Experimental and Numerical Analysis of Cavitation Inception in Jets

摘要：本研究是一项综合实验和数值研究，旨在确定和解释高雷诺数射流中空化发生的条件。实验中，高分辨率PIV将用于测量初级涡内的非定常速度分布，从中可以提取涡度和应变。全息摄影和视频摄影将用于确定人工引入的微观种子气泡的运动。初级涡流内的压力场将用微气泡作为压力传感器来确定。观测到的二次涡（肋）内空化开始的条件将用于估计相应的最小压力。在计算上，将使用实验提供的初始条件和边界条件对初级结构进行拉格朗日模拟。首先将模拟结果与实验结果进行对比验证，然后分析长细比对初级涡内压力场及其引起的应变场的影响。测量的应变场将用于直接数值模拟辫状带中沿流涡度扰动的累积。实验确定的肋内压力最小值可以用来选择合适的流向涡度扰动水平。这种结合的方法可以绘制出射流近场内的压力分布。

ABSTRACT Proposal Number: CTS-9706701 Principal Investigator: Katz The present study is an integrated experimental and numerical effort to determine and explain the conditions for the onset of cavitation in high-Reynolds-number jets. Experimentally, high resolution PIV will be used to measure the unsteady velocity distribution within primary vortices, from which one can extract the vorticity and strain. Holography and video photography will be used to determine the motion of artificially-introduced microscopic seed bubbles. The pressure field within the primary eddies will be determined using microscopic bubbles as pressure sensors. The conditions for cavitation inception within observed secondary vortices (ribs) will be used to estimate the corresponding pressure minima. Computationally, Lagrangian simulations of primary structures will be conducted, with initial and boundary conditions provided by the experiments. The simulations will be first validated by comparison with the experimental results, and then used to analyze the impact of slenderness ratio on the pressure field within primary vortices and the strain field that they induce. The measured strain field will be used in direct numerical simulation of the rollup of streamwise vorticity perturbations in the braids. The experimentally-determined pressure minima within the ribs can then be used to select the appropriate streamwise vorticity perturbation levels. This combined approach will enable a mapping the pressure distribution within the near field of the jet.