Unsteady cavitation causes noise, damage, and performance decline in the marine engineering and fluid machinery systems. Therefore, finding a method to control the cavitation and its destructive effects is important for the industrial applications. In this work, we proposed a passive method to control the unsteady behavior of transient cavitation at the medium Reynolds number. For this aim, we performed an experimental study using a high-speed camera to analyze the effects of hemispherical vortex generators (VGs) on the cavitation dynamics around a hydrofoil surface. In addition, the pressure pulsations induced by the collapse of the cavity structures in the wake region of the hydrofoil were captured with a pressure transducer mounted on the wall downstream of the hydrofoil. The results showed that the instability behaviors of the cavity structures on the hydrofoil were mitigated using the proposed cavitation passive control method. In addition, the pressure pulsations in the wake region of the hydrofoil were reduced significantly. It can be concluded that the suppression of cavitation instabilities can improve the operating life and reliability of the marine and hydraulic systems.
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This paper serves as a summary of our recent work on LES for supersonic MVG. An implicitly implemented large eddy simulation (ILES) by using the fifth-order WENO scheme is applied to study the flow around the microramp vortex generator (MVG) at Mach 2.5 and . A number of new discoveries on the flow around supersonic MVG have been made including spiral points, surface separation topology, source of the momentum deficit, inflection surface, Kelvin-Helmholtz instability, vortex ring generation, ring-shock interaction, 3D recompression shock structure, and influence of MVG decline angles. Most of the new discoveries, which were made in 2009, were confirmed by experiment conducted by the UTA experimental team in 2010. A new 5-pair-vortex-tube model near the MVG is given based on the ILES observation. The vortex ring-shock interaction is found as the new mechanism of the reduction of the separation zone induced by the shock-boundary layer interaction.
In Figure 28, we give the instantaneous numerical schlieren picture at the central plane. From the figure, we can see many vortex rings appear in the circular shapes; after being told the prediction of the vortex rings, the same experimentalists in UT Arlington tried some techniques to validate the discovery. They used techniques of the particle image velocimetry (PIV) and the acetone vapor screen visualization to track the movement of the flow, and specifically the flash of a laser sheet is used to provide the light exposure at the time level of micro seconds. In Figure 29, a typical image at the center plane is presented taken by using PIV and the acetone vapor [13]. It is clearly demonstrated that a chain of vortex rings exist in the flow field after the MVG! And these structures qualitatively resemble those in Figures 27 and 28. 2ff7e9595c
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