A Numerical Study of Laminar and Intermittently Turbulent Boundary Layer on an Oscillating Flat Plate Using Pseudo-Compressible RANS Model

2020 ◽  
Author(s):  
Shivank Srivastava ◽  
Brandon M. Taravella ◽  
Kazim M. Akyuzlu
Keyword(s):  
Boundary Layer ◽  
Turbulent Flow ◽  
Flat Plate ◽  
Turbulent Flows ◽  
Numerical Study ◽  
Navier Stokes ◽  
Flow Conditions ◽  
Rans Model ◽  
Explicit Finite Difference ◽  
Turbulent Flow Conditions

Abstract A numerical study was conducted to study the unsteady characteristics of incompressible boundary layer flows over an oscillating flat plate under laminar and intermittently turbulent flow conditions using pseudo-compressible Reynolds Averaged Navier-Stokes (RANS) model. The numerical study is carried out using an in-house code and a commercial CFD package (Fluent). Two equation (k-ε) turbulence closure model, modified near the wall, is used along with RANS equations to simulate intermittently turbulent flows. Fully Explicit-Finite Difference technique (FEFD) is employed to solve the governing differential equations. For validation purposes, the velocity fields predicted by the in-house code and commercial CFD package are compared to the one given by analytical solution to Stokes’ second problem for an oscillating flat plate. Numerical experiments were conducted for unsteady cases for Stokes’ Reynolds number corresponding to laminar and intermittently turbulent flows, respectively. Time dependent velocity profiles, shear stress distribution, turbulence properties during the accelerating and decelerating stages of oscillations are predicted. The above predictions are then compared to ones predicted by commercial CFD code. The velocity magnitudes predicted by the in-house code and commercial CFD code are within acceptable range for laminar and intermittently turbulent flow conditions.

scholarly journals A Numerical Study of Laminar and Intermittently Turbulent Flow Over a Flat Plate Using Pseudo-Compressibility Model

2019 ◽  
Author(s):  
S. Srivastava ◽  
J. R. Eastridge ◽  
B. M. Taravella ◽  
K. M. Akyuzlu
Keyword(s):  
Boundary Layer ◽  
Finite Difference ◽  
Turbulent Flow ◽  
Flat Plate ◽  
Turbulent Flows ◽  
Numerical Study ◽  
Computer Code ◽  
Second Order ◽  
Boundary Layer Equations ◽  
Grid Convergence Index

Abstract A study was conducted to investigate the characteristics of incompressible unsteady boundary layer flows (laminar and intermittently turbulent), numerically and experimentally. The main objective of the study is to validate and verify (V&V) the accuracy of the proposed pseudo-compressibility model in solving the incompressible Navier-Stokes (NS) equations. This approach will enable one to use a second order accurate (temporally and spatially) implicit finite-difference (FD) technique to solve NS equations (including RANS equations). Here, the proposed pseudo-compressibility model is used for laminar and intermittent turbulent flow simulations. Flow over a flat plate is chosen as the benchmark case for the validation of the proposed pseudo-compressibility model. An in-house code is developed to solve the boundary layer equations using an Alternating-Direction Explicit (ADE) FD technique. The boundary layer equations are discretized using explicit FD techniques which are second order accurate. The velocity field predicted by this code is compared to the one given by Blasius’ analytical solution. A second in-house code is also developed which adopts the proposed model of pseudo-compressibility to solve the incompressible NS equations. The two dimensional, unsteady conservation of mass and momentum equations are discretized using explicit finite-difference techniques. A standard K-ε closure model is used along with RANS equation to simulate turbulent flows. The primitive variables (velocity and pressure) predicted by this code are compared to the ones predicted by a commercial CFD package (Fluent). Once the method of pseudo-compressibility is validated, it is then implemented into another in-house computer code which employs implicit FD technique and Coupled Modified Strongly Implicit Procedure (CMSIP) to solve for the unknowns of the problem under study. The predictions based on the pseudo-compressibility model for laminar flow are validated using the results of the experiments in which Particle Image Velocimetry (PIV) technique was employed. The verification; that is, the numerical uncertainty estimation of the pseudo-compressible code was accomplished by using the Grid Convergence Index (GCI) method. The results of the present study indicate that the proposed pseudo-compressibility model is capable of predicting experimentally observed characteristics of the external flows successfully, and deviations between the predicted velocity magnitudes and experimentally measured velocities are within an acceptable range for laminar and intermittently turbulent flows conditions.

