Simulation of Subsonic Turbulent Nozzle Jet Flow and Its Near-Field Sound

A direct numerical simulation framework is developed and validated for investigating a jet-flow configuration in which a short cylindrical nozzle and the acoustic near field are included in the simulation domain. The nozzle flow is modeled by a potential flow core and a developing turbulent wall boundary layer, which is numerically resolved. The setup allows to create well-controlled physical nozzle-exit flow conditions and to examine their impact on near-nozzle flow dynamics, jet-flow development, and the near-field sound. Turbulence at the nozzle inflow is generated by the synthetic-eddy method using flat-plate boundary-layer direct numerical simulation data and imposed softly in a sponge layer. The jet Mach number in the present investigation is M alpha = 0.9, the diameter-based jet Reynolds number is Re-D = 18,100, and the maximum axial rms fluctuations attain 13% at the nozzle exit. The accuracy of the numerical results is checked by varying grid resolution and computational domain size. The rapid flow development in the changeover region from wall turbulence to the turbulent free shear layer within about one nozzle diameter is documented in detail. Near-field sound pressure levels compare favorably with experimental reference data obtained at the much higher Reynolds number of 780,000. This agreement is essentially attributed to a compensation of the effects of Reynolds number and turbulence level on the noise for which an empirical scaling is derived from published data. A brief comparison is also made to the jet sound field arising from a laminar nozzle-exit boundary layer.