Dynamic Characteristics Of Aeration-induced Internal Waves In A Finite Stratified Fluid

Endogenous pollution has become the main pollution source of the reservoir, and the thermal stratification is the main cause of endogenous pollution.Destratification is the key to control the reservoir 's endogenous pollution,but the traditional technologies of destratification have the common problems of the high energy consumption. To provide a reliable basis for the technology of destratification by aeration-induced internal waves, periodic outflow from a water-lifting aerator was used as a disturbing source, the generation and dynamic characteristics of internal waves under different aeration and stratification level conditions,the possible generation mechanism of aeration-induced internal waves was explored in this study.Under fixed flowrate, the effects of temperature gradient(0.18-0.60?/m) on characteristic parameters of internal waves were studied.Under fixed temperature gradient, the effects of air flowrate(50-150L/h) on characteristic parameters of internal waves were analyzed. Under fixed temperature gradient and air flowrate, the effects of the position of the aerator's outlet on characteristic parameters of internal waves were compared.The main research results are as follows:(1)Under relatively small scale laboratory conditions, by cooling the water near the reservoir bottom, the thermal stratification based on natural convection the heat exchange between the water and air was developed in the model reservoir, which is similar to that in a natural reservoir.( 2) When the aerator's outlet was located at 45 cm from the reservoir bottom,under air flowrates of 75-100 L/h, the internal waves could be generated by the resonance mechanism, in which the period of the internal waves was almost identical to that of the air piston releasing from the aerator. Under other fixed air flowrates, the initial period and amplitude of internal waves decreased with the temperature gradient in the thermocline, but the wave velocity increased with the temperature gradient in the thermocline. Under the same initial temperature gradient in the thermocline, as the air flowrate increased, the period, amplitude and velocity increased to a peak at air flowrate of 75 L/h and then decreased gradually. As the thermocline moved down during destratification, the period and amplitude of internal waves decreased in general except for the case of air flowrate of 75 L/h.(3)When the aerator's outlet was located at 35 cm from the reservoir bottom, the influence of air flowrate and temperature gradient on the characteristic parameters of internal waves were consistent. Compared with the temperature gradient in the thermocline, the air flowrate was the more important factor influencing the characteristics of internal waves.(4)Under fixed temperature gradient, the characteristic parameters of internal wave for outlet at 45 cm from the reservoir bottom were greater than those for outlet at 35 cm from the reservoir bottom.Under fixed flowrate, the periods and amplitudes of internal waves for the case of 45 cm were larger than those for the case of 35 cm, the velocities of internal waves for the case of 35 cm were greater than those for the case of 45 cm in general except for the case of air flowrate of 75-100 L/h.(4)By comparing the characteristic parameters of internal waves under different positions of aerator's outlet, it can be concluded that, two requirements need to be met for the occurrence of resonance, one is that the frequencies of the disturbance and internal waves should be same, the other is the disturbance has to be strong enough. The disturbance intensity had more obvious influence on the velocity of internal waves.