Patent ID: 7422051

Claim:
A method of reducing velocity and pressure fluctuations in a non-zero pressure gradient boundary layer flow using a flexible composite sheet, the flexible sheet comprising a membrane; a substrate supporting said membrane; a plurality of equispaced ridges with two distinct heights coupled to the substrate between said membrane and said substrate; and a gas enclosed in the space between the substrate and the membrane such that modes of flexural oscillation of said membrane which force said gas over the shorter of said ridges experience higher viscous damping compared to other modes the method comprises the steps of: exposing the membrane to a region in a flow of fluid where the streamwise flow pressure gradient changes from favorable to adverse thereby imparting vibratory motion from the flow to a least one segment of a membrane spanning a distance(s) over two of the said ridges, wherein a favorable pressure gradient aids the flow and an adverse pressure gradient opposes the flow; wherein the vibratory motion is reflected from the at least one segment of the membrane to the flow, and; wherein a reduction in fluctuations is caused in the flow pressure gradient and freestream velocity U at all frequencies except where the frequency is approximately equal to ≈U/s.