A Three-Equation Eddy-Viscosity Model for Reynolds-Averaged Navier–Stokes Simulations of Transitional Flow

2008 ◽  
Vol 130 (12) ◽  
Author(s):  
D. Keith Walters ◽  
Davor Cokljat
Keyword(s):  
Boundary Layer ◽  
Turbulent Flows ◽  
Eddy Viscosity ◽  
Flow Behavior ◽  
Applied Pressure ◽  
Plate Boundary ◽  
Low Frequency ◽  
Transitional Flow ◽  
Test Cases ◽  
Eddy Viscosity Model

An eddy-viscosity turbulence model employing three additional transport equations is presented and applied to a number of transitional flow test cases. The model is based on the k-ω framework and represents a substantial refinement to a transition-sensitive model that has been previously documented in the open literature. The third transport equation is included to predict the magnitude of low-frequency velocity fluctuations in the pretransitional boundary layer that have been identified as the precursors to transition. The closure of model terms is based on a phenomenological (i.e., physics-based) rather than a purely empirical approach and the rationale for the forms of these terms is discussed. The model has been implemented into a commercial computational fluid dynamics code and applied to a number of relevant test cases, including flat plate boundary layers with and without applied pressure gradients, as well as a variety of airfoil test cases with different geometries, Reynolds numbers, freestream turbulence conditions, and angles of attack. The test cases demonstrate the ability of the model to successfully reproduce transitional flow behavior with a reasonable degree of accuracy, particularly in comparison with commonly used models that exhibit no capability of predicting laminar-to-turbulent boundary layer development. While it is impossible to resolve all of the complex features of transitional and turbulent flows with a relatively simple Reynolds-averaged modeling approach, the results shown here demonstrate that the new model can provide a useful and practical tool for engineers addressing the simulation and prediction of transitional flow behavior in fluid systems.

Development and Initial Validation of a Two-Equation Transition Sensitive Turbulence Model for CFD Simulations

2006 ◽  
Author(s):  
J. M. Jones ◽  
D. K. Walters
Keyword(s):  
Boundary Layer ◽  
Turbulence Model ◽  
Eddy Viscosity ◽  
Flow Behavior ◽  
Boundary Layer Separation ◽  
Transitional Flow ◽  
Model Framework ◽  
Modeling Framework ◽  
Initial Development ◽  
New Model

This paper presents the initial development and validation of a modified two-equation eddy-viscosity turbulence model for computational fluid dynamics (CFD) prediction of transitional and turbulent flow. The new model is based on a k-ω model framework, making it more easily implemented into existing general-purpose CFD solvers than other recently proposed model forms. The model incorporates inviscid and viscous damping functions for the eddy viscosity, as well as a production damping term, in order to reproduce the appropriate effects of laminar, transitional, and turbulent boundary layer flow. It has been implemented into a commercially available flow solver (FLUENT) and evaluated for simple attached and separated flow conditions, including 2-D flow over a flat plate and a circular cylinder. The results presented show that the new model is able to yield reasonable predictions of transitional flow behavior using a very simple modeling framework, including an appropriate response to freestream turbulence and boundary layer separation.

A Recommended Correction to the kT−kL−ω Transition-Sensitive Eddy-Viscosity Model

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
Maurin Lopez ◽  
D. Keith Walters
Keyword(s):  
Turbulent Flows ◽  
Large Scale ◽  
Eddy Viscosity ◽  
Viscosity Model ◽  
Step Test ◽  
Test Cases ◽  
Turbulent Length Scale ◽  
Eddy Viscosity Model ◽  
Natural Modes ◽  
Viscosity Term

A physics-based modification to the kT−kL−ω transition-sensitive eddy-viscosity model is presented. The modification corrects an anomaly related to the physical mechanism of production of laminar kinetic energy for regions far from the wall in fully turbulent flows, by limiting the production of natural modes in the large-scale eddy-viscosity term by a rescale of the wall-limited turbulent length scale. Round jet and backward facing step test cases are used to reveal the relevant issue and to demonstrate that the new modification successfully addresses the problem.

