Numerical Investigation Of An Open Cavity Flow Including A Passive Control

The cavity is not only the basic structure of the internal weapon bay and leading gear bay,but many of the grooves inside the aircraft engine can be considered as cavity structures.Among them,the open cavity flow has become the prevalent topic in the world as the most universally used and the most complex type of cavity flow.When freestream through the open cavity,it shows violent self-sustained oscillation,this unsteady flow induces strong aerodynamic noise inside the cavity.These will have a negative effect on the separation of weapons and fighters.Therefore,it is significant for engineering application to clarify the mechanism of cavity flow and take effective methods to suppress nosie.In this paper,numerical investigation of open-cavity flow at supersonic and subsonic were performed by Delay Detached-Eddy Simulation.By studying the evolution of the leading edge wave system of the supersonic open cavity flow,the intermittent characteristics of the leading edge wave system was put forward.The differences between supersonic and subsonic open cavity flow mechanisms were analyzed.A new passive control method of placing a spanwise triangular prism around the leading edge was proposed.Two passive flow control conditions were simulated,corresponding to the different distances between prisms and leading edge.The two control cases were respectively applied to the flow control of supersonic and subsonic open cavities,and the control effects of the two control cases were compared.In supersonic open cavity flow,the instability of shear layer trigger alternately compression wave and expansion wave in the leading edge.The probability of occurrence of a compression wave in one of the flow periods is higher than the probability of occurrence of an expansion wave.The intermittent factor of compressional wave was calculated to be 28.8%,and the intermittent factor of expansion wave was 17.1%.This work confirms that leading edge prism is effective to reduce the sound pressure level in cavities under a supersonic flow.The two control cases have the same mechanism,in which the shear layer is raised.Furthermore,the second case is more effective than first case due to the ‘lifted again'.And led to reductions of up to 5~8 dB in the overall sound pressure levels along the cavity floor.Compared with the flow of supersonic open cavity,the velocity of vortex shedding from shear layer in subsonic flow becomes slower and the shedding vortex scale becomes larger.Moreover,the large-scale vortex takes up most of the space inside the cavity during its evolution to the downstream,which leads to the domination of broadband noise in the noise generated by subsonic open cavity flow.Two control cases also achieved certain control effects in the subsonic open cavity flow.The first control case more effective than the second control case.And led to reductions of up to 10 dB in the overall sound pressure levels along the cavity floor in first control case.It is worthy noting that the sound pressure level spectrumfrom Fast Fourier Transformation shows the broadband noise component in the second control case is always the highest.