Instantaneous measurements of pressure and wave flux in stratified incompressible flows are presented for the first time using combined time-resolved particle image velocimetry (PIV) and synthetic schlieren (SS). Corrections induced by variations of the refractive index in this strongly density-stratified fluid are also considered. The test case investigated here is a three-dimensional geometry consisting of a Gaussian ring-type topography forced by an oscillating tide representative of geophysical applications. Density and pressure are reconstructed from SS or PIV in combination with linear theories and combined SS-PIV. We perform a direct comparison between the experimental results and three-dimensional direct numerical simulations of the same flow conditions and control parameters. In particular, we show that the estimated velocity or density and the hence wave flux from linear theory solely based on SS or PIV can be flawed in regions of focusing internal waves. We also show that combined measurements of SS and PIV are capable of circumventing these limitations and accurately reproduce the results computed from the DNS.

中文翻译：

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从聚焦内波的实验室实验估计压力和内波通量

首次使用组合时间分辨粒子图像测速 (PIV) 和合成纹影 (SS) 对分层不可压缩流中的压力和波通量进行瞬时测量。还考虑了由这种强密度分层流体中的折射率变化引起的校正。这里研究的测试案例是一个三维几何结构，由代表地球物理应用的振荡潮汐强迫的高斯环型地形组成。密度和压力是从 SS 或 PIV 结合线性理论和组合 SS-PIV 重建的。我们对相同流动条件和控制参数的实验结果和三维直接数值模拟进行了直接比较。特别是，我们表明，仅基于 SS 或 PIV 的线性理论估计的速度或密度以及因此的波通量在聚焦内波区域可能存在缺陷。我们还表明，SS 和 PIV 的组合测量能够规避这些限制，并准确地再现从 DNS 计算的结果。