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Fundamental Issues and Canonical Flows

# The Effects of a Tripped Turbulent Boundary Layer on Vortex Shedding from a Blunt Trailing Edge Hydrofoil

[+] Author and Article Information
Philippe Ausoni1

ABREMA Agence Brevets et Marques, Avenue du Théâtre 16, P.O. Box 5027, CH-1002 Lausanne, Switzerland

Amirreza Zobeiri, François Avellan, Mohamed Farhat

Ecole Polytechnique Fédérale de Lausanne, Laboratory for Hydraulic Machines, Avenue Cour 33bis, CH-1007 Lausanne, Switzerland

1

Corresponding author.

J. Fluids Eng 134(5), 051207 (May 22, 2012) (11 pages) doi:10.1115/1.4006700 History: Received July 17, 2011; Revised March 23, 2012; Published May 18, 2012; Online May 22, 2012

## Abstract

Experiments on vortex shedding from a blunt trailing edge symmetric hydrofoil operating at zero angle of attack in a uniform high speed flow, $Reh=16.1·103-96.6·103$, where the reference length $h$ is the trailing edge thickness, are reported. The effects of a tripped turbulent boundary layer on the wake characteristics are analyzed and compared with the condition of a natural turbulent transition. The foil surface is hydraulically smooth and a fully effective boundary layer tripping at the leading edge is achieved with the help of a distributed roughness. The vortex shedding process is found to be strongly influenced by the boundary layer development: the tripped turbulent transition promotes the re-establishment of organized vortex shedding. In the context of the tripped transition and in comparison with the natural one, significant increases in the vortex span-wise organization, the vortex-induced hydrofoil vibration, the wake velocity fluctuations, and the vortex strength are revealed. Although the vortex shedding frequency is decreased, a modified Strouhal number based on the wake width at the end of the vortex formation region is constant and evidences the similarity of the wakes in terms of spatial distribution for the two considered boundary layer transition processes.

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## Figures

Figure 1

Blunt trailing edge NACA 0009 hydrofoil and distributed roughness

Figure 2

Waterfall spectra of the vortex-induced vibration signals measured at (x/L, z/B) = (0.8, 0.75) for different free-stream velocities and for (a) natural and (b) tripped transitions

Figure 3

(a) Vortex shedding frequency and (b) Strouhal number for different reduced velocities and for natural and tripped transitions

Figure 4

Vibration amplitude of the hydrofoil, measured at (x/L, z/B) = (0.8, 0.75), for different reduced velocities and for natural and tripped transitions

Figure 5

Top-view visualization of cavitation vortex street and vortex-induced vibration signal for lock-off condition, Reh  = 64.4 · 103 . (a) Natural and (b) tripped transitions

Figure 6

Normalized stream-wise velocity fluctuations along the wake at y/h = 0.33 for different free-stream velocities and for the (a) natural and (b) tripped transitions

Figure 7

Traverse measurements across the wake at the end of the vortex-formation region, for the natural and tripped transitions and different free-stream velocities: normalized mean stream-wise velocity profiles (a) and (b) and normalized stream-wise velocity fluctuations (c) and (d)

Figure 8

Traverse measurements across the wake at different stations downstream from trailing edge for the natural and tripped transitions: normalized mean (a) stream-wise and (b) transverse velocity profiles and (c) stream-wise and (d) transverse velocity fluctuations

Figure 9

Maximum (a) stream-wise and (b) transverse velocity fluctuations for traverse measurement across the wake at different stations downstream from the trailing edge

Figure 10

Coherence at the vortex shedding frequency of the high-speed visualization pixel light intensities, typical samples in Fig. 5, for natural and tripped transitions

Figure 11

Intermittency factor of the vortex-induced vibration signal for natural and tripped transitions. Cavitation free.

Figure 12

Spectrograms of the vortex-induced vibration signal for lock-in and lock-off conditions and for natural and tripped transitions. Cavitation free.

Figure 13

Histograms of stream-wise and transverse velocities at the end of the vortex formation region and for the (a) natural and (b) tripped transitions

Figure 14

Vortex strength at the end of the formation region for different free-stream velocities and for the natural and tripped transitions

Figure 15

Griffin number, Styf=fsyfCref, for different free-stream velocities and for natural and tripped transitions

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