Radial base-pressure gradients in laminar flow.

Abstract

I emphasis during the past few years has been placed upon finding solutions to the laminar-flow basepressure problem. Experimental techniques have been developed by many ground test facilities to obtain interference free base-pressure data ranging from sophisticated freeflight telemetry techniques to models supported by thin wires, trailing wire techniques and various strut designs. A fair amount of laminar-flow base-pressure data are in existence for supersonic Mach numbers of approximately 12 and below, utilizing the aforesaid techniques. However, only limited data are available for hypersonic Mach numbers (near 20) such as the free-flight telemetry data of lannuzzi and Weddington, Griffith and Weddington,. and the trailing wire data of Softley and Graber. The purpose of this note is to present some additional hypersonic base-pressure results derived from full-scale reentry vehicle (R/V) flight data and to show some radial base-pressure gradient trends derived from this data. The flight data were obtained at M « 20 on a sharp 10° cone having a flat base. Data were reduced only for that portion of the flight trajectory where the measured base-pressure levels (Pb) exceeded 10% of full scale of the pressure sensor range to insure data validity. The base-pressure measurements have a tolerance level estimated to be ±25% for the low Reynolds number data (ReL ~ 5 X 10) to ±6% for the high Reynolds number data (ReL « 7 X 10). A radar tracking trajectory and a measured/extrapolated atmosphere were utilized to obtain the ambient pressure (pm). It should be noted that the R/V experienced slight angle-of-attack oscillations ranging from zero to a few degrees during the low Reynolds number portion of the flight; however, the angle of attack oscillations were damped to less than a degree for