Experimental study of the topological flow transformations in an aerial vortex bioreactor with a floating washer.

BACKGROUND: Research into the flow structure in an aerial vortex bioreactor is relevant for developing the methods for growing cell cultures. Determining the optimal cultivation condition for a certain process is especially important in the case when such parameters of the medium as density and viscosity significantly change with the culture growth in the bioreactor. METHODS AND RESULTS: The research of the flow dynamic was carried out in an 8.5 L universal aerial vortex bioreactor, with a washer freely floating on its surface and stabilizing the motion of the working fluid. The regularities of the vortex motion of the culture medium have been determined by Particle Image Velocimetry depending on its volume and the intensity of rotation of the activator, generating vortex motion in the air. CONCLUSION: The observed vortex structure and its dynamics at increasing flow swirl intensity are established to coincide with the structure of a confined vortex flow in a cylindrical container with no washer for both single and two-fluid configurations. This novel methodology of the flow optimization shows that an ascending swirling jet forms in the vicinity of the bioreactor axis, and a bubble-like vortex breakdown forms in the axial region.

Experimental study of cavitating flow around a NACA 0012 hydrofoil in a slit channel.

An experimental study of a cavitating NACA0012 hydrofoil with aspect ratio 0.02 in a slit channel was carried out using a high-speed visualization at sampling rate more than 100 kHz. The features of the formation and development of cavities in a quasi-two-dimensional turbulent flow were studied. The most energetic modes of unsteady cavitation flow around the hydrofoil were obtained using dynamic mode decomposition. The presence of the second and third modes in the cavitation flow is shown here for the first time. It was shown that each of these modes corresponds to a certain period of development of the unsteady cavity. Experimental data on the reverse motion of the vapor-gas mixture into the inner region of supercavitation are presented.

Dual vortex breakdown in a two-fluid whirlpool.

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.