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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 (31 papers in press)

Regular Issues

  • 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;.

  • 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.

  • 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.
    DOI: 10.1504/PCFD.2021.10048084
     
  • 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.

  • 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.

  • 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.
    DOI: 10.1504/PCFD.2022.10047990
     
  • 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   Order a copy of this article
    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.

  • NUMERICAL INVESTIGATION OF THE CO FLOW JET AIRFOIL ON AERODYNAMIC PERFORMANCE   Order a copy of this article
    by Cm Vigneswaran, Vishnu Kumar 
    Abstract: The present project performed the numerical analysis to establish the correlation between the aerodynamic performance of a co-flow jet (CFJ) airfoil and the coefficient of jet momentum (C?). The coefficient of jet momentum is a non-dimensional parameter that can be defined and characterised similarly to coefficient of lift (CL) and coefficient of drag (CD) and it is significantly correlated with the aerodynamic performance of the CFJ airfoil. The CFJ airfoils are designed and analysed with three distinct coefficient of jet momentum of 0.03, 0.04 and 0.05 by altering the injection slot height, injection mass flow rate, injection jet velocity, while retaining the Mach number, Reynolds number and the location of the slots are constant. To carry out the numerical analysis, the Spalart-Allmaras turbulence model was employed to solve RANS equations for 2D incompressible flow. The CFJ airfoils with similar coefficient of jet momentum having the higher injection velocity are increasing the CL and stall margin to a larger extent, yet the higher mass flow rate reduce drag to some extent.
    Keywords: airfoil; co-flow jet airfoil; co-flow jet; CFJ; jet momentum coefficient; injection jet velocity; aerodynamic performance.
    DOI: 10.1504/PCFD.2022.10048024
     
  • An adaptive approach for modeling ice accretion on aircraft   Order a copy of this article
    by Hadi Siyahi, A. Cihat Baytas 
    Abstract: In conventional ice-accretion models, the critical ice thickness $(B_g)$ and time $(t_g)$ in which glaze ice first appear are calculated at the very beginning, then based on these critical transient criteria will be an attempt to apply either the rime ice or the glaze ice calculations. In the proposed ice-accretion model presented in this study, without the need for the calculation of the critical criteria, the calculations of the ice accretion begin with rime-ice, if the results are plausible they would be accepted, otherwise, these results are ignored and the glaze-ice calculation would be applied. The strength of the present approach is that it causes the numerical computations of the icing to progress the same as the real physics of the icing. The results of the present study show that the proposed ice-accretion approach for all rime, mixed, and glaze ice-regimes gives more accurate results than the conventional ice-accretion models.
    Keywords: Aircraft icing; Ice accretion; Messinger model; Extended Messinger model; Run back Water model; FVM.
    DOI: 10.1504/PCFD.2022.10048280
     
  • Numerical investigations on the performance of Darrieus vertical axis wind turbine with NACA0017 blade profile   Order a copy of this article
    by Satyajit Das Karmakar, Syed Rahman, HIMADRI CHATTOPADHYAY 
    Abstract: The selection of effective blade profile for vertical axis wind turbines is an important criterion for harnessing wind energy. In this paper, transient simulation of Darrieus lift type turbine having NACA0017 blade profile is reported. URANS equations are solved with SST K
    Keywords: vertical axis wind turbine; NACA0017 airfoil shape; performance enhancement; power coefficient; URANS.
    DOI: 10.1504/PCFD.2022.10048848
     
  • Comparison between variable forcing techniques of the lattice Boltzmann method for turbulent flow simulations   Order a copy of this article
    by Waleed Abdel Kareem, Hadeer Mohamed 
    Abstract: A comparison between different forcing techniques of the lattice Boltzmann method (LBM) is carried out for isotropic turbulence with resolutions of 1283 and 2563 , respectively. Four forcing techniques are investigated with the lattice Boltzmann D3Q19 model. Few forcing methods were suggested to add a force term to the lattice Boltzmann method (LBM) but they are neither tested nor compared for box turbulence. The first technique is performed by adding the constant force randomly to the collision term. The second is depending on shifting the velocity field. The third technique is achieved by adding the force to the collision term with shifting the velocity field. The fourth technique considered the discrete lattice effects where a forcing function with consistent moments of the hydrodynamics equations is added to the collision operator with shifting the velocity field. Results show that the obtained turbulent velocity fields yield universal characteristics similar to previous studies.
    Keywords: homogeneous isotropic turbulence; HIT; lattice Boltzmann method; LBM; tube-like vortices; variable forcing techniques.
    DOI: 10.1504/PCFD.2022.10048996
     
  • Dynamics of Taylor Bubbles in non-Newtonian Shear Thinning Continuous Phase   Order a copy of this article
    by Shilpi Chatterjee, Abhiram Hens, Kartik Chandra Ghanta, G. Biswas 
    Abstract: Droplet-based microfluidics has emerged as an efficient platform in a number of lab-on-chip devices for chemical or biomedical analysis. In most of such applications, a non-Newtonian complex liquid constitutes the continuous phase. In the present study, a two-phase gas
    Keywords: Taylor bubble; multiphase flow; microchannel; CFD; pressure drop.
    DOI: 10.1504/PCFD.2022.10049300
     
  • An improved alternative weighted essentially non-oscillatory scheme for conservation laws   Order a copy of this article
    by Uttam Rajput, Krishna SINGH 
    Abstract: In the present study, a fifth-order improved alternative weighted essentially non-oscillatory scheme has been developed for non-linear hyperbolic conservation laws. We have proposed an improved fifth-order smoothness indicator to design the present scheme. Further, the numerical flux evaluation is based on the reconstruction of primitive variables rather than conservative variables. The third-order TVD Runge-Kutta method has been used for the time advancement of the solution. The computations have been performed for various one, two, and three-dimensional test cases. Numerical results are compared with the exact solution and results with other high-resolution schemes. The proposed scheme resolves the fine-scale structure with a higher resolution. Further, it is computationally efficient, produces less spurious oscillations, and shows better conservation of kinetic energy for 3D Taylor-Green vortex case.
    Keywords: Alternative WENO scheme; Hyperbolic equations; Unsteady; Numericalrnfluxes; High-resolution scheme; Compressible flow.

