Study the Geometrical Effects on the Unsteady Pulsatile Flow Through a Microchannel With a Sudden Step Shape

In this paper, pulsatile flow through a microchannel with step expansion shape and working as valveless microvalve is investigated. The design of the microchannel is such that it causes the production of different vortex structures in the flow field and near corners. Our primary objective is to investigate how geometrical parameters affect the performance of the microvalve under different flow conditions. Unsteady, two-dimensional axisymmetric flow of an incompressible Newtonian fluid with laminar regime was simulated numerically using finite element approach. In order to imitate the actuation mechanism of a micropump, a time-varying sinusoidal pressure was set at the inlet region of the microchannel. Two basic dimensions were found to have crucial effect on the flow field configuration and vortex generation: the expansion ratio of the channel and the distance of the obstacle from the expansion region. The frequency of the actuation mechanism was varied from 1Hz to 1000Hz to cover the working range for many micropump applications. As the pressure is a key factor and should be manipulated in the right way, the pressure contours were studied. Vortex growth was captured through a single cycle and their size and existence time was compared for different geometrical inputs. At last, Strouhal number which is a measure of unsteadiness of the flow was calculated. This way we can investigate the sensitivity of the flow to changes in block obstacle distance from the expansion section and the expansion ratio. The obtained results lead to better understanding of the physics of pulsatile flows through microchannels and help in improving the efficiency of the existing configuration in designing more efficient micropump systems.