Journal of Spacecraft and Rockets Vol. XX, No. X, X–X 2004 Flat-Faced Leading-Edge Effects in Low-Density Hypersonic Wedge Flow Wilson F. N. Santos * National Institute for Space Research Cachoeira Paulista, SP 12630-000 Brazil A numerical study was performed to determine the upstream effects of leading edge thickness on the rarefied hypersonic flow over truncated wedges at zero angle of attack. The simulations were performed by using the Direct Simulation Monte Carlo (DSMC) method. A method that has demonstrated to excellent comparisons with flight- and ground-test data, and properly accounts for nonequilibrium aspects of the flow that arise near the leading edge, which are especially important at high Mach numbers. Some significant differences between sharp and blunt leading edges were noted on the flowfield structure and on the aerodynamic surface quantities. It was found that the upstream effects have different influence on the stagnation streamline properties ahead of the leading edges depending on the leading edge Knudsen number. Interesting features observed in the surface fluxes showed that small leading edge thickness, compared to the freestream mean free path, has important effects on high Mach number leading edge flows. Also, effects on the skin friction coefficient, pressure coefficient and heat transfer coefficient on the wedge are presented as a function of thickness Knudsen number. Nomenclature a Speed of sound, m/s C d Drag coefficient, 2F/ρ∞V 2 ∞ H C f Skin friction coefficient, 2τw/ρ∞V 2 ∞ C h Heat transfer coefficient, 2qw/ρ∞V 3 ∞ Cp Pressure coefficient, 2(pw - p∞)/ρ∞V 2 ∞ F Drag force, N H Body height at the base, m Knt Knudsen number, λ/l L Body length, m l Characteristic length, m M Mach number, V/a N Number flux, m -2 s -1 n Number density, m -3 p Pressure, N/m 2 q Heat flux, W/m 2 R Circular cylinder radius, m Re Reynolds number, ρV l/μ s Arc length, m St Stanton number, h/ρcpV T Temperature, K t Leading edge thickness, m V Velocity, m/s x, y Cartesian axes in physical space, m γ Ratio of specific heats η Coordinate normal to body surface, m θ Wedge half angle, deg λ Mean free path, m ξ Coordinate tangent to body surface, m ρ Density, kg/m 3 τ Shear stress, N/m 2 Subscripts w Wall condition o Stagnation condition ∞ Freestream condition, infinity * Reference state Introduction H YPERSONIC configurations are generally character- ized by slender bodies and sharp leading edges in order to achieve good aerodynamic properties like high lift and low drag. Certain configurations, such as waveriders 1 are designed analytically with infinity sharp leading edges for * Researcher, Combustion and Propulsion Laboratory. AIAA Member. shock wave attachment. Because the shock wave is attached to the leading edge of the vehicle, the upper and lower sur- faces of the vehicle can be designed separately. Moreover, the shock wave may prevent spillage of higher-pressure air- flow from the lower side of the vehicle to the upper side, resulting in a high-pressure differential enhanced lift. Usually, it is extremely difficult to construct a perfectly sharp leading edge. Any manufacturing error results in a significant deviation from the design contour. Furthermore, sharp edges are difficult to maintain because they are eas- ily damaged. Additionally, because heat transfer increases inversely with the leading edge radius, high heating is asso- ciated with sharp edges. Therefore, for practical hypersonic configurations, leading edges are blunted for heat transfer, manufacturing, and handling concerns. Because blunt lead- ing edge promotes shock standoff, practical leading edges will have shock detachment, making leading-edge blunting a major concern in the design and prediction of flowfields over hypersonic configurations. Experimental and theoretical works on hypersonic flow past wedges have been concentrated primarily on the analy- sis of the flowfield by considering the leading edges as being ”aerodynamically-sharp”. A critical study providing infor- mation on maximum allowable edge thickness for a given flow pattern has not received considerable attention. Such information is important when a comparison is to be made between experimental results in the immediate vicinity of the leading edge and the theoretical results, which generally assume a zero-thickness leading edge. There has been a rather limited investigation of the flow- field associated with wedges under hypersonic flow. Cheng et al. 2 presented results of a theoretical and experimen- tal study of leading-edge bluntness and boundary layer displacement effects in hypersonic flow over thin bodies. Their theoretical solution was developed based on a con- tinuum flow model in the strong interaction region. Ex- perimental heat transfer and pressure data obtained with two-dimensional wedge models were presented by Vidal and Bartz 3 . The purpose of their investigation was to test the available theories dealing with wedges in a continuum flow in order to define their limits of validity, and to provide data in the transition regime, i.e., between the conventional con- tinuum flow and the free-molecular flow. Their comparison was restricted to the boundary layer theory and the viscous shock layer theory. McCroskey et al. 4 investigated experimentally the hyper- sonic flow on plates, wedges and cones. Pressure and density profiles adjacent to the bodies as well as the shock wave shapes were presented downstream of the leading edges. The 1