Expansion Of The Layer Thickness Calculation Of Selective Withdrawal In Lakes And Reservoirs

Withdrawal layer thickness is one of the important parameters for selectivewithdrawal application in lakes and reservoirs. With the longitudinal linear densitydistribution of the lakes and reservoirs, the withdrawal layer thickness is available toexpress in general expressions, the difference exists only in coefficient C. Aiming tothe demanding densities and narrow range of application of selective withdrawal layerthickness theory, this paper simplify the actual density distribution of bilinear densitydistribution. Through the establishment of spherical coordinates for the center withintake system and the Bernoulli equation, a more common theoretical expression oflayer thickness is deduced under the bilinear density distribution of selective withdrawal.Two expressions have the same form, but coefficient C is changed from a fixed valueinto a variable C*, which is determined by the parameters k1, k2and θ. This parameterscan characterize the density distribution. Under the same distribution of the bilineardensity can got the variable C*equal to the fixed value. In accordance with the changesof the withdrawal layer thickness, the selective water district can be divided into tworegions. Near the water intake parts the layer thickness has a rapid increase in the intakeof distance, called variable region, while the layer thickness away from the water intakeis unchanged, saying it was stable region. Temperature stratification intensity has greatinfluence on the withdrawal layer thickness. When water discharge and water intakeposition unchanged, the reservoir temperature stratification weakened and withdrawallayer thickness decreases from summer to winter in the process. Meanwhile thetemperature stratification enhancement, releasing layer thickness increases from winterto summer in the process. Water intake position also has influence on the withdrawallayer thickness. Using two longitudinal temperature distributions measured in summer,the withdrawal layer thickness at different depths in Jinpen reservoir, Xi’an have been simulated by CFD simulation software. Compared with the formula calculation resultsunder the bilinear density distribution, the result shows a good agreement with theaverage error of only1.2%. It shows that the calculated expression of withdrawal layerthickness under bilinear density distribution has good applicability and a broader rangeof applications compared with the expression of withdrawal layer thickness under lineardensity distribution.