A Four-Equation Eddy-Viscosity Approach for Modeling Bypass Transition

2014 ◽  
Vol 6 (4) ◽  
pp. 523-538
Author(s):  
Guoliang Xu ◽  
Song Fu
Keyword(s):  
Kinetic Energy ◽  
Transport Equation ◽  
Eddy Viscosity ◽  
Turbulent Viscosity ◽  
Transitional Region ◽  
Transition Model ◽  
Bypass Transition ◽  
Turbulence Transition ◽  
Sst Turbulence Model ◽  
Layer Flow

AbstractIt is very important to predict the bypass transition in the simulation of flows through turbomachinery. This paper presents a four-equation eddy-viscosity turbulence transition model for prediction of bypass transition. It is based on the SST turbulence model and the laminar kinetic energy concept. A transport equation for the non-turbulent viscosity is proposed to predict the development of the laminar kinetic energy in the pre-transitional boundary layer flow which has been observed in experiments. The turbulence breakdown process is then captured with an intermittency transport equation in the transitional region. The performance of this new transition model is validated through the experimental cases of T3AM, T3A and T3B. Results in this paper show that the new transition model can reach good agreement in predicting bypass transition, and is compatible with modern CFD software by using local variables.

Transition Modelling With the SST Turbulence Model and an Intermittency Transport Equation

2003 ◽  
Author(s):  
Koen Lodefier ◽  
Bart Merci ◽  
Chris De Langhe ◽  
Erik Dick
Keyword(s):  
Turbulence Model ◽  
Turbulent Viscosity ◽  
Transition Model ◽  
Bypass Transition ◽  
Model Following ◽  
Sst Model ◽  
Sst Turbulence Model ◽  
Transition Modelling ◽  
Intermittency Factor

A transition model for describing bypass transition is presented. It is based on a two-equations k–ω model and a dynamic equation for intermittency factor. The intermittency factor is a multiplier of the turbulent viscosity computed by the turbulence model. Following a suggestion by Menter et al. [1], the start of transition is computed based on local variables. The choice of the Shear-Stress Transport (SST) model instead of a k–ε model is explained. The quality of the transition model, developed on flat plate test cases, is illustrated for cascades.

Local-Correlation Based Zero-Equation Transition Model for Turbomachinery

2019 ◽  
Author(s):  
Jatinder Pal Singh Sandhu
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Gamma Transition ◽  
Test Case ◽  
Transition Model ◽  
Bypass Transition ◽  
Local Correlation ◽  
New Model ◽  
Transition Prediction ◽  
Transition Mechanism

Abstract In this paper, we present a new local-correlation based zero-equation transition model. The new model, which is derived from the local-correlation based one-equation gamma transition model (Menter, F. R., Smirnov, P. E., Liu, T., and Avancha, R., A One-Equation Local Correlation-Based Transition Model, Flow, Turbulence and Combustion, vol. 95, 2015, pp. 583619.), does not require any additional equation to be solved, by defining a new variable, which captures the turbulent kinetic energy and intermittency collectively. The new model only adds three more source terms to the existing transport equation of turbulent kinetic energy. Hence the new model is straightforward to implement in already existing RANS solvers and reduces the computational memory requirement as compared to the other transition models. The transition prediction capability of the new model is tested and compared against the one-equation gamma transition model, especially for turbomachinery applications, where bypass transition is the primary transition mechanism, using a standard flat plate test case, and S809 airfoil. Preliminary results show that the new zero-equation transition model produces satisfactory results in terms of transition-location prediction.

An Unsteady RANS Transition Model With Dynamic Description of Intermittency

2005 ◽  
Author(s):  
Koen Lodefier ◽  
Erik Dick
Keyword(s):  
Turbulence Model ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Turbulent Viscosity ◽  
Suction Side ◽  
Transition Model ◽  
Free Stream Turbulence ◽  
Sst Turbulence Model ◽  
Intermittency Factor ◽  
Dynamic Description

A transition model for describing wake-induced transition is presented. It is based on the SST turbulence model by Menter, with the k–ω part in low-Reynolds form according to Wilcox, and two dynamic equations for intermittency: one for near-wall-intermittency and one for free-stream-intermittency. The total intermittency factor, which is the sum of the two, multiplies the turbulent viscosity computed by the turbulence model. The quality of the transition model is illustrated on the T106a test cascade using experimental results for flow with low free-stream turbulence intensity and transition in separated state and for flow with high free-stream turbulence intensity and transition in attached state. The unsteady results are presented in S–T diagrams of the shape factor and wall shear stress on the suction side. Results show the capability of the model to capture the basics of unsteady transition.

