Prediction of the unsteady turbine trailing edge wake flow characteristics and comparison with experimental data

The wakes behind turbine blade trailing edge are characterized by large scale periodic vortex patterns known as the von Karman vortex street. The failure of steady-state Navier-Stokes calculations in modeling wake flows appears to be mainly due to ignoring this type of flow instabilities. In an effort to contribute to a better understanding of the time varying wake flow characteristics behind turbine blades, VKI has performed large scale turbine cascade tests to obtain very detailed information about the steady and unsteady pressure distribution around the trailing edge of a nozzle guide vane. Tests are run at an outlet Mach number of M2,is,=0.4 and a Reynolds number of Rec = 2·106. The key to the high spatial resolution of the pressure distribution around the trailing edge is a rotatable trailing edge with an embedded miniature pressure transducer underneath the surface and a pressure slot opening of about 1.5° of the trailing edge circle. Signal processing allowed or differentiation between random and periodic pressure fluctuations. Ultra-short schlieren pictures help in understanding the physics behind the pressure distribution.

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Effect of the Extended Rigid Flapping Trailing Edge Fringe on an S833 Airfoil

Applied Sciences ◽

10.3390/app12010444 ◽

2022 ◽

Vol 12 (1) ◽

pp. 444

Author(s):

Hongtao Yu ◽

Zifeng Yang

Keyword(s):

Flow Field ◽

Flow Characteristics ◽

Aerodynamic Performance ◽

Substantial Effect ◽

Wake Flow ◽

Trailing Edge ◽

Large Vortex ◽

2D Numerical Simulation ◽

Angular Amplitude ◽

The Impact

A 2D numerical simulation was conducted to investigate the effect of an extended rigid trailing edge fringe with a flapping motion on the S833 airfoil and its wake flow field, as an analogy of an owl’s wing. This study aims to characterize the influence of the extended flapping fringe on the aerodynamic performance and the wake flow characteristics downstream of the airfoil. The length (Le) and flapping frequencies (fe) of the fringe are the key parameters that dominate the impact on the airfoil and the flow field, given that the oscillation angular amplitude is fixed at 5°. The simulation results demonstrated that the airfoil with an extended fringe of 10% of the chord at a flapping frequency of fe = 110 Hz showed a substantial effect on the pressure distribution on the airfoil and the flow characteristics downstream of the airfoil. An irregular vortex street was predicted downstream, thus causing attenuations of the vorticities, and shorter streamwise gaps between each pair of vortices. The extended flapping fringe at a lower frequency than the natural shedding vortex frequency can effectively break the large vortex structure up into smaller scales, thus leading to an accelerated attenuation of vorticities in the wake.

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The Effect of Vortex Shedding on the Unsteady Pressure Distribution Around the Trailing Edge of a Turbine Blade

Journal of Turbomachinery ◽

10.1115/1.2841192 ◽

1997 ◽

Vol 119 (4) ◽

pp. 810-819 ◽

Cited By ~ 31

Author(s):

G. Cicatelli ◽

C. H. Sieverding

Keyword(s):

Pressure Distribution ◽

Turbine Blade ◽

Large Scale ◽

Guide Vane ◽

Turbine Blades ◽

Pressure Fluctuations ◽

Flow Characteristics ◽

Wake Flow ◽

Trailing Edge ◽

Unsteady Pressure

The wakes behind turbine blade trailing edges are characterized by large-scale periodic vortex patterns known as the von Karman vortex street. The failure of steady-state Navier–Stokes calculations in modeling wake flows appears to be mainly due to ignoring this type of flow instabilities. In an effort to contribute to a better understanding of the time-varying wake flow characteristics behind turbine blades, VKI has performed large-scale turbine cascade tests to obtain very detailed information about the steady and unsteady pressure distribution around the trailing edge of a nozzle guide vane. Tests are run at an outlet Mach number of M2,is, = 0.4 and a Reynolds number of ReC = 2 × 106. The key to the high spatial resolution of the pressure distribution around the trailing edge is a rotatable trailing edge with an embedded miniature pressure transducer underneath the surface and a pressure slot opening of about 1.5 deg of the trailing edge circle. Signal processing allowed differentiation between random and periodic pressure fluctuations. Ultrashort schlieren pictures help in understanding the physics behind the pressure distribution.

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Rotors with Trailing Edge Flaps: Analysis and Comparison with Experimental Data

Journal of the American Helicopter Society ◽

10.4050/jahs.43.319 ◽

1998 ◽

Vol 43 (4) ◽

pp. 319-332 ◽

Cited By ~ 61

Author(s):

Judah Milgram ◽

Inderjit Chopra ◽

Friedrich Straub

Keyword(s):

Experimental Data ◽

Trailing Edge ◽

Trailing Edge Flaps ◽

Comparison With Experimental Data

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Characterization of Vortex Dynamics in the Near Wake of an Oscillating Flexible Foil

Journal of Fluids Engineering ◽

10.1115/1.4033959 ◽

2016 ◽

Vol 138 (10) ◽

Cited By ~ 9

Author(s):

Firas F. Siala ◽

Alexander D. Totpal ◽

James A. Liburdy

Keyword(s):

Large Scale ◽

Flow Characteristics ◽

Leading Edge ◽

Wake Flow ◽

Small Scale ◽

Mean Flow ◽

Near Wake ◽

Trailing Edge ◽

Swirling Strength ◽

The Mean

An experimental study was conducted to explore the effect of surface flexibility at the leading and trailing edges on the near-wake flow dynamics of a sinusoidal heaving foil. Midspan particle image velocimetry (PIV) measurements were taken in a closed-loop wind tunnel at a Reynolds number of 25,000 and at a range of reduced frequencies (k = fc/U) from 0.09 to 0.20. Time-resolved and phase-locked measurements are used to describe the mean flow characteristics and phase-averaged vortex structures and their evolution. Large-eddy scale (LES) decomposition and swirling strength analysis are used to quantify the vortical structures. The results demonstrate that trailing edge flexibility has minimal influence on the mean flow characteristics. The mean velocity deficit for the flexible trailing edge and rigid foils remains constant for all reduced frequencies tested. However, the trailing edge flexibility increases the swirling strength of the small-scale structures, resulting in enhanced cross-stream dispersion. Flexibility at the leading edge is shown to generate a large-scale leading edge vortex (LEV) for k ≥ 0.18. This results in a reduction in the swirling strength due to vortex interactions when compared to the flexible trailing edge and rigid foils. Furthermore, it is shown that the large-scale LEV is responsible for extracting a significant portion of energy from the mean flow, reducing the mean flow momentum in the wake. The kinetic energy loss in the wake is shown to scale with the energy content of the LEV.

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