scholarly journals Modeling of Wake Effects in Steady State Mixing Plane Simulations of a High Lift Turbine Cascade with Different Combinations of Wake Passing Frequency and Wake Orientation

2021 ◽  
Vol 1909 (1) ◽  
pp. 012001
Author(s):  
A. Führing ◽  
D. Kožulović ◽  
C. Bode ◽  
M. Franke
Keyword(s):  
Steady State ◽  
Turbine Cascade ◽  
High Lift ◽  
Wake Effects ◽  
State Mixing ◽  
Wake Passing

Experimental investigations on steady wake effects in a high-lift turbine cascade

2004 ◽  
Vol 37 (4) ◽  
pp. 488-496 ◽  
Author(s):  
Wolfram Heinke ◽  
Sven K�nig ◽  
Berthold Matyschok ◽  
Bernd Stoffel ◽  
Andreas Fiala ◽  
...  
Keyword(s):  
Experimental Investigations ◽  
Turbine Cascade ◽  
High Lift ◽  
Wake Effects

scholarly journals Effects of Periodic Wake Passing Upon Aerodynamic Loss of a Turbine Cascade: Part I — Measurements of Wake-Affected Cascade Loss by Use of a Pneumatic Probe

1999 ◽  
Author(s):  
Ken-ichi Funazaki ◽  
Nobuaki Tetsuka ◽  
Tadashi Tanuma
Keyword(s):  
Turbine Cascade ◽  
Flow Angle ◽  
Linear Cascade ◽  
Local Loss ◽  
Aerodynamic Loss ◽  
Free Stream Turbulence ◽  
Pressure Distributions ◽  
Wake Turbulence ◽  
Wake Passing ◽  
Profile Loss

This paper reports on an experimental investigation of aerodynamic loss of a low-speed linear turbine cascade which is subjected to periodic wakes shed from moving bars of the wake generator. In this case, parameters related to the wake, such as wake passing frequency (wake Strouhal number) or wake turbulence characteristics, are varied to see how these wake-related parameters affect the local loss distribution or mass-averaged loss coefficient of the turbine cascade. Free-stream turbulence intensity is changed by use of a turbulence grid. In Part I of this paper a focus is placed on the measurements by use of a pneumatic five-hole yawmeter, which provides time-averaged stagnation pressure distributions downstream of the moving bars as well as of the turbine cascade. Spanwise distributions of wake-affected exit flow angle are also measured. From this study it is found that the wake passing greatly affects not only the profile loss but secondary loss of the linear cascade. Noticeable change in exit flow angle is also identified.

Recognition of Structures Leading to Transition in a Low Pressure Turbine Cascade: Effect of Reduced Frequency

2019 ◽  
Author(s):  
D. Lengani ◽  
D. Simoni ◽  
M. Ubaldi ◽  
P. Zunino ◽  
F. Bertini
Keyword(s):  
Boundary Layer ◽  
Suction Side ◽  
Low Pressure ◽  
Turbine Cascade ◽  
Turbulent Structures ◽  
Time Resolved ◽  
Low Pressure Turbine ◽  
Reduced Frequency ◽  
Displacement Thickness ◽  
Wake Passing

Abstract The boundary layer developing over the suction side of a low pressure turbine cascade operating under unsteady inflow conditions has been experimentally investigated. Time-resolved Particle Image Velocimetry (PIV) measurements have been performed in two orthogonal planes, the blade to blade and a wall parallel plane embedded within the boundary layer, for two different wake reduced frequencies. Proper Orthogonal Decomposition (POD) has been used to analyze the data and to provide an interpretation of the most significant flow structures for each phase of the wake passing cycle. To this purpose, a POD based procedure that sorts the data synchronizing the measurements of the two planes has been developed. Phase averaged data are then obtained for both cases. Moreover, once properly sorted, POD has been applied to sub-ensembles of data at the same relative phase within the wake passing cycle. Detailed information on the most energetic turbulent structures at a particular phase are obtained with this procedure (called phased POD), overcoming the limit of classical phase average that just provides a statistical representation of the turbulence field. Furthermore, the synchronization of the measurements in the two planes allows the computation of the characteristic dimension of boundary layer structures that are responsible for transition. These structures are often identified as vortical filaments parallel to the wall, typically referred to as boundary layer streaks. The largest and most energetic structures are observed when the wake centerline passes over the rear part of the suction side, and they appear practically the same for both reduced frequencies. The passing wake forces transition leading to the breakdown of the boundary layer streaks. Otherwise, the largest differences between the low and high reduced frequency are observed in the calmed region. The post-processing of these two planes further allowed us to compute the spacing of the streaks and make it non-dimensional by the boundary layer displacement thickness observed for each phase. The non-dimensional value of the streaks spacing is about constant, irrespective of the reduced frequency.

