A viscous-inviscid interactive method for unsteady flows.
Hong-Ming Jang · Deep Blue (University of Michigan) · 1990
A model for simulating the incompressible flow over a practical airfoil executing a pitching motion is constructed in terms of solutions of viscous and inviscid flow equations. The inviscid flow is computed by an unsteady panel method involving a blowing-velocity which accounts for viscous effects. The viscous flow is computed by a finite-difference boundary layer scheme which makes use of an interactive boundary condition that provides a coupling between the potential and viscous flows. A simplified unsteady wake model is also devised to represent the effects of the wake on the airfoil-surface flow. The computational model has been tested in relation to steady, quasi-steady (slow pitching airfoil), and unsteady (quick pitching airfoil) flows. The steady and quasi-steady models correctly simulate the stall phenomena and agree with the experimental data. The cases tested with the unsteady model demonstrate reasonable hysteresis and stall-delay phenomena and justify the use of the numerical model for simulating the flows over an airfoil executing harmonic oscillation with a reduced frequency less than 0.5 or a ramp-type motion with a constant pitch rate less than 0.02. However, the simulation of flows over an airfoil performing a higher degree of pitching and the flows with big reversal region requires improvement.