Broadband fan noise prediction using single-airfoil theory

Abstract

The present study is dedicated to the analytical modeling of the broadband noise radiated by subsonic fans, such as encountered in HVAC or automotive engine cooling applications. A fan noise prediction scheme is proposed on the basis of single-airfoil linearized unsteady aerodynamics theories. Two basic spanwise distributed mechanisms are considered, namely the noise from the impingement of upstream turbulence, and the trailing edge noise associated with turbulence boundary layer scattering. The associated analytical models are validated by comparing the theoretical results with experimental data collected in open-jet anechoic wind tunnels, and existing numerical computations found in the literature. Validations involve single-frequency directivity, single-direction spectra and radiation maps in a large range of flow conditions over different mock-ups in the midspan plane. The transfer function between the wall-pressure statistics and the far-field sound should be invariant according to the analytical model and is experimentally found to be within ±5 dB with respect to flow conditions encountered on an isolated airfoil. Finally, a first application of the model to a highly twisted, tapered and swept automotive engine cooling fan is presented. In view of the results, trailing-edge noise is found to be significant contributor, at least in the high frequency range beyond 4 kHz for a chord-based Reynolds number of about 2 x 10 5 and Mach number of about 0.1.

Frequency-domain model of tonal blade thickness and loading noise

“…In another work of Lowson and Ollerhead, 26 noise contribution from the radial loading was taken into account and the similar expression was employed by Huang 7 to characterize the computer cooling fan noise. All the above models were established based on the geometric far-field assumption, while the approximate frequency-domain solutions for the geometric near-field noise of the rotating point source were proposed by Ju et al, 27 Schram et al, 28 and Roger et al 29 For the distributed acoustic source on rotating blade, above point models can be extended to compute the blade noise via dividing the blade surface into numerous acoustically compact elements and the related work was conducted and verified by Khelladi et al 30 Moreover, the noise models for the axial flow blade in low-Mach-number rotation were developed as an extension of the Amiet's airfoil model, and they can be referred to the work of Roger et al, 31 Rozenberg et al, 32 Zhou et al, 33 etc.…”

Turbomachinery Noise Predictions: Present and Future

“…Airfoil responses, as originally derived by Amiet [47,48] and extended by Roger and Moreau [15,49,50] to account for back-scattering effects and subcritical gusts, can then be applied for both leading and trailing-edge noise mechanisms. Such a model has been intensively used and validated for low-speed fans by Moreau and co-workers [51,52]. Sinayoko et al showed that such a model behaves correctly and provide similar results as the exact model based on Bessel functions up to transsonic speeds [53].…”

Impact of Turbulence Models on RANS-Informed Prediction of Fan Broadband Interaction Noise

“…Usually two iterations of the Schwarzschild's technique are used for calculating the high-frequency solution, which leads to a correct prediction at moderate and high frequencies, but overestimates the response of compact sources at low frequencies (see e.g. Paterson and Amiet (1976), Roger et al (2006) and Reboul (2010)). Recently Santana et al (2016) extended Amiet's high-frequency theory with additional iterations of the Schwarzschild's technique in order to improve the solutions for low frequencies.…”