Smeltzer Benjamin K, Rømcke Olav, Hearst R Jason, Ellingsen Simen Å
Department of Energy and Process Engineering, Norwegian University of Science and Technology, N-7491, Trondheim, Norway.
SINTEF Ocean, Marinteknisk senter, N-7052 Trondheim, Norway.
J Fluid Mech. 2023 May 10;962:R1. doi: 10.1017/jfm.2023.280.
When surface waves interact with ambient turbulence, the two affect each other mutually. Turbulent eddies get redirected, intensified and periodically stretched and compressed, while the waves suffer directional scattering. We study these mutual interactions experimentally in the water channel laboratory at the Norwegian University of Science and Technology (NTNU) Trondheim. Long groups of waves were propagated upstream on currents with identical mean flow but different turbulence properties, created by an active grid at the current inlet. The subsurface flow in the spanwise-vertical plane was measured with stereo particle-image velocimetry. Comparing the subsurface velocity fields before and after the passage of a wave group, a strong enhancement of streamwise vorticity is observed which increases rapidly towards the surface for z ≳ -0.3 (: vertical distance from still surface; : carrier wavenumber) in qualitative agreement with theory. Next, we measure the broadening of the directional wave spectrum at increasing propagation distance. The rate of directional diffusion is greatest for the turbulent case with the highest energy at the longest length scales whereas the highest total turbulent kinetic energy overall did not produce the most scattering. The variance of directional spectra is found to increase linearly as a function of propagation time.
当表面波与环境湍流相互作用时，二者会相互影响。湍流涡旋会被重新定向、增强，并周期性地拉伸和压缩，而波浪则会遭受方向散射。我们在挪威科技大学（NTNU）特隆赫姆分校的水槽实验室中对这些相互作用进行了实验研究。长波群在具有相同平均流但湍流特性不同的水流中向上游传播，这些水流由水流入口处的活动格栅产生。利用立体粒子图像测速技术测量了展向-垂直平面内的次表层水流。通过比较波群通过前后的次表层速度场，观察到流向涡度有显著增强，对于z≳ -0.3（z：距静止水面的垂直距离；：载波波数），流向涡度朝着水面迅速增加，这与理论定性一致。接下来，我们测量了在传播距离增加时方向波谱的展宽情况。对于在最长长度尺度上具有最高能量的湍流情况，方向扩散率最大，而总体上最高的总湍流动能并未产生最多的散射。发现方向谱的方差随传播时间呈线性增加。