  • Numerical study of combustion and nitrogen oxide generation for recycled flue gas distribution in supercritical carbon dioxide coal-fired boiler with double furnace   Order a copy of this article
    by Yong Wu, Jinyan Yuan, Mingming Wang, Jimin Wang, Lixin Han, Mingyan Gu, Xiangyong Huang, Huaqiang Chu 
    Abstract: After flue gas recirculation and structural adjustment are adopted to avoid local overheating of the cooling wall, the coal combustion characteristics in the furnace would need to be reevaluated to control nitrogen oxide generation. According to the configuration design of a 1000 MW supercritical carbon dioxide coal-fired boiler with a novel double furnace, a comprehensive model with the Euler-Lagrange framework was used to examine the velocity, the temperature, and the species concentration in the double furnace under the unique heat transfer boundary. The comparative study of the coal combustion and nitrogen oxide generation characteristics on different recycled flue gas distribution ratios was in detail explored. The results indicated that the gas temperature at the exit gradually increases as the recycled flue gas distribution ratio, while the nitrogen oxide concentration gradually increases. When the recycled flue gas rate from different positions is relatively the same, the combustion effect is the best.
    Keywords: supercritical carbon dioxide coal-fired boiler; double furnace; recycled flue gas distribution ratio; combustion characteristics; nitrogen oxide generation; numerical simulation.

  • Numerical comparison of laminar flow and turbulence models of hemodynamics based on pulmonary artery stenosis   Order a copy of this article
    by Fan He, Xinyu Wang, Lu Hua, Tingting Guo 
    Abstract: Pulmonary artery stenosis is closely related to hemodynamics. In this paper, the laminar and turbulent flows in the same three-dimensional model of pulmonary artery stenosis are numerically calculated by using fluid-structure interaction, and the obtained maximum velocity, pressure and wall shear stress are compared and analyzed. The numerical results show that the hemodynamic parameters of laminar flow model are slightly higher than those of k-? turbulence model. Specially, the wall shear stress at both ends of stenosis is more sensitive to laminar flow model. This study provides the effects of laminar flow and k-? turbulence on pulmonary artery hemodynamics. It gives a basis for the follow-up realistic hemodynamic numerical simulation of pulmonary artery model and has a guiding significance for clinical diagnosis and treatment, and promotes the development of the combination of mechanics and medicine.
    Keywords: Pulmonary artery; stenosis; hemodynamics; laminar flow; turbulence.

  • Pre- and Post-Stall Characteristics of a Very Light Aircraft’s Wing for Different Design Parameters   Order a copy of this article
    by Berkan An?l?r, Kurtulus Dilek Funda 
    Abstract: The impact of taper ratio, dihedral angle and wing tip shape on the aerodynamics of a very light aircraft’s wing has been investigated by performing URANS simulations at Reynolds number of 5
    Keywords: very light aircraft; VLA; unsteady flow; computational fluid dynamics; taper ratio; dihedral angle; stall cell; wing aerodynamics; SD7062.
    DOI: 10.1504/PCFD.2022.10050230
     
  • Numerical Investigation of SD7062 Airfoil with SingleSlotted Flap for Different Flight Conditions   Order a copy of this article
    by Berkan An?l?r, Kurtulus Dilek Funda 
    Abstract: The two-dimensional numerical simulations using unsteady Reynolds-averaged Navier-Stokes are performed to investigate the aerodynamic performance of SD7062 airfoil with a 0.30c single-slotted flap at cruise, takeoff, and landing conditions for various angles of attack corresponding to pre-and post-stall regimes. The time-averaged aerodynamic characteristics of the configurations are compared to the different angles of attack results and other configurations. The maximum lift coefficient value of 3.302 is obtained with 35
    Keywords: single-slotted flap; SD7062; computational fluid dynamics; CFD; flap gap size.
    DOI: 10.1504/PCFD.2022.10050486
     
  • Variational Formulation of Incompressible Navier-Stokes Equations in Primitive Variables   Order a copy of this article
    by Akin Ecer 
    Abstract: A "Variational Formulation of Navier-Stokes Equations" are provided on terms of primitive variables. The difference and relationship between the "Mechanical Pressure" and the "Thermodynamic Pressure" is noted. The formulation of the functional requires the distinction between these two variables. The condition of incompressibility also appears in the formulation. The existence of a variational functional suggests the uniqueness of he equations for incompressible flows.rnPrevious formulations require additional variables and an adjoint operator for the formulation of a variational functional. Existence of the present functional suggests that if the pressure is properly defined, the relationship between the compressible and incompressible flows are defined and related to the condition of incompressibility.
    Keywords: Variational Formulation; Incompressible Flows; Navier-Stokes Equations.