URANS Predictions of the Effects of Synthetic Jets on the Separated, Transitional Flow Over a Low-Pressure-Turbine-Like Flat Plate

2010 ◽  
Author(s):  
Michele Marconcini ◽  
Roberto Pacciani ◽  
Andrea Arnone
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Eddy Viscosity ◽  
Synthetic Jet ◽  
Operating Conditions ◽  
Viscosity Model ◽  
Transitional Flow ◽  
High Lift ◽  
Eddy Viscosity Model ◽  
Lp Turbine

A URANS solver has been applied to study the effects of a synthetic jet actuator on the laminar boundary layer separation over a flat plate with adverse pressure gradient. The pressure distribution over the flat plate is representative of the suction side of a ultra-high-lift, LP-turbine airfoil. Measurements for several Reynolds numbers, are provided via experimental tests carried out in the framework of the European project TATMo (Turbulence and Transition Modelling for Special Turbomachinery Applications). The actuator device, in the form of a two-dimensional slot, has been conceived in order to obtain jet aerodynamic characteristics suitable for separation control. The study has been carried out using a novel, transition-sensitive, non-linear eddy-viscosity model. It is based on the coupling of an additional transport equation for the so-called laminar kinetic energy (LKE) to a realizable, quadratic eddy-viscosity model that provides an explicit algebraic formulation for the Reynolds stresses. The analysis covers steady as well as unsteady cases characterized by different actuator frequencies. Comparisons between measurements and computations are presented. The suitability of the proposed approach to simulate the time- and phase-averaged effects of a synthetic jet for boundary layer control at typical operating conditions of high-lift LP-turbine blades will be discussed in detail.

An Assessment of Three-Dimensional Turbulent Boundary Layer Prediction Methods

1973 ◽  
Vol 95 (3) ◽  
pp. 415-421 ◽  
Author(s):  
A. J. Wheeler ◽  
J. P. Johnston
Keyword(s):  
Boundary Layer ◽  
Eddy Viscosity ◽  
Three Dimensional ◽  
High Sensitivity ◽  
Boundary Layer Flows ◽  
Mean Velocity ◽  
Eddy Viscosity Model ◽  
Separating Flow ◽  
Dimensional Boundary ◽  
Stress Models

Predictions have been made for a variety of experimental three-dimensional boundary layer flows with a single finite difference method which was used with three different turbulent stress models: (i) an eddy viscosity model, (ii) the “Nash” model, and (iii) the “Bradshaw” model. For many purposes, even the simplest stress model (eddy viscosity) was adequate to predict the mean velocity field. On the other hand, the profile of shear stress direction was not correctly predicted in one case by any model tested. The high sensitivity of the predicted results to free stream pressure gradient in separating flow cases is demonstrated.

A Method for the Calculation of 3D Boundary Layers on Practical Wing Configurations

1981 ◽  
Vol 103 (1) ◽  
pp. 104-111 ◽  
Author(s):  
J. P. F. Lindhout ◽  
G. Moek ◽  
E. De Boer ◽  
B. Van Den Berg
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Boundary Layer Flow ◽  
Eddy Viscosity ◽  
Separated Flow ◽  
Laminar Boundary Layers ◽  
Eddy Viscosity Model ◽  
Airplane Wing ◽  
Turbulent Boundary Layer Flow ◽  
Layer Flow

This paper gives a description of a calculation method for 3D turbulent and laminar boundary layers on nondevelopable surfaces. A simple eddy viscosity model is incorporated in the method. Special attention is given to the organization of the computations to circumvent as much as possible stepsize limitations. The method is also able to proceed the computation around separated flow regions. The method has been applied to the laminar boundary layer flow over a flat plate with attached cylinder, and to a turbulent boundary layer flow over an airplane wing.

