Comparison of Eddy-Viscosity Turbulence Models in Flows with Adverse Pressure Gradient

AIAA Journal ◽  
2006 ◽  
Vol 44 (10) ◽  
pp. 2156-2169 ◽  
Author(s):  
Alan Celic ◽  
Ernst H. Hirschel
Keyword(s):  
Pressure Gradient ◽  
Eddy Viscosity ◽  
Turbulence Models ◽  
Adverse Pressure Gradient

A Comparison of Some Recent Eddy-Viscosity Turbulence Models

1996 ◽  
Vol 118 (3) ◽  
pp. 514-519 ◽  
Author(s):  
F. R. Menter
Keyword(s):  
Experimental Data ◽  
Finite Difference ◽  
Pressure Gradient ◽  
Eddy Viscosity ◽  
State Of The Art ◽  
Turbulence Models ◽  
Adverse Pressure Gradient ◽  
Gradient Flows ◽  
Grid Convergence ◽  
Sst Model

The performance of recently developed eddy-viscosity turbulence models, including the author’s SST model, is evaluated against a number of attached and separated adverse pressure gradient flows. The results are compared in detail against experimental data, as well as against the standard k-ε model. Grid convergence was established for all computations. The study involves four different, state-of-the-art finite difference (finite volume) codes.

Structural Parameters and Prediction of Adverse Pressure Gradient Turbulent Flows: An Improved k-ε Model

1995 ◽  
Vol 117 (3) ◽  
pp. 424-432 ◽  
Author(s):  
G. Chukkapalli ◽  
O¨. F. Turan
Keyword(s):  
Pressure Gradient ◽  
Turbulent Flows ◽  
Reynolds Stress ◽  
Eddy Viscosity ◽  
Structural Parameters ◽  
Adverse Pressure Gradient ◽  
Reynolds Stress Model ◽  
Model Representation ◽  
Stress Model ◽  
Kinetic Diffusion

A modified k-ε model is proposed to predict complex, adverse pressure gradient, turbulent diffuser flows. The need for an eddy viscosity is eliminated by using three structural parameters. A fuller treatment of the rate of kinetic diffusion terms is incorporated with a Reynolds stress model representation. A thorough evaluation is given of the three structural parameters in three decreasing and one increasing adverse pressure gradient diffuser flows leading to a three-layer representation. The results indicate the need for better modeling of the ε-equation.

Turbulence modeling effects on the aerodynamic characterizations of a NASCAR Generation 6 racecar subject to yaw and pitch changes

2019 ◽  
Vol 233 (14) ◽  
pp. 3600-3620 ◽  
Author(s):  
Chen Fu ◽  
C Patrick Bounds ◽  
Christian Selent ◽  
Mesbah Uddin
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Shear Stress ◽  
Eddy Viscosity ◽  
Turbulence Models ◽  
Flow Region ◽  
Adverse Pressure Gradient ◽  
Navier Stokes ◽  
Shear Stress Transport ◽  
Reynolds Averaged Navier Stokes

