| Summary: | Blade resolved computations of two different horizontal axis rotors are conducted to investigate the tip loss mechanism experienced by horizontal axis rotors. The tip loss mechanism specifically refers to the effect of the vorticity that is shed from the outboard blade sections, which results in the blade loading dropping off as the tip is approached. In this paper, the shed vorticity is shown to induce a downwash at the rotor plane and spanwise flow accelerations along the blade surfaces. While the downwash reduces the angle of attack of the approach flow, the spanwise flow accelerations lead to additional momentum transport along the blade. This spanwise momentum transport reduces the magnitude and changes the distribution of the static pressure developed on the pressure and suction surfaces of the outboard blade sections. As a result of this modification, the torque producing force drops off faster than the thrust producing force as the tip is approached, resulting in a rotation of the net force vector towards the streamwise direction. This anisotropy must be accounted for by tip flow corrections if the loading on the outboard blade sections is to be computed with sufficient accuracy. In addition, it is also shown that changes in the static pressure distribution cannot be accurately approximated by only modifying the angle of attack of the approach flow, as this would lead to blade loading changes that are inconsistent with the observed behaviour of the lift and drag coefficients on the outboard blade sections.
|
|---|