A theoretical investigation of laminar wakes behind airfoils and the resulting noise pattern

Fathy, Ayman; Rashed, M.M.; Lumsdaine, E.

doi:10.1016/0022-460x(77)90556-9

Cited by 7 publications

(12 citation statements)

References 6 publications

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“…I n recent years, a few papers (Paterson et al 1972;Sunyach et al 1973;Tam 1974;Fink 1975;Schlinker, Fink & Amiet 1976;Fathy, Rashed & Lumsdaine 1977) have been devoted to the study of discrete frequencies emitted by airfoils placed in a laminar flow whose Reynolds number, based on the chord, did not exceed some critical value of the order of 6 x lo5, associated with boundary-layer transition. The most significant of the above contributions is that of Paterson, who showed that the Strouhal frequency f of the observed narrowband spectrum exhibited a so-called 'ladder-type ' variation, i.e.…”

Section: Introductionmentioning

confidence: 99%

Noise generated by airfoil profiles placed in a uniform laminar flow

1983

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The present paper is devoted to the experimental study of the noise generated by an airfoil profile placed in a uniform laminar flow. The far-field acoustic spectrum is shown to be composed of a broadband contribution around frequency f, and a discrete contribution a t equidistant frequencies f,, which follow power laws of the forms f ,-P 5 and f,-U0.85. Both contributions can be accounted for by a simple model derived from the original suggestions of Tam (1974) and Fink (1975). It is essentially assumed that the diffraction of the Tollmien-Schlichting instabilities by the trailing edge generates acoustic waves which propagate in the far field and also trigger an aeroacoustic feedback loop, whose length is equal to the distance between the trailing edge and the maximum velocity point of the airfoil.

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Section: Introductionmentioning

confidence: 99%

Noise generated by airfoil profiles placed in a uniform laminar flow

1983

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“…The vortex shedding frequency f can be expressed as follows (Fathy et al, 1977, Lee et al, 1993, Dou et al, 2016 = 0 − (3) where U0 is the free-stream velocity, Vi is the advance velocity of the vortex street, and a is the distance between the vortices within a vortex row. Vi is due to the induced velocity of each vortex in the street, its direction is opposite to U0.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

“…where is the strength of a vortex and s is the vortex spacing ratio which is defined as = (5) where b is the transversal distance between vortex rows. Assuming that the shed vortices form a Karman vortex street, the value of s had been set to 0.281 in Hersh et al, 1974, Fathy et al, 1977, Lee et al, 1993, and Dou et al, 2016. The von Kármán stability criterion assumes isolated, equal, point-vortices existing in a non-viscous fluid.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

“…Using Eq. ( 5), a/c can be expressed as = / (8) b can be expressed in the following way (Hersh et al, 1974, Fathy et al, 1977, Lee et al, 1993, Dou et al, 2016…”

Section: Theoretical Backgroundmentioning

confidence: 99%

“…K establishes the connection between the boundary layer thickness and the transversal distance between the vortex rows (labelled as b in Figure 1) as described later in detail. Independent references (Hersh et al, 1974, Fink, 1975, Fathy et al, 1977 report that the value of K is 0.6, 0.6 and 0.5, respectively. These references have also been cited in more recent works of Lee et al, 1993, andDou et al, 2016. It is desirable to assess the validity of these data for profiles and angles of attack being characteristic of low-speed fan applications.…”

Section: Introduction and Objectivesmentioning

confidence: 99%

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A semi-empirical model for predicting the frequency of profile vortex shedding relevant to low-speed axial fan blade sections

Balla

Vad

2019

European Conference on Turbomachinery Fluid Dynamics and Hermodynamics

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This paper extends existing semi-empirical models on the frequency prediction of vortex shedding. Moderate Reynolds numbers are investigated being of interest in low-speed axial fan design. By an extensive literature review, a new parametrization is proposed for the factor establishing a connection between boundary layer properties and vortex shedding characteristics. Measurement data on symmetrical and non-symmetrical NACA profiles, and on flat and cambered plates, are processed. It is found that the value of the factor is influenced by the relative thickness of the profiles and by the angle of attack. Based on the measurement results, an empirical value is given for the vortex spacing ratio for flow past airfoils. With the use of the proposed empirical model, the vortex shedding frequency of various airfoil profiles and operating conditions can be predicted.

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Vortex shedding noise of aerofoils in smooth flow

Keshavan

1977

Journal of Sound and Vibration

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A theoretical investigation of laminar wakes behind airfoils and the resulting noise pattern

Cited by 7 publications

References 6 publications

Noise generated by airfoil profiles placed in a uniform laminar flow

Noise generated by airfoil profiles placed in a uniform laminar flow

A semi-empirical model for predicting the frequency of profile vortex shedding relevant to low-speed axial fan blade sections

Vortex shedding noise of aerofoils in smooth flow

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