Abstract
Looking for an optimal flow shape for culture growth in vortex bioreactors, an intriguing and impressive structure has been observed that mimics the strong swirling flows in the atmosphere (tornado) and ocean (waterspout). To better understand the flow nature and topology, this experimental study explores the development of vortex breakdown (VB) in a lab-scale swirling flow of two immiscible fluids filling a vertical cylindrical container. The rotating bottom disk drives the circulation of both fluids while the sidewall is stationary. The container can be either sealed with the still top disk (SC) or open (OC). As the rotation strength (Re) increases, a new circulation cell occurs in each fluid—the dual VB. In case SC, VB first emerges in the lower fluid at Re = 475 and then in the upper fluid at Re = 746. In case OC, VB first emerges in the upper fluid at Re = 524 and then in the lower fluid at Re = 538. The flow remains steady and axisymmetric with the interface and the free surface being just slightly deformed in the studied range of Re. Such two-VB swirling flows can provide efficient mixing in aerial or two-fluid bioreactors.
Highlights
Looking for an optimal flow shape for culture growth in vortex bioreactors, an intriguing and impressive structure has been observed that mimics the strong swirling flows in the atmosphere and ocean
A useful model of an aerial vortex bioreactor is a sealed vertical cylindrical container filled with two immiscible fluids having remarkably different density and viscosity
Our work extends the experimental study of the vortex breakdown (VB) development to the two-fluid flows
Summary
Looking for an optimal flow shape for culture growth in vortex bioreactors, an intriguing and impressive structure has been observed that mimics the strong swirling flows in the atmosphere (tornado) and ocean (waterspout). Starting with works by Vogel[3] and Escudier[4], many fundamental studies of VB have been performed using flow in a sealed cylindrical container whose one end-disk rotates while all other walls are stationary. Such a flow is free of unpredictable ambient disturbances and has well-defined boundary conditions and control parameters. The simple geometry and well-defined boundary conditions are convenient for detailed experimental and numerical studies and can aid understanding some intriguing features of two-fluid swirling flows One of these striking features is the development of dual VB
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