On the response of a rectangular supersonic jet to a near-field located parallel flat plate

Romain Gojon (1) , Ephraim J. Gutmark (2) , Mihai Mihaescu (1)

1 KTH - KTH Royal Institute of Technology [Stockholm]
2 UC - University of Cincinnati

In this paper, the flow and acoustic fields of a rectangular over-expanded supersonic jet interacting with a parallel plate are investigated using compressible LES. The jet exits from a converging diverging rectangular nozzle of aspect ratio 2 with a design Mach number 1.5. Four simulations with four different distances between the lower inner lip of the rectangular jet in the minor axis plane and the plate ranging from 0 to 3 equivalent diameters are performed. The geometry of the nozzle, the positions of the plate, and the exit conditions are chosen in order to match those in an experimental study conducted at the University of Cincinnati. Snapshots and mean velocity fields are first presented. A good agreement with the PIV experimental measurements is found. The overall sound pressure levels are then plotted along the minor and major axis. In a previous paper, the corresponding free jet has been found to undergo a strong flapping motion in the minor axis plane due to the screech feedback mechanism. In the present study, it is seen that the intensity of the screech feedback mechanism increases for some distances from the ground and decreases for some others, as compared to the corresponding free jet. A study of the jets shear-layers is then proposed, first by looking at two points space-time cross correlations of the axial velocity. The convection of the turbulent flow structures is thus studied. Then, two points space-time cross correlations of the pressure along the jets shear-layers are proposed and an amplification of the aeroacoustic feedback mechanism leading to screech noise is observed in the lower jet shear-layers for two cases. It is also observed that the screech feedback mechanism establishes mainly between the nozzle lips and the end of the tenth shock cell. The acoustic loading on the plate is finally studied. As pointed out in a previous study, the flapping motion of the jet at the screech frequency seems to yield to an asymmetric organization of the Mach wave radiation also at the screech frequency. Those organized Mach waves impinge on the plate, are reflected, and propagate back towards the jet, exciting the shear-layer at the screech frequency. This will amplify the screech mechanism in the lower jet shear-layer. However, this amplification happens only for some nozzle-to-plate distances. The mechanism leading to this behaviour is explained.

Mots clés: Jet noise; LES; Supersonic flow

Domaines: Autre

Romain Gojon, Ephraim J. Gutmark, Mihai Mihaescu. On the response of a rectangular supersonic jet to a near-field located parallel flat plate. 23rd AIAA/CEAS Aeroacoustics Conference, Jun 2017, Denver, United States. pp.1-17, ⟨10.2514/6.2017-3018⟩. ⟨hal-03205190⟩