Rotor Noise due to BladeTurbulence Interaction.
Abstract
The timeaveraged intensity density function of the acoustic radiation from rotating blades is derived by replacing blades with rotating dipoles. This derivation is done under the following turbulent inflow conditions: turbulent ingestion with no inlet strut wakes, inflow turbulence elongation and contraction with no inlet strut wakes, and inlet strut wakes. Dimensional analysis reveals two nondimensional parameters which play important roles in generating the bladepassing frequency tone and its multiples. The elongation and contraction of inflow turbulence has a strong effect on the generation of the bladepassing frequency tone and its multiples. Increasing the number of rotor blades widens the peak at the bladepassing frequency and its multiples. Increasing the rotational speed widens the peak under the condition that the nondimensional parameter involving the rotational speed is fixed. The number of struts and blades should be chosen so that (the least common multiple of them)(.)(rotational speed) is in the cutoff range of Sears' function, in order to minimize the effect of the mean flow deficit on the time averaged intensity density function. The acoustic intensity density function is not necessarily stationary even if the inflow turbulence is homogeneous and isotropic. The time variation of the propagation path due to the rotation should be considered in the computation of the intensity density function; for instance, in the present rotor specification, the rotor radius is about 0.3 m and the rotational speed Mach number is about 0.2.
 Publication:

Ph.D. Thesis
 Pub Date:
 1983
 Bibcode:
 1983PhDT........14I
 Keywords:

 Physics: Acoustics