Leading edge bluntness effects and their importance in hypersonic inlet design

Abstract

The results of a detailed analytical and experimental investigation of the shock-layer and boundary layer about blunted hvo-dimensional slender bodies are presented. The experimental data obtained a t the NASA-Ames 3 . 5 it. IIypersonic Facility a t Mach numbers 7 and 1 0 includes both pitot and stagnation temperature profile measurements a s well as surface pressure and wall heat t ransfer information. The effects of the entropy layer on the validity of conventional experimental techniques f o r determination of boundary layer height and charac te r a r e discussed and a new, more uniformly valid, method fo r such experimental determinations is suggested. Experimental data regarding natural and forced transition, based on heat t ransfer measurements, chemical coating techniques, surface pitot measurements, and profile analysis is presented. The applicability of presently available analytical techniques fo r the calculation of the boundary layer flow characterist ics (locally s imi la r and non-similar) i s discussed using the obtained experimental data to illustrate specific conclusions. An attempt to develop a new analytical technique for calculating laminar boundary layer growth under the presence of an interacting external shear layer is also discussed. Comments a r e made regarding the importance of bluntness-induced effects in general hypersonic inlet design. I. I n t r o d x c m A practical hypersonic ramjet system designed to operate in both the subsonic and supersonic combustion regimes is dopendent on the development of an efficient engine air induction system over the requisite Mach numb e r range. The development required relates to the integration of the engine and inlet system with the flight vehicle and to the basic fluid mechanical problems encountered in general inlet design. Practical considerations such as vehicle heat transfer, structural integrity, and overall system performance provide strong constraints on the configuration of some engine components i n o rder to satisfy state-of-the-art material limitations. Thc design of realist ic engines of this type can be optimized, therefore, only within these practical limitations and often a t the expense of modification to the ideal aerodynamic design of specific system components. The effect of leading edge bluntness on the shockwave shape, flow field properties, boundary-layer char acterist ics, and shock-wave boundary-layer interactions is a typical aerodynamic phenomenon imposed on the basic inlet design (using sharp leading edges) by the aforementioned practical considerations. p roper understanding of these effects and their influence on the flow conditions delivered to the ramjet combustor is of vital significance in the practical design of high speed a i r breathing engine systems. A s such, the W o r k supported by the Air-Breathing Propulsion Branch of the NASA-Ames Research Center under Contract NAS 7-416. Special c red i t is acknowledged to E. C. Watson and Vernon Gnos of NASA-Ames Research Center as well as Dan Shamshins and John Bocci0 of the Republic Aviation Division fo r their valuable discussion