Buoyancy-driven transformations in a thermal striping flow field

This paper presents measurements of temperature and velocity fields in the wall-impingement region of a dual-jet thermal mixing experiment. Air jets issue from hexagonal channels at the bottom of a glass tank at atmospheric pressure to mix and impinge upon the tank lid. Jet flows were matched at Re≈10000 while mismatched in temperature either 5, 10, 20, or 40 ºC, corresponding to Richardson numbers from about 5 to 60. Temperature and velocity fields below the lid were measured with a fiber optic distributed temperature sensor and particle image velocimetry, respectively. We found the character of both the temperature and velocity fields to depend upon which jet is heated: weak gradients due to good mixing in one case and strong gradients due to poor mixing in the other. Since the jet Reynolds numbers are the same in each case, the dichotomy is due to differences in buoyancy-driven flows.