Performance and Flow Characteristics of an Optimized Supercritical Compressor Stator Cascade

2005 ◽  
Vol 128 (3) ◽  
pp. 435-443 ◽  
Author(s):  
Bo Song ◽  
Wing F. Ng
Keyword(s):  
Boundary Layer ◽  
Numerical Study ◽  
Flow Behavior ◽  
Flow Characteristics ◽  
Navier Stokes ◽  
Flow Conditions ◽  
Supercritical Flow ◽  
Gradient Distribution ◽  
Controlled Diffusion ◽  
Mach Numbers

An experimental and numerical study was performed on an optimized compressor stator cascade designed to operate efficiently at high inlet Mach numbers (M1) ranging from 0.83 to 0.93 (higher supercritical flow conditions). Linear cascade tests confirmed that low losses and high turning were achieved at normal supercritical flow conditions (0.7<M1<0.8), as well as higher supercritical flow conditions (0.83<M1<0.93), both at design and off-design incidences. The performance of this optimized stator cascade is better than those reported in the literature based on Double Circular Arc (DCA) and Controlled Diffusion Airfoil (CDA) blades, where losses increase rapidly for M1>0.83. A two-dimensional (2D) Navier-Stokes solver was applied to the cascade to characterize the performance and flow behavior. Good agreement was obtained between the CFD and the experiment. Experimental loss characteristics, blade surface Mach numbers, shadowgraphs, along with CFD flowfield simulations, were presented to elucidate the flow physics. It is found that low losses are due to the well-controlled boundary layer, which is attributed to an optimum flow structure associated with the blade profile. The multishock pattern and the advantageous pressure gradient distribution on the blade are the key reasons of keeping the boundary layer from separating, which in turn accounts for the low losses at the higher supercritical flow conditions.

Performance and Flow Characteristics of an Optimized Supercritical Compressor Stator Cascade

2005 ◽  
Author(s):  
Bo Song ◽  
Wing F. Ng
Keyword(s):  
Boundary Layer ◽  
Numerical Study ◽  
Flow Behavior ◽  
Flow Characteristics ◽  
Navier Stokes ◽  
Flow Conditions ◽  
Supercritical Flow ◽  
Gradient Distribution ◽  
Controlled Diffusion ◽  
Mach Numbers

An experimental and numerical study was performed on an optimized compressor stator cascade designed to operate efficiently at high inlet Mach numbers (M1) ranging from 0.83 to 0.93 (higher supercritical flow conditions). Linear cascade tests confirmed that low losses and high turning were achieved at normal supercritical flow conditions (0.7 &lt; M1 &lt; 0.8), as well as higher supercritical flow conditions (0.83 &lt; M1 &lt; 0.93), both at design and off-design incidences. The performance of this optimized stator cascade is better than those reported in the literature based on Double Circular Arc (DCA) and Controlled Diffusion Airfoil (CDA) blades, where losses increase rapidly for M1 &gt; 0.83. A 2-D Navier-Stokes solver was applied to the cascade to characterize the performance and flow behavior. Good agreement was obtained between the CFD and the experiment. Experimental loss characteristics, blade surface Mach numbers, shadowgraphs, along with CFD flowfield simulations, were presented to elucidate the flow physics. It is found that low losses are due to the well-controlled boundary layer, which is attributed to an optimum flow structure associated with the blade profile. The multi-shock pattern and the advantageous pressure gradient distribution on the blade are the key reasons of keeping the boundary layer from separating, which in turn accounts for the low losses at the higher supercritical flow conditions.

scholarly journals Simulations of a Single-Phase Flow in a Compound Parabolic Concentrator Reactor

