Predicting Transition in Turbomachinery—Part II: Model Validation and Benchmarking

2004 ◽  
Vol 129 (1) ◽  
pp. 14-22 ◽  
Author(s):  
T. J. Praisner ◽  
E. A. Grover ◽  
M. J. Rice ◽  
J. P. Clark
Keyword(s):  
Experimental Testing ◽  
Local Heat Transfer ◽  
Low Pressure ◽  
Boundary Layer Transition ◽  
Transfer Coefficients ◽  
Layer Transition ◽  
Low Pressure Turbine ◽  
Rans Simulations ◽  
Transition Modeling ◽  
End Wall

The ability to predict boundary layer transition locations accurately on turbomachinery airfoils is critical both to evaluate aerodynamic performance and to predict local heat-transfer coefficients with accuracy. Here we report on an effort to include empirical transition models developed in Part I of this report in a Reynolds averaged Navier-Stokes (RANS) solver. To validate the new models, two-dimensional design optimizations utilizing transitional RANS simulations were performed to obtain a pair of low-pressure turbine airfoils with the objective of increasing airfoil loading by 25%. Subsequent experimental testing of the two new airfoils confirmed pre-test predictions of both high and low Reynolds number loss levels. In addition, the accuracy of the new transition modeling capability was benchmarked with a number of legacy cascade and low-pressure turbine (LPT) rig data sets. Good agreement between measured and predicted profile losses was found in both cascade and rig environments. However, use of the transition modeling capability has elucidated deficiencies in typical RANS simulations that are conducted to predict component performance. Efficiency-versus-span comparisons between rig data and multi-stage steady and time-accurate LPT simulations indicate that loss levels in the end wall regions are significantly under predicted. Possible causes for the under-predicted end wall losses are discussed as well as suggestions for future improvements that would make RANS-based transitional simulations more accurate.

Predicting Transition in Turbomachinery: Part II — Model Validation and Benchmarking

2004 ◽  
Author(s):  
T. J. Praisner ◽  
E. A. Grover ◽  
M. J. Rice ◽  
J. P. Clark
Keyword(s):  
Experimental Testing ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Boundary Layer Transition ◽  
Transfer Coefficients ◽  
Layer Transition ◽  
Airfoil Surface ◽  
Multi Stage ◽  
Rans Simulations ◽  
Transition Modeling

The ability to predict boundary layer transition locations accurately on turbomachinery airfoils is critical both to evaluate aerodynamic performance and to predict local heat-transfer coefficients with accuracy. In state-of-the-art Reynolds Averaged Navier-Stokes (RANS) simulations used to predict flowfields on turbomachinery airfoils, boundary layers are often assumed to be turbulent over the entire airfoil surface. Consequently, losses are not accurately predicted, particularly in the case of stalled airfoils. Here we report on an effort to include empirical transition models developed in Part I of this report in a RANS solver. To validate the new models, a two-dimensional design optimization was performed to obtain a pair of Low-Pressure Turbine (LPT) airfoils with the objective of increasing airfoil loading by 25%. Subsequent experimental testing of the resulting two new airfoils confirmed pre-test predictions of both high and low Reynolds number loss levels. In addition, the accuracy of the new transition modeling capability was benchmarked with a number of legacy cascade and LPT rig data sets. Good agreement between measured and predicted profile losses was found in both cascade and rig environments. However, use of the transition modeling capability has elucidated deficiencies in typical RANS simulations that are conducted to predict component performance. Efficiency-versus-span comparisons between rig data and multi-stage steady and time-accurate LPT simulation results indicate that loss levels in the endwall regions are significantly under-predicted. Possible causes for the under-predicted endwall looses are discussed as wall as suggestions for future improvements that would make RANS-based transitional simulations more accurate.

