Numerical Calculation of Unsteady 3D-Flow Between a Pair of Corotating Disks in a Fixed Enclosure

The laminar, isothermal flow between a pair of corotating disks in a fixed cylindrical enclosure has been calculated numerically. Within the range of Reynolds numbers investigated, 20,000 ≤ Re ≤ 80,000, the flow is 3D and unsteady. Present calculations, carried out on computational grids finer than those employed in prior investigations, confirm the presence of axially-aligned, circumferentially-periodic vortical structures, reported by several authors in the literature. These are a direct consequence of the wavy nature of the flow. A quasi-periodic flow regime is obtained for values of the Reynolds number slightly above the 2D-3D transition, which is detected at Re ≈ 18,000 for the geometrical parameters investigated. In the present study the calculations have been extended to values of the Reynolds up to Re ≈ 80,000. These results allow an analysis of the disk momentum coefficient, CM. The predicted values of CM are almost insensitive to the dimensionality (2D or 3D) of the calculations. The variation of the disk momentum coefficient with Re fits the relation CM α Re−n where the predicted value of the exponent n is larger than the theoretical one, n=0.5. The difference may be due to the relatively low values of the Reynolds number considered or to the different nature of the flow analysed here with respect to the limiting case of an infinite, single rotating disk.