Dai Huichao

Numerical simulation of two-phase turbulent flow in hydraulic and hydropower engineering

In connection with the specific features of high velocity aerated flow generated by hydraulic engineering structures, the mathematical model is developed for high turbulence air-water two-phase flow with the use of twin flow theoretical model in this paper. Furthermore the numerical method is proposed to treat bubbled flows. In addition, on the basis of air-water stratified twin flow model, the new calculation methods and free surface tracking technique are proposed to describe complicated movements of the free surface. Finally, the proposed model is used to calculate artificial aerated flows. The computed results coincide quite well with experimental results. This means that the proposed method can provide solid basis for practical engineering design.

Calculating incipient velocity of non-uniform sediment through stress analysis

The incipient motion of sediment particles is one of the most essential features in sediment dynamics. The inherent mechanism of sediment initial motion, the influences of flow and sediment factors are studied for non-uniform sediment particles. A theory of sediment incipient motion is completed by introducing the concepts of instantaneous velocity of flow, criterion of incipient motion, relative exposure degree of particles on river bed, and additional mass force. A non-dimensional formula for calculating the critical shear stress of non-uniform sediment is derived using a model with the sediment particles rolling along the riverbed. This formula contains several coefficients correlated with flow pulsation and relative exposure degree, and proves to be reasonable by comparison with theoretical solutions and measurements.

Influence on fishes of dissolved gas supersaturation caused by high-dam discharging and its countermeasures

Based on the knowledge of the study achievements domestic and international and some representative projects in China, we study the generation mechanism of dissolved gas supersaturation (DGS) during high-dam discharging, discuss the relationships of DGSs three key indexes (total dissolved gas, dissolved nitrogen and dissolved oxygen) and its varying characteristics downstream along the river, and analyze the influence on fishes of DGS. Through the analysis of the in-situ observation data, we found that among the three key indexes downstream, DO drop quickly, DN almost like TGP drop slowly; high-dam discharging has strong deadly influence on fishes living in surface water-the closer (to the dam), the heavier. Here, we also summarize and analyze the countermeasures (both engineering and non-engineering) and suggest that cascade hydropower stations operation could be an effective action to reduce the influence.