On the flows developed within the gap of two parallel discs

The inflow, or accelerating, or sink flow, is realized when fluid enters the space between two flat discs via the periphery and drains through a centrally located outlet. The flow that is characterized by a monotonically decreasing pressure gradient is known to remain laminar even at very high Reynolds numbers, or to laminarize if the entering fluid is initially turbulent. The outflow, or decelerating, or source flow, is the type of flow where the fluid is admitted through a centrally located inlet and discharged through the periphery. As a result of the area increase, the velocity decreases, and an adverse pressure gradient develops. Analytical and experimental analyses were performed for the inflow and outflow between two discs both with and without swirl. In the analytical study (with and without swirl), it was shown that the radial velocity is expressed only as a function of the radial location and Reynolds number, whereas the static pressure for the swirling flows depends on the Reynolds number, radial position and swirl strength. The analytical model was also validated with present and previously obtained experimental findings and showed good agreement. An experimental investigation was also carried out to explore the flow between two narrowly spaced discs over the range of low and moderate Reynolds numbers. Radial velocity and static pressure measurements were obtained for the non-swirling inflow and outflow, whereas for the swirling cases only static pressures were acquired. The experimental results were then compared with the present theory and showed good agreement. For the inflow case, the results displayed the characteristics of the accelerating flow, whereas for the outflow case without swirl, the vena contracta effects, as well as the phenomenon of the reverse flow at the inlet region were demonstrate