Numerical Simulation of the Noise Radiated by Free Hot Supersonic Twin Jets

Abstract

Numerical simulation of the noise radiated by free hot supersonic twin jets is conducted by combining different numerical tools. These are based on the one hand on a high fidelity LES (Large Eddy Simulation) computation with geometric triggering of the turbulence in the nozzle convergents and on the other hand on the use of a CAA code, coupled with the CFD code, to properly propagate at a lower cost the high level acoustic waves from the jet near field towards the far field microphones. This methodology has demonstrated its benefits by producing very satisfactory results. Numerical velocity profiles are shown in very good agreement with the experimental measurements for several diameters downstream of the nozzle outlets. These results show that marked interactions between the two jets only occurs several diameters after the nozzle outlets. Regarding acoustics, the results are very encouraging. Considering the far field OASPL, the numerical vs. experimental deviation ranges from 0 to 3 dB. Higher levels in the azimuths perpendicular to the two jets with respect to the levels in the azimuths coplanar to the two jets are well recovered by the computation. These higher levels do not exactly reach the theoretical addition of two single jets noise, which suggests that acoustics source efficiency is reduced by interaction effects while lower levels in the coplanar plane traduce a probable masking effect.

Mean Flow and Linear Stability Analysis of Twin Supersonic Jets

“…Figure 9 illustrates the comparison between the actual and tailored RANS twin-jet mean flows and the PIV mean flow, obtained by averaging 500 instantaneous PIV velocity fields. The uncertainty of the PIV measurements is estimated to be ±3.6 m/s, yielding the error bars included in the figure . A good overall agreement is obtained between the RANS solutions and the experimental measurements, with discrepancies that are of the same magnitude as prior comparisons reported in literature based on LES calculations [51]. The best agreement is observed close to the nozzle exit plane.…”