A new scaling for turbulent, twin round jets

The flow field due to a pair of identical uniform round jets emerging from ports in a plane wall depend on the jet velocity U, port diameter d, and port separation S. At Reynolds numbers Ud/ν that are O(1000) or larger, these jets will breakdown into turbulence. The jets grow downstream and merge to have an elliptical cross-section that will develop into a single circular jet downstream. From LES of such configurations at Re of 25000, and 230000 of two experiments and 2 < S < 8, we observed the mean axial velocity to rise to a peak U₀ at distance L₀ from the inflow plane wall, and thereafter to fall off smoothly. U₀ decreases and L₀ increases with S. For all nozzle spacings, a similar development was observed: U_c/U₀ is a function of axial distance x/L₀ only, and is essentially independent of jet spacing S/d, and Re. Since U₀ and L₀ depend linearly on inflow plane parameters, near-fields of all twin round jets can be predicted from one solution.