RANS Modelling of Wake Induced Transition With the Dynamic Intermittency Concept

2006 ◽  
Author(s):  
Koen Lodefier ◽  
Erik Dick
Keyword(s):  
Turbulence Model ◽  
Free Stream ◽  
Stokes Equations ◽  
Turbulent Viscosity ◽  
Suction Side ◽  
Navier Stokes ◽  
Transition Model ◽  
Navier Stokes Equations ◽  
Free Stream Turbulence ◽  
Sst Turbulence Model

A transition model for describing wake-induced transition is presented based on the SST turbulence model by Menter and two dynamic equations for intermittency: one for near-wall intermittency and one for free-stream intermittency. In the Navier-Stokes equations, the total intermittency factor, which is the sum of the two, multiplies the turbulent viscosity computed by the turbulence model. The quality of the transition model is illustrated on the T106A test cascade for different levels of inlet free-stream turbulence intensity. The unsteady results are presented in space-time diagrams of shape factor, wall shear stress, momentum thickness and intermittency on the suction side. Results show the capability of the model to capture the physics of unsteady transition. Inevitable shortcomings are also revealed.

Calculation of High-Lift Cascades in Low Pressure Turbine Conditions Using a Three-Equation Model

2010 ◽  
Vol 133 (3) ◽  
Author(s):  
Roberto Pacciani ◽  
Michele Marconcini ◽  
Atabak Fadai-Ghotbi ◽  
Sylvain Lardeau ◽  
Michael A. Leschziner
Keyword(s):  
Reynolds Number ◽  
Kinetic Energy ◽  
Eddy Viscosity ◽  
Low Reynolds Number ◽  
Low Pressure ◽  
Equation Model ◽  
Bypass Transition ◽  
High Lift ◽  
Wide Range ◽  
Low Reynolds

A three-equation model has been applied to the prediction of separation-induced transition in high-lift low-Reynolds-number cascade flows. Classical turbulence models fail to predict accurately laminar separation and turbulent reattachment, and usually overpredict the separation length, the main reason for this being the slow rise of the turbulent kinetic energy in the early stage of the separation process. The proposed approach is based on solving an additional transport equation for the so-called laminar kinetic energy, which allows the increase in the nonturbulent fluctuations in the pretransitional and transitional region to be taken into account. The model is derived from that of Lardeau et al. (2004, “Modelling Bypass Transition With Low-Reynolds-Number Non-Linear Eddy-Viscosity Closure,” Flow, Turbul. Combust., 73, pp. 49–76), which was originally formulated to predict bypass transition for attached flows, subject to a wide range of freestream turbulence intensity. A new production term is proposed, based on the mean shear and a laminar eddy-viscosity concept. After a validation of the model for a flat-plate boundary layer, subjected to an adverse pressure gradient, the T106 and T2 cascades, recently tested at the von Kármán Institute, are selected as test cases to assess the ability of the model to predict the flow around high-lift cascades in conditions representative of those in low-pressure turbines. Good agreement with experimental data, in terms of blade-load distributions, separation onset, reattachment locations, and losses, is found over a wide range of Reynolds-number values.

Entropy Generation for Bypass Transitional Boundary Layers

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Richard S. Skifton ◽  
Ralph S. Budwig ◽  
John C. Crepeau ◽  
Tao Xing
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Flat Plate ◽  
Entropy Generation ◽  
Boundary Layer Flow ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Transitional Region ◽  
Bypass Transition ◽  
Layer Flow

The principal purpose of this study is to understand the entropy generation rate in bypass, transitional, boundary-layer flow better. The experimental work utilized particle image velocimetry (PIV) and particle tracking velocimetry (PTV) to measure flow along a flat plate. The flow past the flat plate was under the influence of a negligible “zero” pressure gradient, followed by the installation of an adverse pressure gradient. Further, the boundary layer flow was artificially tripped to turbulence (called “bypass” transition) by means of elevated freestream turbulence. The entropy generation rate was seen to behave similar to that of published computational fluid dynamics (CFD) and direct numerical simulation (DNS) results. The observations from this work show the relative decrease of viscous contributions to entropy generation rate through the transition process, while the turbulent contributions of entropy generation rate greatly increase through the same transitional flow. A basic understanding of entropy generation rate over a flat plate is that a large majority of the contributions come within a wall coordinate less than 30. However, within the transitional region of the boundary layer, a tradeoff between viscous and turbulent dissipation begins to take place where a significant amount of the entropy generation rate is seen out toward the boundary layer edge.

