Experimental & Numerical Study On The Characteristics Of The Plunging Pressure Caused By Submerged Plunging Jet With High Velocity

The value of the plunging pressure caused by the submerged plunging jet with high velocity is one of the controlling parameters in the hydraulic design of receiving pools. The designer has not known whether the scale effect exists or not when applying the time-average pressure that was measured on the model to the prototype. This paper summarized the existing results and studied the characteristics of the plunging pressures caused by the submerged plunging jet with high velocity and discussed its scale effect. The main conclusions are as following :There is a sound linear relation between the non-dimensional number of plunging pressure caused by high velocity jet and the non-dimensional number of the jet distance. The plunging pressure can be neglected when the jet distance is 80 times larger than the thickness of the nozzle.Profile similarity is satisfied for the pressure distribution on the vertical central line of the board and the distribution can be described as the formula p/pm =exp(-αη-2), where α=0.7-0.8.The maximum values of the time-average pressure on the board have been measured under the different velocity levels range from 5.0m/s to 50.0m/s. Almost all the values assemble in the same line. There's no evidence to show that the non-dimensional number of plunging pressure differs distinctly from each other dueto the difference of the velocity level. Without considering other factors such asaeration, the scale effect of the plunging pressure is not obvious.The characteristics of the pressure distribution caused by high and low velocity jets have been analyzed contrastively. The results show that the coefficient of the pressure concentration (α) under the high velocity (u0>40.0m/s) is larger than the one under the low velocity (u0<5.0m/s). This result shows that the distribution of the plunging pressure is more concentrated compare with the one under the low velocity jet.The jet flow field had been calculated by means of the numerical method. The detail distributions of the hydraulic factors such as velocity, pressure and turbulent kinetic energy were attained. The maximum pressure calculated with 3D k ~ ε model is approximately equal to the measured one. The calculated flow fields show that the area of energy dissipation is mainly in the area near the jet centerline or near the plunging area. Under the large Reynolds number flow field, the viscosity stress can be nearly neglected compared with the inertia force. So the value of the Reynolds number does not influence the plunging pressure obviously.