A note on the tip noise of rotating blades

A possible cause is suggested for the discrepancies that have arisen between measured results and linear acoustic predictions (based on thickness noise alone), at least at the lower tip Mach number range of the tests. The blade tip is shown to be an effective noise generation area when Isom's thickness noise formula is studied numerically (Farassat and Nystrom, 1980). It is found that neglecting the sources on the airfoil-shaped cut at the very tip of the blade causes serious errors in the predicted thickness noise. It is also found that the tip area becomes less important as the tip speed is increased. The effect of the tip surface on the thickness noise indicates that it should be included in the calculation of the loading noise.