Abstract:

ESDU 99010 provides a graphical method for predicting supersonic base drag of a cylindrical body at zero angle of attack with a central circular propulsive jet. The graphs plot base pressure coefficient against thrust coefficient for various values of freestream and jet Mach numbers, jet exit angle, ratio of jet-to-freestream total temperature, and ratio of jet specific heat capacities. Likely practical ranges of these parameters are suggested. The method was derived by a parametric study using a computer program based on the multi-component flow model for separated flows over a rearward facing step adapted to axisymmetric flow with both internal and external streams. Thevariation of base pressure as jet pressure ratio changes is discussed and illustrated, and the range for which the method is applicable is specified; theupstream separation induced by an underexpanded jet is discussed and provides an upper limit to the thrust coefficient. Likely values of thrust coefficient met in practice are considered and the method is found to cover those cases, which include aircraft as well as missiles in cruise or with moderate boost. Typical behaviour of base pressure coefficient with variations of each of the parameters is also illustrated. Predictions made using the method are shown in sketches compared with experimental results drawn from the literature, mainly for a cold jet, and are accurate to within 0.015 of base drag coefficient. A fully worked example illustrates the use of the method using a calculation blank table provided to assist the process of interpolation between the values of the parameters used on the graphs.