CFD Analysis of a Slatted UH-60 Rotor in Hover

Abstract

The effect of leading-edge slats (LE) on the performance of a UH-60A rotor in hover was studied using the OverTURNS CFD solver. The objective of the study was to quantify the effect of LE slats on the hover stall boundary and analyze the reasons for any potential improvement/penalty. CFD predictions of 2-D slatted airfoil aerodynamics were validated against available wind tunnel measurements for steady angle of attack variations. The 3-D CFD framework was validated by comparing predictions for the baseline UH-60A rotor against available experimental values. Subsequent computations were performed on a slatted UH-60A rotor blade with a 40%-span slatted airfoil section and two different slat configurations. The effect of the slat root and tip vortices as they convect over the main blade element was captured using appropriately refined main element meshes and their impact on the slatted rotor performance was analyzed. It was found that the accurate capture of the slat root and tip vortices using the refined meshes made a significant difference to the performance predictions for the slatted rotors. The calculations were performed over a range of thrust values and it was observed that the slatted rotor incurred a slight performance penalty at lower thrust and was comparable to the baseline rotor at higher thrust conditions. It was also found that shock induced separation near the blade tip was the limiting factor for the baseline UH-60 rotor in hover, causing an increase in rotor power and resulting in a reduction of figure of merit for the baseline rotor at higher thrust values. The shock induced separation occured outboard of the slat tip and therefore limited the performance of the slatted rotors as well. Overall, the study provides useful insights into effects of leading edge slats on rotor hover performance, aerodynamics and wake behavior.