Wall pressure fluctuations of a turbulent separated and reattaching flow affected by an unsteady wake

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The spatio-temporal characteristics of the wall-pressure fluctuations in separated and reattaching flows over a backward-facing step were investigated through pressure-velocity joint measurements carried out using multiple-arrayed microphones and split-film probes. A spoke-wheel-type wake generator was installed upstream of the backward-facing step. The flow structure at the effective forcing frequency (St(f)=0.2) was found to be well organized in terms of wall pressure spectrum, cross-correlation, wavenumber-frequency spectrum, and wavelet auto-correlation. Introduction of the unsteady wake (Stf=0.2) reduced the reattachment length by 10%. In addition, the unsteady wake enhanced the turbulence intensity near the separation edge and, as a consequence, enhanced the quadrupole sound sources; however, the turbulence intensity near the reattachment region was weakened and the overall flow noise was attenuated. The greater organization of the flow structure induced by the unsteady wake led to a weakening of the dipole sound sources, which are the dominant sound sources in this system. The dipole sound sources generated by wall pressure fluctuations were calculated using Curle's integral formula.
Publisher
SPRINGER
Issue Date
2004-10
Language
English
Article Type
Article
Keywords

BACKWARD-FACING STEP; BOUNDARY-LAYER; COHERENT STRUCTURE; BUBBLE; VORTICES; ARRAY

Citation

EXPERIMENTS IN FLUIDS, v.37, pp.531 - 546

ISSN
0723-4864
DOI
10.1007/s00348-004-0839-6
URI
http://hdl.handle.net/10203/13622
Appears in Collection
ME-Journal Papers(저널논문)
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