scholarly journals The Effect of a Pressure-Containing Correlation Model on Near-Wall Flow Simulations With Reynolds Stress Transport Models

2014 ◽  
Vol 136 (6) ◽  
Author(s):  
Svetlana V. Poroseva
Keyword(s):  
Flow Behavior ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Correlation Model ◽  
Transport Models ◽  
Wall Functions ◽  
Wall Flow ◽  
Model Equations ◽  
Rotating Pipe Flow

It is accustomed to think that turbulence models based on solving the Reynolds-averaged Navier–Stokes (RANS) equations require empirical functions to accurately reproduce the behavior of flow characteristics of interest, particularly near a wall. The current paper analyzes how choosing a model for pressure-strain correlations in second-order closures affects the need for introducing empirical functions in model equations to reproduce the flow behavior near a wall correctly. An axially rotating pipe flow is used as a test flow for the analysis. Results of simulations demonstrate that by using more physics-based models to represent pressure-strain correlations, one can eliminate wall functions associated with such models. The higher the Reynolds number or the strength of imposed rotation on a flow, the less need there is for empirical functions regardless of the choice of a pressure-strain correlation model.

scholarly journals An Investigation of Turbulence Modelling in Transonic Fans Including a Novel Implementation of an Implicit κ–ϵ Turbulence Model

1992 ◽  
Author(s):  
Mark G. Turner ◽  
Ian K. Jennions
Keyword(s):  
Turbulence Models ◽  
Algebraic Model ◽  
Turbulence Modelling ◽  
Experimental Results ◽  
Navier Stokes ◽  
Multiple Time Scales ◽  
Multiple Time ◽  
Wall Functions ◽  
Solution Methods ◽  
Explicit Solver

An explicit Navier-Stokes solver has been written with the option of using one of two types of turbulence models. One is the Baldwin-Lomax algebraic model and the other is an implicit k-ϵ model which has been coupled with the explicit Navier-Stokes solver in a novel way. This type of coupling, which uses two different solution methods, is unique and combines the overall robustness of the implicit k-ϵ solver with the simplicity of the explicit solver. The resulting code has been applied to the solution of the flow in a transonic fan rotor which has been experimentally investigated by Wennerstrom. Five separate solutions, each identical except for the turbulence modelling details, have been obtained and compared with the experimental results. The five different turbulence models run were: the standard Baldwin-Lomax model both with and without wall functions, the Baldwin-Lomax model with modified constants and wall functions, a standard k-ϵ model and an extended k-ϵ model which accounts for multiple time scales by adding an extra term to the dissipation equation. In general, as the model includes more of the physics, the computed shock position becomes closer to the experimental results.

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.

On the Investigation of Flow around the Square Cylinder Based on Different LES Models

2012 ◽  
Vol 594-597 ◽  
pp. 2676-2679
Author(s):  
Zhe Liu
Keyword(s):  
Flow Characteristics ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Square Cylinder ◽  
Rans Model ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Reynolds Averaged Navier Stokes ◽  
Les Model

Although the conventional Reynolds-averaged Navier–Stokes (RANS) model has been widely applied in the industrial and engineering field, it is worthwhile to study whether these models are suitable to investigate the flow filed varying with the time. With the development of turbulence models, the unsteady Reynolds-averaged Navier–Stokes (URANS) model, detached eddy simulation (DES) and large eddy simulation (LES) compensate the disadvantage of RANS model. This paper mainly presents the theory of standard LES model, LES dynamic model and wall-adapting local eddy-viscosity (WALE) LES model. And the square cylinder is selected as the research target to study the flow characteristics around it at Reynolds number 13,000. The influence of different LES models on the flow field around the square cylinder is compared.

scholarly journals RANS study of very high Reynolds-number plane turbulent Couette flow

2020 ◽  
Vol 14 (2) ◽  
pp. 6663-6678
Author(s):  
Akshay Sherikar ◽  
P. J. Disimile
Keyword(s):  
Reynolds Number ◽  
Couette Flow ◽  
High Reynolds Number ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Shear Stresses ◽  
Sensitivity Testing ◽  
Wall Functions ◽  
High Reynolds ◽  
Very High

The objective of this study is to expound on the deliverables of a steady-state RANS (Reynolds Averaged Navier Stokes) simulation in one of the simplest flows, Couette flow, at a very high Reynolds number. To that end, a process to perform better grid sensitivity testing is introduced. Three two-equation turbulence models ( , , and ) are compared against each other as well as pitted against formal literature on the subject and core flow velocities, slopes, wall-bounded velocities, shear stresses and kinetic energies are analyzed.  applied with enhanced wall functions is consistently found to be in better agreement with previous studies. Finally, plane turbulent Couette flow at  51,099, the range at which it has not been studied experimentally, numerically or analytically in former studies, is simulated. The results are found to be consistent with the trends asserted by literature and preliminary computations of this study.

