A new blade tip geometry to improve aerodynamic performance and acoustic noise of helicopter blade in hovering flight

The goal of the present study is to improve aerodynamic performance of the helicopter main rotor by geometric redesign of its blades' tips. In this process, the generated noise is examined as well to ensure that it is not increased by the new tip geometry. Three-dimensional flow field around the blades is numerically simulated by the solution of the compressible unsteady Reynolds averaged Navier-Stokes (URANS) equations to calculate torque and thrust coefficients of CQ and CT, and the figure of merit (FoM) ratio. The turbulence model used in this study is "SST k-omega". To check both the thickness noise and the high-speed impulsive (HSI) noise on the rotor plane, the Ffowcs Williams-Hawking (FW-H) equation is solved to obtain the sound pressure level at certain points in the flow field. Following the noticeable aerodynamic improvements that anhedral and dihedral winglets made on the fixed-wings, aerodynamic performance of the blade tip geometries composed of anhedral and dihedral winglets or a combination of them are investigated on the helicopter blades in present research. Redesign of blade tips minimizes the geometric changes needed for a new blade design. Flow fields around blades with nine different tip geometries are three-dimensionally simulated and analyzed in detail at crucial rotational speeds of 1250 rpm and 2540 rpm in hovering flight. To determine the amount of improvement, results obtained for different tip geometries are compared with the reference results of the rectangular blade. Among all of the different tip geometries, it was concluded that Eagle and Anhedral-Eagle make maximum improvements in aerodynamic and aeroacoustic of the main rotor blades. The FoM ratios of these two tip geometries have increased even up to 17% and 21%, respectively. Also, their noise levels of them have decreased by about 4.5% and 1%. (c) 2023 Elsevier Masson SAS. All rights reserved.