OSCILLATING FLOW IN CHANNELS WITH A SUDDEN CHANGE IN CROSS-SECTION

In this paper, we have computationally examined oscillating flow (zero mean) between two parallel plates with a sudden change in cross section. The flow was assumed to be laminar incompressible with the inflow velocity uniform over the channel cross section but varying sinusoidally with time. The cases studied cover wide ranges of Re(max) (from 187.5 to 2000), Va (from 1 to 10.66), the expansion ratio (1:2 and 1:4) and A(r) (2 and 4). Also, three different geometric cases were discussed: (a) asymmetric expansion/contraction; (b) symmetric expansion/contraction; and (c) symmetric blunt body. For these oscillating flow conditions, the fluid undergoes sudden expansion in one-half of the cycle and sudden contraction in the other half. The instantaneous friction factor, for some ranges of Re(max) and Va, deviated substantially from the steady-state friction factor for the same flow parameters. A region has been identified (see Fig. 3) below which the flow is laminar quasi-steady. A videotape showing computer simulations of the oscillating flow demonstrates the usefulness of the current analyses in providing information on the transient hydraulic phenomena.