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

For the development of a new prediction method for the noise from subsonic single-stream jets, a model-scale experiment was conducted. The measured spectra were normalized with the concept of one velocity exponent and two velocity exponents. When the spectra were normalized with one velocity exponent, at aft angles the normalized spectra are collapsed perfectly if the Strouhal number is greater than 0.5, but a noticeable scatter of spectra is observed if the Strouhal number is less than 0.5. The scatter observed in the results of one velocity exponent at the Strouhal number smaller than 0.5 disappeared in the results of two velocity exponents. A new empirical method for the prediction of noise from single-stream jets is proposed based on the spectra normalized with two velocity exponents. The velocity component of the low Strouhal number region is used to scale the normalized large-scale spectra and the velocity component of the high Strouhal number region is used to scale the normalized fine-scale spectra. It is observed that the predicted spectrum is in good agreement with the model-scale data. It can be concluded that the new concept of two velocity exponents provides good prediction capability of noise from subsonic single-stream jets.