Far-field noise prediction for jets using large-eddy simulation and Ffowcs Williams–Hawkings method

Abstract

Large-eddy simulations are performed for hot and cold jets with and without a flight stream. The acoustic and flight stream Mach numbers are 0.875 and 0.3, respectively. The temperature ratios for the hot and cold jets are 2.7 and 1.0, respectively. The mean flow field results are in good agreement with the measurements. The Ffowcs Williams–Hawkings equation is used to predict far-field noise. Several axisymmetric Ffowcs Williams–Hawkings surfaces at increasing radial distances are used. They show that the surfaces closer to the jet can be affected by the hydrodynamic pressure. It is important to close the Ffowcs Williams–Hawkings surfaces at the ends to account for all the acoustic signals emanating from the jet. In this work, 11 end discs are used at the downstream end of the Ffowcs Williams–Hawkings surface. It is found that the simple averaging processes to cancel hydrodynamic sound at the end discs are insufficient for slowly decaying jets. In such cases, a partially closed disc can be a better choice. To remove hydrodynamic signals, a filtering scheme for the end discs is suggested. For slowly decaying jets, this gives better results.