Numerical Simulation of Unsteady Wake/Blade Interactions in Low-Pressure Turbine Flows Using an Intermittency Transport Equation

2004 ◽  
Vol 127 (3) ◽  
pp. 431-444 ◽  
Author(s):  
Y. B. Suzen ◽  
P. G. Huang
Keyword(s):  
Numerical Simulations ◽  
Transport Equation ◽  
Transport Model ◽  
Separated Flow ◽  
Low Pressure ◽  
Equation Model ◽  
Suction Surface ◽  
Intermittent Behavior ◽  
Unsteady Wake ◽  
Intermittency Factor

An extensive computational investigation of the effects of unsteady wake/blade interactions on transition and separation in low-pressure turbines has been performed by numerical simulations of two recent sets of experiments using an intermittency transport equation. The experiments considered have been performed by Kaszeta and Simon and Stieger in order to investigate the effects of periodically passing wakes on laminar-to-turbulent transition and separation in low-pressure turbines. The test sections were designed to simulate unsteady wakes in turbine engines for studying their effects on boundary layers and separated flow regions over the suction surface. The numerical simulations of the unsteady wake/blade interaction experiments have been performed using an intermittency transport model. The intermittent behavior of the transitional flows is taken into account and incorporated into computations by modifying the eddy viscosity, with the intermittency factor. Turbulent quantities are predicted by using Menter’s two-equation turbulence model (SST). The intermittency factor is obtained from the transport equation model, which can produce both the experimentally observed streamwise variation of intermittency and a realistic profile in the cross-stream direction. Computational results are compared to the experiments. Overall, general trends are captured and prediction capabilities of the intermittency transport model for simulations of unsteady wake/blade interaction flowfields are demonstrated.

Numerical Simulation of Unsteady Wake/Blade Interactions in Low Pressure Turbine Flows Using an Intermittency Transport Equation

2004 ◽  
Author(s):  
Y. B. Suzen ◽  
P. G. Huang
Keyword(s):  
Numerical Simulations ◽  
Transport Equation ◽  
Transport Model ◽  
Separated Flow ◽  
Low Pressure ◽  
Equation Model ◽  
Suction Surface ◽  
Intermittent Behavior ◽  
Unsteady Wake ◽  
Intermittency Factor

An extensive computational investigation of the effects of unsteady wake/blade interactions on transition and separation in low-pressure turbines has been performed by numerical simulations of two recent sets of experiments using an intermittency transport equation. The experiments considered have been performed by Kaszeta and Simon [1] (Kaszeta et al. [2,3]), and Stieger [4] (Stieger and Hodson [5]) in order to investigate the effects of periodically passing wakes on laminar-to-turbulent transition and separation in low-pressure turbines. The test sections were designed to simulate unsteady wakes in turbine engines for studying their effects on boundary layers and separated flow regions over the suction surface. The numerical simulations of the unsteady wake/blade interaction experiments have been performed using an intermittency transport model. The intermittent behavior of the transitional flows is taken into account and incorporated into computations by modifying the eddy viscosity, with the intermittency factor. Turbulent quantities are predicted by using Menter’s two-equation turbulence model (SST). The intermittency factor is obtained from the transport equation model which can produce both the experimentally observed streamwise variation of intermittency and a realistic profile in the cross stream direction. Computational results are compared to the experiments. Overall, general trends are captured and prediction capabilities of the intermittency transport model for simulations of unsteady wake/blade interaction flowfields are demonstrated.

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.

Comprehensive validation of an intermittency transport model for transitional low-pressure turbine flows

2005 ◽  
Vol 109 (1093) ◽  
pp. 101-118 ◽  
Author(s):  
Y. B. Suzen ◽  
P. G. Huang
Keyword(s):  
Transport Model ◽  
Low Pressure ◽  
Operating Conditions ◽  
Transitional Flow ◽  
Pressure Gradients ◽  
Transport Modelling ◽  
Transitional Flows ◽  
Low Pressure Turbine ◽  
Unsteady Wake ◽  
Intermittency Factor

Abstract A transport equation for the intermittency factor is employed to predict transitional flows under the effects of pressure gradients, freestream turbulence intensities, Reynolds number variations, flow separation and reattachment, and unsteady wake-blade interactions representing diverse operating conditions encountered in low-pressure turbines. The intermittent behaviour of the transitional flows is taken into account and incorporated into computations by modifying the eddy viscosity, μτ with the intermittency factor, γ. Turbulent quantities are predicted by using Menter’s two-equation turbulence model (SST). The onset location of transition is obtained from correlations based on boundary-layer momentum thickness, accelaration parameter, and turbulence intensity. The intermittency factor is obtained from a transport model which can produce both the experimentally observed streamwise variation of intermittency and a realistic profile in the cross stream direction. The intermittency transport model is tested and validated against several well documented low pressure turbine experiments ranging from flat plate cases to unsteady wake-blade interaction experiments. Overall, good agreement between the experimental data and computational results is obtained illustrating the predicting capabilities of the model and the current intermittency transport modelling approach for transitional flow simulations.

