Swirling hot air is a promising heat transfer enhancement technology for anti-icing applications in aircrafts, where the swirling flow is accompanied by pretty high turbulence and a quite thin boundary layer. It is of interest to investigate the compound heat transfer characteristics of the swirling air configuration combined with surface structures on the internal wall. This paper carries out a series of numerical computations to obtain the Nusselt number and pressure loss data in such a swirling air heat transfer system with four kinds of surface structures (trenches, ribs, dimples and bulges) on the wall and with different tangential inlet jets placed along the tube. At a tube Reynolds number from 10,000 to 50,000, the results show that the surface dimples and bulges are conducive to improving the Nusselt number, but the surface trenches and ribs show a Nusselt number deterioration relative to the smooth swirl tube. Among the four investigated surface structures, the surface bulges perform best, which can enhance the Nusselt number by up to 15.0%, increase the total heat transfer quantity by up to 17.3% and reduce the hot air pressure loss by up to 15.6%. Furthermore, the circumferential velocity distribution and swirl number are introduced to describe the flow fields. The surface trenches and ribs lead to less of a reduction in the circumferential velocity and swirl intensity, while the surface dimples and bulges could significantly suppress the in-tube swirl intensity.

The tangential jet-induced swirling flow is a highly efficient technology for enhancing heat transfer. This paper explores the application of swirling flow of an airfoil/aero-engine in a hot air anti-icing chamber, aiming to improve the anti-icing performance and achieve a more uniform temperature on the surface. A series of numerical computations adopting the SST k − ω turbulent model was carried out to obtain the internal flow and heat transfer characteristics, as well as the surface temperature distributions, considering water evaporation and solid heat conduction. Three jet arrangements, including impingement jets, offset jets, and swirl jets, were studied and compared, which evidently showed that the swirling effect was helpful to elevate the internal heat transfer. Compared to the impingement jets at the Reynolds number of 40,000, the Nusselt number with the offset jets is increased by 19.5%, while the corresponding Nusselt number of the swirl jets is augmented by 44.3%. The swirling flow significantly elevates the swirl number within the internal chamber, intensifying the vortex strength near the wall and increasing the circumferential velocity, which also results in an augmentation of internal pressure loss. By adopting the swirling internal flow, the temperature distribution on the anti-icing surface is more uniform and is increased by up to about 4.1 K in the leading edge when the internal-to-external temperature difference is 80 K. Simultaneously, the heat absorption of water evaporation and the matches between the internal heat transfer and external icing load are of particular importance to determine the anti-icing performance, and this has been discussed in this paper.