Numerical Investigation of Low-Reynolds Number Airfoil Flows Using Transition-Sensitive and Fully Turbulent RANS Models

2014 ◽  
Author(s):  
Varun Chitta ◽  
Tausif Jamal ◽  
D. Keith Walters
Keyword(s):  
Boundary Layer ◽  
Turbulent Flows ◽  
Eddy Viscosity ◽  
Boundary Layer Transition ◽  
Transition Flow ◽  
Layer Transition ◽  
Laminar Separation ◽  
Viscosity Models ◽  
Separation Bubbles ◽  
Laminar Separation Bubbles

A numerical analysis is performed to study the pre-stall and post-stall aerodynamic characteristics over a group of six airfoils using commercially available transition-sensitive and fully turbulent eddy-viscosity models. The study is focused on a range of Reynolds numbers from 6 × 104 to 2 × 106, wherein the flow around the airfoil is characterized by complex phenomena such as boundary layer transition, flow separation and reattachment, and formation of laminar separation bubbles on either the suction, pressure or both surfaces of airfoil. The predictive capability of the transition-sensitive k-kL-ω model versus the fully turbulent SST k-ω model is investigated for all airfoils. The transition-sensitive k-kL-ω model used in this study is capable of predicting both attached and separated turbulent flows over the surface of an airfoil without the need for an external linear stability solver to predict transition. The comparison between experimental data and results obtained from the numerical simulations is presented, which shows that the boundary layer transition and laminar separation bubbles that appear on the suction and pressure surfaces of the airfoil can be captured accurately by the use of a transition-sensitive model. The fully turbulent SST k-ω model predicts a turbulent boundary layer on both surfaces of the airfoil for all angles of attack and fails to predict boundary layer transition or separation bubbles. Discrepancies are observed in the predictions of airfoil stall by both the models. Reasons for the discrepancies between computational and experimental results, and also possible improvements in eddy-viscosity models, are discussed.

scholarly journals A rational method for determining intermittency in the transitional boundary layer

2019 ◽  
Vol 61 (1) ◽  
Author(s):  
Dhamotharan Veerasamy ◽  
Chris Atkin
Keyword(s):  
Boundary Layer ◽  
Plate Boundary ◽  
Threshold Value ◽  
Normal Direction ◽  
Transitional Flow ◽  
Streamwise Direction ◽  
Transitional Boundary Layer ◽  
Rational Procedure ◽  
Selection Of ◽  
Flat Plate Boundary Layer

Abstract A new rational procedure is proposed for determining the intermittency in the streamwise direction. One of the key parameters for the intermittency determination is the selection of a threshold value, which often involves a certain level of subjectivity. Here, a reliable way of choosing the threshold value in a more objective manner is proposed. The proposed approach involves a single threshold value, equal to the magnitude of the maximum laminar perturbation in the transitional flow. The results obtained are validated with the widely used dual-slope method. In this paper, the measurements are carried out on an experimental arrangement, involving the interaction of an upstream aerofoil wake with a downstream flat plate boundary layer. As a by-product of the study, a scaling parameter has been identified which captures the length of the transition zone as the proximity of the aerofoil in the wall-normal direction is varied. Graphic abstract

Simulation of Turbulent Flows in Turbine Blade Passages and Disc Cavities

2008 ◽  
Author(s):  
Konstantin N. Volkov ◽  
Nicholas J. Hills ◽  
John W. Chew
Keyword(s):  
Flat Plate ◽  
Turbulent Flows ◽  
Turbine Blade ◽  
Plate Boundary ◽  
Turbulence Models ◽  
Benchmark Problems ◽  
Test Cases ◽  
Cavity Model ◽  
Rotating Disc ◽  
Wall Functions

The main objectives of the paper are to test widely used turbulence models against selected benchmark problems identifying range of applicability and limitations of the models used and to help accurately predict flow in turbine blade passages and disc cavities. The following models are considered: the k–ε model with and without a Kato–Launder correction and a Richardson number correction, the two-layer k–ε/k–l model, and the Spalart–Allmaras model with and without correction for rotation. Weaknesses in the models are identified and suggestions made for possible improvements. Numerical implementation of the wall functions approach is also considered. The test cases considered include flat plate boundary layer, flat plate heat transfer, enclosed rotating disc, and a combined turbine blade/disc cavity model. Comparisons are made with experimental data and computations from different CFD codes.

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