The Effect of Jet Entrainment on Loss of Thrust for a Two-Dimensional Symmetrical Jet-Flap Aerofoil

Abstract

SummaryJet drag, defined as the form drag associated with jet entrainment in otherwise inviscid fluid, has been analysed by replacing a two-dimensional incompressible jet with a suitable continuous distribution of sinks. Exact solutions for the jet drag, with the flow incompressible and the jet turbulent, are presented for uncambered struts of various shapes (including an ellipse and a circular cylinder), various thickness ratios, and with blowing slots of various widths in both quiescent and uniform streaming flow. In uniform streaming flow the jet is blowing in the direction of the external flow. The extension of the theory to cross-stream blowing (as in the jet flap) is discussed.The present theory compares favourably with the few available experimental results when the ratio of jet velocity to streaming-flow velocity is sufficiently large.