Empirical prediction of noise from subsonic dual-stream jets using the concept of two components of single-stream jet noise

A new prediction method for the noise from subsonic dual-stream jets is proposed. In the predictions previously developed, it has been widely accepted that there are four different noise sources in dual-stream jets: (1) the inner shear layer between the primary and secondary streams; (2) the outer shear layer between the secondary and ambient streams; (3) the fully mixed jet well downstream of the end of the primary potential core; and (4) a source associated with an interaction region. However, it was difficult to identify the boundary of the region where a specific source is dominant. Therefore, a variety of filtering functions, which are very tricky, were used to manipulate double-bookkept or triple-bookkept source regions in other prediction approaches. In the new prediction method, it is assumed that each of four sources has two sub-components: fine-scale and large-scale components, which was motivated from the prediction of supersonic jet noise proposed by C.K.W. Tam. Potentially there could be eight sub-components in total. However, it is found that only three components are enough to predict the noise from dual-stream jets with the minimal use of additional filter functions. The new method shows good prediction results for a variety of nozzle operating conditions.