Noncavitating Lifting Sections

Blake, William K.

doi:10.1016/b978-0-12-809274-3.00005-2

Cited by 4 publications

(5 citation statements)

References 170 publications

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“…A total comparison of the sound pressure levels of all airfoils of the present study at a geometrical angle of attack of 4 • and all flow speeds is given in Figure 13. Thereby, the sound pressure level is scaled with the fifth power of the Mach number, following common trailing edge noise theory [31], and displayed as a function of the chord based Strouhal number Sr = f c • b/U. Basically, it can be seen that some airfoils lead to a noise reduction especially at low and medium Strouhal numbers, while several airfoils also lead to a noise increase at high Strouhal numbers, which is due to a contribution of surface roughness noise [4,5,22].…”

Section: Acoustic Resultsmentioning

confidence: 99%

Self Noise Reduction and Aerodynamics of Airfoils with Porous Trailing Edges

Geyer

Sarradj

2019

Acoustics

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The application of open-porous materials is a possible method to effectively reduce the aerodynamic noise of an airfoil. However, the porous consistency may have a negative effect on the aerodynamic performance of the airfoil, since very often the lift is decreased while the drag increases. In a recent investigation, the generation of trailing edge noise of a set of airfoil models made from different porous materials was examined experimentally. The materials were characterized mainly by their airflow resistivity. Besides the material, the chordwise extent of the porous material was varied, which was done by covering the front part of the porous airfoil with a thin, impermeable adhesive foil. Acoustic measurements were performed in an open jet wind tunnel using microphone array technology, while the aerodynamic performance was measured simultaneously using a six-component balance. In general, both the airflow resistivity and the extent of the porous material have an influence on the trailing edge noise. However, if a suitable material is chosen, the results show that a noticeable reduction of trailing edge noise is possible even with only a small chordwise extent of the porous material.

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Section: Acoustic Resultsmentioning

confidence: 99%

Self Noise Reduction and Aerodynamics of Airfoils with Porous Trailing Edges

Geyer

Sarradj

2019

Acoustics

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“…Consequently, the energy is transferred to the larger-scale vortices (lower frequency), while the smaller-scale vortices diminish in this process. In § 2.2, we presented a series of theoretical 3D AAF models of thin aerofoils (Filotas 1969a,b;Graham 1970Graham , 1971Mugridge 1970Mugridge , 1971Blake 1986). It is not convenient to compare the measured 3D AAF with the theoretical results directly, so we validate our proposed theory by comparing the 1D AAF obtained by the measured 3D AAF, defined as in (2.26), with those obtained by empirical 3D AAF models.…”

Section: Experimental Validationmentioning

confidence: 99%

“…For cases in which neither the aerofoil span nor the spanwise wavelength of the incident turbulence is effectively infinite with respect to the chord (Blake 1986), a variety of attempts have been made to find a proper aerodynamic transfer function to describe the pressure distribution on the aerofoil. Reissner & Stevens (1947a,b) introduced a correction factor to the basic function of the two-dimensional theory to study the effect of three-dimensionality of the flow and gave the corresponding methods for the numerical evaluation of the results.…”

Section: Introductionmentioning

confidence: 99%

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The lift on an aerofoil in grid-generated turbulence

Liao

2015

J. Fluid Mech.

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The three-dimensional effects of turbulence cannot be neglected when the spanwise wavelength of the incident turbulence is not effectively infinite with respect to the chord, which may invalidate the strip assumption. Based on three-dimensional theory, a general approach, expressed in terms of a two-dimensional Fourier transform of the correlation of the buffeting force, is proposed to identify the two-wavenumber spectrum and aerodynamic admittance of the lift force on an aerofoil. It is essential that the approach presented can be validated in wind tunnel experiments. The coherence of the lift force on an aerofoil in grid-generated turbulence is obtained by simultaneous measurements of unsteady surface pressures around several chordwise strips on a stiff sectional model, which controls the accuracy of results. For the purpose of the Fourier transform, three empirical coherence models of the lift force are presented to fit the experimental results. Compared with the linearized theory, the two-wavenumber aerodynamic admittance can describe well the pressure distribution and the pattern of energy transition in an isotropic turbulence field. Thus, the failure mechanism of the traditional strip assumption can be demonstrated explicitly. In addition, the results obtained also validate the theory proposed by Graham (Aeronaut. ). The present approach can be extended to study the three-dimensionality of the buffeting force on line-like structures with arbitrary cross-configurations, such as long-span bridges and high-rise buildings.

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“…The theoretical results closely followed those obtained by an experimental campaign. However, Blake 6 later contested that the orifice plates employed in Jenvey’s work had too small of a hole-to-pipe diameter ratio, therefore favoring the quadrupole source linked to turbulence proper over the dipole source due to the interaction with the solid surfaces. This last observation may be of particular importance for the case of subsonic flows, as demonstrated by Nelson and Morfey.…”

Section: Introductionmentioning

confidence: 99%

Estimation of aerodynamic noise of diaphragms through IEC 60534-8-3 and CFD

Fenini

Quaroni

Malavasi

2021

Measurement and Control

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The aerodynamic noise emitted by a subsonic flow of dry air through an orifice plate is estimated in terms of internal sound power level and external sound pressure level (SPL) by application of the methodology described in the international standard IEC 60534-8-3. A shortcoming of the standard in defining the efficiency of the transformation of the mechanical energy of the flow into acoustic energy is discussed. Experimental evidence of the matter is also described. An alternative model employing the resolution of Reynolds Averaged Navier-Stokes equations (RANS) by means of Computational Fluid Dynamics (CFD) techniques for the calculation of the acoustic power generated by the turbulent flow through the orifice plate is applied so as to overcome the issue.

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Noncavitating Lifting Sections

Cited by 4 publications

References 170 publications

Self Noise Reduction and Aerodynamics of Airfoils with Porous Trailing Edges

Self Noise Reduction and Aerodynamics of Airfoils with Porous Trailing Edges

The lift on an aerofoil in grid-generated turbulence

Estimation of aerodynamic noise of diaphragms through IEC 60534-8-3 and CFD

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