Study of flow bifurcation phenomena using a parallel characteristics based method

Flow instabilities in sudden-expansion geometries have been studied using a parallel characteristics-based method. The method utilises the artificial compressibility formulation, for coupling the continuity with the momentum equations, and a third-order upwind scheme for the discretisation of the convection terms. The time integration of the equations is obtained by the fourth-order Runge-Kutta scheme. The multi-block and domain decomposition techniques have also been implemented in conjunction with the above method. Flow bifurcation phenomena have been studied in suddenly-expanded channel and three-dimensional pipe geometries with expansion ratio of 1:2. For the 2D channel case the flow instability appears at Reynolds number of about 216. Preliminary calculations for the 3D suddenly-expanded pipe flow at Reynolds number equal to 800 and plug inlet velocity profile reveal that the reattachment length does not vary Linearly with the inflow Reynolds number while asymmetric secondary flow patterns appear downstream of the expansion.