Modeling of Cube Array Roughness: RANS, LES, and DNS

2021 ◽  
Author(s):  
Samuel Altland ◽  
Haosen H. A. Xu ◽  
Xiang I. A. Yang ◽  
Robert Kunz
Keyword(s):  
Reynolds Stress ◽  
Significant Degree ◽  
Reynolds Stress Model ◽  
Stress Model ◽  
Mean Velocity ◽  
Flow Features ◽  
Drag Partition ◽  
Flow Phenomena ◽  
Rans Models ◽  
Packing Densities

Abstract Flow over arrays of cubes is an extensively studied model problem for rough wall turbulent boundary layers. While considerable research has been performed in computationally investigating these topologies using DNS and LES, the ability of sublayer-resolved RANS to predict the bulk flow phenomena of these systems is relatively unexplored, especially at low and high packing densities. Here, RANS simulations are conducted on six different packing densities of cubes in aligned and staggered configurations. The packing densities investigated span from what would classically be defined as isolated, up to those in the d-type roughness regime, filling in the gap in the present literature. Three different sublayer-resolved turbulence closure models were tested for each case; a low Reynolds number k-ε model, the Menter k-ω SST model, and a full Reynolds stress model. Comparisons of the velocity fields, secondary flow features, and drag coefficients are made between the RANS results and existing LES and DNS results. There is a significant degree of variability in the performance of the various RANS models across all comparison metrics. However, the Reynolds stress model demonstrated the best accuracy in terms of the mean velocity profile as well as drag partition across the range of packing densities.

A Robust Implementation of a Reynolds Stress Model for Turbomachinery Applications in a Coupled Solver Environment

2020 ◽  
Author(s):  
David Roos Launchbury ◽  
Luca Mangani ◽  
Ernesto Casartelli ◽  
Francesco Del Citto
Keyword(s):  
Reynolds Stress ◽  
Turbulence Modeling ◽  
Computational Cost ◽  
Reynolds Stress Model ◽  
Tip Vortex ◽  
Stability And Convergence ◽  
Stress Model ◽  
Robust Implementation ◽  
Flow Phenomena ◽  
The Stability

Abstract In the industrial simulation of flow phenomena, turbulence modeling is of prime importance. Due to their low computational cost, Reynolds-averaged methods (RANS) are predominantly used for this purpose. However, eddy viscosity RANS models are often unable to adequately capture important flow physics, specifically when strongly anisotropic turbulence and vortex structures are present. In such cases the more costly 7-equation Reynolds stress models often lead to significantly better results. Unfortunately, these models are not widely used in the industry. The reason for this is not mainly the increased computational cost, but the stability and convergence issues such models usually exhibit. In this paper we present a robust implementation of a Reynolds stress model that is solved in a coupled manner, increasing stability and convergence speed significantly compared to segregated implementations. In addition, the decoupling of the velocity and Reynolds stress fields is addressed for the coupled equation formulation. A special wall function is presented that conserves the anisotropic properties of the model near the walls on coarser meshes. The presented Reynolds stress model is validated on a series of semi-academic test cases and then applied to two industrially relevant situations, namely the tip vortex of a NACA0012 profile and the Aachen Radiver radial compressor case.

A ROBUST IMPLEMENTATION OF A REYNOLDS STRESS MODEL FOR TURBOMACHINERY APPLICATIONS IN A COUPLED SOLVER ENVIRONMENT

2021 ◽  
pp. 1-31
Author(s):  
David Roos Launchbury ◽  
Luca Mangani ◽  
Ernesto Casartelli ◽  
Francesco Del Citto
Keyword(s):  
Reynolds Stress ◽  
Turbulence Modeling ◽  
Computational Cost ◽  
Reynolds Stress Model ◽  
Tip Vortex ◽  
Stability And Convergence ◽  
Stress Model ◽  
Robust Implementation ◽  
Flow Phenomena ◽  
The Stability

