An Experimental Study on Compressible Cavity Flows

  • 李 冠篁

Student thesis: Doctoral Thesis


Improvement of the aerodynamic performance is one of the major goals for aircraft design A flow over cavity such as the weapon bay of an aircraft suffers from its complex fluid dynamics A cavity with a large ratio of length to depth induces drag and inhibits the deployment of storage For a cavity with a small ratio of length to depth the shear layer separates from the leading edge and impinges on its rear face The feedback mechanism with the upstream propagation of the disturbance leads to strong self-sustained oscillation which results in unsteady structural loading There have been enormous studies on the rectangular cavities However further investigation is inevitable for more insight including the geometric effect and the flow condition The experimental study determines the characteristics for a compressible turbulent flow over cylindrical cavities and rectangular cavities at yaw The freestream Mach number ranges from 0 64 to 0 83 and the thickness of incoming turbulent boundary layer is about 7 mm The ratio of diameter to depth for the cylindrical cavities are 4 43--43 00 The ratio of length to depth and the yaw angles for the rectangular cavities are 4 43--21 50 and 5 deg --45 deg respectively The results for unswept rectangular cavities are used for comparison Flush-mounted dynamic pressure transducers for mean and fluctuating pressure measurements are installed along the streamwise and spanwise directions The self-sustained oscillation phenomenon is examined by spectral density analysis with fast Fourier transform The empirical constants are also evaluated and compared with those in the classical Rossiter's formula The present study shows that the boundaries of flow types for cylindrical cavities are similar to those for rectangular cavities Yaw angle for a rectangular cavity also has a minor effect on the flow types A transitional cylindrical cavity has a higher surface pressure coefficient near the rear face than a transitional rectangular cavity but there is a minor difference on the amplitude of pressure gradient The maximum pressure fluctuations that generated by the cylindrical cavities are less than those generated by the rectangular cavities Yaw angle of a rectangular cavity alleviates the trailing-edge expansion and surface pressure fluctuation near the rear corner The ratio of the incoming boundary layer thickness to the depth of the cavity has an evident influence only near the rear corner of cavity including the trailing-edge expansion and the maximum pressure fluctuation For the empirical constants there are smaller time lags and lower ratios of convection velocity to freestream velocity for either cylindrical cavities or rectangular cavities at yaw than those used in the Rossiter's formula The power spectral density shows that low mode dominates for a rectangular cavity with large yaw angle
Date of Award2017 Jul 3
Original languageEnglish
SupervisorKeh-Chin Chang (Supervisor)

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