Jet mixing noise from fine-scale turbulence

It is known that turbulent mixing noise from high-speed jets consists of tw o components. They are the noise from large turbulent structures in the for m of Mach wave radiation and the less directional fine-scale turbulence noi se. The Mach wave radiation dominates in the downstream direction. The fine -scale turbulence noise dominates in the sideline and upstream directions. A semiempirical theory is developed for the prediction of the spectrum, int ensity, and directivity of the fine-scale turbulence noise. The prediction method is self-contained, The turbulence information is supplied by the k-e psilon turbulence model. The theory contains three empirical constants beyo nd those of the k-epsilon model. These constants are determined by best fit of the calculated noise spectra to experimental measurements. Extensive co mparisons between calculated and measured noise spectra over a wide range o f directions of radiation,jet velocities, and temperatures have been carrie d out. Excellent agreements are found. It is believed that the present theo ry offers significant improvements over current empirical or semiempirical jet noise prediction methods in use. There is no first principle jet noise theory at the present time.