MECHANISM ANALYSIS AND STRUCTURAL OPTIMIZATION OF SUDDEN INCREASE OF NEGATIVE PRESSURE NEAR WATER INLET PIPE OF A DROPSHAFT

To clarify the mechanism of the sudden increase of negative pressure near the water inlet pipe and reduce the negative pressure in the dropshaft, the water-air two-phase and air pressure distribution in the dropshaft model were simulated based on the computational fluid dynamics software Fluent. Then, the relationship between the water tongue and the air pressure change near the water inlet pipe was analyzed. Finally, an optimized dropshaft model was proposed and its effect was evaluated. The results showed that when the dimensionless water flow rate was greater than 0.08, the negative pressure near the water inlet pipe began to increase suddenly, and there was basically no change under a small flow rate. The water tongue was the main reason for the sudden increase of negative pressure, which occupied the space of air circulation and increased the loss of airflow. The air supply under the water tongue was insufficient, so the negative pressure would suddenly increase. The study also showed that the optimized dropshaft model formed a water-free cavity area in the space enclosed by the circular diaphragm and the shaft wall opposite the water intake pipe, which expanded the space for airflow, basically ensuring that the airflow near the water inlet pipe was not affected by the water flow, and also reduced the negative pressure and air pressure gradient in the dropshaft.