Thickness noise of helicopter rotors at high tip speeds

Farassat, F.; Pegg, R. J.; Hilton, David A.

doi:10.2514/6.1975-453

Cited by 23 publications

(21 citation statements)

References 2 publications

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“…The test case is a three-bladed rotor, designed to reduce acoustic emissions. The design is yielded from a low-cost numerical tool developed at ISAE-Supaero based on blade element and momentum theory (BEMT) 28 for the aerodynamic prediction and formulation of the Ffowcs-Williams and Hawkings equation as expressed by Farassat 29 coupled with broadband noise models for the acoustic prediction. The distributions of lift and drag are estimated from the local lift and drag coefficients on 2D sections.…”

Section: Geometry and Grid Convergence Studymentioning

confidence: 99%

Application of a lattice Boltzmann method to some challenges related to micro-air vehicles

Gourdain

Jardin

Serré

et al. 2018

International Journal of Micro Air Vehicles

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The demand for micro-air vehicles is increasing as well as their potential missions. Whether for discretion in military operations or noise pollution in civilian use, the improvement of aerodynamic and acoustic performance of micro-air vehicles propeller is a goal to achieve. Micro-and nano-air vehicles operate at Reynolds numbers ranging from 10 3 to 10 5. In these conditions, the aerodynamic performance of conventional fixed and rotary wings concepts drastically decreases due to the increased importance of flow viscous forces that tend to increase drag and promote flow separation, which leads to reduced efficiency and reduced maximum achievable lift. Reduced efficiency and lift result in low endurance and limited payloads. The numerical simulation is a potential solution to better understand such low Reynolds number flows and to increase the micro-air vehicles' performance. In this paper, it is proposed to review some challenges related to micro-air vehicles by using a Lattice-Boltzmann method. The method is first briefly presented, to point out its strengths and weaknesses. Lattice-Boltzmann method is then applied to three different applications: a DNS of a single blade rotor, a large eddy simulation of a rotor operating in-ground effect and a large eddy simulation of a rotor optimised for acoustic performance. A comparison with reference data (Reynolds Averaged Navier-Stokes, DNS or experimental data) is systematically done to assess the accuracy of lattice-Boltzmann method-based predictions. The analysis of results demonstrates that lattice-Boltzmann method has a good potential to predict the mean aerodynamic performance (torque and thrust) if the grid resolution is chosen adequately (which is not always possible due to limited computational resources). A study of the turbulent flow is conducted for each application in order to highlight some of the physical flow phenomena that take place in such rotors. Different designs are also investigated, showing that potential improvements are still possible in terms of aerodynamic and aero-acoustic performance of low-Reynolds rotors.

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Section: Geometry and Grid Convergence Studymentioning

confidence: 99%

Application of a lattice Boltzmann method to some challenges related to micro-air vehicles

Gourdain

Jardin

Serré

et al. 2018

International Journal of Micro Air Vehicles

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“…The time-dependent surface data computed by NLAS is used to solve the FW–H equation for noise propagations in arbitrary observer points. The penetrable integral solution of FW–H equation solved by Farassat et al 25–27 can be written in the form of …”

Section: Numerical Simulation Methodologymentioning

confidence: 99%

Aerodynamic noise radiating from the inter-coach windshield region of a high-speed train

Dai

Zheng

Zhou

et al. 2018

Journal of Low Frequency Noise, Vibration and Active Control

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The aerodynamic noise has been the dominant factor of noise issues in high-speed train as the traveling speed increases. The inter-coach windshield region is considered as one of the main aerodynamic noise sources; however, the corresponding characteristics have not been well investigated. In this paper, a hybrid method is adopted to study the aerodynamic noise around the windshield region. The effectiveness of simulation methods is validated by a simple case of cavity noise. After that, the Reynolds-averaged Navier-Stokes simulation is used to obtain the characteristics of flow field around the windshield region, which determine the aerodynamic noise. Then the nonlinear acoustic solver approach is employed to acquire the near-field noise, while the Ffowcs-Williams/Hawking equation is solved for farfield acoustic propagation. The results indicate that the windshield region is approximately an open cavity filled with severe disturbance flow. According to the analysis of sound pressure distribution in the near-acoustic field, both sides of the windshield region appear symmetrical two-lobe shape with different directivities. The results of frequency spectrum analysis indicate that the aerodynamic noise inside inter-coach space is a typical broadband one from 100 Hz to 5k Hz, and most acoustic power is restricted in the low-medium frequency range (below 500 Hz). In addition, the acoustic power in the low frequency range (below 100 Hz) is closely related to the cavity resonance with the resonance peak frequency of 42 Hz. The overall sound pressure level at different speeds shows that the acoustic power grows approximately 5th power of the train speed. Two forms of outside-windshields are designed to reduce the noise around the windshield region, and the results show the full-windshield form is better in noise reduction, which apparently eliminates interior cavity noise of inter-coach space and lessens the overall sound pressure level on the sides of near-field by about 13 dB.

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“…It is necessary to fit the integral formulation closely to the simplified model of the measurement of aerodynamic noise in the wind tunnel test. The propagation medium is considered to be static in Farassat’s formulations (Formulations 1 and 1A 2–4 ) and Di Francescantonio’s formulations (penetrable control surface formulations 11 ). For wind tunnel tests with obvious uniform flow components, the implementation of these integral formulations for the simplified model will become quite unintuitive and complex, meanwhile they do not fit well with physical problems.…”

Section: Test Case: a Simplified Model Of Noise Measurement In Wind Tmentioning

confidence: 99%

“…The Ffowcs Williams and Hawkings’ equation (FW–H) 1 is the most appropriate theoretical support for understanding the mechanisms involved in the generation of aerodynamic noise from bodies in complex motion. With a view toward application to helicopter rotors and propellers, the complex equation is successfully solved by Farassat 2,3 and Farassat and Succi. 4 The solving method is called the retarded time approach.…”

Section: Introductionmentioning

confidence: 99%

The incomplete reception error in acoustic analogy integral with source time domain algorithm

2019

International Journal of Aeroacoustics

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There are two algorithms to solve the retarded time equation in the acoustic analogy. One is the classic retarded time method, and the other is the source time domain algorithm or the advanced time approach. The latter is more effective and simple than the former. However, difficulties may arise in the reconstruction of the acoustic signal in the observer time domain. The signal interpolation in every observer time step and a completeness check at the end are necessary for the reconstruction. In addition, two error regions which cannot to be ignored in frequency domain are generated by the latter. They are called the incomplete reception error. It is the main purpose of present work to analyze the formation process and characteristics of the incomplete reception error. Then the analysis is tested with a simplified model and the numerical results show that there are some spurious numerical oscillations in frequency domain if the incomplete reception regions are not removed. Finally, the difference between the method of directly removing the incomplete reception regions and the standard acoustic signal post-processing method is compared. The comparison results show that the method of removing incomplete reception regions directly is better.

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Thickness noise of helicopter rotors at high tip speeds

Cited by 23 publications

References 2 publications

Application of a lattice Boltzmann method to some challenges related to micro-air vehicles

Application of a lattice Boltzmann method to some challenges related to micro-air vehicles

Aerodynamic noise radiating from the inter-coach windshield region of a high-speed train

The incomplete reception error in acoustic analogy integral with source time domain algorithm

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