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D.W. van Hoogstraten
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1
Noise radiation of a low Reynolds propeller at an angle of attack
An experimental and analytical study
This work presents an experimental and analytical investigation of unsteady loading of a low Reynolds number propeller and its relation to aeroacoustics. The propeller is positioned at an angle of attack with respect to the freestream which causes a variation in loading along the azimuth. The propeller is operated at 4000 RPM with an advance ratio of J = 0.4, corresponding to a free stream velocity of 8 m/s. The chord-based Reynolds number of the propeller is of the order of 104 and is investigated at two angles of attack: αr = 7.5° and αr = 15°. For reference, a steady case, αr = 0◦, is presented as well. Loads and noise measurements were carried out in the A-Tunnel of TU-Delft. Two microphone array configurations were used to mimic the observers positions above and underneath the flightpath of the propeller. Underneath the flightpath, an increase in SPL was found with increase of the rotor angle of attack. Above the flightpath, the opposite effect was observed, resulting in an asymmetrical directivity profile when the rotor is at an angle of attack. A quasi-steady loading model, based on the lifting line code Xrotor, is used to determine the azimuthal variation in loading. The variation in tip speed along the azimuth due to the propeller angle of attack is prescribed to determine the variation in loading in one rotation. Far-field loading and thickness noise are computed using an aeroacoustic model based on the Ffowcs-Williams & Hawkings’ equation to predict the harmonic noise in the frequency domain of a rotating dipole and monopole, respectively. The numerical predictions for the steady case show good agreement for both the aerodynamic and aeroacoustic performance when compared with loading and noise measurements. For the αr≠ 0° cases it was shown that unsteady loading noise increases the SPL for all harmonics, with a larger contribution at higher harmonics.
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This work presents an experimental and analytical investigation of unsteady loading of a low Reynolds number propeller and its relation to aeroacoustics. The propeller is positioned at an angle of attack with respect to the freestream which causes a variation in loading along the azimuth. The propeller is operated at 4000 RPM with an advance ratio of J = 0.4, corresponding to a free stream velocity of 8 m/s. The chord-based Reynolds number of the propeller is of the order of 104 and is investigated at two angles of attack: αr = 7.5° and αr = 15°. For reference, a steady case, αr = 0◦, is presented as well. Loads and noise measurements were carried out in the A-Tunnel of TU-Delft. Two microphone array configurations were used to mimic the observers positions above and underneath the flightpath of the propeller. Underneath the flightpath, an increase in SPL was found with increase of the rotor angle of attack. Above the flightpath, the opposite effect was observed, resulting in an asymmetrical directivity profile when the rotor is at an angle of attack. A quasi-steady loading model, based on the lifting line code Xrotor, is used to determine the azimuthal variation in loading. The variation in tip speed along the azimuth due to the propeller angle of attack is prescribed to determine the variation in loading in one rotation. Far-field loading and thickness noise are computed using an aeroacoustic model based on the Ffowcs-Williams & Hawkings’ equation to predict the harmonic noise in the frequency domain of a rotating dipole and monopole, respectively. The numerical predictions for the steady case show good agreement for both the aerodynamic and aeroacoustic performance when compared with loading and noise measurements. For the αr≠ 0° cases it was shown that unsteady loading noise increases the SPL for all harmonics, with a larger contribution at higher harmonics.
Bachelor thesis
(2016)
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T.H.E. Gulikers, D.W. van Hoogstraten, R. Iordache, I.C. Kleinbekman, M.R. Koch, D. Kroezen, L. Müller, M.M. Otting, M.A. Pieters, P. Proesmans, W.J.C. Verhagen, M. Hernandez Santana
As more and more people choose the airplane as a means of transportation, the aviation industry faces new challenges in order to fulfill the increasing demand, while decreasing the costs and emissions. In this report, the authors present a design of a narrow-body aircraft that is meant to provide a 30 % direct operating costs reduction, as well as a 20 % reduction in NOx and CO2 emissions while being ready for market introduction by 2030. Furthermore, the aircraft should provide a noise reduction of 10 % which translates to a reduction of 29 [EPNdB] and it should house 177 passengers.
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As more and more people choose the airplane as a means of transportation, the aviation industry faces new challenges in order to fulfill the increasing demand, while decreasing the costs and emissions. In this report, the authors present a design of a narrow-body aircraft that is meant to provide a 30 % direct operating costs reduction, as well as a 20 % reduction in NOx and CO2 emissions while being ready for market introduction by 2030. Furthermore, the aircraft should provide a noise reduction of 10 % which translates to a reduction of 29 [EPNdB] and it should house 177 passengers.