Abstract In the industrial simulation of flow phenomena, turbulence modeling is of prime importance. Due to their low computational cost, Reynolds-averaged methods (RANS) are predominantly used for this purpose. However, eddy viscosity RANS models are often unable to adequately capture important flow physics, specifically when strongly anisotropic turbulence and vortex structures are present. In such cases the more costly 7-equation Reynolds stress models often lead to significantly better results. Unfortunately, these models are not widely used in the industry. The reason for this is not mainly the increased computational cost, but the stability and convergence issues such models usually exhibit. In this paper we present a robust implementation of a Reynolds stress model that is solved in a coupled manner, increasing stability and convergence speed significantly compared to segregated implementations. In addition, the decoupling of the velocity and Reynolds stress fields is addressed for the coupled equation formulation. A special wall function is presented that conserves the anisotropic properties of the model near the walls on coarser meshes. The presented Reynolds stress model is validated on a series of semi-academic test cases and then applied to two industrially relevant situations, namely the tip vortex of a NACA0012 profile and the Aachen Radiver radial compressor case.

Investigation of an Algebraic Reynolds Stress Model for Simulation of Wall-Bounded Turbulent Flows With and Without Buoyancy Effects

2020 ◽  
Author(s):  
Tausif Jamal ◽  
D. Keith Walters
Keyword(s):  
Heat Flux ◽  
Turbulent Flows ◽  
Reynolds Stress ◽  
Nuclear Reactor ◽  
Reynolds Stress Model ◽  
Stress Model ◽  
Reynolds Analogy ◽  
Suitable Alternative ◽  
Rans Models ◽  
Algebraic Reynolds Stress Model

Abstract Complex turbulent flows such as those encountered in nuclear reactor cooling systems pose considerable challenges for computational fluid dynamics (CFD) simulation using traditional Reynolds-averaged Navier-Stokes (RANS) models based on the linear eddy-viscosity modeling (LEVM) framework. One particular difficulty is the use of low Prandtl number (Pr) fluids such as liquid metal coolants, which considerably alters the fluctuating thermal field and violates the Reynolds analogy upon which turbulent heat flux modeling in LEVMs is based. Although previous studies have shown that Reynolds Stress Models (RSM) offer some improvements over traditional LEVMs for flows containing complex inter-component interaction and Reynolds stress anisotropy, the added complexity, increased computational requirements, and the lack of robustness introduced by traditional RSMs do not always result in an overall improvement. This study evaluates the performance of a newly proposed Algebraic Reynolds Stress Model (ARSM) including an Algebraic Heat Flux Model (AHFM) against two industry standard RANS models, standard k-ε and realizable k-ε model, for a set of canonical test cases relevant to nuclear reactor cooling applications. Numerical simulations using the spectral element code Nek5000 are performed for fully developed channel flows with varying values of Reynolds number (Re) and Pr, both with and without the effects of buoyancy. Results are compared to Direct Numerical Simulation (DNS) data in terms of the velocity and thermal statistics. For all cases investigated, the ARSM model consistently outperforms the other RANS models in this study and it is concluded that the new ARSM model can be a suitable alternative to traditional LEVMs for complex turbulent flows without significant penalty to efficiency and robustness that are commonly associated with traditional RSMs.

Application of Reynolds-Stress Transport Models to Stern and Wake Flows

1995 ◽  
Vol 39 (04) ◽  
pp. 263-283 ◽  
Author(s):  
F. Sotiropoulos ◽  
V. C. Patel
Keyword(s):  
Reynolds Stress ◽  
Turbulence Model ◽  
Stokes Equations ◽  
Reynolds Stress Model ◽  
Equation Model ◽  
Navier Stokes ◽  
Tensor Model ◽  
Stress Model ◽  
Wake Flows ◽  
Flow Features

ABSTRACT The Reynolds-averaged Navier-Stokes equations are solved to assess the importance of the turbulence model in the prediction of ship stern and wake flows. Solutions are obtained with a two-equation scalar turbulence model and a seven-equation Reynolds-stress tensor model, both of which resolve the flow up to the wall, holding invariant all aspects of the numerical method, including solution domain, initial and boundary conditions, and grid topology and density. Calculations are carried out for two tanker forms used as test cases at recent workshops, and solutions are compared with each other and with experimental data. The comparisons reveal that the Reynolds-stress model accurately predicts most of the experimentally observed flow features in the stern and near-wake regions whereas the two-equation model predicts only the overall qualitative trends. In particular, solutions with the Reynolds-stress model clarify the origin of the stern vortex.

