The Process And Mechanism Of Destrtification By Aeration-induced Internal Waves In A Stratified Water

Groundwater exploitation is restricted because of serious water pollution, the reservoir has become a major source of water supply in most cities, but it suffers from water pollution to a certain degree. The reservoir water pollution is mainly caused by the endogenous pollution. Thermal stratification is a major incentive of endogenous pollution, and destratification is the key to control such water quality problems.Internal waves are the carriers of energy, momentum and mass, which can mix the water between the upper and lower layers. In this study, under different conditions of temperature gradient and air flowrate, the relationship between the falling rate of the thermocline and characteristic parameters of internal waves was analyzed, the impacts of temperature gradient and air flowrate to the process and effect of destratification by the aeration-induced internal waves were explored, and the mechanism of destratification by internal waves in limited fluids was revealed. And the impact of outlet position of aerator to the process and effect of destratification was also analyzed. The main conclusions are as follows:(1)Under conditions of same air flowrate and different temperature gradients, internal waves induced by aeration could be observed in the thermocline before the waters was completely mixed, the amplitudes of internal waves were higher in the middle of thermocline and shorter on the edge of thermocline. During the destratification, the thermocline fell gradually, the falling rate and stability factor gradually decreased, the duration times, periods and amplitudes of internal waves increased. Under similar conditions, the falling rate of the thermocline decreased with the increase of temperature gradients, stability factor increased with the increase of temperature gradients, stability factor approached to 0 g·cm/cm2 after the waters was completely mixed.(2)Under conditions of same temperature gradient and different air flowrates, during the destratification, the thermocline fell gradually, the falling rate and stability factor gradually decreased, the duration times and periods of internal waves increased.Uunder similar conditions, the falling rate of the thermocline increased with the increase of air flowrates, stability factor remained around 1.64g·cm/cm2 before aeration, and approached to 0 g·cm/cm2 after the water was completely mixed.(3)The mixing in limited stratified waters was mainly achieved by the alternant transport of water particles in the vertical direction by the aeration-induced internal waves during destratification, which is different to the conventional theory of mixing due to the breaking of internal waves in the open oceans.(4)When the aerator's outlet was at 35 cm from the reservoir bottom, the thermocline fell gradually, the duration times and periods of internal waves increased during the destratification process.Compared with the outlet at 45 cm from the reservoir bottom, overall periods of internal waves decreased. At 45 cm and 30 cm distance from the reservoir bottom, the duration times of internal waves decreased slightly, but they increased obviously at 15 cm distance from the reservoir bottom. The time required for complete mixing of water increased, and the mixing effect was reduced when the outlet was 35 cm from the reservoir bottom.