Beamforming Method for Extracting the Broadband Noise Sources of Counter-Rotating Open Rotors

Abstract

Counter-Rotating Open Rotors (CROR) are known to have advantageous propulsive efficiency properties, but at the same time many noise emission issues related to this technology still need to be investigated. The noise they generate consists of tonal and broadband components, of which the tonal components often appear in narrow frequency bands with large amplitudes. During beamforming investigations this often makes sorting them out from among other noise sources in the same frequency bin rather straight forward.On the other hand, the broadband noise sources can be characterized as having small amplitudes, and in general they are not the dominant noise sources in many frequency bins, but overall a significant noise component that needs to be investigated. The literature has provided a single microphone signal pre-processing method for removing the tonal components and hence isolating the broadband noise of a CROR, the signal of which has been shown to be appropriate for the investigation of broadband spectra. In this article, this preprocessing method is further developed into a beamforming method which can be used in order to localize the broadband noise sources of CROR. The resulting beamforming maps have been compared to the results of earlier broadband noise CROR studies, showing the

Stand-Alone Extraction of Cyclostationary Broadband Components from Aeroacoustic Signals

“…The extraction of AT-CS2 components is now illustrated on aeroacoustic signals recorded on an CROR engine in a wind tunnel. The CROR data typically comprise a mixture of tonal and broadband components [7,11]. Denoting by y m t the signal measured by the mth sensor, by p m t the tonal contribution, and by x m t the broadband contribution, the signal model reads…”

“…Several methods have been proposed in the literature to do so, with various degrees of refinement [1][2][3]. Once removed from the signals, they leave the place to the broadband content of the signals [4][5][6][7]. Far fewer works have attempted to further decompose broadband signals into more constituents that originate from distinct physical phenomena or sound sources, at least without explicit knowledge of the propagation mechanisms.…”

“…As far as the authors know, this topic has rarely been reported in the literature. The aforementioned works [1,2,[4][5][6][7] have contented themselves with the total broadband part left after removal of tonal components, yet without further decomposing it. A notable exception is Ref.…”

Standalone Extraction of Tonal Components from Aeroacoustic Signals

“…The extraction of tones is now illustrated on aeroacoustic signals recorded on a CROR engine [32,33]. This CROR data considered particularly difficult for several reasons [34][35][36].…”

Effect of a pylon on the broadband noise sources of counter-rotating turbomachinery

“…Phased array microphone systems and beamforming technology provide a valuable measurement tool, often used to localize and investigate the dominant noise sources of turbomachinery components, such as isolated airfoils and cascades, [15][16][17] industrial fans, 18,19 single rotor engines, [20][21][22][23] and CROR systems. [24][25][26][27][28][29] Using beamforming technology, the locations and the amplitudes of the most dominant noise sources can be investigated, making it possible to determine the most dominant noise generation mechanisms. Upon identifying the noise generation mechanisms, further developments explicitly aimed at decreasing the noise characteristics can be made.…”