Browsing by Author "Xu, M."

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    Lock-in mechanism of flow over a low-Reynolds-number airfoil with morphing surface
    (Elsevier, 2019-12-19) Kang, W.; Xu, M.; Yao, Weigang; Zhang, J.
    To understand the frequency lock-in mechanism of flow separation control of an airfoil at low Reynolds number, a systematic analysis is performed by extracting the Lagrangian Coherent Structures (LCSs) from the unsteady flow. The actuation is considered via periodic morphing surface, and the dynamical behaviors between morphing surface and unsteady flow are studied from the viewpoint of fluid transport. Attention is drawn to fluid transport and lift improvement when the actuation frequency is locked onto the vortex shedding frequency. The results show that the fluid particle near the actuator is accelerated by the actuation and interacts with the slow fluid particle in boundary layer on the airfoil surface. The so-called stirring jet mechanism is observed, whereby a cusp structure is formed like a jet acting on the flow, which enhances the fluid transport from main stream into separation zone by reducing dead air zone effectively. The results also show that the actuation frequency is found to be the key factor for lift enhancement and determines the cusp structures and the vortex strength on the upper surface of the airfoil.
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    Nonlinear reduced order modeling for nonlinear response simulation of panels via Large Eddy Simulation
    (Elsevier, 2021-06-20) Xu, W.; Xu, M.; An, X.; Yao, Weigang
    Supersonic vehicles are subject not only to aerodynamic heating, but also to different acoustics, one of which is aeroacoustic induced by pressure fluctuation of high speed flow. The state-of-art structure sonic fatigue analysis is conducted by using uniformly distributed random White Gaussian Noise (WGN). However, uniformly distributed excitation is usually not consistent with the actual situation, and the validity of the method needs further investigation. In the present study, a nonlinear reduced-order model (NLROM) is presented to compute nonlinear response of isotropic and composite plates. The NLROM is based on finite element (FE) model and is constructed by means of Galerkin projection of the full order system onto a small subspace. The input of the NLROM is aerodynamic and aeroacoustic loads, which are computed by Large Eddy Simulation (LES) and interpolated from aerodynamic grid to structure node by using Radial Basis Function (RBF). The nonlinear response of the isotropic and composite plates is computed by NLROM and compared with WGN. The results show that the NLROM offers nearly an order of magnitude speed up as compared with direct FE simulation and predicts shorter sonic fatigue life than WGN.