科研之友
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摘要
The intrinsic 3D vortical structures of turbulent cavitating flow are difficult to be measured in experiment. In the present work, the compressible large eddy simulation (LES) was performed to investigate the cavitating flow around NACA66 hydrofoil, with a special emphasis put on the laminar-turbulent transition, the turbulence-cavitation interaction and the dynamics features. The mesh is constructed with sufficient resolution to capture the coherent structure and energy spectrum of turbulence, with the prerequisites of y(+), Delta x(+) and Delta z(+) fulfilled to resolve at least 80% of the turbulence kinetic energy. The LES captured the subtle coherent structures of laminar-turbulent transition, including the evolution of pressure disturbance, 3D vortical wave and hairpin vortices. It manifests that, the cavity shedding produces super large-scaled vortices in the wake, and the Batchelor's pressure spectrum of conventional mono phase turbulence is no longer met in turbulent cavitating flows. It is found that the conventional cavity shedding mechanism by re-entrant jet is not accurate if strong turbulence is present. The sweeping effect of the jet front expands the turbulent fluctuation along the cavity surface which eventually makes it broken. The various vorticity transport mechanisms are analyzed to clarify the role of cavitation effects in the evolution of the vortical structures. The counterintuitive drastic oscillation of lift and drag is studied, finding that the pressure is focused during the cavity collapses and a violent pressure rise is induced. By formulating approximate one-dimensional analytic formulas, the far-field pressure disturbance is found to be in strict accordance with the second-order time derivative of cavity volume.
- 出版日期2019-3
- 单位上海交通大学
