Abstract
The cooling technique on the turbine blade is a well-known problem in design and operation of turbomachines. Heat transfer in rotating passages has attracted much attention of researchers because of their wide application in a variety of rotary machinery such as aircraft, industrial and military. To increase the thermal efficiency, the turbine inlet temperature must be increased. The increased high temperature may cause the material degradation and therefore shortens the turbine blade life. Consequently, the cooling capacity of the turbine should be enhanced to meet the requirement of high inlet temperature. Similarly, the cooling of conductors of electrical machinery should be also improved to reduce the machine size and prolong the machine life.Due to the strong interaction among the centrifugal, coriolis, and viscous forces of the coolant air flow in rotating channels, the flow field becomes more complex than that for non-rotating ones. In a heated radially rotating channel, one pair or multi-pairs of vortices may appear in the flow field depending on the flow and thermal parameters. Therefore the friction factor and the Nusselt number may be increased simultaneously. Besides, rotation may delay the laminar-turbulent flow transition and the centrifugal buoyancy may also effect the heat transfer. The main governing parameters are the Prandtl number, the Reynolds number for forced convection, the rotation number for the coriolis force induced cross stream secondary flow and the Grashof number for natural convection.The internal cooling has been widely used for cooling elements exposed to high temperature and high heat flux environments because of its advantages in effective removal of locally concentrated heat and easy adjustment to the where cooling is needed. To simulate the operation conditions of a real gas turbine, the present study kept the parameters in the test rig approximately the same as those in a real engine, the air in the present serpentine channel was pressurized to increase the air density for making up the low rotational speed in the experiment. Before entering the rotating ducts, the air was also cooled to gain a high density ratio of approximately 0.3 in the ducts. This high density ratio will give a similar order of magnitude of Grashof number in a real operation condition. The ranges of parameters in the present test rig and an aircraft engine are compared. The local heat transfer rate for radially rotating serpentine channels with smooth and rib turbulators walls are presented and compared with that in the existing literature.