Prediction of Separation-Induced Transition on High Lift Low Pressure Turbine Blade

2011 ◽  
Author(s):  
Abdelkader Benyahia ◽  
Lionel Castillon ◽  
Robert Houdeville
Keyword(s):  
Experimental Data ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Transition Model ◽  
Freestream Turbulence ◽  
Low Pressure Turbine ◽  
European Program ◽  
Inlet Conditions ◽  
Development And Validation ◽  
Good Agreement

This paper deals with the development and validation of the Menter and Langtry correlation-based transition model in the RANS code elsA. Two types of experimental linear cascades of low pressure turbine (LPT) airfoils having different loading distributions have been considered for the validation: the T106C and T108 blades. Experimental data have been provided by the Von Karman Institute in the framework of the European program TATMo. Different Reynolds numbers varying from 80 000 to 250 000 and different freestream turbulence intensities have been investigated. The results obtained for the T106C blade are in good agreement with the experimental data: the bubble size and the kinetic energy losses are well predicted. Sensitivity to freestream turbulence is also well demonstrated for the considered Reynolds numbers. However the results for the T108 blade show the limitations of the current version. These limitations are explained and discussed in this paper. The second part of this paper deals with the numerical and physical aspects of periodical unsteady inlet conditions which are introduced in order to take into account the incoming wakes. The original Menter and Langtry transition model has required a modification for performing correct unsteady computations of wake induced transition which is discussed in this paper. The unsteady results obtained with elsA are in quite good agreement with the experimental data.

Experimental and Computational Investigations of Separation and Transition on a Highly Loaded Low-Pressure Turbine Airfoil: Part 2 — High Freestream Turbulence Intensity

2008 ◽  
Author(s):  
Ralph J. Volino ◽  
Olga Kartuzova ◽  
Mounir B. Ibrahim
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Shear Layer ◽  
Separation Bubble ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Transition Model ◽  
Freestream Turbulence ◽  
Low Pressure Turbine ◽  
Separated Shear Layer

Boundary layer separation, transition and reattachment have been studied on a very high lift, low-pressure turbine airfoil. Experiments were done under high (4%) freestream turbulence conditions on a linear cascade in a low speed wind tunnel. Pressure surveys on the airfoil surface and downstream total pressure loss surveys were documented. Velocity profiles were acquired in the suction side boundary layer at several streamwise locations using hot-wire anemometry. Cases were considered at Reynolds numbers (based on the suction surface length and the nominal exit velocity from the cascade) ranging from 25,000 to 300,000. At the lowest Reynolds number the boundary layer separated and did not reattach, in spite of transition in the separated shear layer. At higher Reynolds numbers the boundary layer did reattach, and the separation bubble became smaller as Re increased. High freestream turbulence increased the thickness of the separated shear layer, resulting in a thinner separation bubble. This effect resulted in reattachment at intermediate Reynolds numbers, which was not observed at the same Re under low freestream turbulence conditions. Numerical simulations were performed using an unsteady Reynolds averaged Navier-Stokes (URANS) code with both a shear stress transport k-ω model and a 4 equation shear stress transport Transition model. Both models correctly predicted separation and reattachment (if it occurred) at all Reynolds numbers. The Transition model generally provided better quantitative results, correctly predicting velocities, pressure, and separation and transition locations. The model also correctly predicted the difference between high and low freestream turbulence cases.

An Experimental Investigation of the Effect of Freestream Turbulence on the Wake of a Separated Low-Pressure Turbine Blade at Low Reynolds Numbers

1999 ◽  
Vol 122 (2) ◽  
pp. 431-433 ◽  
Author(s):  
C. G. Murawski ◽  
K. Vafai
Keyword(s):  
Reynolds Number ◽  
Turbine Blade ◽  
Turbulence Intensity ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Freestream Turbulence ◽  
Suction Surface ◽  
Low Reynolds Numbers ◽  
Low Pressure Turbine ◽  
Flow Reynolds Number

An experimental study was conducted in a two-dimensional linear cascade, focusing on the suction surface of a low pressure turbine blade. Flow Reynolds numbers, based on exit velocity and suction length, have been varied from 50,000 to 300,000. The freestream turbulence intensity was varied from 1.1 to 8.1 percent. Separation was observed at all test Reynolds numbers. Increasing the flow Reynolds number, without changing freestream turbulence, resulted in a rearward movement of the onset of separation and shrinkage of the separation zone. Increasing the freestream turbulence intensity, without changing Reynolds number, resulted in shrinkage of the separation region on the suction surface. The influences on the blade’s wake from altering freestream turbulence and Reynolds number are also documented. It is shown that width of the wake and velocity defect rise with a decrease in either turbulence level or chord Reynolds number. [S0098-2202(00)00202-9]

Transition Modelling for Vortex Generating Jets on Low-Pressure Turbine Profiles

2011 ◽  
Author(s):  
Florian Herbst ◽  
Dragan Kozˇulovic´ ◽  
Joerg R. Seume
Keyword(s):  
Total Pressure ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Quantitative Prediction ◽  
Design Parameters ◽  
Transition Model ◽  
Pressure Losses ◽  
Low Pressure Turbine ◽  
Wide Range ◽  
Local Transition