A Methodology for Simulating Compressible Turbulent Flows

2005 ◽  
Vol 73 (3) ◽  
pp. 405-412 ◽  
Author(s):  
Hermann F. Fasel ◽  
Dominic A. von Terzi ◽  
Richard D. Sandberg
Keyword(s):  
Turbulent Flows ◽  
Compressible Flows ◽  
Bluff Body ◽  
Turbulence Modeling ◽  
Flow Behavior ◽  
Flow Simulation ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Fine Grid ◽  
Local Flow

A flow simulation Methodology (FSM) is presented for computing the time-dependent behavior of complex compressible turbulent flows. The development of FSM was initiated in close collaboration with C. Speziale (then at Boston University). The objective of FSM is to provide the proper amount of turbulence modeling for the unresolved scales while directly computing the largest scales. The strategy is implemented by using state-of-the-art turbulence models (as developed for Reynolds averaged Navier-Stokes (RANS)) and scaling of the model terms with a “contribution function.” The contribution function is dependent on the local and instantaneous “physical” resolution in the computation. This physical resolution is determined during the actual simulation by comparing the size of the smallest relevant scales to the local grid size used in the computation. The contribution function is designed such that it provides no modeling if the computation is locally well resolved so that it approaches direct numerical simulations (DNS) in the fine-grid limit and such that it provides modeling of all scales in the coarse-grid limit and thus approaches a RANS calculation. In between these resolution limits, the contribution function adjusts the necessary modeling for the unresolved scales while the larger (resolved) scales are computed as in large eddy simulation (LES). However, FSM is distinctly different from LES in that it allows for a consistent transition between RANS, LES, and DNS within the same simulation depending on the local flow behavior and “physical” resolution. As a consequence, FSM should require considerably fewer grid points for a given calculation than would be necessary for a LES. This conjecture is substantiated by employing FSM to calculate the flow over a backward-facing step and a plane wake behind a bluff body, both at low Mach number, and supersonic axisymmetric wakes. These examples were chosen such that they expose, on the one hand, the inherent difficulties of simulating (physically) complex flows, and, on the other hand, demonstrate the potential of the FSM approach for simulations of turbulent compressible flows for complex geometries.

Simulation of a 3D Axisymmetric Hill: Comparison of RANS and Hybrid RANS-LES Models

2016 ◽  
Author(s):  
Tausif Jamal ◽  
D. Keith Walters
Keyword(s):  
Experimental Data ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Boundary Layer Separation ◽  
Navier Stokes ◽  
Leeward Side ◽  
Mean Flow ◽  
Rans Model ◽  
Reynolds Number Flow ◽  
Low Dissipation

Computational fluid dynamics (CFD) prediction of high Reynolds number flow over a 3D axisymmetric hill presents a unique set of challenges for turbulence models. The flow on the leeward side of the hill is characterized by the presence of complex vortical structures, unsteady wakes, and regions of boundary layer separation. As a result, traditional eddy-viscosity Reynolds-averaged Navier-Stokes (RANS) models have been found to perform poorly. Recent studies have focused on the use of Large Eddy Simulation (LES) and hybrid RANS-LES (HRL) methods to improve accuracy. In this study, the capability of a dynamic hybrid RANS-LES (DHRL) model to resolve the flow over a 3D axisymmetric hill is investigated and compared to numerical results using a traditional RANS model and a conventional hybrid RANS-LES model, and to experimental data. Results show that the RANS model fails to accurately predict the mean flow features in the wake region, which is in agreement with prior studies. The conventional HRL model provides better prediction of the flow characteristics but suffers from grid sensitivity and delayed transition to LES mode. The DHRL method provides the best agreement with experimental data overall and shows least sensitivity to grid resolution. Results also highlight the importance of using a low dissipation flux formulation for flow simulations in which a portion of the turbulence spectrum is resolved, including hybrid RANS-LES.

scholarly journals Optimization of artillery projectiles base drag reduction using hot base flow

2019 ◽  
Vol 23 (1) ◽  
pp. 353-364
Author(s):  
Mohammed Dali ◽  
Slobodan Jaramaz
Keyword(s):  
Drag Reduction ◽  
Stokes Equations ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Combustion Products ◽  
Base Flow ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Base Bleed ◽  
Base Drag

