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

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.