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_j, port diameter d and port separation S. At Reynolds numbers U_jd/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 25 000, and 230 000 of two experiments, in close quantitative agreement, over the range 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: Scaled, configuration centerline velocity U_c/U₀ is a function of distance x/L₀ only, and is essentially independent of S/d and Re. Since U₀ and L₀ linearly on inflow plane parameters, near-fields of all twin round jets can be predicted from one solution.