Abstract:
The boundary layer transition characteristics on both sides of a BK117-type full-scale helicopter main rotor were measured in hover conditions in a whirl tower experiment for various pitch angles. Accompanying state-of-the-art FLOWer simulations of a rigid isolated rotor with transition prediction based on empirical criteria were conducted for comparison with the measurements. The results reveal a slow upstream transition movement in the radial direction on the upper side of the blade, and a general upstream shift of the transition with increasing pitch angle. On the lower side, fully laminar flow exists in the inner part of the blade and a strong transition movement to the leading edge occurs outboard, which is shifted further outboard with increasing pitch angle. The predicted transition characteristics show qualitative agreement with the measured data on both sides of the rotor blade but quantitative differences occur.