction Control,Overall sound pressure level.
Benchmark simulations of flow past rigid bodies using an open-source, sharp interface immersed boundary method
by Utku Senturk, Daniel Brunner, Hrvoje Jasak, Nicoleta Herzog, Clarence W. Rowley, Alexander J. Smits
Abstract: This study reports benchmark results for a new immersed boundary method based finite-volume solver within the framework of the open-source toolbox foam-extend 3.2. The immersed boundary formulation uses a discrete forcing approach based on a weighted least squares approximation that preserves the sharpness of the boundary. Five test cases with increasing complexity are used. Results are also presented for the flow past a low-aspect-ratio plate that pitches about its leading edge at a Reynolds number of 2000. Force coefficient results are compared with available experimental and computational data. The results show that foam-extend 3.2 appears to be a promising open-source tool for solving flows with steady and unsteady immersed boundaries.
Keywords: Computational fluid dynamics; open source; OpenFOAM; immersed boundary method; discrete.
Investigation of numerical simulation of non-Newtonian flows dam break and dam breach in open channels using modified VOF method
by Esmail Lakzian, Mostafa Niazi
Abstract: This paper concerns modeling dam break flows of non-Newtonian Herschel-Bulkley (HB) fluid by using the volume of fluid (VOF) method and high resolution advection schemes. The VOF method is based on the fact that two or more fluids (or phases) are not interpenetrating. In the present study, a modified approach is used to overcome this problem. The OpenFoam software is employed and inter-Foam solver is used in two and three-dimensional model with non-Newtonian fluid. The numerical results of the present study are compared with analytical, numerical, and experimental results found in literature. The numerical code which is used showed better agreement with the experimental data than those using shallow water equations and PLIC method.
Keywords: Volume of Fluid Method (VOF); Dam Break flows; non-Newtonian Model.
Use of nanofluids as coolants in buoyancy-driven thermal management of embedded heating components of small-scale devices
by Massimo Corcione, Alessandro Quintino, Elisa Ricci, Andrea Vallati, Paweł Ocłoń
Abstract: A two-phase model based on the double-diffusive approach is used to perform a numerical study on natural convection of water-based nanofluids in square cavities partially heated at the bottom wall and cooled at both sides, assuming that Brownian diffusion and thermophoresis are the only slip mechanisms by which the solid phase can develop a significant relative velocity with respect to the liquid phase. The system of the governing equations of continuity, momentum and energy for the nanofluid, and continuity for the nanoparticles, is solved through a computational code which incorporates three empirical correlations for the evaluation of the effective thermal conductivity, the effective dynamic viscosity, and the thermophoretic diffusion coefficient, all based on literature experimental data. The pressure-velocity coupling is handled by the way of the SIMPLE-C algorithm. Numerical simulations are executed for three different nanofluids, using the diameter and the average volume fraction of the suspended nanoparticles, the cavity width, the heated fraction of the bottom wall, the average temperature, and the temperature difference imposed across the cavity, as independent variables. It is found that the cooperation between the solutal and thermal buoyancy forces results in a significant enhancement of the heat transfer performance of the nanofluid compared with the pure base liquid. Moreover, the impact of the nanoparticle dispersion into the base liquid is found to increase notably with increasing the average temperature, whereas, by contrast, the other controlling parameters have moderate or negligible effects.
Keywords: Nanofluid; Natural convection; Square enclosure; Partially-heated bottom wall; Twophase modeling; Enhanced heat transfer.
Fictitious Domain Method Combined with the DEM for Studying Particle-Particle/Particle-Wall Collision in Fluid
by Shengli Ma, Zhengying Wei, Xueli Chen
Abstract: The interaction between particles and a fluid is very important in the industrial and agricultural fields. In recent years, the development of "four-way coupling" resolved method can be used as an effective tool to study particles flow. The hydrodynamic characteristics of both spheroidal particles and non-spherical particles sediment in the fluid and their rebound dynamics was investigated by using the Fictitious Domain Method-Discrete Element Method (FDM-DEM) in this paper. The novelty lies in the combination of the Monte Carlo scheme with FDM to improve the accuracy in calculating the volumetric solid fraction in a fluid cell, and accordingly the accuracy of hydrodynamic force. A soft-sphere scheme of DEM is used to model the collision of particles. The hydrodynamic force on the particle is fully resolved by the FDM. The numerical results are verified by comparing the previous numerical and experimental results implemented by Cate. The results are in good agreement with the corresponding published data. The simulation results show that the key factor that affects the particle rebound is Stokes number. No rebound occurs when Stokes number is equal to 3.74. The results of non-spherical particles sediment show that the phenomenon of "helical sediment" appears at the process of the sediment when the particle has a larger AR number. The results also show that the path instability of sedimentation of the non-spherical particle occurs. This conclusion is consistent with previous research results. The method presented in this paper can be used in practical applications.
