Effect of Base Fluids on the Initiation of Vortex Shedding for Nanofluid Flow Over a Circular Object

Abstract

An inherently steady separated flow of a nanofluid around a two-dimensional circular object can be transformed into an unsteady periodic flow by controlling the nanoparticle concentration. This has been established in the contemporary literature 2022 by Garai et al. (2022, “Triggering Vortex Shedding for the Free Stream Flow of Nanofluids Around Bluff Objects,” ASME J. Fluids Eng., 144(3), p. 034502.) using Cu–H2O and Ag–H2O nanofluids, where the base fluids remain the same (H2O) and the nanoparticles are different (Cu, Ag). However, it may be anticipated that changing the base fluid may cause certain alterations in the flow dynamics. Two different base fluids, e.g., propylene glycol (C3H8O2) and ethylene glycol (C2H6O2) are selected in which copper (Cu) nanoparticles are mixed to produce Cu–C3H8O2 and Cu–C2H6O2 nanofluids. The nanofluids flow over a circular object with Reynolds number in the range 15≤Re≤40. The Cu nanoparticle concentration is gradually increased and it is observed that the vortex shedding can be initiated with a lesser concentration of Cu in case of C3H8O2 based nanofluid compared to C2H6O2 and also H2O based nanofluids. Hence, the critical solid volume fractions (φcr) for Cu–C2H6O2 based nanofluid are more compared to Cu–C3H8O2 and Cu–H2O nanofluids. Further, φcr for all the nanofluids are found a decreasing function of Re in its chosen range. The critical solid fraction is estimated from an extended Stuart–Landau model and the phenomena are demonstrated qualitatively through the streamlines and vorticity contours and quantitatively through the lift signal analysis and phase diagrams. Finally, a regime diagram is constructed to demarcate the steady and unsteady zones of operation.