Abstract:

3-D numerical simulations were presented for studying the flow structures and convective heat transfer characteristics in a cylinder tube embedded with wing-finned vortex generators. In the numerical simulation, the winglet was upstream placed at an angle of 45 to the tube wall and 1／6 of channel was selected for studying due to symmetry. The results showed that two counter-rotating longitudinal vortices were induced downstream the winglet, forming a symmetric vortex pair. The flow inner vortex pair was towards the wall while the flow outer vortex pair was backwards the wall. The longitudinal vortex could improve the magnitude of velocity in the radial direction, and the maximum value in near wall region reached 80％ of the average mainstream velocity downstream the winglet. As a result, the winglet booted the disturbance of the velocity boundary layer. The improved velocity field could make the temperature field in the tube more uniform. Compared with the smooth tube, the temperature gradient near the wall could improve approximately an order of magnitude. The flow induced by the longitudinal vortex rushed to the wall, which strengthened the convective heat transfer significantly. The maximum value of the local Nu on the wall surface could reach 50 times of the smooth tube. The improved convective heat transfer performance lead by longitudinal vortex enhanced with the Reynolds numbers increasing.

Key words: winglet, longitudinal vortex, tube, laminar flow, heat transfer enhancement