Investigation on water and air characteristics in Helicoidal Ramp Dropshafts

Plunge dropshafts are widely used in urban drainage systems, but they can carry large amounts of air into the system, endangering the safety of the system. In this paper, a 3D numerical model is established to investigate the water flow configuration and air characteristics in a helicoidal ramp dropshaft. The simulations under different outlet pressures and water flow rates were simulated, and the results show that the air demand decreases with the increase of outlet pressure, especially in the case of low water flow. In the case of higher outlet pressure, the air demand first increases then decreases with the increase of the water flow rate. The dragging force of water has little effect on the pressure gradient in the dropshaft. The increase of ramp turns leads to the increase of terminal velocity at the same flow rate, and the air demand first increases and then decreases with the increase of ramp turns. HIGHLIGHTS The water flow configuration and air entrainment in a helicoidal ramp type dropshaft was investigated.; The air demand decreases with the increase of outlet pressure, especially in the case of low water flow.; The increase of spiral turns leads to the increase of maximum velocity at the same flow rate, and the air demand first increases and then decreases with the increase of spiral turns.;