Steady blowing vortex generating jets (VGJ) on highly-loaded low-pressure turbine profiles have shown to be a promising way to decrease total pressure losses at low Reynolds-numbers by reducing laminar separation. In the present paper, the state of the art turbomachinery design code TRACE with RANS turbulence closure and coupled γ-ReΘ transition model is applied to the prediction of typical aerodynamic design parameters of various VGJ configurations in steady simulations. High-speed cascade wind tunnel experiments for a wide range of Reynolds-numbers, two VGJ positions, and three jet blowing ratios are used for validation. Since the original transition model overpredicts separation and losses at Re2is ≤ 100·103 an extra mode for VGJ induced transition is introduced. Whereas the criterion for transition is modelled by a filtered Q vortex criterion the transition development itself is modelled by a reduction of the local transition-onset momentum-thickness Reynolds number. The new model significantly improves the quality of the computational results by capturing the corresponding local transition process in a physically reasonable way. This is shown to yield an improved quantitative prediction of surface pressure distributions and total pressure losses.

Experimental Study of the Unsteady Aerodynamics in a Linear Cascade With Low Reynolds Number Low Pressure Turbine Blades

1997 ◽  
Author(s):  
Christopher G. Murawski ◽  
Rolf Sondergaard ◽  
Richard B. Rivir ◽  
Kambiz Vafai ◽  
Terrence W. Simon ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Turbulence Intensity ◽  
Turbine Blades ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Freestream Turbulence ◽  
Suction Surface ◽  
Linear Cascade ◽  
Low Pressure Turbine ◽  
Flow Reynolds Number

Low pressure turbines in aircraft experience large changes in flow Reynolds number as the gas turbine engine operates from takeoff to high altitude cruise. Low pressure turbine blades are also subject to regions of strong acceleration and diffusion. These changes in Reynolds number, strong acceleration, as well as elevated levels of turbulence can result in unsteady separation and transition zones on the surface of the blade. An experimental study was conducted in a two-dimensional linear cascade, focusing on the suction surface of a low pressure turbine blade. The intent was to assess the effects of changes in Reynolds number, and freestream turbulence intensity. Flow Reynolds numbers, based on exit velocity and suction surface length, have been varied from 50,000 to 300,000. The freestream turbulence intensity was varied from 1.1 to 8.1 percent. Separation was observed at all test Reynolds numbers. Increasing the flow Reynolds number, without changing freestream turbulence, resulted in a slightly rearward movement of the onset of separation and shrinkage of the separation zone. Increasing the freestream turbulence intensity, without changing Reynolds number resulted in a shrinkage of the separation region on the suction surface. Increasing both flow Reynolds numbers and freestream turbulence intensity compounded these effects such that at a Reynolds number of 300,000 and a freestream turbulence intensity of 8.1%, the separation zone was almost nonexistent. The influences on the blade’s wake from altering freestream turbulence and Reynolds number are also documented. The width of the wake and velocity defect rise with a decrease in either turbulence level or chord Reynolds number. Numerical simulations were performed in support of experimental results. The numerical results compare well qualitatively with the low freestream turbulence experimental cases.

Experimental and Computational Investigations of Separation and Transition on a Highly Loaded Low-Pressure Turbine Airfoil: Part 1 — Low Freestream Turbulence Intensity

2008 ◽  
Author(s):  
Mounir Ibrahim ◽  
Olga Kartuzova ◽  
Ralph J. Volino
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Transport Model ◽  
Separation Bubble ◽  
Pressure Coefficient ◽  
Low Pressure ◽  
Transition To Turbulence ◽  
Transition Model ◽  
Freestream Turbulence ◽  
Low Pressure Turbine

Boundary layer separation, transition and reattachment have been studied on a new, very high lift, low-pressure turbine airfoil. Experiments were done under low freestream turbulence conditions on a linear cascade in a low speed wind tunnel. Pressure surveys on the airfoil surface and downstream total pressure loss surveys were documented. Velocity profiles were acquired in the suction side boundary layer at several streamwise locations using hot-wire anemometry. Cases were considered at Reynolds numbers (based on the suction surface length and the nominal exit velocity from the cascade) ranging from 25,000 to 330,000. In all cases the boundary layer separated, but at high Reynolds number the separation bubble remained very thin and quickly reattached after transition to turbulence. In the low Reynolds number cases, the boundary layer separated and did not reattach, even when transition occurred. Three different CFD URANS (unsteady Reynolds averaged Navier-Stokes) models were utilized in this study (using Fluent CFD Code), the k-ω shear stress transport model, the ν2-fk-ε model, and the 4 equation Transition model of Menter. At Re = 25,000, the Transition model seems to perform the best. At Re = 100,000 the Transition model seems to perform the best also, although it under-predicts the pressure coefficient downstream of the suction peak. At Re = 300,000 all models perform very similar with each other. The Transition model showed a small bump in the pressure coefficient downstream from the suction peak indicating the presence of a small bubble at that location.

