Shear-Layer Along a Perforated Surface: Large and Small-Scale Instabilities
Abstract
Shear flow past a perforated or slotted plate, with a cavity on its backside, can give rise to highly coherent, self-sustained oscillations. In fact, the coherence and magnitude of these oscillations can actually exceed those from the corresponding open cavity. The fundamental features of such oscillations are determined using a technique of high-image-density particle image velocimetry. A cinema version of this technique allows space-time representations of the flow structure. Global instantaneous and phase-averaged patterns are interpreted in conjunction with spectral and cross-spectral analysis of the unsteadiness on either side of the perforated or slotted plate. Using these approaches, a new type of instability has been defined. It is centered on development of a large-scale structure along the surface of the plate, in accord with the evolution of patterns of small-scale structures within each of the perforations or slots. By interpreting the phase shifts associated with the streamwise propagation of the disturbance on either side of the plate, relative to the phase shift of the unsteady volume flux through the plate, it is possible to arrive at a detailed physical model. This model is a generic one, valid for a range of perforated and slotted plate configurations. The consequences of the geometrical parameters of the plate, including the plate thickness and the scale of the individual perforations/perforations or slots, are shown to have a substantial influence. Furthermore, the detailed flow structure is interpreted in accord with the dimensionless frequency and amplitude of oscillation. Understanding of the basic flow physics leads to proposed concepts for attenuation of these oscillations.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 30, 2005
- Accession Number
- ADA442420
Entities
People
- Donald Rockwell
Organizations
- Lehigh University