Study On The Flow Field Near The Intake And Thermal Structures In Large Reservoirs

A large area of water field is formed after a reservoir is built. Because of solar radiation and other factors, the temperature in a large reservoir is seriously stratified seasonally. Temperature stratification makes the temperature of released water keep lower. The released lower temperature water can cause negative effect on irrigation and aquatic lives downstream. In order to control the temperature of released water, selective withdrawal is increasingly adopted by the practical engineering. It is important for the designing and working of selective withdrawal, to study on the formation of water thermal stratification, flow field near the intake and released water temperature systematically.This paper studied on the formation of water thermal stratification by setting up the numerical model of a large reservoir based on EFDC. Developed a measurement system by PIV, forced on the mechanism and law of flow characteristics under temperature stratification, measured the released water temperature and flow characteristics near the intake. And used the software FLUENT to simulate flow field near the intake and released water temperature. We analyzed the effect on the flow field and released water temperature due to the temperature stratification, the intake submerge depth and withdraw flow rate, respectively. The main research contents and achievements of this paper include the following aspects:(1)Introduced the formation mechanism of thermal stratified reservoirs, the harm of released lower temperature water, the methods for reducing the negative effect of lower temperature water and the multi-level withdrawal used commonly. Research methods of the formation mechanism of thermal stratified reservoirs and released water temperature are classified and summarized.(2)ASTER GDEM data was transformed into common terrain data by Global Mapper software and the Fotran language. Applied the data to the topography of a reservoir, based on the EFDC, took the similar water temperature numerical model as reference; a two-dimensional numerical model was developed to simulate the formation of water thermal stratification. The surface water was fluctuant obviously; not only in season, but also in day. The bottom water was more stable, only slightly changed by season.(3)As the distribution of spectral energy and solar spectrum should be the same, the dysprosium lamp was used to mimic the solar radiation. Through the radiation from the water surface, measure the vertical temperature structure, observe the heating effect of dysprosium lamp on water, and explore the experiment method of heat exchange between water and air.(4) The “similarity theory of withdrawn water temperature” and PIV technology were combined, and a flow field measure system was developed, and be used to study on the mechanism and law of stratified flow by measuring flow field near the intake and the temperature of released water. Based on three typical water distribution, change the submerge depth of intake, we analyze the flow characteristics near the intake and the released water temperature.(5)The mode of side type intakes of different submerge depth were developed based on the FLUENT software. According to typical water temperature distributions and different submerge depths; we conducted a series of computation. We analyzed the effect on the flow field and released water temperature due to the temperature stratified structures, submerge depth of intakes and withdraw flow rates, respectively. And analysis the response relationship between the flow field near the intake and the withdrawn water temperature.