Noise Source Distribution of Coaxial Subsonic Jet-Short-Cowl Nozzle

Abstract

The noise source distribution of a short-cowl coaxial jet operating at different velocity ratios is described in this work. This was motivated by an ongoing research about noise prediction of coaxial jets through Acoustic Analogy with purposes of industrial engine application. This research has been carried out between Universidade Federal de Uberlândia (UFU), Brazil and the Institute of Sound and Vibration Research (ISVR) at Southampton University, UK. The numerical approach employed is originally based on Lighthill Acoustic Analogy. This technique, although likely known, is associated with an improved energy transfer timescale , used in the turbulence two-point correlation function, in order to enhance the source model. The source model is coupled with the aerodynamic calculation of flow through turbulence quantities evaluated by using a standard k-ε turbulence modeling. The Computational Fluid Dynamics data have also been used to provide complementary information about the coaxial jet noise production mechanisms. Experimental data were used in order to corroborate the results from the current model. Good agreement has been found, showing that high and low frequency contributors to the radiated noise for low velocity ratio are aggregated in a region about seven to ten secondary diameters downstream, while at higher velocity ratios sources are continuously spread from about one up to ten secondary diameters from the jet exit.

Flow and Noise Predictions of Coaxial Jets

“…Hence, from the practical viewpoint, when the simulation time is an important factor, there is a question what is the "value for money" of LES in comparison with the fast-turn-around-time RANS methods. For example, the low cost of RANS flow solutions methods explain the popularity of low-fidelity methods for coaxial jet flow and noise calculation such as a combination of the RANS solutions and the Lighthill acoustic analogy [15] as well as a semi-analytical investigation of the hydrodynamic stability and noise generation mechanisms in CoJeN jets [16]. Furthermore, RANS solutions of the CoJeN jets were used for noise predictions based on the Goldstein generalized acoustic analogy in [18].…”