The interaction of a submerged shallow synthetic jet with a parallel free surface has gathered substantial interest, owing to its relevance to the operation of marine vehicles viz. ships that move close to the water surface. However, despite exhaustive research on the perturbation on a free surface, very few studies have experimentally investigated the effect of unconfined water surface height on the evolution and propagation of a submerged synthetic jet. This study experimentally investigates a synthetic jet submerged in a quiescent flow at shallow depths ejecting parallel to the free surface, through qualitative analysis and quantitative measurements. The qualitative study includes the visualization of the flow using plane laser induced fluorescence (PLIF) technique, whereas the velocity measurements are carried out by a five-beam laser Doppler velocimetry (LDV) probe. The primary objective of these analysis and measurements is to gain a physical insight into the characteristics of vortex ring in a synthetic jet ejected from a fixed orifice at different water depths and at varying Reynolds number. Our studies indicate that the behavior of the vortex rings drastically changes as the depth of the jet crosses a certain threshold. Although no significant change in the path of synthetic jet is observed beyond a threshold depth in our experiments, the jet trajectory shows an interesting dependence on the Reynolds number based on circulation for shallow water depths. It has been found that at the shallow depths, the vortex ring drifts upwards and interacts with the free surface at lower Reynolds number, whereas for larger Reynolds number, the vortex ring rebounds near the free surface and moves downward. Based on our observations, it can be concluded that the phenomenon of upward/downward flection of vortex rings depends both upon its circulation and ejection depth.

淹没的浅层合成射流与平行的自由表面之间的相互作用引起了人们的极大兴趣，这是由于其与海上航行器的操作相关。靠近水面的船只。然而，尽管对自由表面上的扰动进行了详尽的研究，但很少有研究通过实验研究无限制水面高度对淹没式合成射流的演化和传播的影响。这项研究通过定性分析和定量测量，以淹没在平行于自由表面的浅深度浸没在静态流中的方式对合成射流进行了研究。定性研究包括使用平面激光诱导荧光（PLIF）技术可视化流动，速度测量是通过五光束激光多普勒测速仪（LDV）进行的。这些分析和测量的主要目的是获得对从固定孔口喷出的不同水深和不同雷诺数的合成射流中旋涡环特性的物理了解。我们的研究表明，随着射流深度越过某个阈值，涡流环的行为会急剧变化。尽管在我们的实验中，没有观察到超过阈值深度的合成射流路径发生显着变化，但是基于浅水深度的循环，射流轨迹显示出对雷诺数的有趣依赖性。已经发现，在较浅的深度，涡环向上漂移并在较低的雷诺数下与自由表面相互作用，而对于较大的雷诺数，涡环在自由表面附近反弹并向下移动。根据我们的观察，可以得出结论，涡环向上/向下弯曲的现象取决于其环流和喷射深度。