Probing vortex-shedding at high frequencies in flows past confined microfluidic cylinders using high-speed microscale particle image velocimetry

Abstract

Modeling the interplay between the shear layer and leading edge suction during dynamic stall

Surface tension driven flow of blood in a rectangular microfluidic channel: Effect of erythrocyte aggregation

“…μm size, at 1% concentration) suspended in distilled water, and compared against brightfield μPIV measurements (JPIV software) using milk particles as tracers in a 1:3 milk/water Newtonian solution. The experimental setup for the fluorescent μPIV experiments is described in previous studies by Zhang et al 43,44 The system comprised a 16 Hz Nd-YAG laser source at 532 nm (Litron Laser, UK) for illumination, The Stokes number of the tracer particles can be calculated from St=…”

Mixing in flows past confined microfluidic cylinders: Effects of pin and fluid interface offsetting

“…These correspond to the reciprocal of the blockage ratio and the aspect ratio respectively, that are commonly used in macroscale flows past cylinders. Nevertheless, vortexshedding can be induced in such confined microchannels at sufficiently high Reynolds number (Re = U o D h /υ, where U o is the mean freestream velocity in the channel, D h is the hydraulic diameter of microchannel and υ is the kinematic viscosity of the fluid) as shown in our previous work [11], inducing periodic changes in the local direction of the flow. Flow vortices are excellent candidates to further increase mixing through stretching and folding of the species streams [12].…”

“…6. This Re number is below the critical one for the onset of vortexshedding [11] and hence the flow fields in Fig. 6 are steady.…”

“…Thus, cylindrical obstacles in micromixers are bounded both by the side and top walls, i.e. they are both laterally and vertically confined, and the flow is inherently modified by this confinement, as the latter can suppress vortex-shedding [11]. The lateral and vertical confinement in such microconfined cylinder flows can be expressed in terms of w*=W/D and h*=H/D respectively, where W is the channel width, H the height and D the cylinder diameter.…”

“…for a specific x/D). It is plausible that the M for a cross-section will be influenced by the 3D nature of the confined flows that are not captured here[11]; hence, strictly speaking, M values reported here should be considered limited to a line in the plane of the LIF measurements. The error bars indicate the standard deviation of M evaluated from the number of experimental images used in the averaging (100 images in each case).…”