scholarly journals Predictions of separated and transitional boundary layers under low-pressure turbine airfoil conditions using an intermittency transport equation

2001 ◽  
Author(s):  
Y. Bor ◽  
P. Huang ◽  
Lennart Hultgren ◽  
David Ashpis
Keyword(s):  
Transport Equation ◽  
Boundary Layers ◽  
Low Pressure ◽  
Low Pressure Turbine

scholarly journals Predictions of Separated and Transitional Boundary Layers Under Low-Pressure Turbine Airfoil Conditions Using an Intermittency Transport Equation

2003 ◽  
Vol 125 (3) ◽  
pp. 455-464 ◽  
Author(s):  
Y. B. Suzen ◽  
P. G. Huang ◽  
Lennart S. Hultgren ◽  
David E. Ashpis
Keyword(s):  
Transport Equation ◽  
Boundary Layers ◽  
Eddy Viscosity ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Equation Model ◽  
Intermittent Behavior ◽  
Low Pressure Turbine ◽  
Transitional Boundary Layer ◽  
Intermittency Factor

A new transport equation for the intermittency factor was proposed to predict separated and transitional boundary layers under low-pressure turbine airfoil conditions. The intermittent behavior of the transitional flows is taken into account and incorporated into computations by modifying the eddy viscosity, μt, with the intermittency factor, γ. Turbulent quantities are predicted by using Menter’s two-equation turbulence model (SST). The intermittency factor is obtained from a transport equation model, which not only can reproduce the experimentally observed streamwise variation of the intermittency in the transition zone, but also can provide a realistic cross-stream variation of the intermittency profile. In this paper, the intermittency model is used to predict a recent separated and transitional boundary layer experiment under low pressure turbine airfoil conditions. The experiment provides detailed measurements of velocity, turbulent kinetic energy and intermittency profiles for a number of Reynolds numbers and freestream turbulent intensity conditions and is suitable for validation purposes. Detailed comparisons of computational results with experimental data are presented and good agreements between the experiments and predictions are obtained.

Investigation of Variated Unsteady Inflow Boundary Conditions on the Transition Behavior of a Low Pressure Turbine Cascade Family

2014 ◽  
Author(s):  
Franz F. Blaim ◽  
Roland E. Brachmanski ◽  
Reinhard Niehuis
Keyword(s):  
Boundary Condition ◽  
Transport Equation ◽  
Flow Separation ◽  
Total Pressure ◽  
Low Pressure ◽  
Test Facility ◽  
Number Range ◽  
Pressure Losses ◽  
Low Pressure Turbine ◽  
Transition Behavior

The objective of this paper is to analyze the influence of incoming periodic wakes, considering the variable width, on the integral total pressure loss for two low pressure turbine (LPT) airfoils. In order to reduce the overall weight of a LPT, the pitch to chord ratio was continuously increased, during the past decades. However, this increase encourages the development of the transition phenomena or even flow separation on the suction side of the blade. At low Reynolds numbers, large separation bubbles can occur there, which are linked with high total pressure losses. The incoming wakes of the upstream blades are known to trigger early transition, leading to a reduced risk of flow separation and hence minor integral total pressure losses caused by separation. For the further investigation of these effects, different widths of the incoming wakes will be examined in detail, here. This variation is carried out by using the numerical Unsteady Reynolds Averaged Solver TRACE developed by the DLR Cologne in collaboration with MTU Aero Engines AG. For the variation of the width of the wakes, a variable boundary condition was modeled, which includes the wake vorticity parameters. The width of the incoming wakes was used as the relevant variable parameter. The implemented boundary condition models the unsteady behavior of the incoming wakes by the variation of the velocity profile, using a prescribed frequenc. TRACE can use two different transition models; the main focus here is set to the γ–Reθt transition model, which uses local variables in a transport equation, to trigger the transition within the turbulence transport equation system. The experimental results were conducted at the high speed cascade open loop test facility at the Institute for Jet Propulsion at the University of the German Federal Armed Forces in Munich. For the investigation presented here, two LPT profiles — which were designed with a similar inlet angle, turning, and pitch are analyzed. However, with a common exit Mach number and a similar Reynolds number range between 40k and 400k, one profile is front loaded and the other one is aft loaded. Numerical unsteady results are in good agreement with the conducted measurements. The influence of the width of the wake on the time resolved transition behavior, represented by friction coefficient plots and momentum loss thickness will be analyzed in this paper.

scholarly journals A Computational Fluid Dynamics Study of Transitional Flows in Low-Pressure Turbines Under a Wide Range of Operating Conditions

2006 ◽  
Vol 129 (3) ◽  
pp. 527-541 ◽  
Author(s):  
Y. B. Suzen ◽  
P. G. Huang ◽  
D. E. Ashpis ◽  
R. J. Volino ◽  
T. C. Corke ◽  
...  
Keyword(s):  
Experimental Data ◽  
Transport Equation ◽  
Low Pressure ◽  
Equation Model ◽  
Operating Conditions ◽  
Computational Results ◽  
Transitional Flows ◽  
Low Pressure Turbine ◽  
Wide Range ◽  
Intermittency Factor