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.

Large Eddy Simulation and CDNS Investigation of T106C Low-Pressure Turbine

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Site Hu ◽  
Chao Zhou ◽  
Zhenhua Xia ◽  
Shiyi Chen
Keyword(s):  
Large Eddy Simulation ◽  
Flow Separation ◽  
Separated Flow ◽  
Low Pressure ◽  
Secondary Flows ◽  
Computational Domain ◽  
Suction Surface ◽  
Low Pressure Turbine ◽  
Eddy Simulation ◽  
Large Eddy

This study investigates the aerodynamic performance of a low-pressure turbine, namely the T106C, by large eddy simulation (LES) and coarse grid direct numerical simulation (CDNS) at a Reynolds number of 100,000. Existing experimental data were used to validate the computational fluid dynamics (CFD) tool. The effects of subgrid scale (SGS) models, mesh densities, computational domains and boundary conditions on the CFD predictions are studied. On the blade suction surface, a separation zone starts at a location of about 55% along the suction surface. The prediction of flow separation on the turbine blade is always found to be difficult and is one of the focuses of this work. The ability of Smagorinsky and wall-adapting local eddy viscosity (WALE) model in predicting the flow separation is compared. WALE model produces better predictions than the Smagorinsky model. CDNS produces very similar predictions to WALE model. With a finer mesh, the difference due to SGS models becomes smaller. The size of the computational domain is also important. At blade midspan, three-dimensional (3D) features of the separated flow have an effect on the downstream flows, especially for the area near the reattachment. By further considering the effects of endwall secondary flows, a better prediction of the flow separation near the blade midspan can be achieved. The effect of the endwall secondary flow on the blade suction surface separation at the midspan is explained with the analytical method based on the Biot–Savart Law.

Transition Over C4 Leading Edge and Measurement of Intermittency Factor Using PDF of Hot-Wire Signal

1995 ◽  
Author(s):  
Birinchi K. Hazarika ◽  
Charles Hirsch
Keyword(s):  
Separated Flow ◽  
Leading Edge ◽  
Threshold Value ◽  
Angle Of Incidence ◽  
Bypass Transition ◽  
Hot Wire ◽  
Suction Surface ◽  
Intermittency Factor ◽  
Conditional Averaging

The variation of intermittency factors in the transition region of a C4 leading edge flat plate is measured at three incidence angles in a low turbulence free-stream. During the determination of intermittency factor the threshold value of the detector function and the validity of conditional averaging are verified by a method based on the direct application of PDF of the hot-wire output. As the angle of incidence is increased, the transition progressively moves through all the three modes on the suction surface : at zero incidence the bypass transition, at 2° incidence the natural transition and at 4° incidence the separated-flow transition occur respectively. All the three modes of transition exhibited the chord-wise intermittency factor variation in accordance with Narasimha’s universal intermittency distribution, thus the method based on spot production rate is applicable to all the three modes of transition. In the transition zone of the attached boundary layers, the conditionally averaged inter-turbulent profiles are fuller than the Blasius profile while the conditionally averaged turbulent profiles follow a logarithmic profile with a variable additive parameter.

Effects of Surface Groove on Separated Flow Transition on a High-Lift Low-Pressure Turbine Profile Under Steady Inflow Conditions

2009 ◽  
Author(s):  
Hualing Luo ◽  
Weiyang Qiao ◽  
Kaifu Xu
Keyword(s):  
Boundary Layer ◽  
Separated Flow ◽  
Low Pressure ◽  
Separation Point ◽  
Flow Transition ◽  
Suction Surface ◽  
High Lift ◽  
Low Pressure Turbine ◽  
Surface Groove ◽  
Inflow Conditions

LES (Large-Eddy Simulation) computations for a high-lift low-pressure turbine profile equipped with the span-wise groove on the suction surface are done to investigate the mechanism of the surface groove for separated flow transition control under steady inflow conditions, employing the dynamic Smagorinsky model. In addition to the baseline case (no groove), three groove positions which depend on the relative position of the groove trailing edge and the separation point on the suction surface are considered at two Reynolds numbers (Re, based on the inlet velocity and axial chord length). The results show that all grooves can reduce the calculated loss for Re = 50000, due to the further upstream transition inception in the separated shear layer. The analyses indicate two kinds of control mechanism such as the thinning of boundary layer behind the groove and the introduction of disturbances within the groove, depending on the groove position and Reynolds number. At Re = 50000, for the groove located upstream of the separation point, the reason for the further upstream transition inception location is the thinning of boundary layer behind the groove, and for the groove located downstream of the separation point, the reason is the introduction of disturbances within the groove. At Re = 100000, disturbances can also be generated within the groove located upstream of the separation point, promoting earlier transition inception.

scholarly journals Modeling of Flow Transition Using an Intermittency Transport Equation

2000 ◽  
Vol 122 (2) ◽  
pp. 273-284 ◽  
Author(s):  
Y. B. Suzen ◽  
P. G. Huang
Keyword(s):  
Experimental Data ◽  
Transport Equation ◽  
Eddy Viscosity ◽  
Test Cases ◽  
Flow Transition ◽  
Transitional Flows ◽  
Intermittent Behavior ◽  
Wall Flows ◽  
Sst Model ◽  
Intermittency Factor

