E​RCOFTAC PC France

A Turbulent Jet at Mach 0.9 Impinging on a Plate

Hugo Vincent and Christophe Bogey
(Ecole Centrale de Lyon, CNRS, Universite Claude Bernard Lyon, France)

An animation of a large-eddy simulation of a turbulent jet at Mach number 0.9 and Reynolds number 105 impinging on a flat plate is presented. The periodic formation and impingement of large-scale coherent structures can be observed, in addition to fine-scale turbulent eddies. These large structures are involved in an aeroacoustic feedback loop responsible for the generation of strong tonal noise components. The simulation was performed at LMFA, Centrale Lyon, using high-order finite-difference schemes on a cylindrical grid of 640 million points to solve the full unsteady compressible Navier-Stokes equations. More than 1TB of vorticity-magnitude data are visualized using ParaView’s volume-rendering functionality.

Scientific abstract

Jets impinging on surfaces are encountered in a wide range of industrial configurations, including aircraft propulsion systems and rocket launch pads. When operating at high subsonic or supersonic Mach numbers, they can generate strong tonal noise components due to the establishment of aeroacoustic feedback loops between the nozzle and the impingement surface. These loops involve large-scale coherent flow structures and acoustic waves generated close to the plate, which propagate upstream, excite instability waves in the jet mixing layers, and subsequently trigger the formation of new coherent structures, thus closing the feedback loop.

Among the parameters influencing jet development and noise generation, the nozzle-exit conditions are known to play a major role in free jets. In particular, the thickness, shape and turbulent state of the boundary layers at the nozzle exit strongly affect the growth of instability waves, the resulting organization of coherent vortical structures, and therefore the noise produced by the jets. These effects have been extensively investigated at LMFA, Centrale Lyon, using large-eddy simulations of free jets, in which the nozzle-exit conditions can be prescribed with high accuracy, in contrast to experiments. Despite the recognized importance of nozzle-exit conditions in free jets, their influence on the flow and noise of impinging jets has not been much documented.

In this context, the sensitivity of impinging jet noise to nozzle-exit conditions was investigated during the PhD of the first author, extending previous numerical work on impinging jets by Varé & Bogey [2]. The objectives were to determine the effects of the boundary-layer thickness and turbulence levels at the nozzle exit on the frequencies and amplitudes of the tones produced by impinging jets. For that, 14 large-eddy simulations of round jets impinging on flat plates were carried out for various Mach numbers, nozzle-to-plate distances, boundary-layer thickness, and nozzle-exit turbulence levels. They were performed at Centrale Lyon by solving the full unsteady compressible Navier-Stokes equations using high-order finite-difference schemes on cylindrical grids of several hundred million points. The results indicated that the nozzle-exit conditions can strongly affect the amplitudes of the dominant tonal noise components, but not significantly their frequencies [1, 3].

The submitted movie was produced at an advanced stage of the research. It provides a global view of the flow organization and clearly shows the periodic formation of large-scale coherent structures developing in the jet mixing layers and impinging on the plate.

This work was granted access to the HPC resources of PMCS2I (Pôle de Modélisation et de Calcul en Sciences de l’Ingénieur et de l’Information) of Ecole Centrale de Lyon. The first author was supported by the FUI25 CALM-AA (CiblAge des sources par voie Logicielle et Méthodes inverses pour l’AéroAcoustique) regional project, co-financed by the European regional development fund.

List of selected recent references

[1] Vincent, H. & Bogey, C. (2024). Influence of the boundary-layer thickness on the generation of tonal noise components by subsonic impinging jets. Journal of Fluid Mechanics, 985, A26. doi:10.1017/jfm.2024.281
[2] Varé, M. & Bogey, C. (2024). Acoustic tones generated by impinging jets: Differences between laminar and highly-disturbed nozzle-exit boundary layers. International Journal of Aeroacoustics, 23(3–4), 342–362. doi:10.1177/1475472X241230647
[3] Bogey, C. & Vincent, H. (2025). Effects of boundary-layer tripping on the acoustic tones of impinging jets. Acta Acustica, 9, 70. doi:10.1051/aacus/2025059