The characterization of a racecar’s aerodynamic behavior at various yaw and pitch configurations has always been an integral part of its on-track performance evaluation in terms of lap time predictions. Although computational fluid dynamics has emerged as the ubiquitous tool in motorsports industry, a clarity is still lacking about the prediction veracity dependence on the choice of turbulence models, which is central to the prediction variability and unreliability for the Reynolds Averaged Navier–Stokes simulations, which is by far the most widely used computational fluid dynamics methodology in this industry. Subsequently, this paper presents a comprehensive assessment of three commonly used eddy viscosity turbulence models, namely, the realizable [Formula: see text] (RKE), Abe–Kondoh–Nagano [Formula: see text], and shear stress transport [Formula: see text], in predicting the aerodynamic characteristics of a full-scale NASCAR Monster Energy Cup racecar under various yaw and pitch configurations, which was never been explored before. The simulations are conducted using the steady Reynolds Averaged Navier–Stokes approach with unstructured trimmer cells. The tested yaw and pitch configurations were chosen in consultation with the race teams such that they reflect true representations of the racecar orientations during cornering, braking, and accelerating scenarios. The study reiterated that the prediction discrepancies between the turbulence models are mainly due to the differences in the predictions of flow recirculation and separation, caused by the individual model’s effectiveness in capturing the evolution of adverse pressure gradient flows, and predicting the onset of separation and subsequent reattachment (if there be any). This paper showed that the prediction discrepancies are linked to the computation of the turbulent eddy viscosity in the separated flow region, and using flow-visualizations identified the areas on the car body which are critical to this analysis. In terms of racecar aerodynamic performance parameter predictions, it can be reasonably argued that, excluding the prediction of the %Front prediction, shear stress transport is the best choice between the three tested models for stock-car type racecar Reynolds Averaged Navier–Stokes computational fluid dynamics simulations as it is the only model that predicted directionally correct changes of all aerodynamic parameters as the racecar is either yawed from the 0° to 3° or pitched from a high splitter-ground clearance to a low one. Furthermore, the magnitude of the shear stress transport predicted delta force coefficients also agreed reasonably well with test results.

Assessment of Various Turbulence Models in a High Pressure Ratio Centrifugal Compressor With an Object Oriented CFD Code

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Luca Mangani ◽  
Ernesto Casartelli ◽  
Sebastiano Mauri
Keyword(s):  
Boundary Layer ◽  
High Pressure ◽  
Pressure Gradient ◽  
Centrifugal Compressor ◽  
Pressure Ratio ◽  
Turbulence Models ◽  
Object Oriented ◽  
Adverse Pressure Gradient ◽  
High Mass ◽  
High Pressure Ratio

The flow field in a high pressure ratio centrifugal compressor with a vaneless diffuser has been investigated numerically. The main goal is to assess the influence of various turbulence models suitable for internal flows with an adverse pressure gradient. The numerical analysis is performed with a 3D RANS in-house modified solver based on an object-oriented open-source library. According to previous studies from varying authors, the turbulence model is believed to be the key parameter for the discrepancy between experimental and numerical results, especially at high pressure ratios and high mass-flow. Particular care has been taken at the wall, where a detailed integration of the boundary layer has been applied. The results present different comparisons between the models and experimental data, showing the influence of using advanced turbulence models. This is done in order to capture the boundary layer behavior, especially in large adverse pressure gradient single stage machinery.

scholarly journals Studi Numerik Steady RANS Aliran Fluida di Dalam Asymmetric Diffuser

2017 ◽  
Vol 4 (1) ◽  
pp. 20 ◽  
Author(s):  
Yiyin Klistafani
Keyword(s):  
Fluid Flow ◽  
Pressure Gradient ◽  
Numerical Study ◽  
Maximum Velocity ◽  
Turbulence Models ◽  
Adverse Pressure Gradient ◽  
Positive Pressure ◽  
Front Wall ◽  
Human Beings ◽  
Vertical Side

Research on fluid flow becomes a necessity to develop technology and for the welfare of human beings on earth. One of them is study of fluid flow in the diffuser. The example of diffuser application is used as a flue gas duct in the car or motorcycle. In addition, diffuser is also applied in air conditioning systems. Diffuser is a construction that able to control the behavior of the fluid. The increasing of cross section area in the diffuser will generate a positive pressure gradient or also called adverse pressure gradient (APG). The greater APG that happens, the greater energy required by the fluid to fight it, because APG will lead to separation. This study aimed to evaluate the numerical fluid flow in the asymmetric diffuser with divergence angle (θ) = 10 ° (upper wall) and widening one vertical side (α) of 20 ° (front wall). The Reynolds number is 8.7 x 104 by high inlet diffuser and the maximum velocity at the inlet diffuser. Turbulence models used are standard k-ɛ, realizable k-ε, and shear stress transport (SST) k-ω. Numerical study of steady RANS used Fluent 6.3.26 software. Results of numerical visualizations show that huge vortex established in diffuser, that’s why performance of diffuser is not optimal. In addition the location of separation point shown by SST k-ω is earlier than other turbulence models (standard k-ε and realizable k-ε).

