Direct computation of the noise generated by a hot coaxial jet

A coaxial jet originating from parallel coplanar pipe nozzles is computed by a compress-ible Large Eddy Simulation (LES) of 1,800 CPU hours on a Nec SX5, using low-dissipation and low-dispersion numerical schemes in order to determine its generated noise. The jet streams are at high velocities, the primary stream is heated, and the Reynolds number based on the primary velocity and the secondary diameter is around 106. High levels of turbulence intensity are also specified at the nozzle exit. The jet aerodynamic develop-ment and the near pressure field obtained directly by the LES are presented. The far-field noise is calculated by solving the linear acoustic equations, from the unsteady LES data on cylindrical surfaces surrounding the jet. A good agreement is observed with corresponding noise measurements carried out during the EU CoJeN project in terms of directivity, levels and narrow-band spectra. Some unexpected peaks are however noticed in the simulation spectra, and they are attributed to the development of a Von Karman alley within the inner mixing layer. I