Experimental study of flow dynamics of a sweeping jet in a slot channel

In recent years, fluidic oscillators have been actively applied as devices for flow control in the field of aero and hydrodynamics. This study aims to investigate the structure of a flow of sweeping jet ejected from a fluidic oscillator into a confined area – slot channel. Dynamics of sweeping jet flow are investigated using the PIV method with high temporal resolution. The effect of the Re number on the sweeping jet oscillation frequency was studied in the range from 1 500 to 8 000. Linear frequency dependence on Re number was obtained. Bounding walls affect the dynamics of sweeping jet flow that leads to a change of average velocity field. For low Re numbers, obtained results are in good agreement with the results of other studies.

Instabilities of Pre-Stretched Viscoelastic Flow in Microfluidic Cross-Slot Devices

In this paper we experimentally studied the instabilities of pre-stretched viscoelastic fluid in cross-slot devices. We first investigate the instability of the flow in a standard cross-slot at different Weissenberg numbers without pre-stretch. It is found the viscoelastic flow is transformed from the steady symmetric state to the instabilities states including the steady asymmetric state and the non-periodically oscillated asymmetric state. This is due to the extension of the polymer in the viscoelastic fluid at the stagnation point stretched by the extensional flow in the cross-slot. We then modified the cross-slot channel in which the viscoelastic fluid is pre-stretched before entering the crossroad region. Due to the pre-stretch, elastic energy is pre-stored in the polymer, and the energy required to fully extend the polymer is also different with those extending from equilibrium state. As a result, the flow remains in the steady asymmetric state in all tested Weissenberg number condition.