Intensification of Heat Transfer in an Impinging Jet Using Turbulent Superstructures

An experimental study of the effect of spatially localized super-large-scale motion structures, propagating in a laminar gas impinging jet, on the dynamics and heat transfer was carried out. A hot-wire anemometer, a high-speed 2D PIV with a frequency of 7 kHz and gradient heat flux sensors were used as equipment. Air and carbon dioxide used as working gases. Puff-type superstructures with a longitudinal size of up to 20-30 nozzle diameters formed in a long pipe in a laminar-turbulent transition regime. These structures have a complex internal topology. Jet containing superstructures impinging on an obstacle leads to deforming of the flow near the surface and a decrease in heat transfer at the stagnation point. Data are obtained on local heat transfer in the region of the flow stagnation point at large distances to the obstacle (h/d = 20) in the Reynolds number range of 250-10000. It is shown that a laminar flow in a jet source corresponds to a more localized heat flux compared to the case of a turbulent regime in the source. The maximum heat transfer is achieved not for the Poiseuille profile in the channel, but in the case of a transitional regime with a small percentage of turbulent vortex structures