Wall shear stress (WSS) is commonly accepted as the primary influence affecting characteristics of anchored endothelial cells when subjected to fluid flow. Orbital shakers are commonly used to study cellular responses due to their ease of use, ability to run several experiments simultaneously, and since they exert physiologically relevant oscillatory shear. These studies require comprehensive resolution of WSS, however the fluid dynamics inside orbiting culture dishes has not yet been well described since the flow is complex and difficult to quantify analytically. A computational fluid dynamics (CFD) model of flow in an orbiting dish has been developed that yields detailed spatial and temporal resolution of WSS. The model was initially validated against primitive single point laser Doppler velocimetry data from the literature. A more comprehensive validation of the model was then performed here using both Particle Image Velocimetry (PIV) and a limited analytical solution that neglects wall effects. Average computational normalized velocity magnitudes varied by an average of just 0.3% from experimental PIV and from the analytical solution by 2.4%. WSS contours also compared very well qualitatively. Turbulence intensities were generated from PIV for a wide range of Reynolds numbers, Froude numbers, Stokes numbers, and Slope Ratios in order to determine transition to turbulent flow. Froude number best defined the transition to turbulence with the transition occurring between 0.69 and 0.86. Velocity contours from PIV showed distinct patterns indicating laminar, transitional, and turbulent flow.
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Model validation and transition to turbulence in orbiting culture dishes.
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