(94c) Turbulence Transition in Orbiting Culture Dishes

Orbiting culture dishes are widely used in the cell culture industry because they can deliver pulsatile biaxial flow while allowing for tens or hundreds of test cases to be run simultaneously. The orbiting dish system provides a means of mixing the fluid containing nutrients while simultaneously applying shear stress to cells in culture. Wall shear stresses (WSS) are widely accepted as the primary influence affecting characteristics of anchored cells subjected to fluid flow. Detailed, accurate information about the fluid forces acting on cells must be known in order to understand the cause and effect relationship between shear stresses and cellular responses, such as proliferation rates, morphology, and gene expression.

Computational fluid dynamics models describe how the traveling waveform in the dish was influenced by dimensionless Froude and Stokes numbers as well as a slope parameter defined as the ratio of the steady-state acceleration-induced free surface slope to the static fluid aspect ratio. The computational model provided complete spatial and temporal resolution of WSS over the bottom surface of a dish throughout the orbital cycle. Modeling the fluid dynamics in these orbiting dishes has always assumed laminar flow. Accurate experimental measurements have been very recently obtained using particle image velocimetry, which indicate that biologically relevant experimental conditions are in fact turbulent in many cases. Flow regime was determined by examining turbulent kinetic energy and velocity fluctuations. Randomly fluctuating velocities indicate turbulence while relatively stable velocities indicate laminar flow. Transition from laminar to turbulent flow was then defined and correlated with the above dimensionless parameters. The Froude number best described the transition to turbulence