Analysis of a Low Boom Supersonic Flying Wing Preliminary Design

摘要

This paper presents the numerical analysis of a low boom supersonic bi-directional flying wing (SBiDir-FW) preliminary design to demonstrate the advantages of the concept. The mission requirements include cruise Mach number of 1.6, cruise altitude around 50kft, payload of 100 passengers, and a range of 4000nm. The gross takeoff weight is about 197kLb. The configuration is a flying wing symmetric about both the longitudinal and span axes. The sweep angle varies from 82° at the very leading edge to 78° at the tip. Two designs with same sweep angles and planform shapes are presented by varying airfoil meanline angle distributions to achieve different overpressure signatures and L/D ratios. The first design D82-78.4 achieves an L/D of 8.16, C_L of 0.54, and the ground sonic boom noise level of 71.7PLdB. The second design D82-78.8 increases the C_L and L/D with C_L =0.60 and L/D = 8.54, while keeping a low level of ground sonic boom at 71.9PLdB by cruising at a little higher altitude of 52kft. A typical near field overpressure signature has a strong shock wave followed by a strong expansion in the overall process of expansion. The strong shock-expansion is mostly canceled out by themselves during the process of the wave propagation to ground. The designs indicate that the overpressure signature and aerodynamic efficiency are very sensitive and controllable by the variation of meanline angle distributions of the airfoils. This is an important relationship between the geometry parameters and the sonic boom/aerodynamic efficiency so that a design optimization strategy can be developed. All the designs with varied meanline angle distributions in this paper are conducted manually. With the encouraging results achieved so far, it is believed that the NASA's N+2 and N+3 goal to have ground sonic boom below 70PLdB for a supersonic civil transport is close to reach if a systematic design optimization is conducted.