Rotating Blade Trailing-Edge Noise: Experimental Validation of Analytical Model

This paper dealswith the experimental validation of an analytical trailing-edge noisemodel dedicated to low-speed fans operating in free field. The model is intrinsically related to the aerodynamics of the blades and should lead to a useful fast-running tool to be included in a blade-design process in an industrial context. The investigations aremade on a two-bladed low-speed axial fan without shroud, installed inside an anechoic room. The blades are instrumented with two sets of embedded small-size microphones (2.5 mm diam), and the wall-pressure signals are acquired via a slip ring mounted on the fan axis. The chord-based Reynolds number is about 200,000, and the tip Mach number about 0.07. The data base is completed by far-field measurements made with a single microphone on a moving support. The analytical model is based on a previously published extension of Amiet’s trailing-edge noise theory. A blade is split into several strips in the spanwise direction, and themodel is applied to each strip. For this the input data are interpolated from the measurements performed with the aforementioned sets of microphones. The trailing-edge noise model is more reliable for observer positions within 30 from the fan-rotation plane. Nomenclature B = fan-blade number bc = nondimensional parameter in Corcos’s model Cf = friction coefficient c = blade-strip chord c0 = sound speed K1 = streamwise hydrodynamic wave number k = acoustic wave number L = blade-strip span L = aeroacoustic transfer function ly = spanwise correlation length Mt = tip Mach number N = fan rotational speed R = radial distance RA = position vector of the middle of the trailing-edge segment in the moving reference frame Re = Reynolds number R0 = distance between observer position and fan center r1 = distance between the fan axis and the midspan network r2 = distance between the fan axis and the tip network Spp = acoustic-pressure power spectral density Spp = acoustic-pressure power spectral density due to one blade segment