Influence of crossflow-induced swirl and impingement on heat transfer in an internal coolant passage of a turbine airfoil

Detailed heat transfer distributions are presented inside a two-pass coolan t channel with crossflow-induced swirl and impingement. The impingement and passage crossflow are generated from one coolant passage to the adjoining coolant passage through a series of straight or angled holes along the divi ding wall. The holes provide for the flow turning from one passage to anoth er typically achieved in a conventional design by a 180-deg U-bend. The hol es direct the flow laterally from one passage to another and generate diffe rent secondary flow patterns in the second pass. These secondary flows prod uce impingement and swirl and lead to higher heat transfer enhancement. Thr ee different lateral hole configurations are tested for three Reynolds numb ers (Re=10,000, 25,000, 50,000). The configurations were varied by angle of delivery and location on the divider wall. A transient liquid crystal tech nique is used to measure the detailed heat transfer coefficient distributio ns inside the passages. Results with the new crossflow feed system are comp ared with the results from the traditional 180-deg turn passage. Results sh ow that the crossflow feed configurations produce significantly higher Nuss elt numbers on the second pass walls without affecting the first pass heat transfer levels. The heat transfer enhancement is as high as seven to eight times greater than obtained in the second pass for a channel with a 180-de g turn. The increased measured pressure drop (rise in friction factor) caus ed by flow through the crossflow holes are compensated by the significant h eat transfer enhancement obtained by the new configuration.