Aerodynamic Comparison and Validation of RANS, URANS and SAS Simulations of Flat Plate Film-Cooling

2010 ◽  
Author(s):  
Stefan Voigt ◽  
Berthold Noll ◽  
Manfred Aigner
Keyword(s):  
Experimental Data ◽  
Reynolds Stress ◽  
Film Cooling ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Stress Model ◽  
3 Dimensional ◽  
Commercial Code ◽  
Sst Model ◽  
Rans Models

The present paper deals with the detailed numerical simulation of film cooling including conjugate heat transfer. Five different turbulence models are used to simulate a film cooling configuration. The models include three steady and two unsteady models. The steady RANS models are the Shear stress transport (SST) model of Menter, the Reynolds stress model of Speziale, Sarkar and Gatski and a k-ε explicit algebraic Reynolds stress model. The unsteady models are a URANS formulation of the SST model and a scale-adaptive simulation (SAS). The solver used in this study is the commercial code ANSYS CFX 11.0. The results are compared to available experimental data. These data include velocity and turbulence intensity fields in several planes. It is shown that the steady RANS approach has difficulties with predicting the flow field due to the high 3-dimensional unsteadiness. The URANS and SAS simulations on the other hand show good agreement with the experimental data. The deviation from the experimental data in velocity values in the steady cases is about 20% whereas the error in the unsteady cases is below 10%.

Simulations of Channel Flows With Effects of Spanwise Rotation or Wall Injection Using a Reynolds Stress Model

2000 ◽  
Vol 123 (1) ◽  
pp. 2-10 ◽  
Author(s):  
Bruno Chaouat
Keyword(s):  
Experimental Data ◽  
Reynolds Stress ◽  
Reynolds Stress Model ◽  
Channel Flows ◽  
Fluid Injection ◽  
Turbulent Regime ◽  
Stress Model ◽  
Mean Velocity ◽  
Wall Injection ◽  
Spanwise Rotation

Simulations of channel flows with effects of spanwise rotation and wall injection are performed using a Reynolds stress model. In this work, the turbulent model is extended for compressible flows and modified for rotation and permeable walls with fluid injection. Comparisons with direct numerical simulations or experimental data are discussed in detail for each simulation. For rotating channel flows, the second-order turbulence model yields an asymmetric mean velocity profile as well as turbulent stresses quite close to DNS data. Effects of spanwise rotation near the cyclonic and anticyclonic walls are well observed. For the channel flow with fluid injection through a porous wall, different flow developments from laminar to turbulent regime are reproduced. The Reynolds stress model predicts the mean velocity profiles, the transition process and the turbulent stresses in good agreement with the experimental data. Effects of turbulence in the injected fluid are also investigated.

scholarly journals Reynolds Stress Model for Viscoelastic Drag-Reducing Flow Induced by Polymer Solution

Polymers ◽  
2019 ◽  
Vol 11 (10) ◽  
pp. 1659 ◽  
Author(s):  
Wang
Keyword(s):  
Polymer Solution ◽  
Reynolds Stress ◽  
Reynolds Numbers ◽  
Reynolds Stress Model ◽  
Computational Time ◽  
Stress Model ◽  
Turbulent Model ◽  
Mean Velocity ◽  
Conformation Tensor ◽  
Computational Ability

Viscoelasticity drag-reducing flow by polymer solution can reduce pumping energy of pipe flow significantly. One of the simulation manners is direct numerical simulation (DNS). However, the computational time is too long to accept in engineering. Turbulent model is a powerful tool to solve engineering problems because of its fast computational ability. However, its precision is usually low. To solve this problem, we introduce DNS to provide accurate data to construct a high-precision turbulent model. A Reynolds stress model for viscoelastic polymer drag-reducing flow is established. The rheological behavior of the drag-reducing flow is described by the Giesekus constitutive Equation. Compared with the DNS data, mean velocity, mean conformation tensor, drag reduction, and stresses are predicted accurately in low Reynolds numbers and Weissenberg numbers but worsen as the two numbers increase. The computational time of the Reynolds stress model (RSM) is only 1/120,960 of DNS, showing the advantage of computational speed.

Prediction of strongly curved turbulent duct flows with Reynolds stress model

AIAA Journal ◽  
1997 ◽  
Vol 35 ◽  
pp. 91-98
Author(s):  
Jiang Luo ◽  
Budugur Lakshminarayana
Keyword(s):  
Reynolds Stress ◽  
Reynolds Stress Model ◽  
Stress Model
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