Experimental study on the interaction of non-buoyant jets and waves

This paper presents experimental results of a turbulent non-buoyant jet vertically discharged in a stagnant ambient and of the same jet discharged in a flow field of regular waves. The study was carried out in a wave channel and jet velocities were measured with a backscatter four-beam two-component fiber-optic LDA system. The signal of the two velocity components was sampled simultaneously to that of a resistance probe of the water surface profile in wave field configurations. This transducer was placed in the transversal section of the channel crossing the measurement point of the LDA system. The present study also includes a comparative investigation of the main fluid mechanics characteristics in cases of jet discharged in a stagnant ambient, and the same jet discharged in flow fields of regular waves characterized by different periods. Analysis of these characteristics underlines the substantial differences between the two cases under study. Concerning jets in a wave environment, the present study confirms the existence of the following three different regions of the jet-wave field starting from the nozzle: (1) Deflection region, where the jet momentum dominates the wave-induced momentum; (2) Developed jet region, where a large volume of environment fluid is subject to a jet attraction mechanism, with subsequent entrapment; and (3) Transition region between the two regions outlined above. Although the existence of distinct regions has been described in the literature, their behavior still lacks experimental study. The present study shows the differences found experimentally between each flow region. A new criterion for the definition of the extension of the flow regions is also proposed.