VISUALIZATION OF NEAR-FIELD TURBULENCE IN BUOYANT JET BY COMBINED LIF PIV MEASUREMENT

摘要

The flow structure of buoyant jet in the near field is studied by flow visualization and simultaneous measurement of temperature and velocity field using combined LIF PIV. The flow visualization study shows that the buoyant jet is unstable to the buoyancy forces, which promote the laminar to turbulent transition of the buoyant jet. The turbulence is found in the near field of the buoyant jet by the generation of buoyancy-induced flow along the nozzle surface, which is correlated with the source Froude number and the Reynolds number. With a decrease in source Froude number, the flow becomes turbulent due to the formation of convective flow pattern inside the nozzle. The instantaneous flow structure and the statistical characteristics of near-field turbulence are investigated by measuring simultaneously the temperature and velocity field in the buoyant jet. The turbulence intensities and the turbulent heat fluxes show their peaks in the near field, which indicates the presence of convective flow-pattern inside the nozzle. These results indicate that the near-field turbulence of the buoyant jet is promoted by the convective motion of the flow inside the nozzle due to the buoyancy-induced flow along the nozzle surface.