ESDU 02012 provides@ for a body at zero angle of attack@ an empirical graphical method derived from a correlation of wind-tunnel data for the increments in base and boat-tail pressure drags due the presence of the jet. To obtain total values therefore requires the addition of those increments to values in the absence of the jet which may be determined from ESDU 96012. The boat-tails may be of circular- or parabolic-arc or other similar profile. The cylindrical body upstream of the boat-tail must be 3 or more calibres long and must run into the boat-tail without discontinuity. The nozzles can be convergent or parallel and there must be an annular rear-facing base of width exceeding 0.05 of base diameter. For cases with negligible annular base area@ ESDU 01012 may be used. It is found that the base pressure plotted against a simple geometric parameter involving only the body@ base and jet diameters is a straight line. To provide an easy estimation method@ it was found convenient to provide two graphs; one plots against jet pressure ratio the slope of that line and the other plots as a function of jet pressure ratio and boat-tail angle the intercept on the axis for the case of a cold jet. A simple correction for jet total temperature is applied. The boat-tail pressure drag coefficient increment is found to be a unique function of the base pressure increment; a third graph plots its slope against boat-tail angle. The ranges of the flow conditions and dimensions of the models used in developing the correlation are indicated and sketches show the accuracy of the correlations. The increment in base drag coefficient due to the presence of the jet was predicted to within ±0.015@ the boat-tail pressure drag coefficient to within ±0.02 and the total pressure drag coefficient to within ±0.025; the coefficients being based on body cross-sectional area. A fully-worked example illustrates the use of the method.
ESDU 02012 A-2005 history
2005ESDU 02012 A-2005 Subsonic base and boat-tail pressure drag of cylindrical bodies with circular-arc boat-tails and a central propulsive jet.