Numerical analysis of transient flow through a pipe orifice (Time constant for settling flow)

As a fundamental consideration in hydraulic valve dynamics, transient flow through a pipe orifice has been studied via a numerical analysis. Steady axisymmetric viscous fluid flow was first investigated to confirm the present SIMPLER-based finite volume methodology. Time-dependent calculation for a suddenly imposed pressure gradient has shown two distinct characteristic time constants for the transient state. The first characteristic time is commonly considered to correspond to the flow rate change, while the second one concerning the variation of flow structure has not been treated in earlier studies. The final settling of flow is completed in the second characteristic time which is almost ten times larger than the first one under the present condition.