Characteristics Of Destrstification And Internal Waves Induced By Intermittent Water Flow

In view of the current lack of economical and efficient destratification technologies in deep stratified water environments,destratification bu internal waves induced by a mechanical mixing device was investigated and developed,the flow fields were measured with a UVP Doppler ultrasonic flow meter.In order to establish a connection between the model water body and the actual water environment,the influence of the thermal structure difference on the characteristics of internal waves and destratification was studied.Affected by the outflow disturbance of the mechanical mixing device,a circulation was generated in the model reservoir.When the water is not stratified,the distribution of the flow field in the water was mainly affected by the circulation.When the water was stratified,the horizontal outflow energy was affected by the reduced gravity and some energy wasconverted to internal wave energyn.When the mechanical mixing device was operated continuously and intermittently,the circulation of the flow field was similar.When the intermittent operation was performed,the flow velocities decreased,and there were differences in flow velocities at different times.The flow velocities at the inlet and outlet weres significantly greater than the other flow fields,and the horizontal outflow from the device induced the internal waves.In the period of internal wave generation,the vertical velocity of the water particle increased and the amplitudes of the internal wave sincreased.In the steady propagation period,the amplitudes of the wave crests were basically the same,and the waveforms were basically the same and stable.The maximum amplitude of the internal waves was observed at 50 cm from the reservoir bottom.In the destratification process,thetemperature difference between the epilimnion and hypolimnion decreased gradually,and the thermocline were thinned and impelled upwards.The maximum amplitude position of the internal wave moved up with the thermocline,and the decreasing speed of the temperature difference between the upper and lower interfaces of thermocline gradually decreased until the stratified water environment was completely destroyed.Under the same conditions of the temperature gradient,disturbance intensity and water depth,with the thermocline thickness increasing,water stability coefficient increases,wave energy loss in critical layer reduces,the maximum amplitude of internal wave and wave energy increase,hence the mixing efficiency improves.At the same time,the wave energy transformed into the energy of vibration up and down is increased,the driving force and the wave velocity in the propagation direction decreases.Fixing thermocline thickness,with the increase of temperature gradient,the horizontal motion fluid transmits more energy to the internal waves,and impels the wave energy and the amplitude increases,which increases the energy transformation efficiency of destratification.The circulated outflow induced the the internal waves,which has the advantages of small energy loss and large impact range.The higher efficiency of mixing by internal waves will be achieved in lakes and reservoirs with deep thermocline and strong stratification.