Numerical Simulation On Characteristics Of Stratified Flow In Reservoirs

There are lots of reservoirs in China,and they account for a large proportion of freshwater resources.At present,the reservoir water environment is more prominent,because the reservoir pollution water quality deterioration phenomenon often occurs.In recent years,reservoir water resources protection and water quality safety are getting more and more attention.Most large and medium reservoirs belong to stratified reservoir,and also are important drinking water sources,so that it is particularly important to protect or improve its water quality.The existence of water temperature and water quality stratification in deep reservoirs is not conducive to the reservoir water ecological environment.For the stratified reservoir,if people can choose to discharge the poor water rich of "harmful water-quality" in the reservoir to improve reservoir water quality,it will provide a new way for the improvement of reservoir water environment.This paper simulates the stratified flow of the generalized reservoirs in the stable stratification period and analyzes the characteristics of the stratified flow in the reservoir,which provides the basis for the regulation and control of the stratified discharge of the reservoir.The main contents and achievements of this paper are as follows:(1)The 2-D laterally-averaged reservoir model is used to simulate the reservoir flow field comes from the stratified discharging while ignoring the reservoir temperature,density stratification.By analyzing the flow field in the reservoir,it is fuond that the temperature stratification is the prerequisite for the formation of stratified flow in the reservoir.(2)The vertical 2-D temperature stratified flow model is applied in this paper to simulate the stratified flow comes from the stratified discharging while the reservoir temperature,density is stratified.By analyzing the flow field in the stratified reservoir under different working conditions,it is found when the reservoir is discharged stratified,the water layer near the height of the outlet will not affect the other water layers.Therefore,a stable stratified flow with the height of the outlet can be formed in the reservoir.The thickness of the stratified flow formed by the discharge of the different outlet in the same discharge flow is different.The thickness of the stratified flow formed by the middle outlet discharge is the largest,followed by the surface outlet discharge,and finally the bottom outlet discharge.The flow velocity of the stratified flow area increases first and then decreases,showing a parabolic distribution,and the other water bodies of the reservoir are almost stationary.In the case of the same discharge outlet and the constant water level,the thickness of the stratified flow is related to the storage flow and the discharge flow of the reservoir.The smaller the storage flow,the more obvious the density stratification of the reservoir,the stratified flow is more stable and the thickness is smaller.As the discharge flow increases,the thickness of the laminar flow increases.However,when the discharge flow increases to a certain extent,the flow field in the reservoir is no longer affected by the density stratification.Therefore,the velocity distribution in the reservoir is similar to that of the open channel.(3)Through the three-dimensional numerical simulation of the bottom outlet discharge of the reservoir,the characteristics of the stratified flow pattern of the reservoir are obtained.By analyzing its characteristics,it is found that for the stratified reservoir,the lateral width of the reservoir has little effect on the vertical distribution of the reservoir flow field.In order to simplify the numerical simulation of the reservoir discharge,the reservoir can be generalized into a vertical two-dimensional model.For the stratified reservoir,through different discharge openings,it is possible to control the discharge of different elevation water layers,and by adjusting the discharge flow,it is possible to control the thickness of the laminar flow.Therefore,we can use the stratified flow characteristics of reservoirs,combined with the monitoring of the vertical distribution of reservoir water quality.Through the reservoir dispatching and selection the different elevation openings in the reservoir,to exclude the poor water quality that is not conducive to the improvement of water quality,in order to achieve the goal of improving reservoir water quality.This paper explores a new way to improve reservoir water quality.