This paper introduces a novel concept for supersonic airplane: supersonic bi-directional (SBiDir) flying wing (FW) concept, which is to achieve low sonic boom, low supersonic wave drag, and high subsonic performance. The SBiDir-FW planform is symmetric about both longitudinal and span axes. For supersonic flight, the planform will have low aspect ratio and high sweep angle to minimize wave drag. For subsonic mode, the airplane will rotate 90 • and the sweep angle will be reduced and the aspect ratio will be increased. To minimize sonic boom, the pressure surface of the flying wing will employ an isentropic compression surface. At zero angle of attack (AoA) as the example studied in this paper, a flat pressure surface achieves this purpose. The CFD simulation shows that it obtains low ground sonic boom overpressure of 0.3psf with L/D p = 5.3. Furthermore, the ground pressure signature is not the N shape wave with two strong shock wave pulses, but is in a smooth sin wave shape. The results show that it is possible to remove or achieve very low sonic boom using a supersonic bi-directional flying wing or blended wing body configuration. Future work will optimize the SBiDir-FW concept to achieve high aerodynamic efficiency and maintain low sonic boom.

Delayed Detached Eddy Simulation of supersonic flutter of a 3D wing is conducted at free stream Mach number of 1.141 using a fully coupled fluid/structure interaction (FSI). Unsteady 3D compressible Navier-Stokes equations are solved with a system of 5 decoupled structure modal equations in a fully coupled manner. The low diffusion E-CUSP scheme with a 5th order WENO reconstruction for the inviscid flux and a set of 4th order central differencing for the viscous terms are used to accurately capture the shock wave/turbulent boundary layer interaction of the vibrating wing. The predicted flutter boundary at supersonic Mach number achieves excellent agreement with experiment. It appears to be the first time that a numerical prediction of supersonic flutter boundary matches with experiment accurately.

Multistage 3D steady and unsteady viscous computations are conducted for a transonic axial compressor with an IGV, rotor and stator blade row. A fully conservative sliding technique is developed with high order shock capturing schemes to better capture the interaction between stationary and rotating blade row. A 1/7th annulus is used for the unsteady simulation with a phase lag BC. For comparison purpose, a steady simulation of the same multistage compressor with single blade passage is performed using the mixing plane approach. It is shown that the sliding BC captures wake propagation very well in the interaction between blade rows. The unsteady multistage simulation using sliding BC and phase lag BC predicts almost identical loading distribution to the steady state simulation at the mid-span, but have significant loading distribution difference at tip section.

Delayed-Detached Eddy Simulation (DDES) is conducted to simulate aerodynamic stall flow over NACA0012 airfoil at 45 • angle of attack. DDES is an improved version of DES97 to avoid Modeled-Stress Depletion (MSD) in attached boundary layer by redefining the length scale of DES97. The test of DDES for the flat plate shows that the delayed LES function facilitates DDES to preserve eddy viscosity even with a severe grid that makes DES to undergo MSD. For comparison, DES97 and URANS also were conducted for the stalled NACA 0012 airfoil flow. DDES and DES predicted the drag coefficient accurately, while URANS overpredicted the drag by 33.6%. Both DES and DDES appear to be satisfactory to simulate the stalled airfoil flow at high angle of attack, in which the large structure of vortex are dominant.

Detached eddy simulation of an aeroelastic self-excited instability, flutter in NASA Rotor 67 is conducted using a fully coupled fluid/structre interaction. Time accurate compressible 3D Navier-Stokes equations are solved with a system of 5 decoupled modal equations in a fully coupled manner. The 5th order WENO scheme for the inviscid flux and the 4th order central differencing for the viscous flux are used to accurately capture interactions between the flow and vibrating blades with the DES (detached eddy simulation) of turbulence. A moving mesh concept that can improve mesh quality over the rotor tip clearance was implemented. Flutter simulations were first conducted from choke to stall using 4 blade passages. Stall flutter initiated at rotating stall onset, grows dramatically with resonance. The frequency analysis shows that resonance occurs at the first mode of the rotor blade. Before stall, the predicted responses of rotor blades decayed with time, resulting in no flutter. Full annulus simulation at peak point verifies that one can use the multi-passage approach with periodic boundary for the flutter prediction.