2018 ◽  
Vol 2018 ◽  
pp. 1-8 ◽  
Author(s):  
Tzayam Pérez ◽  
José L. Nava
Keyword(s):  
Turbulent Flow ◽  
Flow Visualization ◽  
High Speed ◽  
Turbulent Viscosity ◽  
Navier Stokes ◽  
Flow Conditions ◽  
Compound Parabolic Concentrator ◽  
Convection Model ◽  
Diffusion Convection ◽  
Turbulent Flow Conditions

This paper deals with the analysis and interpretation of flow visualization and residence time distribution (RTD) in a compound parabolic concentrator (CPC) reactor using computational fluid dynamics (CFD). CFD was calculated under turbulent flow conditions solving the Reynolds averaged Navier–Stokes (RANS) equation expressed in terms of turbulent viscosity and the standard k−ε turbulent model in 3D. A 3D diffusion-convection model was implemented in the CPC reactor to determine the RTD. The fluid flow visualization and RTD were validated with experimental results. The CFD showed that the magnitude of the velocity field remains almost uniform in most of the bulk reactor, although near and inside the 90° connectors and the union segments, the velocity presented low- and high-speed zones. Comparisons of theoretical and experimental RTD curves showed that the k−ε model is appropriate to simulate the nonideal flow inside the CPC reactor under turbulent flow conditions.

Lattice Boltzmann Method Based on Large-Eddy Simulation (LES) Used to Investigate the Unsteady Turbulent Flow on Series of Cavities

2020 ◽  
Author(s):  
Insaf Mehrez ◽  
Ramla Gheith ◽  
Fethi Aloui
Keyword(s):  
Boltzmann Equation ◽  
Turbulent Flow ◽  
Turbulent Flows ◽  
Lattice Boltzmann ◽  
Turbulence Modeling ◽  
Stokes Equations ◽  
Numerical Study ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Large Eddy

Abstract A numerical study is proposed to analyze the turbulent flow structures. This paper aims to determine the effect of the series of the cavities. The configuration is similar to that represented by two walls with infinite width, one of which is mobile and the other is fixed. The series of cavity are placed on the fixed wall. The objectives are to study the aero acoustic capabilities of LBM and to build and to assess the efficiency of the Lattice Boltzmann Equation (LBE) as a new computational tool to perform the Large-Eddy Simulations (LES) for turbulent flows. In the first part, the background of LBM is presented and the construction of Navier-Stokes equations from Boltzmann equation is discussed. The LBM-LES model for solving transition is developed and turbulence modeling is implemented. In the second part, the dynamics of the flows in the vicinity of cavities with symmetric or asymmetric edges are considered, to then discuss the oscillation phenomenon. The effect of the geometric of the cavity and the Reynolds numbers were studied to investigate the fluid flow dynamics. We were focusing on the dynamics of asymmetric deep cavity flows, to put forward the topology of the cavity flow and to highlight the effects of dissymmetry and aspect ratio.

Numerical Study of Boundary Layers With Reverse Wedge Flows Over a Semi-Infinite Flat Plate

2009 ◽  
Vol 77 (2) ◽  
Author(s):  
R. Ahmad ◽  
K. Naeem ◽  
Waqar Ahmed Khan
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Numerical Study ◽  
Boundary Layer Equation ◽  
Wedge Angle ◽  
Adverse Pressure Gradient ◽  
Problem Solution ◽  
Weighted Residual Method ◽  
Boundary Layer Problem ◽  
Layer Problem

This paper presents the classical approximation scheme to investigate the velocity profile associated with the Falkner–Skan boundary-layer problem. Solution of the boundary-layer equation is obtained for a model problem in which the flow field contains a substantial region of strongly reversed flow. The problem investigates the flow of a viscous liquid past a semi-infinite flat plate against an adverse pressure gradient. Optimized results for the dimensionless velocity profiles of reverse wedge flow are presented graphically for different values of wedge angle parameter β taken from 0≤β≤2.5. Weighted residual method (WRM) is used for determining the solution of nonlinear boundary-layer problem. Finally, for β=0 the results of WRM are compared with the results of homotopy perturbation method.

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