藤井 孝藏

Low-speed wind tunnel tests are carried out to investigate the control surface effectiveness at low Reynolds numbers (Re = 20,000-80,000). A thick airfoil, NACA0012, has a nonlinearity of the control surface effectiveness, which are associated with flow separation both on the upper and lower surfaces and a formation of a laminar separation bubble. Thin airfoils such as NACA0006 and a 3%c flat plate have a much smaller nonlinearity of the control surface effectiveness. These differences in the control surface effectiveness are due to the nonlinearity of the lift curve for each airfoil, and the flow separation behavior has a profound effect on the control surface effectiveness.

In this study, aerodynamic design exploration for reusable launch vehicle (RLV) is conducted using genetic algorithm with Navier-Stokes solver to understand the aerodynamic characteristics for various body configurations and find design information such as tradeoff information among objectives. The multi-objective aerodynamic design optimization for minimizing zero-lift drag at supersonic condition, maximizing maximum lift-to-drag ratio (L/D) at subsonic condition, maximizing maximum L/D at supersonic condition, and maximizing volume of shape is conducted for bi-conical shape RLV based on computational fluid dynamics (CFD). The total number of evaluation in multi-objective optimization is 400, and it is necessary for evaluating one body configuration to conduct 8 CFD runs. In total, 3200 CFD runs are conducted. The analysis of Pareto-optimal solutions shows that there are various trade-off relations among objectives clearly, and the analysis of flow fields shows that the shape for the minimum drag configuration is almost the same as that of the shape for the maximum L/D configuration at supersonic condition. The shape for the maximum L/D at subsonic condition obtains additional lift at the kink compared with the minimum drag configuration. It leads to enhancement of L/D.

We analyze the asymmetric vortices in the flow over a slender body at high angle of attack by numerical simulations aiming a proportional control of the side forces generated by vortices with a device such as dielectric barrier discharge (DBD) plasma actuator. With regard to the computational method, Reynolds averaged Navier Stokes/large-eddy simulation hybrid method is adopted with high-order compact spatial difference scheme. The grid convergence analysis is firstly conducted and the results show that the computational grid adopted in this study is fine enough for qualitative discussion. The total number of the grid point is 411 million points. Then, the effects of bump height on flow fields and aerodynamic characteristics are discussed. Note that bump is added near the body apex to simulate the symmetry-breaking imperfection. As a higher bump is adopted, stronger asymmetry is observed in the flow fields. On the other hand, side-force has nonlinearity with the bump height.