Base Pressure at Supersonic Velocities

Citation

Chapman, Dean Roden (1948) Base Pressure at Supersonic Velocities. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/F2ZC-4B47. https://resolver.caltech.edu/CaltechETD:etd-12122008-143236

Abstract

The existing theories of base pressure are described in detail and are shown to be unsatisfactory. An "exact" analysis is then made of the base pressure in an inviscid fluid, both for two-dimensional and axially-symmetric flow. It is shown that for a given body there are, in general, an infinite number of possible solutions satisfying all necessary boundary conditions. For the particular case of inviscid flow about projectile-shaped bodies only one solution is possible, but it corresponds to zero base drag. This latter result is generalized and the following conjecture made: it is impossible for a steady axially-symmetric inviscid supersonic flow to converge toward, and to meet the axis at a finite (non-zero) angle. Since the inviscid-fluid theory does not adequately describe the conditions in a real fluid, an approximate theory for base pressure in a viscous fluid is developed. This latter theory is based in part on the inviscid-flow calculations and in part on dimensional analysis. It includes the effects of Mach number, Reynolds number, body shape, and type of boundary-layer flow. A comparison of the theory with the available experimental data indicates satisfactory agreement. It is shown that under certain conditions the airfoil contour for minimum profile drag in a viscous fluid necessarily has a blunt trailing edge. Approximate calculations indicate that very substantial reductions in profile drag are possible by designing airfoils with blunt trailing edges. Consideration is briefly given to the interference of a support rod on base pressure measurements in a supersonic wind tunnel.

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