Viscous Effects and Truncation Effects in Axisymmetric Busemann SCRamjet Intakes

Abstract

While designing a Busemann intake, we encountered two main constraints: First, caused by the displacement of the boundary layer, the pressure levels in a Busemann intake were higher (40%) than the values predicted analytically; these effects were labeled viscous effects. Second, truncating the flow field also changed the properties of the classical Busemann flow; these effects were labeled truncation effects and we distinguished between truncating the intake at the leading edge and at the rear side. To take into account viscous effects, we calculated the boundary layer displacement thickness with an integral method and widened the inviscid Busemann contour. To quantify the leading edge truncation effect, an oblique shock at the leading edge was assumed, and also the intake contraction ratio was stretched. The change in flow properties during the rear side truncation was derived in a stream thrust analysis. We separately investigated the effects with Reynoldsaveraged Navier-Stokes and Euler simulations, respectively. After the viscous correction, the deviation between numerically and analytically calculated pressure levels was below 10%. When truncating at the leading edge, the numerically calculated pressure level was generally too low, while the temperature level was within 5% of the prediction. After stretching the contraction ratio, we were able to keep the pressure within 5% of the design value, however in this case, the temperatures were generally too high. The stream thrust approach was highly accurate and for rear side truncated intakes we were able to predict the numerical pressure and temperature levels within 1% of the design values.