Triggering Vortex Shedding for the Freestream Flow of Nanofluids Around Bluff Objects

Abstract

The freestream flow around a bluff object shows steady symmetric nature in the low Reynolds number laminar regime. However, when the Reynolds number increases to a critical value, the flow shows unsteadiness with alternate shedding of vortices. We show here numerically that the vortex shedding could be initiated for flow of a nanofluid over a bluff object even when the Reynolds number is lying in the steady regime (10≤Re≤30). Cu–H2O and Ag–H2O nanofluids are used and the volume fractions of Cu and Ag nanoparticles are gradually increased. At some critical values of the volume fractions, the flow shows unsteadiness with vortex shedding. The critical solid volume fraction is estimated from the convective stability analysis following the extended Landau model. The shedding phenomenon is established through contour plots, phase diagrams, and analysis of the time signals of lift coefficient. The critical volume fractions for the two different nanofluids for transition of steady to unsteady flow over circular and square-shaped bluff objects are observed to decrease with increasing Reynolds number.