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Pressure fluctuations on an oscillating trailing edge

  • Thomas Staubli (a1) (a2) and Donald Rockwell (a1)
Abstract

Turbulent boundary layers separating from a blunt trailing edge give rise to organized vortical structures in the downstream wake. The perturbation of this inherent flow-instability at f0 by controlled oscillations of the edge at fe produces corresponding, organized components of unsteady surface pressure along the edge. For edge excitation near the ‘natural’ vortex shedding frequency f0, the phase between the local pressure fluctuations and the edge displacement shows large changes for small changes in excitation frequency. Moreover, in this range of excitation, there is quenching (or attenuation) of the surface pressure component at f0 and resonant peaking of the component at fe. These phenomena are related to the change in sign of the energy transfer between the fluid and the body. Integration of the instantaneous pressure distributions along the surfaces of the edge leads to the instantaneous lift at fe and f0 acting upon the oscillating trailing edge. The location of the lift varies as the cotangent of the dimensionless time during an oscillation cycle. When the edge is excited near, or at, the natural vortex shedding frequency, there is a resonant peak in the amplitude of oscillation of the lift location at fe; that at f0 is invariant. Moreover, the mean location of the lift at fe undergoes abrupt changes in this region of excitation. Flow visualization allows determination of the phasing of the organized vortical structures shed from the trailing edge relative to the edge displacement. Modulation of the flow structure at the frequencies f0 and fe, as well as interaction of small-scale vortices at high excitation frequencies, was observed. These aspects of the near-wake structure are related to the instantaneous pressure field.

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References
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Journal of Fluid Mechanics
  • ISSN: 0022-1120
  • EISSN: 1469-7645
  • URL: /core/journals/journal-of-fluid-mechanics
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