Keywords: FDM; Particle-wall collision; Particle-laden flow; DEM.
Colocated Pressure-Velocity Coupling in Finite Difference Methods
by Mikael Ersson
Abstract: A simple method to be used for colocated pressure-velocity coupling in incompressible flows is presented with a full derivation. A number of standard test cases are shown that demonstrate the ability of the method to produce accurate results. The method avoids spurious pressure oscillations while keeping the pressure Poisson equation stencil compact. This is obtained by discretizing the continuity and pressure derivatives with first order differences with opposite directions, i.e. backward difference for continuity and forward difference for pressure (BCFP). The equations are also approximated using a forward difference for continuity and a backward difference for pressure (FCBP). In order to obtain a second order approximation the mean between BCFP and FCBP is used, i.e. a central difference. The paper gives a useful alternative to existing methods for pressure-velocity coupling in Finite Difference Methods in which a staggered arrangement is not desirable.
Keywords: Finite Difference Method; FDM; Spurious Oscillations; Colocated Variable Arrangement; Collocated Variable Arrangement.
INVESTIGATION OF PEMFC PERFORMANCE WITH VARIOUS CONFIGURATIONS OF SERPENTINE AND INTERDIGITATED FLOW CHANNEL
by LAKSHMINARAYANAN VARADHARAJAN, Karthikeyan Palaniswamy
Abstract: The Proton Exchange Membrane Fuel Cell (PEMFC) performance is influenced by design and operating parameters like rib to channel width ratio (R: C), the depth of the channel, the number of passes on the flow channel, operating pressure, temperature, relative humidity and the inlet gases stoichiometric ratio. In this paper, the PEMFC performance in an effective area of 25 cm2 with various ribs to channel width ratios (R: C - 1:1, 1:2, 2:1 and 2:2) on serpentine and interdigitated flow channels was investigated numerically and experimentally. The numerical and experimental maximum power density deviation of serpentine and interdigitated flow channel results with rib to channel width 1:2 were found to be 12.16 % and 12.2 % respectively.
Keywords: Rib to channel width ratio; CFD; Operating parameters; Stoichiometric ratio; Design parameters; Serpentine flow channel; interdigitated flow channel.
Effects of magnetohydrodynamics on temperature and shock standoff distance in a supersonic flow over a blunt body
by Sanjiv Paudel, Saleen Bhattarai, Sudip Bhattrai
Abstract: Magnetohydrodynamics has been one of the promising ways of increasing efficiency of supersonic as well as hypersonic propulsion systems, mostly by applying magnetic fields over shockwaves. This paper presents the effects of magnetic fields with different strengths both along and transverse to an electrically conducting flow at Mach 2.94 over a blunt body using a density-based solver implemented with MHD equations in OpenFOAM. The solver utilizes Riemann method with an AUSM+ flux splitting technique along with limited linear interpolation. The effects of imposed magnetic field on temperature and shock standoff distance are observed. Movement of the shockwave due to the application of magnetic field on the geometry, along with a consequent change in shock standoff distance is presented in the paper. The influence of a magnetic fields direction on the Mach number of the flow is also shown. Likewise, the stagnation temperature of the blunt body is demonstrated to be independent to the direction of applied magnetic field.
Keywords: bow shock; flow control; supersonic; re-entry; OpenFOAM.
