Mean Flow Field and Reynolds Stress Behavior in Coannular Jet Flow With Swirl Along a Centerbody

An experimental study was conducted of an incompressible turbulent flow which exits from two concentric annular nozzles and develops along an unconfined centerbody. The operating Reynolds number based on centerbody diameter and the axial bulk velocity of the inner stream at the nozzle exit was 8 × 10⁴. Swirl was imparted only to the inner stream, and the outer-to-inner stream mass flow rate ratio was fixed at unity. The results show that streamwise oscillations exist in the mean flow which apparently arise when vortices shed at the nozzle lip separating the two streams interact with the centerbody boundary layer. A comparison of Reynolds shear stress profiles with mean strain rates in the flow indicates that departures from local equilibrium exist in the mixing layer downstream of the nozzle exit. Local law-of-the-wall behavior is observed, however, near the centerbody surface. Analysis of the results shows that the use of conventional wall functions for the turbulence kinetic energy may not be appropriate for this flow situation, and that closure at the full Reynolds stress transport equation level is required for prediction purposes.