Unsteady pulsating characteristics of the fluid flow through a sudden expansion microvalve

This paper investigates the unsteady characteristics of flow in a specific type of microvalve with sudden expansion shape. The resultant vortex structures cause different flow resistance in forward and backward flow directions. This may be used in applications such as a microvalve in micropump system and MEMS-based devices. A time-varying sinusoidal pressure was set at the inlet of the microchannel to produce unsteadiness and simulate the pumping action. The existence of block obstacle and expansion shoulders leads to various sizes of vortex structures in each flow direction. All simulation results are based on the numerical simulation of two-dimensional, unsteady, incompressible and laminar Navier-Stokes equations. Two fundamental parameters were varied to investigate the vortex growth throughout the time: the frequency of the inlet actuating mechanism (1 Hz a parts per thousand currency sign f a parts per thousand currency sign 1,000 Hz) and the amplitude of the inlet pressure. In this way, one can see the effect of actuation mechanism on the onset of separation and follow the size and duration of the vortex growth. In order to better understand the effect of geometry and frequency on flow field, the pressure and velocity distributions are studied through one cycle. Strouhal number is calculated for frequency, and a critical value of f = 250 Hz is found for St = 1. The obtained results provide a deep insight into the physics of unsteady flow in valveless micropumps and leads to better use of current design as a part of microfluidic system.