边界层人工转捩的大涡模拟及壁面脉动压力研究

Large Eddy Simulation of Boundary Layer Artificial Transition and Wall Pressure Fluctuation

为了验证边界层人工转捩技术实现船模边界层壁面脉动压力载荷相似的可行性,采用大涡模拟以及功率谱估计获得平板湍流边界层壁面脉动压力功率谱,并与试验值、半经验模型值进行了对比,验证了数值模拟的可靠性。采用大涡模拟获得了绊线上下游壁面脉动压力的均方值、自功率谱和波数频率谱;以脉动压力均方值、自功率谱特征为判据,对比了方形、锯齿形绊线的转捩效果。结果表明:绊线高度雷诺数大于吉宾斯雷诺数;两种绊线均可实现边界层转捩,且壁面脉动压力的功率谱特征、谱级相近;与同流速平板湍流边界层相比,即使在当地雷诺数较低时,绊线下游边界层壁面脉动压力自功率谱平台区仍然高出10 dB左右。设计的绊线可用于减弱船模边界层壁面脉动压力的尺度效应,并有助于实现壁面脉动压力载荷相似。

To validate the feasibility of boundary layer artificial transition technique for boundary layer wall pressure load similarity of scaled ship, the wall fluctuating pressure power spectra of plate turbulent layer were acquired by large eddy simulation(LES) and spectrum estimation, the calculated values were compared with the data from experiment and semi-empirical model, and the reliability of numerical simulation was verified. The mean square values, auto-power spectra and wave number-frequency spectra of wall pressure fluctuation up/downstream the trips were acquired by LES. Taking the mean square values and auto-power spectra characteristics as criterion, the transition effects of square trip and zigzag trip were compared. The result shows that: as the Reynolds number at trip height gets greater than Gibbings Reynolds number, both trips are able to generate transition, and their wall pressure fluctuation spectra appear similar to each other in characteristic and magnitude;compared with plate turbulent boundary layer at equal velocity, although the local Reynolds number is lower, the wall pressure fluctuation auto-power spectrum downstream the trip gets 10 dB higher in its flat region. The designed trips could weaken the scale effect of boundary layer wall pressure of scaled ships and contribute to wall pressure load similarity.