Experimental and Numerical Analysis of Cavitation Inception in Jets

建议编号：CTS-9706701首席研究员：KATZ本研究是一项综合的实验和数值研究，目的是确定和解释高雷诺数射流中空化发生的条件。实验上，将使用高分辨率PIV测量主涡内部的非定常速度分布，从中提取涡量和应变。全息摄影和视频摄影将被用来确定人工引入的微小种子气泡的运动。使用微型气泡作为压力传感器，可以确定初级涡流内的压力场。在观测到的二次涡(肋骨)内空化开始的条件将被用来估计相应的压力最小值。在计算上，将对主要结构进行拉格朗日模拟，初始条件和边界条件由实验提供。数值模拟将首先与实验结果进行比较，然后用来分析长细比对主涡内压力场及其引起的应变场的影响。测得的应变场将用于对辫子内流向涡度扰动卷曲的直接数值模拟。由实验确定的肋骨内的压力极小值可以用来选择合适的流向涡度扰动水平。这种结合的方法将能够绘制出喷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.