Flow and heat transfer in a ribbed channel with complex structure characters

The ribbed channels are widely used in the internal cooling structure of turbine blade. Many investigations on this kind of channel were carried on in the channel with rectangle cross section and straight inlet. Nevertheless, in mid-chord region of a real blade, the channel characters are more complex and may affect the heat transfer performance in the channel. The heat transfer investigation in a channel with 3 legs was conducted by numerical simulation. Aim to get the influence of channel structure feature to heat transfer and flow characteristics, the channel was simplified from a real turbine internal cooling channel and main structure features were kept. In order to make the velocity in the first leg close to that in the real structure, the entrance is changed to the contraction entrance. The first leg of channel section is simplified as trapezoid. The legs are connected by 2 U-turns with bend angle for imitating the bend because of the airfoil in real blade. A supplement hole in the inlet of 3rd leg was kept as same as the real channel. Some coolant was supplement to the 3rd leg. Furthermore, 3 rib arrangements (45° ribs, 135° ribs and V-shape ribs) were studied for presenting the interaction between rib arrangement and channel structure character. The results show that: 1) the shape of the inlet cross section has a continuous effect on the irregular velocity in the first leg, the velocity pattern cause by inlet may interact with the secondary flow caused by ribs and lead to different heat transfer distribution compared with the channel with uniform inlet velocity and rectangle cross section. The heat transfer performance in channel with 135° ribs is different from that in the channel with 45° ribs. 2) In the second leg, the secondary flow is generated at the inlet by the bending structure of the leg connection. This secondary flow may suppress or promote the secondary flow produced by ribs. The composed secondary flow leads to the asymmetry flow pattern in the channel and causes the different heat transfer performance in two ribbed walls. 3) In the third leg, the interaction between the flow coming from the supplement hole, the secondary flow caused by ribs and the flow coming from upstream form the complex flow structure. The different rib angle affects the position of high-velocity area. 4) The heat transfer distribution is asymmetry because of the asymmetry channel cross section and bending connecting of legs. The heat transfer performance is different between that in channel with 45° ribs and 135° ribs, whereas is same in the channel with rectangle cross section. Generally speaking, the heat transfer performance is best in the channel with V-shape ribs and is worst in the channel with 45° ribs.