Journal ArticleDOI
Investigation of Rotor Noise Source Mechanisms with Forward Speed Simulation
F. R. Grosche,H. Stiewitt +1 more
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TLDR
In this article, the authors measured the noise of a model propeller with and without forward speed simulation in the open test section of a low-speed wind tunnel at velocities up to 60 m/s and blade tip Mach numbers up to 0.6.Abstract:
The noise of a model propeller was measured with and without forward speed simulation in the open test section of a low-speed wind tunnel at velocities up to 60 m/s and blade tip Mach numbers up to 0.6. Compared to the static tests, even low wind velocities reduced the propeller noise by up to 20 dB. Strong sound radiation occurred due to interaction of the propeller blades with the wake of the supporting beam when the propeller was mounted as a pusher propeller. At wind velocities above 20 m/s, the high-frequency part of the propeller noise depends strongly on the angle of attack of the blades. At moderate angles of attack, laminar vortex shedding noise dominates the high-frequency sound radiation. This noise component could be eliminated by tripping the boundary layer on the suction surface of the blades. The frequencies of maximum noise radiation were predicted fairly well by existing theories. The laminar vortex shedding noise disappears at higher angles of attack of the propeller blades. If the angle of attack is further increased, strong braodband noise occurs which is generated probably by the turbulent boundary layer and local flow separations.read more
Citations
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Journal ArticleDOI
Experimental and Analytical Investigation of the Tonal Trailing-Edge Noise Radiated by Low Reynolds Number Aerofoils
TL;DR: In this article, an experimental and analytical study of the tonal trailing edge noise of a symmetric NACA-0012 aerofoil and of a cambered SD7003 was performed.
Proceedings ArticleDOI
Wind tunnel experiments on airframe noise sources of transport aircraft
TL;DR: In this paper, the authors used an elliptical acoustic mirrormicrophone system to measure the airframe noise of a transport aircraft in the anechoic test section of the German-Dutch Wind Tunnel.
Journal ArticleDOI
Exterior noise on the fuselage of light propeller driven aircraft in flight
TL;DR: In this article, the authors describe experimental studies of exterior noise (pressure fluctuations) on the fuselage of a twin-engined, propeller driven light commercial aircraft in flight by means of 31 flush mounted special static pressure probes.
The acoustic spectrum of axial flow machines
TL;DR: In this paper, the authors compared rotor spectra from a variety of axial flow machines and acoustic trends examined, and found that the minimum broad band noise generated by ducted and free field rotors corresponds to laminar and turbulent boundary layer shedding.
Book ChapterDOI
Noise From Rotating Machinery
TL;DR: In this article, the authors focus on the flow-acoustics of axial flow machinery from helicopter blades to automotive cooling fans, and consider the special acoustic considerations brought about by the rotational motion of the blades relative to the acoustic medium.
References
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Journal ArticleDOI
Vortex Noise of Isolated Airfoils
TL;DR: Hohenemser et al. as mentioned in this paper proposed a stability and control theory for Hingeless Rotors, which is based on the theory of self-excited mechanical oscillations of Hinged Rotor Blades.
Journal ArticleDOI
The acoustic spectrum of axial flow machines
TL;DR: In this paper, the authors compared rotor spectra from a variety of axial flow machines and acoustic trends examined, and found that the minimum broad band noise generated by ducted and free field rotors corresponds to laminar and turbulent boundary layer shedding.
Journal ArticleDOI
Vortex shedding noise of low tip speed, axial flow fans
TL;DR: In this paper, the authors conducted noise and performance tests on three low tip speed, half-stage, axial flow fans to determine the nature of the vortex shedding noise mechanism, which is due to instabilities in the laminar boundary layer on the suction side of the blade where these instabilities are in the form of Tollmien-Schlichting (T-S) waves.
Journal ArticleDOI
Prediction of Airfoil Tone Frequencies
TL;DR: It has been demonstrated that the use of CSOR b results in material savings in computational times over theuse of Jh, GSh, andSORh.
Proceedings ArticleDOI
Vortex noise from nonrotating cylinders and airfoils
TL;DR: In this article, an experimental study of vortex shedding noise was conducted in an acoustic research tunnel over a Reynolds-number range applicable to full-scale helicopter tail-rotor blades.
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