The CFD numerical simulations were carried out to investigate the base drag characteristics of a projectile with base bleed unit with a central jet. Different base bleed grain types with different combustion temperatures were used. The goal was to find a way to effectively control the base flow for base drag reduction and optimisate the latter using an adequate CFD software. Axisymmetric, compressible, mass-averaged Navier-Stokes equations are solved using the k-? SST, transition k-kl-?, and RSM turbulence models. The various base flow characteristics are obtained by the change in the non-dimensionalized injection impulse. The results obtained through the present study show that there is an optimum bleed condition for all base bleed grains tested. That optimum is dependent on the temperature of the grain combustion products. The optimum reduces the total drag for 6,9% in the case of air injection at temperature of 300 K and reaches up to 28% in the case of propellant combustion products injection at almost 2500 K. Besides, the increasing of molecular weight has a role no less important than temperature of the combustion products in terms of base drag reduction.

scholarly journals LES and RANS Analysis of the End-Wall Flow in a Linear LPT Cascade With Variable Inlet Conditions: Part II — Loss Generation

2018 ◽  
Author(s):  
Michele Marconcini ◽  
Roberto Pacciani ◽  
Andrea Arnone ◽  
Vittorio Michelassi ◽  
Richard Pichler ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Companion Paper ◽  
Wall Boundary Layer ◽  
Wall Flow ◽  
Inlet Conditions ◽  
End Wall ◽  
The Impact

In low-pressure-turbines (LPT) at design point around 60–70% of losses are generated in the blade boundary layers far from end-walls, while the remaining 30%–40% is controlled by the interaction of the blade profile with the end-wall boundary layer. Increasing attention is devoted to these flow regions in industrial design processes. Experimental techniques have shed light on the mechanism that controls the growth of the secondary vortices, and scale-resolving CFD have provided a detailed insight into the vorticity generation. Along these lines, this paper discusses the end-wall flow characteristics of the T106 profile with parallel end-walls at realistic LPT conditions, as described in the experimental setup of Duden and Fottner (1997) “Influence of Taper, Reynolds Number and Mach Number on the Secondary Flow Field of a Highly Loaded Turbine Cascade”, P. I. Mech. Eng. A-J. Pow., 211 (4), pp.309–320. The simulations target first the same inlet conditions as documented in the experiments, and determines the impact of the incoming boundary layer thickness by running additional cases with modified incoming boundary layers. Calculations are carried out by both RANS, due to its continuing role as the design verification workhorse, and highly-resolved LES. Part II of the paper focuses on the loss generation associated with the secondary end-wall vortices. Entropy generation and the consequent stagnation pressure losses are analyzed following the aerodynamic investigation carried out in the companion paper. The ability of classical turbulence models generally used in RANS to discern the loss contributions of the different vortical structures is discussed in detail and the attainable degree of accuracy is scrutinized with the help of LES and the available test data. The purpose is to identify the flow features that require further modelling efforts in order to improve RANS/URANS approaches and make them able to support the design of the next generation of LPTs.

3D Simulation of Flow in a Vortex Cell Using RANS and Hybrid RANS-LES Turbulence Models

2017 ◽  
Author(s):  
Tausif Jamal ◽  
D. Keith Walters ◽  
Varun Chitta
Keyword(s):  
Large Scale ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
General Information ◽  
Navier Stokes ◽  
Test Case ◽  
Computational Domain ◽  
Vortex Cell ◽  
Curvature Effects ◽  
Low Dissipation

A vortex cell is a cylindrical aerodynamic cavity that traps separated vortices to prevent the formation of large-scale vortex shedding. Due to the presence of complex vortical structures, regions with varying turbulent intensities, and rotation-curvature effects on turbulent structure; the flow inside a vortex cell is a valuable test case for newly proposed turbulence models and numerical schemes. In the present study, numerical simulations were carried using a Reynolds-averaged Navier-Stokes (RANS) turbulence model and two hybrid RANS/large-eddy-simulation (LES) models. The computational domain consists of a cylindrical cavity with an incoming transitional boundary layer and a Reynolds number of 9.4 × 104 based on the diameter of the cavity. Results indicate that the RANS model provides general information about the flow characteristics, while the hybrid RANS-LES models predict the flow characteristics with more accuracy but suffer inaccuracies due to the details of the RANS to LES transition. Most significantly, the dynamic hybrid RANS-LES (DHRL) model in combination with a low-dissipation numerical scheme overpredicts the turbulent mixing in the vortex cell and fails to provide an accurate representation of the physics of the trapped vortex. It is concluded that the hybrid RANS-LES models used in this study need further work to be able to fully and accurately predict the flow in a vortex cell.

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.

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