Three-dimensional Water Temperature Simulation Of High Dam Reservoir In Upper Yellow River Based On Unstructured Grid

With the improvement of computer performance and the development of simulation technology application,the numerical simulation technology of reservoir water temperature has become an important tool for predicting and analyzing the thermal stratification pattern of large reservoirs.For the characteristics of high dam reservoirs,the establishment of 3D hydrodynamicwater temperature model is more comprehensive to accurately describe the actual water flow movement and water temperature change process,and the model computational domain is divided by non-structural grid,which is more advantageous to effectively deal with the complex terrain boundary conditions of reservoirs.In this paper,the three-dimensional water temperature model of Longyangxia reservoir based on unstructured grid is constructed using MIKE3 software,and the applicability of the model is studied based on the multi-year operation process of the reservoir and the prototype water temperature observation data.The effects of different grid division scales,vertical turbulence model and heat exchange parameters on the simulation results of vertical water temperature distribution are analyzed,and finally,the Finally,different typical operation years of the reservoir were selected to simulate and calculate the vertical water temperature distribution during the stratification period of the reservoir,and the accuracy of the model calculation was verified.The main research results obtained are as follows:(1)A three-dimensional water temperature model of Longyangxia reservoir was established based on a non-structural grid,and the parameter rate determination and model validation were carried out to analyze the water temperature distribution and variation of the reservoir from horizontal direction and longitudinal profile,and to compare the vertical water temperature results with the measured data.The analysis illustrates that the simulated water temperature process of the model under the operation condition of 2009 has good accuracy with the measured water temperature from the distribution characteristics in all three dimensions,and The simulated intra-annual water level changes are consistent with the actual measurements.(2)The encryption of the non-structural horizontal computational grid will lead to faster bottom temperature transfer during the thermal stratification period;the two grid stratification positions in the vertical direction using the combined Sigma/Z-level division should be determined according to the actual reservoir operating water level,and the differences in the position points will cause differences in the bottom water temperature results;the turbulence model with the horizontal Smagorinsky/vertical k-epsilon equation can better reflect the reservoir actual water temperature change process;solar radiation absorption coefficient a2 and light extinction coefficient have great influence on the simulated thermally stable stratification structure.(3)Based on the model validation,we analyzed the differences between structural and nonstructural grids for simulating water temperature at different operation levels with the same parameter settings.In particular,the temperature distribution of the hysteresis and thermocline layers can reflect the actual process better,which is more advantageous than the structural grid in these aspects.Based on these results,we can provide a scientific basis for predicting the water temperature structure of other reservoirs in the upper reaches of the Yellow River with the same operating level and storage capacity as Longyangxia.