A new transport equation for intermittency factor is proposed to model transitional flows. The intermittent behavior of the transitional flows is incorporated into the computations by modifying the eddy viscosity, μt, obtainable from a turbulence model, with the intermittency factor, γ:μt*=γμt. In this paper, Menter’s SST model is employed to compute μt and other turbulent quantities. The proposed intermittency transport equation can be considered as a blending of two models—Steelant and Dick and Cho and Chung. The former was proposed for near-wall flows and was designed to reproduce the streamwise variation of the intermittency factor in the transition zone following Dhawan and Narasimha correlation and the latter was proposed for free shear flows and a realistic cross-stream variation of the intermittency profile was reproduced. The new model was used to predict the T3 series experiments assembled by Savill including flows with different freestream turbulence intensities and two pressure-gradient cases. For all test cases good agreements between the computed results and the experimental data were observed. [S0098-2202(00)02302-6]

Numerical Simulations of Combustion and Decomposition Processes in Precalciner with Two Different Heights of Raw Meal Inlets

2012 ◽  
Vol 268-270 ◽  
pp. 477-482
Author(s):  
Shu Xia Mei ◽  
Jun Lin Xie ◽  
Feng He ◽  
Ming Fang Jin
Keyword(s):  
Coordinate System ◽  
Numerical Simulations ◽  
Decomposition Rate ◽  
Transport Model ◽  
Solid Phase ◽  
Equation Model ◽  
Discrete Phase Model ◽  
Decomposition Processes ◽  
Discrete Phase ◽  
Lagrange Coordinate

To reduce energy consumption, numerical simulations of combustion and decomposition processes in a precalciner were carried out with two different heights of raw meal inlets. In Euler coordinate system the gas phase is expressed with k-ε two-equation model, in Lagrange coordinate system the solid phase is expressed with discrete phase model (DPM), the chemical reaction is expressed with species transport model, and the radiation is expressed with P1 radiation model. The results show that when the raw meal inlets are near the jetting coal pipes, there is much better dispersing condition of CaCO3 but a much poorer coal combustion condition, resulting in a much higher CaCO3 decomposition rate but a lower coal burn-off rate than that when the raw meal inlets are far away from the jetting coal pipes. It is advised to install both the two heights of raw meal inlets in order to obtain not only high CaCO3 decomposition rate but also high coal burn-off rate.

Effects of periodic wakes on boundary layer development on an ultra-high-lift low pressure turbine airfoil

2016 ◽  
Vol 231 (1) ◽  
pp. 25-38 ◽  
Author(s):  
Xingen Lu ◽  
Yanfeng Zhang ◽  
Wei Li ◽  
Shuzhen Hu ◽  
Junqiang Zhu
Keyword(s):  
Boundary Layer ◽  
Transition Process ◽  
Low Pressure ◽  
Suction Surface ◽  
High Lift ◽  
Low Pressure Turbine ◽  
Turbulent Transition ◽  
Boundary Layer Development ◽  
Unsteady Wake ◽  
Layer Development

The laminar-turbulent transition process in the boundary layer is of significant practical interest because the behavior of this boundary layer largely determines the overall efficiency of a low pressure turbine. This article presents complementary experimental and computational studies of the boundary layer development on an ultra-high-lift low pressure turbine airfoil under periodically unsteady incoming flow conditions. Particular emphasis is placed on the influence of the periodic wake on the laminar-turbulent transition process on the blade suction surface. The measurements were distinctive in that a closely spaced array of hot-film sensors allowed a very detailed examination of the suction surface boundary layer behavior. Measurements were made in a low-speed linear cascade facility at a freestream turbulence intensity level of 1.5%, a reduced frequency of 1.28, a flow coefficient of 0.70, and Reynolds numbers of 50,000 and 100,000, based on the cascade inlet velocity and the airfoil axial chord length. Experimental data were supplemented with numerical predictions from a commercially available Computational Fluid Dynamics code. The wake had a significant influence on the boundary layer of the ultra-high-lift low pressure turbine blade. Both the wake’s high turbulence and the negative jet behavior of the wake dominated the interaction between the unsteady wake and the separated boundary layer on the suction surface of the ultra-high-lift low pressure turbine airfoil. The upstream unsteady wake segments convecting through the blade passage behaved as a negative jet, with the highest turbulence occurring above the suction surface around the wake center. Transition of the unsteady boundary layer on the blade suction surface was initiated by the wake turbulence. The incoming wakes promoted transition onset upstream, which led to a periodic suppression of the separation bubble. The loss reduction was a compromise between the positive effect of the separation reduction and the negative effect of the larger turbulent-wetted area after reattachment due to the earlier boundary layer transition caused by the unsteady wakes. It appeared that the successful application of ultra-high-lift low pressure turbine blades required additional loss reduction mechanisms other than “simple” wake-blade interaction.

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