各向异性湍流积分长度数值预报研究

文章针对目前模型试验只能获得各向同性湍流积分长度这一现状,建立了各向异性湍流积分长度数值预报方法:(1)RANS预报初始定常流场;(2)大涡模拟计算脉动速度场;(3)脉动速度相关函数计算各向同性湍流积分长度;(4)计算各向异性湍流积分长度。通过二维水翼模型试验验证了水中各向同性湍流积分长度的数值预报精度,平均误差6.81%;通过风洞螺旋桨验证了空气中各向异性湍流积分长度计算方法。对SUBOFF桨盘面处各向异性湍流积分长度的预报研究发现,各方向湍流积分长度外半径大于内半径;潜艇上部涡团扩散较下部明显,内半径湍流积分长度波峰随着角度增大而内移;Λ11、Λ12和Λ13周向分布受指挥台围壳和稳定翼马蹄涡影响,波峰出现在20°和90°左右;Λ31和Λ32的频率峰值受指挥台围壳和稳定翼马蹄涡脱落频率(约15 Hz)影响,峰值集中在30 Hz以下。该文提出的各向异性湍流积分长度预报方法,为下一步螺旋桨低频宽带噪声预报中构造新的湍流波数谱以提高预报精度提出了思路。

Numerical prediction and research on anisotropic turbulence integral length

This paper proposes a numerical method to predict the anisotropic turbulence integral length in view of this situation that the classic (isotropic) turbulence integral length is mainly acquired from experi-ments. Where RANS is utilized to predict the initial steady flow field; LES is used to calculate fluctuating velocity; the classic turbulence integral length is calculated based on cross-correlation function and the anisotropic turbulence integral length is finally predicted. The numerical method to predict isotropic turbu-lence integral length is validated the experimental data from 2-D hydrofoil, and the average error is 6.81%;and anisotropic turbulence integral length prediction method is validated by wind tunnel test. Then the anisotropic turbulence integral length of SUBOFF is studied and understood: the integral lengths at outside radius are lager then those at inside radius in all directions; the vortexes in the upper part diffuse more in-tensely than that in the under part, leading to the peak bars moving inside along with the angle increasing;the peak bars of Λ1 1,Λ1 2 and Λ1 3 are all near 20° and 90° according to the exists of horse-shoe vortex-es of conning tower and stabilizers;The peak frequency of Λ3 1 and Λ3 2 are both lower than 30 Hz as the shedding frequency of the horse-shoe vortexes is about 15 Hz. The current work lays the foundation of con-structing new turbulence spectrum to improve the accuracy of prediction of low-frequency broadband noise.