DNS of fully turbulent jet flows in flight conditions including a canonical nozzle

Abstract

Direct numerical simulations are conducted of a canonical nozzle/jet conflguration. The ∞ow exiting the nozzle into a laminar co-∞ow is fully turbulent and serves as a well deflned turbulent inlet condition for the study of sound radiation from fully turbulent jets. The sound radiation from this conflguration is studied for three subsonic jet Mach numbers and varying co-∞ows. The target Reynolds number, based on jet exit centreline velocity and nozzle diameter is Rej = 7; 500 for all cases. Pressure power spectral densities (PSD) obtained from within the hydrodynamic fleld show that most of the energy is contained in the axisymmetric mode, although the PSD amplitudes of azimuthal modes with m > 0 exhibit very similar energy levels over the entire spectrum when considering locations within the jet shear layer. In the acoustic fleld, the amplitudes of the spectra at small angles with respect to the streamwise axis are considerably higher than at large angles, in particular for low frequencies. In contrast to the PSDs from the hydrodynamic fleld, the energy content in the acoustic fleld decreases rapidly for higher mode numbers. Contours of pressure in the frequency domain suggest the presence of trailing-edge noise for selected azimuthal modes and frequencies. The directivity of the overall sound pressure level flts the expected directivity behaviour of subsonic jets. An unexpected result is that the velocity scaling of mean square far-fleld pressure is found to be close to u 4 over the range of Mach numbers considered here.