Numerical study of the effect of suction at a compressible and high Reynolds number flow to control the flow separation over Naca 2415 airfoil
by Esmaeel Fatahian, Ali Lohrasbi Nichkoohi, Hossein Fatahian
Abstract: This study focused on delaying and controlling the flow separation over Naca 2415 airfoil by finding the best slot location with the most effective suction velocity ratio and suction angle to apply suction at a compressible and high Reynolds number flow using computational fluid dynamics method. The results were obtained with two dimensional compressible Reynolds-averaged Navier-Stokes equations, and the turbulence was simulated with k-ԑ RNG turbulence model. The results indicated that the most effective slot locations for applying suction were between 0.3 to 0.6 of the airfoil chord length. Also, it was found that the maximum value of the lift coefficient was obtained at an angle of attack of 16
Keywords: Flow control; Suction; Lift coefficient; Drag coefficient; Flow separation; Boundary layer.
Choice of Model Parameters in Turbulent Gas-Solid Flow Simulations of Particle Classifiers
by Arun Appadurai, Vasudevan Raghavan
Abstract: Comprehensive numerical simulations of particle laden gas flows are complex in general and its complexity increases dramatically when real world equipment are modelled. In this study, several model parameters required to economically simulate such a flow in a lab-scale classifier are tested. Initially, numerical results obtained from a single-phase (gas alone) model of a static classifier are validated against experimental results from literature. For flows characterised with dominant swirl, Reynolds Stress Model is capable of predicting the measured gas velocities with reasonable accuracy. The single-phase model is further extended to two-phase by the addition of particle phase in a static separator through Lagrangian formulation. Several parameters such as turbulence dispersion, particle rough wall model and wall restitution coefficients are investigated. On comparing the numerical results against experimental data from literature, it is found that the accuracy of particle separation is improved with the inclusion of turbulence dispersion. Particle rough wall model and wall restitution coefficients are found to affect the flow of coarse particles only. The validated single-phase model is further used to simulate single-phase flow in a dynamic classifier with a rotor. The influence of rotor rotation is captured by using a multiple frames of reference model. The predicted results in terms of pressure drop across the classifier from the model are validated against the experimental results from literature. Physics involved in the flow inside a dynamic separator are explained using the simulated results.
Keywords: Gas-solid flow; swirl flow; particle separation; turbulence models; particle rough wall model; turbulence particle dispersion; multiple reference frame.
A local and fast interpolation method for mesh deformation
by Jing Tang, Mingsheng Ma, Bin Li, Pengcheng Cui
Abstract: In this study, a local interpolation approach is developed to deal with the deformation of a mesh containing structured and stretched viscous elements. A new strategy is proposed to compute the local influence distance at each movable mesh point. This strategy not only helps to exclude unnecessary donor points from the computation of the new position of the mesh point, but also gets those viscous elements stiffened appropriately such that they are no longer inverted easily. Further improvements on the efficiency of the proposed algorithm are achieved by parallelizing the algorithm and developing a bounding box technique to speed up the procedure of searching donor points. Meanwhile, the robustness of the proposed algorithm in the case of large boundary movement is enhanced by incorporating a state-of-the-art multi-step technique. Various numerical experiments are conducted, and the results show that the proposed algorithm could treat cases involving complex boundary movements at a low level of computing consumptions.
Keywords: mesh deformation; local interpolation; acceleration method; parallel algorithm.
Comparative RANS turbulence modelling of lost salt core viability in high pressure die casting
by Sebastian Kohlstädt, Michael Vynnycky, Alexander Neubauer, Andreas Gebauer-Teichmann
Abstract: In this work, the implementation of three turbulence models inside the open-rnsource C++ computational fluid dynamics (CFD) library OpenFOAM were tested in 2Drnand 3D to determine the viability of salt cores in high pressure die casting. A finite-volume and volume of fluid approach was used to model the two-phase flow of molten metal and air, with the latter being treated as compressible. Encouragingly, it is found that, although the choice of turbulence model seems to affect the dispersion of the two-phase interface, the force acting at the surface of the salt core depends only very weakly on the turbulence model used. The results were also compared against those obtained using the commercially available and widely-used casting software MAGMA5.
Keywords: turbulence; RANS; volume-of-fluid method; OpenFOAM; high-pressure die casting; aluminum; lost cores; salt core viability.
