Further Steps in LES-Based Noise Prediction for Complex Jets

The paper presents the status of a CFD/CAA numerical system developed by this team starting in 2001. The aim is to predict the noise from jets of airliner engines with an accuracy of 2-3 dB over a meaningful range of frequencies, while having no empiricism and a general-geometry capability. The first part of the paper outlines the system itself and some results of its testing (a full-length description is given in a recent two-part paper ), and the second part presents the latest developments and achievements. These include: an accurate algorithm for shock capturing in LES based on local automatic activation of flux-limiters; a two-step RANS-LES approach to complex nozzles; and a set of simulations of cold and heated jets from round and beveled single nozzles, sonic jets with shocks, jets from dual nozzles (co-planar and staggered, in still air and in co-flowing flow), dual nozzles with fanflow deflecting vanes, and chevron nozzles. Although all the simulations were carried out on PC clusters with a maximum of six processors and on rather modest grids (2-4 million nodes), in most cases the system is close to the 2-3 dB target accuracy both in terms of directivity and spectrum, albeit limited in terms of frequency (to a diameter Strouhal number that ranges from 2 to 4 depending on the grid used and flow regime). The overall message of the paper is that available CFD/CAA numerical and physical models, if properly combined, are capable of predicting the noise of rather complex jets with quite affordable computational resources and already today can be helpful in a rapid low-cost analysis of different noise-reduction concepts.

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