Effect of wall cooling on boundary-layer-induced pressure fluctuations at Mach 6
Effect of wall cooling on boundary-layer-induced pressure fluctuations at Mach 6
复制标题
DOI：
10.1017/jfm.2017.212
复制
发表时间：
2017-05
影响因子：
3.7
通讯作者：
Chao Zhang;L. Duan;Meelan Choudhari
中科院分区：
文献类型：
--
作者：
Chao Zhang;L. Duan;Meelan Choudhari
在壁面与恢复温度比为 $T_{w}/T_{r}=0.25$ 的情况下，对标称自由流马赫数为 $6$、雷诺数为 $Re_{\unicode[STIX]{x1D70F}}\约 450$ 的湍流边界层进行直接数值模拟，并与之前的数据库进行了比较$T_{w}/T_{r}=0.76$ 以研究压力波动及其对壁温的依赖性。高速湍流边界层广泛使用的速度和温度缩放定律的壁温依赖性与之前的研究一致。壁温条件会显着改变近壁压力脉动强度。在不同的壁温下，压力脉动强度的变化作为壁法向距离的函数在近壁区域中显着改变，但远离壁的区域几乎保持不变。壁冷却也对壁压力波动的频谱有很大影响，导致更高的主频率和更尖锐的频谱峰值，并且在高频和低频端都有更快的滚降。壁冷却对自由流噪声频谱的影响很大程度上可以通过边界层速度和长度尺度的相关变化来解释。 The pressure structures within the boundary layer and in the free stream evolve less rapidly as the wall temperature decreases, resulting in an increase in the decorrelation length of coherent pressure structures for the colder-wall case.对于两种壁温，压力结构以相似的速度传播。由于壁冷却，产生的压力扰动在辐射到自由流之前经历较少的折射，从而导致自由流中的辐射波前稍微陡峭。声源主要集中在近壁区域；壁冷却通过增强粘性子层中的膨胀波动同时抑制缓冲层和原木层中的涡旋波动，对声源项的非线性（慢速）分量产生最显着的影响。
Direct numerical simulations of turbulent boundary layers with a nominal free-stream Mach number of $6$ and a Reynolds number of $Re_{\unicode[STIX]{x1D70F}}\approx 450$ are conducted at a wall-to-recovery temperature ratio of $T_{w}/T_{r}=0.25$ and compared with a previous database for $T_{w}/T_{r}=0.76$ in order to investigate pressure fluctuations and their dependence on wall temperature. The wall-temperature dependence of widely used velocity and temperature scaling laws for high-speed turbulent boundary layers is consistent with previous studies. The near-wall pressure-fluctuation intensities are dramatically modified by wall-temperature conditions. At different wall temperatures, the variation of pressure-fluctuation intensities as a function of wall-normal distance is dramatically modified in the near-wall region but remains almost intact away from the wall. Wall cooling also has a strong effect on the frequency spectrum of wall-pressure fluctuations, resulting in a higher dominant frequency and a sharper spectrum peak with a faster roll-off at both the high- and low-frequency ends. The effect of wall cooling on the free-stream noise spectrum can be largely accounted for by the associated changes in boundary-layer velocity and length scales. The pressure structures within the boundary layer and in the free stream evolve less rapidly as the wall temperature decreases, resulting in an increase in the decorrelation length of coherent pressure structures for the colder-wall case. The pressure structures propagate with similar speeds for both wall temperatures. Due to wall cooling, the generated pressure disturbances undergo less refraction before they are radiated to the free stream, resulting in a slightly steeper radiation wave front in the free stream. Acoustic sources are largely concentrated in the near-wall region; wall cooling most significantly influences the nonlinear (slow) component of the acoustic source term by enhancing dilatational fluctuations in the viscous sublayer while damping vortical fluctuations in the buffer and log layers.