Influence of Deposit on the Flow in a Turbine Cascade

1988 ◽  
Vol 110 (4) ◽  
pp. 512-519 ◽  
Author(s):  
A. Bo¨lcs ◽  
O. Sari
Keyword(s):  
Steady State ◽  
Gas Turbine ◽  
Side Wall ◽  
Boundary Layer Separation ◽  
Turbine Cascade ◽  
Flow Conditions ◽  
Choked Flow ◽  
Time Marching ◽  
Mach Numbers ◽  
Laser Holography

An experimental study on a gas turbine cascade operating under transonic flow conditions is presented. The flow is compared for airfoil shapes corresponding to the design geometry and the geometry taken from a rotor blade, in an industrial gas turbine burning heavy oil, after a few thousand hours of operation. Steady-state data have been obtained in a linear cascade over a range of isentropic exit Mach numbers from 0.6 to 1.6. The flow field was determined by static pressure measurements on the side walls up- and downstream of the cascade, on one side wall in the blade passage, and on the blade surface at midspan. Furthermore, the flow was visualized by the methods of Schlieren and laser holography. The results show that the choked flow conditions are reached at different steady-state isentropic outlet Mach numbers for the two blade shapes. The deposit, typical for a gas turbine, does not however significantly modify the boundary layer separation point. The flow visualization indicates that the shock wave fluctuations have not been significantly influenced by the important roughness and thickness of the deposit. The experimental results on the two cascades are also compared with two-dimensional time-marching calculations after Denton. In the subsonic regime, good agreement was found for the “clean” blade. For the profile with deposit, the flow cannot be correctly predicted by the time-marching calculation, even in subsonic flow condition. The sonic line calculated by the numerical model under transonic outlet conditions (0.9 < M2S < 1.20) does not agree with the laser holography measurements for either of the two cascades.

scholarly journals An Experimental Study of the Effect of Wake Passing on Turbine Blade Film Cooling

1997 ◽  
Author(s):  
James D. Heidmann ◽  
Barbara L. Lucci ◽  
Eli Reshotko
Keyword(s):  
Turbine Blade ◽  
Film Cooling ◽  
Experimental Film ◽  
Turbine Cascade ◽  
Cooling Performance ◽  
Blowing Ratio ◽  
Nusselt Numbers ◽  
Wake Passing ◽  
Expected Increase ◽  
Effectiveness Data

The effect of wake passing on the showerhead film cooling performance of a turbine blade has been investigated experimentally. The experiments were performed in an annular turbine cascade with an upstream rotating row of cylindrical rods. Nickel thin-film gauges were used to determine local film effectiveness and Nusselt number values for various injectants, blowing ratios, and Strouhal numbers. Results indicated a reduction in film effectiveness with increasing Strouhal number, as well as the expected increase in film effectiveness with blowing ratio. An equation was developed to correlate the span-average film effectiveness data. The primary effect of wake unsteadiness was found to be correlated by a streamwise-constant decrement of 0.094·St. Steady computations were found to be in excellent agreement with experimental Nusselt numbers, but to overpredict experimental film effectiveness values. This is likely due to the inability to match actual hole exit velocity profiles and the absence of a credible turbulence model for film cooling.

Investigation of Wake Induced Transition in Low-Pressure Turbines Using Large Eddy Simulation

2013 ◽  
Author(s):  
V. Nagabhushana Rao ◽  
P. G. Tucker ◽  
R. J. Jefferson-Loveday ◽  
J. D. Coull
Keyword(s):  
Pressure Distribution ◽  
Flat Plate ◽  
Free Stream ◽  
Transition Process ◽  
Large Eddy Simulations ◽  
Suction Surface ◽  
High Lift ◽  
Separated Shear Layer ◽  
Large Eddy ◽  
Wake Passing

Modern ‘high-lift’ blade designs incorporated into the low pressure turbine (LPT) of aero-engines typically exhibit a separation bubble on the suction surface of the airfoil. The size of the bubble and the loss it generates is governed by the transition process in the separated shear layer. However, the wakes shed by the upstream blade rows, the turbulent fluctuations in the free-stream and the roughness over the blade complicates the transition process. The current paper numerically investigates the transition of a separated shear layer over a flat plate with an elliptic leading edge using large eddy simulations (LES). The upper wall of the test section is inviscid and specifically contoured to impose a streamwise pressure distribution over the flat plate to simulate the suction surface of a LPT blade. The influences of free-stream turbulence (FST), periodic wake passing and streamwise pressure distribution (blade loading) are considered. The simulations were carried out at a Reynolds number of 83,000 based on the length of the flat plate (S0 = 0.5m) and the velocity at the nominal trailing edge (UTE ∼ 2.55 m/s). A high turbulence intensity of 4% and a dimensionless wake passing frequency (fr = fwakeS0/UTE, where fwake is the dimensional wake frequency) of 0.84 is chosen for the study. Two different distributions representative of a ‘high-lift’ and an ‘ultra-high-lift’ turbine blade are examined. An in-house, high order, flow solver is used for the Large Eddy Simulations (LES). The Variational Multi-scale approach is used to account for the sub-grid scale stresses. Results obtained from the current LES compare favorably with the extensive experimental data previously obtained for the test cases considered. The LES results are then used to further explore the flow physics involved in the transition process, in particular the role of Klebanoff streaks and their influence on performance. The additional effect of surface roughness of the blade has also been studied for one of the blade loadings. The benefit that roughness can offer for highly loaded turbine blades is demonstrated.

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