UTA Department of Mathematics

Applied Mathematics Seminar

Date/Time/Room: Friday (02/28/2003) at 2:00pm in 304 Pickard Hall

Speaker: Chaoqun Liu, Department of Mathematics, University of Texas at Arlington

"Coupled Cell Systems
A Potpourri of Theory and Examples"

Abstract: This work consists of two parts. The first part is direct numerical simulation (DNS) for flow separation and transition around a NACA 0012 airfoil with an attack angle of 40 and Reynolds number of 100,000. The details of the flow separation, formation of the detached shear layer, Kelvin- Helmoholtz instability (inviscid shear layer instability) and vortex shedding, interaction of non-linear waves, breakdown, and re-attachment are obtained and analyzed. Though no external disturbances are introduced in the baseline case study, the self-excited mechanism is observed, which may reveal the origin of the disturbance for airfoil with attack angle. The power spectral density of pressure shows the low frequency of vortex shedding caused by the Kelvin-Helmoholt instability still dominates from the leading edge to trailing edge. The simulation shows that the nonlinear wave interaction and breakdown is driven by the generation and growth of the stream-wise vortex which leads to the deformation, stretching, and eventually breakdown of the shedding prime vortex. The second part is DNS for flow separation control by blowing jets (steady, pulsed, and pitched and screwed jets). The effects of unsteady blowing on the surface at the location just before the separation points on the transition and separation are also studied. The separation zone is significantly reduced (almost removed) after unsteady blowing technology is applied. In this work, DNSUTA, a code with high-order accuracy and high-resolution developed by the CFD group at University of Texas at Arlington CFD is applied.