Abstract

Multielement airfoil configurations have shown promise in improving the aerodynamic characteristics of the inboard section of megawatt-scale wind turbine blades by increasing the lift-to-drag ratios, lift coefficients, and structural efficiency. Steady-state, twodimensional CFD calculations were carried out for a closely-coupled multielement airfoil system with one main element and two flaps at a Reynolds number of 1,000,000. Five configurations of the multielement airfoil system were simulated with varying flap deflection, gap, and overhang. Simulations were performed with ANSYS FLUENT, which is a hybridgrid Navier-Stokes solver. Computational results were obtained using the four-equation Langtry-Menter Shear Stress Transport (SST) Transition turbulence model. Grid convergence studies were carried out by examining three grids with progressively higher grid resolutions and quantifying their effects on lift and drag coefficients. Computed solutions were obtained for angles of attack ranging from 9 to 20 deg. Lift and drag coefficients were computed to understand the effect of gap, overhang, and flap deflection on the multielement airfoil system performance. Wake bursting, a multielement airfoil phenomenon, was observed by visualizing off-the-surface flow downstream of the airfoil.

No abstract

Sensing of vortex shedding in unsteady airfoil flows can be beneficial in controlling and positively harnessing their effects for increased aerodynamic performance. The time variation of the leading-edge suction parameter (LESP), which is a non-dimensional measure of the leading-edge suction force, is shown to be useful in deducing the various events related to vortex shedding from unsteady airfoils. The recently developed leading-edge flow sensing (LEFS) technique, which uses a few pressures in the airfoil leading-edge region for deducing the aerodynamic state of an airfoil, is adapted to deduce the variation of LESP during an unsteady motion in incompressible flow. For this purpose, the flow over the airfoil is divided into an outer-region flow over the chord, modeled using thin airfoil theory, and an inner-region flow over the leading edge, modeled as a flow past a parabola. By matching these two flows, relations are derived for calculating the LESP from a few pressures at the leading edge. By studying the variations of the LEFS outputs and the calculated LESP for various unsteady motions, guidelines are presented for detecting events related to vortex shedding: initiation, pinch-off, and termination. Computational and experimental results for additional unsteady motions confirm the effectiveness of the LEFS as a sensing technique for events associated with vortex shedding on unsteady airfoils.

No abstract