The Pressure Footprint of a Turbulent Layer on a Compliant Boundary.
Abstract
An examination was made of one way in which a compliant boundary may affect the low wave number pressure field measured at the surface under a turbulent boundary layer. Specifically, we assume that the low wavenumber pressure field measured at the wall results from the large scale motions in the outer part of the flow, and that these are triggered by the bursting in the buffer layer, which is caused in its turn by secondary instabilities growing on inflectionary profiles caused by longitudinal vortices in the sub and buffer layers. The direct effect of the compliant boundary on the growth of these longitudinal vortices, using the energy method, was examined. We represent the compliant boundary by a half space filled with a linear visco-elastic medium with a single time constant. We find that the effect of the boundary is to introduce an effective slip in the boundary condition on the disturbance (the longitudinal vortices), producing a boundary condition intermediate between the inviscid boundary condition and the no-slip boundary condition. Since this boundary condition is less dissipative, the vortices are less stable, and have a higher growth rate. They might consequently be expected to grow faster and occur more frequently, if this were the only mechanism involved, resulting in a shift of the low wavenumber pressure spectrum to higher frequencies. This appears to be the opposite of observations, suggesting that other mechanisms are involved.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jul 31, 1980
- Accession Number
- ADA087296
Entities
People
- John L. Lumley