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Post-doctoral position of 18 months at Institut Polytechnique de Paris: Modelling of turbulent jet and airfoil noise and simulation on unstructured grids, LadHyx & IMSIA, Palaiseau (France)

Du 1 avril 2022 au 31 octobre 2023

18 months contract
Site actualite
Ladhyx (Ecole Polytechnique) and IMSIA (ENSTA), Palaiseau (20km from Paris), France

Contact :
benjamin.cotte@ensta-paris.fr
lutz.lesshafft@ladhyx.polytechnique.fr

The objective of the present project is to develop a numerical tool for compressible flows, by use of unstructured meshes and the finite-element package FEniCS. This code will then be used to identify near-field fluctuations that optimally radiate sound, both in subsonic jets and in the flow around an airfoil. The study program is based on theoretical concepts from linear instability analysis and from aeroacoustics.

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Post-doctoral position of 18 months at Institut Polytechnique de Paris: Modelling of turbulent jet and airfoil noise and simulation on unstructured grids

Context

Turbulence in shear flows, such as jets, wakes and boundary layers, is known to contain energetic structures of high spatial and temporal coherence, which are the dominant sources of aeroacoustic sound (see Figure 1). In recent years, it has been demonstrated that these co- herent structures can be modelled as linear fluctuations around the turbulent mean flow: such modelling is theoretically well-founded, and leads to quantitatively correct results [1].

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Figure 1: A turbulent jet: near-field temperature and far-field pressure fluctuations [2]

In the framework of the PIBE ANR project (https://www.anr-pibe.com), we have experimentally characterized airfoil noise at high angles of attack in the static and dynamic regimes [3]. For a NACA 633418 airfoil, that is typically used on wind turbine blades, the radiated noise increases significantly at low frequencies when the boundary layer is separated, as it is the case above an angle of attack of 15◦ in Figure 2. It can be shown that the diffraction of turbulent structures by the trailing edge of the airfoil remains the dominant mechanism even at high angles of attack, but these turbulent structures have not been clearly identified and localized yet.

Thus the modelling of the aeroacoustic sound field associated with coherent flow structures remains an open field of study at present, for jet noise and airfoil noise configurations. An important prerequisite for such studies is an efficient numerical tool, which would allow us to resolve the short length scales of the turbulent near field as well as the long acoustic wavelengths over a sufficiently large portion of the far field.

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Figure 2: View of the dynamic stall noise experiment in the anechoic wind tunnel of the E ́cole Centrale de Lyon.

Objective

The objective of the present project is to develop a numerical tool for compressible flows, by use of unstructured meshes and the finite-element package FEniCS. This code will then be used to identify near-field fluctuations that optimally radiate sound, both in subsonic jets and in the flow around an airfoil. The study program is based on theoretical concepts from linear instability analysis and from aeroacoustics.

Practical information

• Profile: the candidate must hold a PhD degree in a field related to Fluid Mechanics.

Supervision : Lutz Lesshafft from LadHyX at Ecole Polytechnique and Benjamin Cotté from IMSIA at ENSTA Paris.

• Duration and location: funding for 18 months is provided. The work will take place at the Institut Polytechnique de Paris in Palaiseau (20 km south of Paris).

• Salary: minimum gross salary of 2700 euros per months depending on the applicant’s experience.

• To apply: send a detailed CV with a list of publications, a short cover letter and a list of references to lutz.lesshafft@ladhyx.polytechnique.fr and benjamin.cotte@ensta-paris.fr.

References

  1. [1]  Lesshafft, Semeraro, Jaunet, Cavalieri & Jordan, Resolvent-based modelling of coherent wavepackets in a turbulent jet, Physical Review Fluids, vol. 4, art. 063901, 2019.

  2. [2]  Bre`s, Jordan, Jaunet, Le Rallic, Cavalieri, Towne, Lele, Colonius & Schmidt, Importance of the nozzle-exit boundary-layer state in subsonic turbulent jets. Journal of Fluid Mechanics, vol. 851, p. 83-124.

  3. [3]  Raus, Sicard, Cotte ́, Monchaux, Jondeau, Souchotte & Roger, Experimental characterization of the noise generated by an airfoil oscillating above stall, AIAA AVIATION 2021 Forum, AIAA 2021-2291, doi:10. 2514/6.2021-2291.