Transition Modeling for Vortex Generating Jets on Low-Pressure Turbine Profiles

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
Florian Herbst ◽  
Dragan Kožulović ◽  
Joerg R. Seume
Keyword(s):  
Total Pressure ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Quantitative Prediction ◽  
Design Parameters ◽  
Transition Model ◽  
Pressure Losses ◽  
Low Pressure Turbine ◽  
Wide Range ◽  
Local Transition

Steady blowing vortex generating jets (VGJ) on highly-loaded low-pressure turbine profiles have shown to be a promising way to decrease total pressure losses at low Reynolds-numbers by reducing laminar separation. In the present paper, the state of the art turbomachinery design code TRACE with RANS turbulence closure and coupled γ-ReΘ transition model is applied to the prediction of typical aerodynamic design parameters of various VGJ configurations in steady simulations. High-speed cascade wind tunnel experiments for a wide range of Reynolds-numbers, two VGJ positions, and three jet blowing ratios are used for validation. Since the original transition model overpredicts separation and losses at Re2is≤100·103, an extra mode for VGJ induced transition is introduced. Whereas the criterion for transition is modeled by a filtered Q vortex criterion the transition development itself is modeled by a reduction of the local transition-onset momentum-thickness Reynolds number. The new model significantly improves the quality of the computational results by capturing the corresponding local transition process in a physically reasonable way. This is shown to yield an improved quantitative prediction of surface pressure distributions and total pressure losses.

scholarly journals Low-Pressure Turbine Separation Control: Comparison With Experimental Data

2002 ◽  
Author(s):  
Vijay K. Garg
Keyword(s):  
Experimental Data ◽  
Computational Study ◽  
Vortex Generator ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Separation Control ◽  
Suction Surface ◽  
Low Reynolds Numbers ◽  
Low Pressure Turbine ◽  
Control Comparison

The present work details a computational study, using the Glenn-HT code, that analyzes the use of vortex generator jets (VGJs) to control separation on a low-pressure turbine (LPT) blade at low Reynolds numbers. The computational results are also compared with the experimental data of Bons et al. [1] for steady VGJs. It is found that the code determines the proper location of the separation point on the suction surface of the baseline blade (without any VGJ) for Reynolds numbers of 50,000 or less. Also, the code finds that the separated region on the suction surface of the blade vanishes with the use of VGJs. However, the separated region and the wake characteristics are not well predicted. The wake width is generally over-predicted while the wake depth is under-predicted.

Investigation of the Laminar Separation-Induced Transition With the γ-Re~θt Transition Model on Low-Pressure Turbine Rotor Blades at Steady Conditions

2012 ◽  
Author(s):  
Jayson Babajee ◽  
Tony Arts
Keyword(s):  
Reynolds Number ◽  
Numerical Test ◽  
Low Pressure ◽  
Rotor Blades ◽  
Experimental Results ◽  
Transition Model ◽  
Flow Topology ◽  
Trailing Edge ◽  
Low Pressure Turbine ◽  
Good Agreement

The present study focuses on the assessment and the validation of the Langtry and Menter γ-Re~θt correlation-based transition model, recently implemented in the RANS code elsA from ONERA. The test cases are two Low-Pressure Turbine (LPT) rotor blades, with the same compressible Zweifel loading coefficient but different load distributions. The corresponding experimental results are provided by the von Karman Institute. The outlet isentropic Reynolds number, based on blade chord and outlet isentropic velocity, ranges from 60000 to 250000 in order to investigate the complex separation-induced transition phenomenon occurring at low Reynolds number cruise condition. The turbulence intensity is the natural freestream turbulence of the facility (0.9%). The numerical test campaign gives good predictions, particularly when accurately tailoring the trailing edge and wake regions of the mesh. The numerical mass-averaged kinetic losses are in good agreement with the experimental ones. Moreover, the flow topology parameters (the transition onset, the transition end and the separation) show good agreement in comparison to the experimental results and correlations from the open literature. One is even able to detect separation-induced transition with reattachment before the trailing edge at the lowest Reynolds number. However, the authors stress the turbulence Reynolds number effect on the prediction of separation-induced transition for strong diffusion LPT blades and particularly when the flow is subjected to a long bubble or even an open separation.

An Approach for Inclusion of a Nonlocal Transition Model in a Parallel Unstructured Computational Fluid Dynamics Code

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
Dragan Kožulović ◽  
B. Leigh Lapworth
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Shape Factor ◽  
Nonlocal Boundary ◽  
Reynolds Numbers ◽  
Transition Model ◽  
Low Pressure Turbine ◽  
Computational Overhead ◽  
Transition Modeling ◽  
Good Agreement

The implementation of an integral transition model in a parallel unstructured computational fluid dynamics code is described. In particular, an algorithm for gathering the nonlocal boundary layer values (momentum thickness and shape factor) from parallel distributed computational domains is presented. Transition modeling results are presented for a flat plate and for a low pressure turbine, covering a large variation of Reynolds numbers, Mach numbers, turbulence intensities, and incidence angles. Contrary to fully turbulent simulations, transitional predictions are in very good agreement with measurements. Furthermore, the computational overhead of transitional simulations is only 7% for one multigrid cycle.

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