Abstract: The effects of inlet angle on the flow pattern and pressure drop in Φ50mm hydrocyclones have been investigated numerically by means of Reynolds stress model (RSM) and volume of fluid multi-phase flow model(VOF). Results show that the tangential velocity increases by increasing the inlet angle， leading to the increase of collection efficiency. Meanwhile， the mass of short-circuit flow can be enhanced and the split ratio can be decreased through increasing the axial velocity and the maximum radial velocity under the vortex finder caused by increasing the inlet angle. Besides， no significant influence on turbulence structure has been found as the inlet angle increases. The air core diameter also increases with the increase of the inlet angle， reducing the effective separation space.The hydrocyclone pressure drop is mainly generated by the pressure losses in the hydrocyclone body (under vortex finder) and in the inlet section. There is an increase in the pressure drop and the power of guiding and accelerating the input flow with increasing of inlet angle， while there is a decrease in energy utilization efficiency.Furthermore， the optimum guiding and accelerating effect is obtained with an inlet angle of 20°.

Key words: hydrocyclone, numerical simulation, inlet angle, flow pattern, pressure drop