NUMERICAL SIMULATION OF LIQUID MASS COLLISION WITH A WALL
by Alexander Aganin, Tatiana Guseva
Abstract: Numerical simulation of high-speed liquid mass collision with dry or wetted rigid walls by the CIP-CUP method on dynamically adaptive Soroban grids is studied. A number of specially selected test problems is used for validating the resolution of the main features of the collision separately: 1D uniform liquid flow impact onto a wall, 1D plane discontinuity breakdown at the gas-liquid interface, 2D cylindrical discontinuity breakdown in liquid, blunt liquid cone and plane semi-infinite liquid flow impacts onto a dry wall in the attached shock wave mode, sharp liquid cone impact onto a dry wall in the shockless mode with laterally spreading liquid flow. The results of their calculations are in good correlation with the corresponding analytical and numerical solutions. A problem of hemispherically-ended high-speed jet collision with a wall covered by a thin liquid layer is considered as a benchmark to illustrate the capabilities of the CIP-CUP/Soroban-grid approach to resolving the main features of the high-speed liquid collision together. Its numerical solution is in good agreement with the known similar results.
Keywords: liquid jet impact; shock waves; large deformations of gas-liquid interface; Euler equations; CIP-CUP method; Soroban grid; artificial viscosity; interface capturing.
Experimental and computational study of optically-driven electrothermal vortex
by Xudong Pan, Jae-Sung Kwon, Jian Wei Khor, Steven T. Wereley
Abstract: Optically-driven electrothermal vortex flow is one of the most effective ways to induce convection in microscale domains. In this work, side view microscopic imaging is used for qualitative flow visualization as well as quantitative μPIV measurements of the vortex pattern in microfluidic chips between simple parallel-plate electrodes. The uniform electric field is generated from parallel-plate, indium tin oxide (ITO) electrodes separated by 400 μm. Alternating current (AC) electric fields at a range of frequencies (9kHz-100kHz) and voltages (5V-40V) are applied to the electrodes to drive the flow. Simultaneously, a near-infrared (1064 nm) laser beam at various intensities is focused on the bottom electrode surface of the microchannel. Strong electrothermal vortices are observed in the flow visualization experiments and measured by μPIV. A realistic computational model featuring a laser heat source and an applied electrical field is constructed. Computational simulations are performed under the same conditions as the experiments. The simulations and the experiments show the same qualitative behaviors and also agree quantitatively when comparing the maximum velocities.
Keywords: electrothermal vortex flow; qualitative flow; μPIV,optically-driven; microfluidics.
A numerical analysis of air flow through the IC engine intake manifold
by A. Cebula, Piotr Swiatek, Sebastian Kowalczych
Abstract: Engine intake systems should be carefully designed to provide a uniform flow to all cylinders. The current note presents the initial phase of the redesign process of an intake manifold of a 4 cylinder aircraft IC engine. By means of Computational Fluid Dynamics analysis, the deficiency of the initial design in splitting the air flow among the runners is discovered, and an improvement of the original design is proposed. It is shown that a significant improvement in the flow distribution can be achieved by an appropriately installed guide vane, whereas the flow split is observed to be very sensitive to the geometry of the guide vane, necessitating a very careful design.
Keywords: intake manifold; CFD; combustion engines; flow split.
A High Order MOOD Method For Compressible Navier-Stokes Equations : Application To Hypersonic Viscous Flows
by Rodolphe Turpault, Tanh-Ha Nguyen-Bui
Abstract: A very high-order finite volumes numerical method is designed for the\r\nsimulation of Navier-Stokes equations on 2D unstructured meshes. This scheme is based on the MOOD methods described for Eulers equations, its an interesting alternative in the design of a scheme adapted to accurate simulations of flows with discontinuities, in all the domain. The main originality of our method is to include the diffusion and viscosity terms of Navier-Stokes equations. These terms are discretized with the same accuracy that convection terms. It allowss to treat the hypersonic viscous interactions with high\r\naccuracy. Numerical experiments are conducted to demonstrate the performance of the proposed method.
Keywords: MOOD Methods; High-Order; Viscous Fluids; Supersonic; Discontinuities; Simulations.
