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.

A high speed 1–1/2 axial compressor stage is simulated in this paper using an unsteady Reynolds-averaged Navier–Stokes (URANS) solver for a full-annulus configuration to capture its nonsynchronous vibration (NSV) flow excitation with rigid blades. A third-order weighted essentially nonoscillatory scheme for the inviscid flux and a second-order central differencing for the viscous terms are used to resolve nonlinear unsteady fluid flows. A fully conservative rotor/stator sliding boundary condition (BC) is employed with multiple-processor capability for rotor/stator sliding interface that accurately captures unsteady wake propagation between the rotor and stator blades while conserving fluxes across the rotor/stator interfaces. The predicted dominant frequencies using the blade tip response signals are not harmonic to the engine order, which is the NSV excitation. The simulation is based on a rotor blade with a 1.1% tip-chord clearance. Comparison with the previous 1/7 annulus simulations show that the time-shifted phase-lag BCs used in the 1/7 annulus are accurate. For most of the blades, the NSV excitation frequency is 6.2% lower than the measurement in the rig test, although some blades displayed slightly different NSV excitation frequencies. The simulation confirms that the NSV is a full annulus phenomenon. The instability of the circumferential traveling vortices in the vicinity of the rotor tip due to the strong interaction of incoming flow is the main cause of the NSV excitation. This instability is present in all blades of the rotor annulus. For circumferentially averaged parameters like total pressure ratio, NSV is observed to have an effect on the radial profile, particularly at radial locations above 70% span. A design with a lower loading of the upper blade span and a higher loading of the midblade spans is recommended to mitigate or remove NSV.

This paper study the non-synchronous vibration (NSV) of a high speed multistage axial compressor using rigid blade and vibrating blade with fluid-structural interaction (FSI). The unsteady Reynolds-averaged Navier-Stokes (URANS) equations and mode based structural dynamic equations are solved. A low diffusion E-CUSP Reimann solver with a 3rd order WENO scheme for the inviscid fluxes and a 2nd order central differencing for the viscous terms are employed. A 1/7th annulus sector of IGV-rotor-stator is used with a time shifted phase lag BC at circumferential boundaries. An interpolation sliding boundary condition is used for the rotor-stator interaction. The URANS simulation for rigid blades shows that the leading edge (LE) tornado vortices, roughly above 80% rotor span, travel backwards relative to the rotor rotation and cause an excitation with the frequency agreeing with the measured NSV frequency. The predicted excitation frequency of the traveling vortices in the rigid blade simulation is a non-engine order frequency of 2603 Hz, which agrees very well with the NSV rig testing. For the FSI simulation, the results show that there exist two dominant frequencies in the spectrum of the blade vibration. The lower dominant frequency is close to the first bending mode. The higher dominant frequency close to the first torsional mode agrees very well with the measured NSV frequency. The simulation conducted in this paper appears to indicate that the NSV is excited by the traveling vortex.

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In this paper, a parametric study is conducted to optimize a business jet using supersonic bi-directional (SBiDir) flying wing (FW)aiming at achieving high aerodynamic efficiency and low sonic boom. The SBiDir-FW concept has a symmetric planform about both longitudinal and span axes, allowing the plane to achieve high efficiency at both supersonic and subsonic by rotating by 90 o in flight. With this parametric study, the L/Dp achieves 15 at M=1.6, 16 at M=2.0, whereas the sonic boom remains smooth without N-wave. The smooth peak over pressure value is 0.3 psf at M=1.6, 0.4 psf at M=2.0. It indicates that the conventional N-wave could be replaced by a strong acoustic wave, which generates a much less impulsive force and hence noise. The supersonic aspect ratio of the present configuration is 0.33 and the subsonic aspect ratio is 33, which ensures high performance at both supersonic and subsonic. The study shows that the sharp and long nose configuration with ultra-slender body is favorable to both high aerodynamic efficiency and low sonic boom. The numerical results demonstrate that the SbiDir-FW could be a very promising concept for supersonic flight. Further improvement can still be made by using systematic automated design optimization.