On the Relevance of Convection Effects for a Laser-Generated Sound Source

Rossignol, Karl-Stéphane; Delfs, Jan; Boden, Fritz

doi:10.2514/6.2015-3146

Cited by 13 publications

(9 citation statements)

References 2 publications

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“…The digital filter helps to isolate the sound of the LIP in the time domain, as the background noise of the SWT is mainly limited below this frequency. The maximum energy content of the LIP in the frequency domain was observed well above 10 kHz by previous studies [11,22], therefore, the frequency content of the LIP is well separated from the corner frequency of the high-pass filter (1 kHz). For this reason, the digital filter is expected to have a negligible effect on the signal of the LIP.…”

Section: Measured Arrival Timesupporting

confidence: 72%

“…As was shown by Rossignol et al [22], the far field sound pressure of a LIP sound source must be corrected for Doppler effect. This correction can be approximated by multiplying Amiet's pressure ratio with…”

Section: Modeled Pressure Correctionmentioning

confidence: 95%

“…While some work has also been done in numerically and analytically modeling the noise source generated by LIP [22,23], its fundamental properties (such as overall sound pressure level and pressure signature) are still challenging to determine by purely relying on the laser-optical system used to generate the plasma itself (laser energy, pulse width, focal distance, ambient conditions of air, etc). To gain an understanding of how the properties of the laser-optical system can be linked with the acoustic output of the LIP, some fundamentals of plasma dynamics must be understood.…”

Section: Introductionmentioning

confidence: 99%

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Propagation characteristics of laser-induced acoustic sources in hybrid anechoic wind tunnels

Szőke

Devenport

2021

Journal of Sound and Vibration

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Section: Measured Arrival Timesupporting

confidence: 72%

Section: Modeled Pressure Correctionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

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Propagation characteristics of laser-induced acoustic sources in hybrid anechoic wind tunnels

Szőke

Devenport

2021

Journal of Sound and Vibration

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“…12 Instead, and as numerically verified in ref. 13, the plasma source convects with the flow during sound production. The duration of the sound production is estimated to be approximately 0.1 ms (as shown in Fig.…”

Section: B Sound Source Directivitymentioning

confidence: 99%

“…The shielding levels obtained with and without freestream flow for the same source and observer locations discussed above are presented in Figs. 13, 14 and 15. The airfoil angle of attack is 0°.…”

Section: B Effect Of Flowmentioning

confidence: 99%

Experimental Study of Noise Shielding by a NACA 0012 Airfoil

Hutcheson

Bahr

Thomas

et al. 2018

2018 AIAA/CEAS Aeroacoustics Conference

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The effects of sound source location, Mach number and angle of attack on the shielding of a laser-induced sound source by a NACA 0012 airfoil are examined. The sound source is a small plasma generated by a high energy, laser beam focused to a point. In-flow microphone measurements are acquired in the midspan plane of the airfoil over a broad range of streamwise stations, and shielding levels are calculated over different frequency ranges from the measurements acquired with and without the airfoil installed. Shielding levels are shown to increase as the source is positioned closer to the mid-chord of the airfoil, and to significantly decrease with increasing flow Mach number, except when the source is positioned near the leading edge of the airfoil. Both with and without flow, changes in angle of attack are associated with a corresponding shift of the shadow region. Finally, the effects of multipath signals, observer distance and signal scatter on the measured shielding levels are discussed.

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Identifying the flap side‐edge noise contribution of a wind turbine blade section with an adaptive trailing edge

et al. 2022

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Active trailing-edge technology is a promising application for localized load alleviation of large-diameter wind turbine rotors, accomplished using one or more control surfaces in the rotor blade's outer region. This work focuses on identifying noise contributions from the flap side-edge and the trailing edge in a laboratory condition.Measurements were conducted in the Acoustic Wind Tunnel Braunschweig (AWB) at the German Aerospace Center's (DLR) Braunschweig site. The small-scale model has a span of 1,200 mm and a chord length of 300 mm. The control surface, a plain flap, has a span of 400 mm and a chord length of 90 mm. Far-field noise was measured using a phased-microphone array for various flow speeds, angles of attack, and flap deflection angles. Due to the size of the model and assumed closeness of the sound sources, two noise reduction addons were installed interchangeably: trailing-edge brush and flap side-edge porous foam for sound source identification. Analysis of the far-field noise reveals that, while changes to the flap deflection angle alter the farfield noise spectra, the trailing-edge noise remains the predominant noise source at deflection angles À5 ∘ and 5 ∘ . No additional noise level was observed from the flap side edge within the measurable frequency range at these angles. The flap side-edge noise has an increased role for frequency larger than 2 kHz for the larger flap deflection angles of À10 ∘ and 10 ∘ .

show abstract

On the Relevance of Convection Effects for a Laser-Generated Sound Source

Cited by 13 publications

References 2 publications

Propagation characteristics of laser-induced acoustic sources in hybrid anechoic wind tunnels

Propagation characteristics of laser-induced acoustic sources in hybrid anechoic wind tunnels

Experimental Study of Noise Shielding by a NACA 0012 Airfoil

Identifying the flap side‐edge noise contribution of a wind turbine blade section with an adaptive trailing edge

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