Drag reduction by compliant walls

Abstract

The turbulent boundary layer flow over a flat plate, smooth and hard except for a finite section, is considered. In this section the plate may be compliant, have a prescribed waviness, or consist of an ’’active wall’’, etc. The section thus constitutes a disturbance to the turbulent boundary layer flow over a completely smooth and hard plate. An exact integral equation for the resulting disturbances of the fluid stresses at the plate is derived. To a reasonable approximation, this integral equation reduces to an explicit integral representation of the stress disturbances at the plate in terms of the undisturbed flow and the properties of the disturbing plate section. Further evaluation then requires the use of measured data. For a certain type of compliant wall a drag reduction of 1%–10% is estimated. PFL