Supersonic flow over a cruciform configuration at angle of attack

Abstract

EXPERIMENTAL data of the flow about a cruciform configuration is compared with an inviscid finite difference Euler code, SWINT, to assess its predictive capabilities, accuracy, and limitations. Surface pressure distributions and overall aerodynamic coefficients are in good agreement with the computed values using the SWINT code for angles of attack up to 20 deg at Mach 2.7. Contents SWINT is an inviscid flowfield prediction code which treats conventional type missiles by approximating the fins as thin surfaces in meridional planes.1 The code semi-empirically models the cross-flow separation on the leeward surfaces of the body, which occurs at moderate to high angles of attack. The limitations and accuracy of this analysis are considered herein. The aerodynamics of the configuration are also reported. The experiments,2 were conducted with a 1.905-cm-diam model, Fig. 1. A Mach-2.7 blowdown wind tunnel facility was operated at the three stagnation pressures (0.11, 0.45, and 1.24 MPa) and with ambient-temperature air. The purpose of the tests was to assess the Reynolds-number effects on the aerodynamic coefficients. Tests at low Reynolds numbers Cfo?D = 0.19xl06 and 0.38 xlO6) were subsequently conducted with a pressure and force instrumented model 3.831 cm in diam.3 The measured pressure distributions along the most windward ray of the body, shown in Fig. 2, for the cross configuration (4> = 45 deg) are in excellent agreement with the SWINT code for angles of attack less than 20 deg. At higher incidences, the body shock interacts with the ventral fin, subsonic flow regions appear in the fin-body juncture regions on the windward side, and the flow on the leeward surfaces of the body and fins separates. The SWINT code does not handle these situations.2 The pressure variation around the cylindrical portion of the body, at an axial station upstream of the fins, is compared with SWINT in Fig. 3. On the leeward surfaces, the measured data for angles of attack greater than 10 deg show cross-flow separation and the occurrence of a cross-flow shock. Axial pressure distributions at three radial locations (6, 37.5, and 62.5 percent of the fin span) on the windward side of one fin are compared in Fig. 4 with the calculated values for a- 15 deg and 0 = 45 deg. The agreement with the available data is good. The fin shocks appear to be detached at about 40% of the span.