Novel MILES computations for jet flows and noise

The influence of swirl on jet flow structure and noise is explored. A novel DES (detached eddy simulation) type procedure is tested for a jet with co-flow case. The approach uses a k–l near wall RANS (Reynolds averaged Navier–Stokes) model. Away from walls MILES (monotone-integrated large eddy simulation) is used. Blending of the RANS and MILES regions is achieved using a Hamilton–Jacobi type equation. The MILES solution content enables correct turbulence development on relatively coarse grids. The new hybrid MILES–RANS approach is validated for a plane channel flow. A good law of the wall is gained. For swirling flows, far-field noise levels are essentially calculated using the surface integral of Ffowcs Williams and Hawkings/Curl. Despite MILES use with mostly fourth-order centred differencing, jet turbulence decays excessively downstream. Streamwise vorticity introduced by swirl (unlike with chevrons) increases noise, slightly biasing it to higher frequencies. Lower swirl levels might bring more success. The hybrid MILES–RANS method appears promising. However, for the jet with co-flow case (due to the low co-flow Reynolds number) it is perhaps only very mildly tested.