Investigation of Rotor Noise Source Mechanisms with Forward Speed Simulation

Grosche, F.-R.; Stiewitt, H.

doi:10.2514/3.61041

Cited by 7 publications

(5 citation statements)

References 7 publications

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“…In fact, different acoustic signatures can be produced depending on blade design and on the portion of span actually involved in the generation of noise. For instance, a peak at much higher frequencies than the rotational noise has been reported for a low-speed fan by Longhouse [1], whereas a signature very similar to those of rectangular isolated aerofoils with multiple tones has been observed during the wind-tunnel testing of model propellers by Grosche and Stiewitt [2]. Both examples are discussed later on in the paper.…”

Section: Introductionmentioning

confidence: 79%

“…Stating about the possible occurrence of aforementioned observed phenomena in true rotating-blade environments is a matter of practical interest. It is addressed in this section by inspection of previous works by Grosche and Stiewitt [2] and Longhouse [1], on the one hand, and of unpublished results for a small 9-bladed low-speed fan used for cooling electronic racks, on the other hand. Grosche and Stiewitt's investigation refers to a four-bladed model propeller with a conventional blade design.…”

Section: Comparison With Rotating-blade Configurationsmentioning

confidence: 99%

“…The similarity of the results is even surprising in view of the spanwise-variable conditions encountered on the propeller. The design of the blades makes their outer part nearly rectangular with no sweep and moderate twist [2]; therefore, only the tip region very likely experiences the favorable conditions for sustained LBL waves.…”

Section: Comparison With Rotating-blade Configurationsmentioning

confidence: 99%

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Experimental and Analytical Investigation of the Tonal Trailing-Edge Noise Radiated by Low Reynolds Number Aerofoils

et al. 2020

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An experimental and analytical study of the tonal trailing-edge noise of a symmetric NACA-0012 aerofoil and of a cambered SD7003 aerofoil has been achieved. It provides a complete experimental database for both aerofoils and improves the understanding of the underlying mechanisms. The analysis stresses the high sensitivity of the tonal noise phenomenon to the flow velocity and the angle of attack. Several regimes of the noise emission are observed depending on the aforementioned parameters. The contributions of the pressure and the suction sides are found to vary with the flow parameters too. A special attention has been paid to the role of the separation bubble in the tonal noise generation. Hot-wire measurements and flow visualization prove that the separation bubble is a necessary condition for the tonal noise production. Moreover, the bubble must be located close enough to the trailing edge. Several tests with small-scale upstream turbulence confirm the existence of the feedback loop. Analytical predictions with a classical trailing-edge noise model show a good agreement with the experimental data; they confirm the cause-to-effect relationship between the wall-pressure fluctuations and the radiated sound. Finally, previously reported works on fans and propellers are shortly re-addressed to show that the tonal noise associated with laminar-boundary-layer instabilities can take place in rotating blade technology.

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Section: Introductionmentioning

confidence: 79%

Section: Comparison With Rotating-blade Configurationsmentioning

confidence: 99%

Section: Comparison With Rotating-blade Configurationsmentioning

confidence: 99%

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Experimental and Analytical Investigation of the Tonal Trailing-Edge Noise Radiated by Low Reynolds Number Aerofoils

et al. 2020

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“…Here, the authors stress that, in order to guarantee the validity of Equation ( 9), the blade chord along the blade span was fixed, so c(r b ) = constant. The tendency toward keeping the chord constant along the span in the blade design is supported by the literature examples of [19,20]. Based on the well-known Cordier diagram [46] for turbomachines of favorable efficiency, axial flow fans have the specific diameter and the specific speed within the approximate ranges of 1 ≤ δ ≤ 1.5 and 2 ≤ σ ≤ 3, respectively.…”

Section: Aerodynamics: Blade Designmentioning

confidence: 97%

“…Furthermore, the spanwise variation of free-stream velocity tended to broaden the noise signature of PVS, thus acting against a remarkable, well-detectable tonal PVS character. Grosche and Stiewitt [20] examined a four-bladed propeller-type axial fan rotor with a moderate sweep and twist. They observed PVS noise at α ≈ 4 • angle of attack, viewed in the rotating frame of reference near the blade tip, for three different Reynolds numbers based on the chord length (Re c = 9 × 10 4 , 1.3 × 10 5 , 2.6 × 10 5 ).…”

Section: Introductionmentioning

confidence: 99%

Preliminary Design Guidelines for Considering the Vibration and Noise of Low-Speed Axial Fans Due to Profile Vortex Shedding

Daku

Vad

2022

IJTPP

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This paper presents a critical overview on worst-case design scenarios for which low-speed axial flow fans may exhibit an increased risk of blade resonance due to profile vortex shedding. To set up a design example, a circular-arc-cambered plate of 8% relative curvature is investigated in twofold approaches of blade mechanics and aerodynamics. For these purposes, the frequency of the first bending mode of a plate of arbitrary circular camber is expressed by modeling the fan blade as a cantilever beam. Furthermore, an iterative blade design method is developed for checking the risky scenarios for which spanwise and spatially coherent shed vortices, stimulating pronounced vibration and noise, may occur. Coupling these two approaches, cases for vortex-induced blade resonance are set up. Opposing this basis, design guidelines are elaborated upon for avoiding such resonance. Based on the approach presented herein, guidelines are also developed for moderating the annoyance due to the vortex shedding noise.

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