Investigation of Variable-Diffusion Turbulence Model Correction for Round Jets

A Reynolds -Averaged Navier -Stokes ( RANS) correction is described to account for a key effect of acoustic interaction near the end of the potential core for axisymmetric jets. Specifically, the Variable -Diffusion (Var -D) co rrection is formulated to mimic the effect of increased shear layer instability/motion near the end of the potential core by adjusting the local diffusion of k and . The proposed Var -D correction is initially evaluated for an unheated axisymmetric jet wi th a perfectly expanded jet Mach number of 0.5. Results for centerline velocity distribution and turbulent kinetic energy contours using commonly employed turbulence models (i.e. SST and k-) and k- with the Var -D correction are compared. Substantial im provement for prediction of potential core length, centerline velocity decay, and k field is demonstrated with the Var -D correction. The sensitivity of the proposed model to the closure coefficients associated with the correction is also examined using th is cold subsonic jet case. Similar turbulence model performance comparisons are made for three other jets to evaluate the sensitivity of the correction to increased jet exhaust compressibility and heated jet flow conditions. The effect of the improved me an and turbulence field predictions obtained using the Var -D correction on farfield noise prediction is also evaluated using the JeNo acoustic analogy code, and shown to be negligible. Although the approach holds promise, the applicability of the Var -D co rrection is currently limited to round jets.