Abstract:

ESDU 77020 gives graphs enabling pressure drag to be predicted for boat-tails on axisymmetric bodies with at least three diameters of constant diameter section upstream of the boat-tail, at zero incidence, with a turbulent boundary layer and no jet efflux. The graphs were obtained by a correlation of experimental test data drawn from the literature. This showed that the drag coefficient, based on body maximum cross-sectional area, did not vary with Mach number below values of 0.6; graphs are therefore given at Mach numbers of 0.6, 0.7 and 0.8 and plot the drag coefficient against boat-tail angle (up to 45 degrees at which point the flow is fully-detached) and boat-tail diameter ratio. The method is found to predict the drag coefficient to within 0.015 for 90 per cent of the data and, when used with ESDU 76033 which gives values of base drag coefficient, predicts the overall drag coefficient to within 0.025 for 90 per cent of the data.

Software for the method is provided as Toolbox Boat-tail Pressure Drag and ESDUpac A7720.