水下开孔结构流激振荡频率特性分析

Analysis of frequency characteristic of underwater flow-induced cavity oscillation

为了研究水下流激开孔的自持振荡机理及振荡频率预估的问题,对开孔模型进行自由上浮试验和流场数值模拟.试验模型选用无开孔和开孔围壳模型,开孔后围壳表面会测得一系列振动线谱.建立开孔结构的流场仿真模型,采用大涡模拟法对开孔结构流场进行精细的模拟,数值计算的压力振荡频率和试验测得的振动加速度线谱频率基本一致,证明试验测得的线谱是来自空腔流场振荡.对空腔附近涡量和脉动压力变化的观测结果表明,水下空腔自持振荡是来自水动力静压的反馈机制.对自持振荡频率分析表明,经典的Rossiter公式不适用于水下开孔自持振荡问题,应根据自浮试验数据予以修正.

Buoyant model experiment and numerical simulation of flow field were performed to investigate the mechanism of flow induced underwater cavity and the problem of frequency prediction.Normal fairwater model and opening fairwater were chosen in the experiment.A series of vibration line spectrums caused by the opening were detected.Detailed flow field of the opening model was established and simulated with large eddy simulation.The pressure oscillation frequencies of simulation agreed well with the vibrating acceleration line spectrums,which indicated that the line spectrums detected in the buoyant model experiment were excited by the self-sustained oscillation of the cavity.Observations of the vorticity and fluctuating pressure around the opening prove that the self-sustained oscillation of the underwater cavity was caused by the mechanism of the feedback of hydrodynamics static pressure.Analysis of the frequencies of self-sustained oscillation shows that the classical Rossiter formula is not applicable in the underwater situation,which should be modified based on the buoyant experiment data.