Heat Transfer in Counterswirled Coaxial Jet Mixing

Convective heat transfer data are presented for the mixing of two counterswirled coaxial jets conŽ ned by a constant-diameter tube. The inner jet Reynolds number was 3 10, its swirl number was 1, and its diameter was approximately twice the annular gap dimension. Annular jet swirl numbers varied from 0 to 1.2. Annular  ow rates were characterized by a ratio of annular-to-inner jet axial momentum (denoted by MFR), which was varied from 0 to 8.2. Plots of local Nusselt numbers show minimums and maximums corresponding to the separation and reattachment points associated with wall-bounded recirculation cells. Local heat transfer coefŽ cients were found to be a strong function of streamwise position and annular swirl number at low values of MFR, yet at high values of MFR, there is minimal streamwise variation in heat transfer coefŽ cient as the mean  ow largely dictates heat transfer rates. The product of MFR and annular swirl number is shown to be a key parameter in describing heat transfer enhancement downstream of wall-bounded recirculation cells. Several quantitative results should be useful to gas turbine combustor design efforts.