Highly Loaded Low-Pressure Turbine: Design, Numerical, and Experimental Analysis

2010 ◽  
Author(s):  
J. T. Schmitz ◽  
S. C. Morris ◽  
R. Ma ◽  
T. C. Corke ◽  
J. P. Clark ◽  
...  
Keyword(s):  
High Speed ◽  
Numerical Solutions ◽  
Pressure Ratio ◽  
Low Pressure ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
Low Pressure Turbine ◽  
The Mean ◽  
Highly Loaded

The performance and detailed flow physics of a highly loaded, transonic, low-pressure turbine stage has been investigated numerically and experimentally. The mean rotor Zweifel coefficient was 1.35, with dh/U2 = 2.8, and a total pressure ratio of 1.75. The aerodynamic design was based on recent developments in boundary layer transition modeling. Steady and unsteady numerical solutions were used to design the blade geometry as well as to predict the design and off-design performance. Measurements were acquired in a recently developed, high-speed, rotating turbine facility. The nozzle-vane only and full stage characteristics were measured with varied mass flow, Reynolds number, and free-stream turbulence. The efficiency calculated from torque at the design speed and pressure ratio of the turbine was found to be 90.6%. This compared favorably to the mean line target value of 90.5%. This paper will describe the measurements and numerical solutions in detail for both design and off-design conditions.

scholarly journals Numerical Investigation of Wake Interaction in a Low Pressure Turbine

1998 ◽  
Author(s):  
Frank Eulitz ◽  
Karl Engel
Keyword(s):  
Phenomenological Study ◽  
Separated Flow ◽  
Low Pressure ◽  
Skin Friction Coefficient ◽  
Boundary Layer Transition ◽  
Navier Stokes ◽  
Layer Transition ◽  
Low Pressure Turbine ◽  
Wake Interaction ◽  
Large Fluctuations

A time-accurate Reynolds-averaged Navier-Stokes solver has been extended for a phenomenological study of wake/bladerow interaction in a low pressure turbine near midspan. To qualitatively account for unsteady laminar-turbulent boundary layer transition, a variant of the Abu-Ghanam Shaw transition correlation has been coupled with the Spalart-Allmaras one-equation turbulence model. The method is shown to be capable of capturing separated-flow and wake-induced transition, as well as becalming and relaminarization effects. The model turbine investigated consists of three stator and two rotor rows. Instantaneous Mach number and eddy-viscosity plots are presented to monitor the wake migration and interaction with downstream boundary layers. Especially on the suction sides, very large fluctuations of the skin friction coefficient are observed. Effects of the near and far wakes are identified.

The Effects of a Trip Wire and Unsteadiness on a High-Speed Highly Loaded Low-Pressure Turbine Blade

2004 ◽  
Vol 127 (4) ◽  
pp. 747-754 ◽  
Author(s):  
M. Vera ◽  
H. P. Hodson ◽  
R. Vazquez
Keyword(s):  
Boundary Layer ◽  
High Speed ◽  
Low Pressure ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Low Pressure Turbine ◽  
Roughness Elements ◽  
Unsteady Inflow ◽  
Mach Numbers ◽  
Inflow Conditions

This paper presents the effect of a single spanwise two-dimensional wire upon the downstream position of boundary layer transition under steady and unsteady inflow conditions. The study is carried out on a high turning, high-speed, low pressure turbine (LPT) profile designed to take account of the unsteady flow conditions. The experiments were carried out in a transonic cascade wind tunnel to which a rotating bar system had been added. The range of Reynolds and Mach numbers studied includes realistic LPT engine conditions and extends up to the transonic regime. Losses are measured to quantify the influence of the roughness with and without wake passing. Time resolved measurements such as hot wire boundary layer surveys and surface unsteady pressure are used to explain the state of the boundary layer. The results suggest that the effect of roughness on boundary layer transition is a stability governed phenomena, even at high Mach numbers. The combination of the effect of the roughness elements with the inviscid Kelvin–Helmholtz instability responsible for the rolling up of the separated shear layer (Stieger, R. D., 2002, Ph.D. thesis, Cambridge University) is also examined. Wake traverses using pneumatic probes downstream of the cascade reveal that the use of roughness elements reduces the profile losses up to exit Mach numbers of 0.8. This occurs with both steady and unsteady inflow conditions.

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.

