Research Of Reynolds Number Effects For Shock-Induced Separations On Supercritical Airfoils

The supercritical airfoil has been widely applied to large airplanes for sake ofexcellent aerodynamic characteristics. But at transonic speeds, the complicatedshock-induced separation on the upper surface of supercritical airfoil will change theflow structure and pressure distribution, which will influence the aerodynamiccharacteristics of large airplanes. The shock-induced separation is sensitive toReynolds number that different Reynolds numbers will result in differentboundary-layer separation structure, which will influence the safety and economy oflarge airplanes. The influencing factors of separation structure and Reynolds numbereffects of supercritical airfoil were analyzed, while the mechanism of shock-inducedseparation and Reynolds number effects were simply investigated in this paper.The transonic characteristics of supercritical airfoil CH were simulated with EFDand CFD methods. The effects of macroscopically aerodynamic characteristics wereinvestigated via the microcosmic flow structure simulation.Results indicate that the EFD and the CFD methods are reliable and feasible. Itwas shown that with the attack angle increasing, the separation bubble occurred on theupper surface firstly, then the trailing-edge separation occurred, and the trailing-edgewould separate totally at last. The boundary-layer separation was influenced by attackangles, Mach numbers and Reynolds numbers, but the influencing tendency and areaswere quite different. With the shock-induced separation occured, the lift ofsupercritical airfoil decreased while the drag was increased. With the Reynoldsnumber increasing, the shock wave on the upper surface moved afterward and theintensity was increased, while the boundary-layer thickness decreased and thetrailing-edge separation area decreased, which would result in a higher lift coefficientand a lower drag coefficient.The results in this paper are crucial to investigate and analyses the aerodynamiccharacteristics of the supercritical airfoil. The Reynolds number effects mechanism ofshock-induced separation on supercritical airfoil is analyzed via the flow structuresimulation, which is crucial to the understanding of the complicated transonic flowand the correction of the Reynolds number effects.