Monday, July 16, 2001

(Dr. Paul Neitzel, advisor)

"Numerical Simulation of the Fluid Mechanics of a Spinner Flask Bioreactor"

__Abstract__

During the growth of articular cartilage in bioreactors, parameters
such as composition, shape, and cell function of the final construct are
known to be strongly influenced by the hydrodynamic forces present in the
bioreactor. Therefore, it is necessary to understand and precisely determine
the characteristics of the flow field of the bioreactor to achieve more
efficient and controlled methods for *in vitro* tissue growth. Polymer
scaffolds are placed in the spinner-flask bioreactor in where the flow
is driven by a rotating magnetic bar. The Reynolds number based on the
angular velocity and bar length is 1750, which induces a turbulent state.
The presence of turbulent flow in such a complex geometry makes the use
of numerical techniques necessary to solve the governing equations.

Fluent, a commercial software package, was used to numerically simulate
the flow field in the spinner flask. To model the bar rotation, the moving-rotating
mesh feature was used, and to model the turbulent flow the k-**e**
turbulence model with standard wall functions was employed. The Reynolds-averaged
Navier-Stokes equations were solved and the mean values of the flow field
parameters were determined. In addition, scaffolds were modeled first as
solid, which simulates the final state of the tissue, and then as porous
media with different permeabilities, which simulates the initial state
of the fibrous felt and the variation of the porosity with the growth of
tissue. The forces acting on the felt faces were determined for all these
regimes and the flow rate through the porous scaffolds was found. Finally,
the results for the case of the scaffold modeled as solid cylinder were
compared with the values obtained by PIV measurements.