Critical Conditions For Internal Waves Induced By Periodic Circulation In A Stratified Water Environments

With the rapid development of economy and the acceleration of modernization,surface water such as reservoirs and lakes has become the main source of drinking water for most cities.However,the endogenous pollution is one of the water quality problems that most reservoirs need to solve.Stratification is one of the main inducements for endogenous pollution in reservoirs.The strong ability of mixing water of the internal wave can effectively destroy the water temperature stratification and effectively remediation the water environments of the source water and can also reduce the comprehensive cost of water treatment processes.Therefore,it is of great economic significance and practical importance to combine the internal wave technology with the water remediation technology of source water.In this study,the periodic circulated flow which produced by intermittent mechanical mixing device was used as a source of disturbance.The critical conditions of forming internal waves in the laboratory model reservoir under different temperature gradients,through the methods of adjusting the motor speed or the outlet opening area to change the outlet velocity.And the characteristic parameter---Froude was selected as a judgment standard of internal wave formation.In addition,the characteristics of the generated internal waves under different operational conditions were investigated.The main conclusions are as follows:?1?The critical value F_rcc under different temperature gradients of 0.44?/cm,0.35?/cm,0.27?/cm,0.22?/cm were explored by changing the motor speed to control the strength of the wave disturbance source when the intermittent operation period of motor is running 45s and stopping 10s,and the opening area of the outlet of the intermittent mechanical mixing device is 10cm?45cm.The results show that the critical F_rcc is not dependent on the temperature gradient.?2?Under the same intermittent operation period of motor,the critical value F_rcc under different temperature gradients by changing the opening area of the outlet of the intermittent mechanical mixing device to control the strength of the wave disturbance source when the motor speed is 600rpm/min.The results show that the critical F_rcc of different temperature gradients are the same.?3?Under the same temperature gradient,the result of the critical F_rcc obtained by fixing outlet opening area and adjusting the motor speeds is consistent with fixing the motor speed and adjusting outlet opening when the intermittent operation period of motor is running 45s and stopping 10s.?4?Under the intermittent operation period of motor running 45s and stopping20s,The internal wave cycle is basically equal to the operating period of the intermittent mechanical mixing device;Under the same conditions of the temperature gradient and the opening degree of the outlet,the amplitude and speed or length of the internal wave increase with the increase of the motor speed and then decrease,while the mixing time of internal wave decreases with the increase of the motor speed;Under the same temperature gradient and motor rotation speed,the internal wave amplitude decreases with the increase of outlet opening,while the mixing time of internal wave increases;Under the same conditions of the motor speed and the opening degree of the outlet,the amplitude of the internal wave and the mixing time of internal wave increase with the increase of temperature gradient.