Abstract: Based on the experimental data of swirling impinging jet from published literature, a numerical simulation method with RNG-k-ε turbulence model was developed to accurately simulate heat transfer characteristics of swirling impinging jets. Three types of inserts, screw rod, twisted tape and guide vane, were used to produce the swirl flow. Swirling impinging jets issuing from the nozzles of these inserts were numerically studied. The effect of jet Reynolds number on swirling number at the exit of the nozzles was evaluated and the effect of swirl number on heat transfer of the swirling impinging jets was analyzed. Numerical results show that the large deviation of swirl number occurs as jet Reynolds number is not considered. The swirl number of the swirling jets by the inserts with medium helix angles of 30° and 45° is very sensitive to changes in jet Reynolds number. Different patterns of red spot with high heat transfer rates are shown on the target surface by swirling impinging jet issuing from the nozzles. Shapes and sizes of red spots are related to swirl number of the swirl jets. The peak of Nussle number is increased and the uniformity of heat transfer is enhanced as the swirl number increases. Heat transfer characteristics of the swirling jets depend on the combined effect of jet Reynolds number and swirl number of the jets. The optimum swirl generator is the type of insert with screw rod. Comparing to the other two swirl generators of the inserts with twisted tape and guide vane, the highest heat transfer coefficient with the best uniformity on the target surface by this swirl generator can be achieved under the same working condition.

Key words: thermal engineering, swirling impinging jets, swirl number, heat transfer enhancement, uniformity of heat transfer