Calculations of High-Lift Cascades in Low Pressure Turbine Conditions Using a Three-Equation Model

2009 ◽  
Author(s):  
Roberto Pacciani ◽  
Michele Marconcini ◽  
Atabak Fadai-Ghotbi ◽  
Sylvain Lardeau ◽  
Michael A. Leschziner
Keyword(s):  
Reynolds Number ◽  
Kinetic Energy ◽  
Low Pressure ◽  
Equation Model ◽  
Transitional Region ◽  
Bypass Transition ◽  
High Lift ◽  
Production Term ◽  
Free Stream Turbulence ◽  
Wide Range

A three-equation model has been applied to the prediction of separation-induced transition in high-lift low-Reynolds-number cascade flows. Classical turbulence models fail to predict accurately laminar separation and turbulent reattachment, and usually over-predict the separation length, the main reason for this being the slow rise of the turbulent kinetic energy in the early stage of the separation process. The proposed approach is based on solving an additional transport equation for the so-called laminar kinetic energy, which allows the increase of the non-turbulent fluctuations in the pre-transitional and transitional region to be taken into account. The model is derived from that of Lardeau and Leschziner, which was originally formulated to predict bypass transition for attached flows, subject to a wide range of free-stream turbulence intensity. A new production term is proposed, based on the mean shear and a laminar eddy-viscosity concept. After a validation of the model for a flat-plate boundary layer, subjected to an adverse pressure gradient, the T106 and T2 cascades, recently tested at the von Ka´rma´n Institute, are selected as test cases to assess the ability of the model to predict the flow around high-lift cascades in conditions representative of those in low-pressure turbines. Good agreement with experimental data, in terms of blade-load distributions, separation onset, reattachment locations and losses, is found over a wide range of Reynolds-number values.

Analysis of an Airfoil Using a Transition and Turbulence Model

2016 ◽  
Vol 819 ◽  
pp. 356-360
Author(s):  
Mazharul Islam ◽  
Jiří Fürst ◽  
David Wood ◽  
Farid Nasir Ani
Keyword(s):  
Fluid Dynamics ◽  
Boundary Layer ◽  
Computational Fluid Dynamics ◽  
Kinetic Energy ◽  
Turbulence Model ◽  
Original Version ◽  
Transitional Region ◽  
Cfd Analysis ◽  
Computational Fluid Dynamics Cfd

In order to evaluate the performance of airfoils with computational fluid dynamics (CFD) tools, modelling of transitional region in the boundary layer is very critical. Currently, there are several classes of transition-based turbulence model which are based on different methods. Among these, the k-kL- ω, which is a three equation turbulence model, is one of the prominent ones which is based on the concept of laminar kinetic energy. This model is phenomenological and has several advantageous features. Over the years, different researchers have attempted to modify the original version which was proposed by Walter and Cokljat in 2008 to enrich the modelling capability. In this article, a modified form of k-kL-ω transitional turbulence model has been used with the help of OpenFOAM for an investigative CFD analysis of a NACA 4-digit airfoil at range of angles of attack.

Heat Transfer Committee and Turbomachinery Committee Best Paper of 1996 Award: The Path to Predicting Bypass Transition

1997 ◽  
Vol 119 (3) ◽  
pp. 405-411 ◽  
Author(s):  
R. E. Mayle ◽  
A. Schulz
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Energy Equation ◽  
Free Stream ◽  
Bypass Transition ◽  
Turbulence Level ◽  
Free Stream Turbulence ◽  
Energy Profiles ◽  
Computer Codes ◽  
Good Agreement

A theory is presented for calculating the fluctuations in a laminar boundary layer when the free stream is turbulent. The kinetic energy equation for these fluctuations is derived and a new mechanism is revealed for their production. A methodology is presented for solving the equation using standard boundary layer computer codes. Solutions of the equation show that the fluctuations grow at first almost linearly with distance and then more slowly as viscous dissipation becomes important. Comparisons of calculated growth rates and kinetic energy profiles with data show good agreement. In addition, a hypothesis is advanced for the effective forcing frequency and free-stream turbulence level that produce these fluctuations. Finally, a method to calculate the onset of transition is examined and the results compared to data.

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