Large Eddy Simulations of a Low-Pressure Turbine: Roughness Modeling and the Effects on Boundary Layer Transition and Losses

2018 ◽  
Author(s):  
F. Hammer ◽  
Neil D. Sandham ◽  
Richard D. Sandberg
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Low Pressure ◽  
Large Eddy Simulations ◽  
Boundary Layer Transition ◽  
Immersed Boundary ◽  
Spanwise Direction ◽  
Layer Transition ◽  
Low Pressure Turbine ◽  
Large Eddy

Large eddy simulations of a linear low-pressure turbine cascade with the T106A profile and different surface roughness patches were carried out. The aim was to investigate the effects on the laminar and turbulent boundary layer on the blade suction surface. Two different approaches were used to represent the roughness patches. Firstly, a forcing model, reducing the computational costs compared to fully resolved roughness surfaces, was incorporated. Secondly, an immersed boundary method representing an as-cast roughness surface was used, for a more detailed analysis of flow mechanisms over roughness. It was found that the roughness model was able to induce boundary layer transition and alter the turbulent boundary layer, with the results in line with findings in the literature. The instantaneous flow data at different time instants of the as-cast roughness case showed the development of streaks due to distinct roughness peaks, resulting in highly uneven transition positions across the spanwise direction.

The Effects of a Trip Wire and Unsteadiness on a High Speed Highly Loaded Low-Pressure Turbine Blade

2004 ◽  
Author(s):  
M. Vera ◽  
H. P. Hodson ◽  
R. Vazquez
Keyword(s):  
Boundary Layer ◽  
High Speed ◽  
Low Pressure ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Low Pressure Turbine ◽  
Roughness Elements ◽  
Unsteady Inflow ◽  
Mach Numbers ◽  
Inflow Conditions

This paper presents the effect of a single spanwise 2D wire upon the downstream position of boundary layer transition under steady and unsteady inflow conditions. The study is carried out on a high turning, high-speed, low pressure turbine (LPT) profile designed to take account of the unsteady flow conditions. The experiments were carried out in a transonic cascade wind tunnel to which a rotating bar system had been added. The range of Reynolds and Mach numbers studied includes realistic LPT engine conditions and extends up to the transonic regime. Losses are measured to quantify the influence of the roughness with and without wake passing. Time resolved measurements such as hot wire boundary layer surveys and surface unsteady pressure are used to explain the state of the boundary layer. The results suggest that the effect of roughness on boundary layer transition is a stability governed phenomena, even at high Mach numbers. The combination of the effect of the roughness elements with the inviscid Kelvin-Helmholtz instability responsible for the rolling up of the separated shear layer (Stieger [1]) is also examined. Wake traverses using pneumatic probes downstream of the cascade reveal that the use of roughness elements reduces the profile losses up to exit Mach numbers of 0.8. This occurs with both steady and unsteady inflow conditions.

scholarly journals Description of the Flow in a Two-Stage Low-Pressure Turbine With Hub Cavities

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
Maxime Fiore ◽  
Nicolas Gourdain ◽  
Jean-François Boussuge ◽  
Eric Lippinois
Keyword(s):  
Boundary Layer ◽  
Gas Turbine ◽  
Low Pressure ◽  
Secondary Flows ◽  
Boundary Layer Transition ◽  
Two Stage ◽  
Layer Transition ◽  
Low Pressure Turbine ◽  
Aspect Ratios ◽  
Multi Stage

Abstract In gas turbine, multi-stage row blading and technological effects can exhibit significant differences for the flow compared with isolated smooth blade rows. Upstream stages promote a non-uniform flow field at the inlet of the downstream rows that may have large effects on mixing or boundary layer transition processes. The rows of current turbines (and compressors) are already very closely spaced. Axial gaps between adjacent rows of approximately 1/4 to 1/2 of the axial blade chord are common practice. Future designs with higher loading and lower aspect ratios, i.e., fewer and bigger blades, and the ever present aim at minimizing engine length or compactness, will aggravate this condition even further. Interaction between cascade rows will therefore keep increasing and need to be taken into account in loss generation estimation. Also the cavities at hub platform induce purge flow blowing into main annulus and additional losses for the turbine. A robust method to account for the loss generated due to these different phenomena needs to be used. The notion of exergy (energy in the purpose to generate work) provides a general framework to deal with the different transfers of energy between the flow and the gas turbine. This study investigates the flow in a two-stage configuration representative of a low-pressure turbine including hub cavities based on large eddy simulation (LES). A description of the flow in the cavities, the main annulus, and at rim seal interface is proposed. The assessment of loss generated in the configuration is proposed based on an exergy analysis. The study of losses restricted to boundary layer contributions and secondary flows show the interaction processes of secondary vortices and wake generated in upstream rows on the flow in downstream rows.

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