Abstract:

The subsonic flow of the turbulent boundary layers over the upper and lower surfaces of a flat plate with a blunt trailing edge separate at the base to form an unsteady, periodic wake in the form of a vortex street. The oscillating wake induces a substantial base drag, a prediction method for which is given in Appendix B of ESDU 10016. For aircraft, and in many other applications, it is important to maintain low drag and so various means have been tested whereby the periodicity is controlled - either eliminated or moderated.

ESDU 10017 describes the devices used and provides guidance on their effectiveness in the reduction of base drag at subsonic and low supersonic speeds. The four classes of trailing-edge device that have been tested, i.e. base bleed, splitter plates, cavities and non-linear trailing edges, are discussed with particular reference to base drag alleviation and any other useful aerodynamic aspects. The concluding remarks include a table summarising possible base drag reductions for the various devices.