Separated Turbulent Boundary Layer Under Unsteady Adverse Pressure Gradients: DNS and RANS

2014 ◽  
Author(s):  
Junshin Park
Keyword(s):  
Numerical Simulation ◽  
Boundary Layer ◽  
Pressure Gradient ◽  
Eddy Viscosity ◽  
Adverse Pressure Gradient ◽  
Velocity Profiles ◽  
Navier Stokes ◽  
Pressure Gradients ◽  
Recirculation Bubble ◽  
Rans Models

Predicitve capabilities of Reynolds Averaged Navier-Stokes (RANS) techniques have been assessed using SST k–ω model and Spalart-Allmaras model by comparing its results with direct numerical simulation (DNS) results. It has been shown that Spalart-Allmaras and SST k–ω model predict an earlier separation point and a bigger recirculation bubble as compared to the DNS result. Velocity profiles predicted by RANS for both models closely match with DNS results for the steady adverse pressure gradient case. However, the RANS fail to predict correct velocity profiles for unsteady adverse pressure gradients not only for inside the bubble but also after the reattachment zone. To provide the backgrounds for improving RANS models, these differences are explained with Reynolds stress and eddy viscosity which differ between the steady and unsteady adverse pressure gradient RANS cases.

Turbulence in a separated boundary layer

1991 ◽  
Vol 226 ◽  
pp. 91-123 ◽  
Author(s):  
M. Dianat ◽  
Ian P. Castro
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Low Frequency ◽  
Turbulence Models ◽  
Adverse Pressure Gradient ◽  
Spanwise Direction ◽  
Wall Region ◽  
Thin Wall ◽  
Wall Boundary Layer ◽  
Stress Ratios

This paper presents and discusses the results of an extensive experimental investigation of a flat-plate turbulent boundary subjected to an adverse pressure gradient sufficiently strong to lead to the formation of a large separated region. The pressure gradient was produced by applying strong suction through a porous cylinder fitted with a rear flap and mounted above the boundary layer and with its axis in the spanwise direction. Attention is concentrated on the structure of the turbulent flow within the separated region and it is shown that many features are similar to those that occur in separated regions produced in a very dissimilar manner. These include the fact that structure parameters, like Reynolds stress ratios, respond markedly to the re-entrainment of turbulent fluid transported upstream from the reattachment region, the absence of any logarithmic region in the thin wall boundary layer beneath the recirculation zone and the lack of any effective viscous scaling in this wall region, and the presence of a significant low-frequency motion having timescales much longer than those of the large-eddy structures around reattachment.Similarities with boundary layers separating under the action of much weaker pressure gradients are also found, despite the fact that the nature of the flow around separation is quite different. These similarities and also some noticeable differences are discussed in the paper, which concludes with some inferences concerning the application of turbulence models to separated flows.

Study of Turbulence Models in Flows Through Adverse Pressure Gradient System

2005 ◽  
Author(s):  
E. Karunakaran ◽  
V. Ganesan
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Pressure Gradient ◽  
Numerical Simulations ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Adverse Pressure Gradient ◽  
Reynolds Stress Model ◽  
Gradient System ◽  
Field Development

This paper is concerned with the study of performance of popular turbulence models used in the CFD analysis. Turbulence models considered for evaluation include the eddy viscosity models and the Reynolds stress model. The recent k-ε-v2-f model recommended for a flow with separation is also studied. Evaluation of the turbulence models in the present study focuses on a three-dimensional flow field development with adverse pressure gradient and flows that simulate wall-bounded turbulence. Numerical calculations are performed using SIMPLE based algorithm. Nowadays, decelerating flow in a diffuser is assessed by numerical simulations and the validation is done with experimental results. A comparison of the numerical results and the experimental data are presented. The main objective of the comparison is to obtain information on how well the numerical simulations representing the flow field with the standard turbulence models, are able to reproduce the experimental data.

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