Simulating High Rayleigh Number Natural Convection in High Aspect Ratio Horizontal Rectangular Enclosures Using Code Saturne Platform
by Fahad Sarfraz Butt, Abdul Waheed Badar, Abdullah Zafar, Ajaz Bashir Janjua
Abstract: In the present study, buoyancy driven flows of water and air in very high aspect ratio (12-48) horizontal rectangular enclosures are studied numerically for Rayleigh numbers ranging from 103 to 107 using open-source CFD tools to obtain natural convection heat transfer coefficients which are then compared with established empirical correlations based on experimental results. This study has been motivated by the finding that hardly any CFD based literature on very high aspect ratio rectangular enclosures exist and also by the fact that such enclosures have numerous applications in solar thermal systems such as solar collectors, solar passive heating/cooling systems, and solar stills etc. It has been reported in the literature that at high aspect ratios, the numerical solution suffers from convergence issues. In the present study, using Code_Saturne as flow solver, the convergence issues have not risen and the error between numerical and experimental results increases with an increase in Rayleigh number bounded by maximum relative error of approximately 8%.
Keywords: CFD; Heat-Transfer; Convection; Enclosures; Code saturne.
A numerical approach to solve fluid-solid two-phase flows using time splitting projection method with a pressure correction technique
by Kambiz Farahi Moghadam, Mohammad Ali Banihashemi, Peyman Badiei, Ali Shirkavand
Abstract: This study used a vertical 2D model to simulate the sediment transport pattern in open channels by applying the EulerEuler two-phase flow model or the complete two-fluid model based on the Favre averaging method. In this study, a two-phase hydrodynamic method was developed to simulate the dynamics of water flow and sediment. The projection method with a pressure correction technique, along with the time splitting algorithm was used for the first time to solve the EulerEuler complete two-phase equations of fluid-sediment. Moreover, the conservation of mass and momentum of both phases was assured generally and partially in the equation discretization stage by providing a novel method developed from integration of the momentum and continuity equations of each phase. In addition, the horizontal and vertical velocities of both phases were discretized independently, without multiplying them by additional parameters, such as the phase concentration. At the end, the models performance in simulating the sediment flow process in a direction perpendicular to the flow was assessed. This assessment for the first time used a Favre averaging-based two-phase model to investigate longitudinal changes in the sediment profile. Moreover, the sediment concentration profile was evaluated in a specific type of flow, known as the sheet flow. Assessment of the model showed its high capability in dynamic simulation of water and sediment flows either at the flow depth or along the channel.
Keywords: complete two fluid model; Favre averaging; numerical modelling; pressure correction technique; sediment transport; timesplitting; two-phase flow; vertical 2-D model.
Computational investigation and optimization study on system performance of heat sink using perforated pin fins mounted at different angles
by Ambarish Maji, Dipankar Bhanja, Promod K. Patowari
Abstract: The current work investigates the performance of heat sink using perforated pin fins of different shapes with various perforation geometries like circular, diamond shaped and elliptical type. Three dimensional CFD simulations have been performed to explore the effects of fin shape, perforation geometry and perforation size on system performance. This work also analyzes the variations in heat transfer enhancement through elliptical and square shaped staggered pin fins with elliptical perforations mounted at different angular position on the path of the flow. Multi Objective Optimization under Ratio Analysis is applied to select the best heat sink configuration. Exergy efficiencies, entropy generations and irreversibilities are also calculated for all the fin shapes having various sizes of perforations. It is observed that heat transfer rate of perforated fins up to certain perforation number and size are always greater than their solid counterparts and with the change in perforation geometry and fin shape heat dissipation rate enhances significantly.
Keywords: Heat Transfer; Perforated fin; System performance; Angular position; Optimization; Computational fluid dynamics.
A Numerical Investigation of the Compressible Flow in the Ejector of a Vapor Ejector Refrigeration System
by Arumugam Megalingam, Viswanath Babu
Abstract: Numerical simulations of the flow in a vapor ejector have been carried out. Real gas effects are accounted for in the calculations. Both ejection as well as flow-through studies have been performed. Effects of the generator and evaporator temperatures and position of the primary nozzle have been investigated. Predicted values of the suction pressure and COP havernbeen compared with experimental values reported in the literature. In addition, secondary flow area has also been evaluated and correlated with the COP. By tracking the sonic line and the edge of the primary stream and flow separation, insights on the gas dynamic and fluid dynamic aspects of the flow field and how they influence the entrainment of the secondary stream and consequently the COP are brought out. The study reveals that, in addition to the choking of thernsecondary stream, the expansion of the primary stream and the area available for the secondary stream also play a key role in affecting the performance of the vapor ejector.
Keywords: Numerical simulation;Ejector; Real gas effects; Solar Refrigeration.