A transport equation for the intermittency factor is employed to predict the transitional flows in low-pressure turbines. The intermittent behavior of the transitional flows is taken into account and incorporated into computations by modifying the eddy viscosity, μt, with the intermittency factor, γ. Turbulent quantities are predicted by using Menter’s two-equation turbulence model (SST). The intermittency factor is obtained from a transport equation model which can produce both the experimentally observed streamwise variation of intermittency and a realistic profile in the cross stream direction. The model had been previously validated against low-pressure turbine experiments with success. In this paper, the model is applied to predictions of three sets of recent low-pressure turbine experiments on the Pack B blade to further validate its predicting capabilities under various flow conditions. Comparisons of computational results with experimental data are provided. Overall, good agreement between the experimental data and computational results is obtained. The new model has been shown to have the capability of accurately predicting transitional flows under a wide range of low-pressure turbine conditions.

Numerical and Experimental Studies on Separated Boundary Layers Over Ultra-High Lift Low-Pressure Turbine Cascade Airfoils With Variable Solidity: Effects of Free-Stream Turbulence

2008 ◽  
Author(s):  
Ken-Ichi Funazaki ◽  
Kazutoyo Yamada ◽  
Yasuhiro Chiba ◽  
Nozomi Tanaka
Keyword(s):  
Boundary Layers ◽  
Free Stream ◽  
Separation Bubble ◽  
Experimental Studies ◽  
Low Pressure ◽  
Freestream Turbulence ◽  
High Lift ◽  
Free Stream Turbulence ◽  
Low Pressure Turbine ◽  
Turbine Airfoils

This paper deals with LES investigation, along with measurements, on the interaction between inlet freestream turbulence and boundary layers with separation bubble over ultra-high lift low-pressure turbine airfoils. The cross section of the test airfoils is typical for highly-loaded LP turbines for civil aeroengines. The solidity of the cascade can be reduced by increasing the airfoil pitch by at least 25%, while maintaining the throat in the blade-to-blade passage. Reynolds number examined is 57,000, based on chord length and averaged exit velocity. Free-stream turbulence is about 0.85% (no grid condition) and 2.1% (with grid condition). Hot-wire probe measurements of the boundary layer are carried out to obtain time-averaged and time-resolved characteristics of the boundary layers under the influence of the freestream turbulence. A newly developed probe positioning tool, which is installed downstream of the cascade with minimal blockage, enables precise probe positioning along lines normal to the airfoil surface. Numerical analysis based on high-resolution LES (Large-Eddy Simulation) is executed to enhance the understanding of the flow field around the Ultra-High Lift and High Lift LP turbine airfoils. Emphasis is placed on the relationship of inherent instability of the shear layer of the separation bubble and the free-stream turbulence. Standard Smagorinsky model is employed for subgrid scale modeling. The flow solver used is an in-house code that was originally developed by one of the authors as FVM (Finite Volume Method)-based fully implicit and time-accurate Reynolds-Averaged Navier-Stokes code. Homogeneous isotropic turbulence created with SNGR (Stochastic Noise Generation and Radiation) method using von Karman-Pao turbulent energy spectrum is applied in the present study for the emulation of inlet turbulence.

Influence of Jet-Induced Transition on Separating Low-Pressure Turbine Boundary Layers

2007 ◽  
Vol 23 (5) ◽  
pp. 996-1006 ◽  
Author(s):  
D. Reimann ◽  
M. Bloxham ◽  
K. L. Crapo ◽  
J. D. Pluim ◽  
J. P. Bons
Keyword(s):  
Boundary Layers ◽  
Low Pressure ◽  
Low Pressure Turbine

Numerical Investigation of Unsteady Boundary Layer Transition Induced by Periodically Passing Wakes With an Intermittency Transport Equation

2004 ◽  
Author(s):  
Rene Pecnik ◽  
Wolfgang Sanz ◽  
Paul Pieringer
Keyword(s):  
Transport Equation ◽  
Numerical Study ◽  
Low Pressure ◽  
Boundary Layer Transition ◽  
Experimental Investigations ◽  
Turbine Cascade ◽  
Layer Transition ◽  
Production Term ◽  
Low Pressure Turbine ◽  
Highly Loaded

A numerical study was performed to investigate unsteady flow transition under the effect of periodically passing wakes on a highly loaded low-pressure turbine cascade. The simulation was done by a time-accurate 2D Navier-Stokes solver, which was developed at the Institute for Thermal Turbo-machinery and Machine Dynamics. The transition process was modeled by coupling a baseline two-equation k-ω turbulence model with an intermittency transport equation via the turbulence production term. The experimental investigations on the highly loaded low-pressure turbine cascade, called T106D-EIZ were carried out at the Institut fu¨r Strahlantriebe der Universita¨t der Bundeswehr Mu¨nchen (Germany). The available experimental data contains three test cases by varying the isentropic exit Reynolds number from 200.000 to 60.000. The objective of this paper is to show the ability of an intermittency transport equation to model unsteady wake induced transition and separation mechanisms. The numerical results are compared by the pressure distribution, shape factor and loss behavior to the experiments.

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