STUDY OF LAMINAR, UNSTEADY PISTON-CYLINDER FLOWS

The present paper concerns numerical investigation of a piston-driven, axisymmetric flow in a pipe assembly containing a sudden expansion. T he piston closes the larger of the two pipes. The impulsively starting intake flow is the topic of this investigation. Results of numerical calculations and laser-Doppler measurements are presented to provide a n insight into the features of the flow. The calculation procedure emp loyed in this study is based on a finite-volume method with staggered grids and SIMPLE-algorithm for pressure-velocity coupling (Patankar an d Spalding, 1972). The convection and diffusion fluxes in the Navier-S tokes equations are discretized with first order upwind and second ord er central differences, respectively. A fully implicit Euler scheme is used to discretize the temporal derivatives. The Navier-Stokes equati ons were suitably transformed to allow prediction of the flow within t he inlet pipe (fixed grid) and cylinder region (moving grid) simultane ously (once-through procedure). Laser-Doppler measurements of both axi al and radial velocity components were performed. Refractive index mat ching was used to eliminate the wall curvature effects. For each measu ring point 20 cycles were measured, showing high repetition rates. Com parison of measured and predicted velocity profiles shows good agreeme nt.