Abstract
Developing high-performance cooling technologies for removing excess thermal stress from rotating components of turbomachinery is becoming of great significance for engineers because of its potential applications in industry. To improve the thermodynamic efficiency and to reduce the specific fuel consumption for the compact design of advanced gas turbine engines, it is necessary to increase the turbine entry temperature. However, high operating temperature environment might cause material degradation on rotating components and excess ohm loss in electrical conductor. Accordingly, we must find a effective cooling method to protect the blade from direct impact of high temperature gas, and film cooling is one of these useful cooling methodologies.In the experiment, one used a wake generator for simulating turbine stator, and a rotating cylinder fore turbine blade. Furthermore, one utilized cold air-hot cylinder in the experiment instead of hot air-cold blade in a real engine. The three major objectives of the present study are : To investigate the effect of wake generator on the heat transfer of a stationary cylinder; to study the effect of unsteady wake on the heat transfer of a rotating cylinder; to determine the heat transfer coefficient distribution on a rotating test cylinder with film cooling. The dominant parameters of this experiments are the main-stream Reynolds number (Re); turbulence intensity (Tu); the rotation number (Ro); injected air Reynolds number (Red); Blowing ratio (B); and the centrifugal-buoyancy. Experimental study was conducted to investigate the heat transfer characteristic, with varying the main-stream Re; the secondary flow Red; the strength of unsteady wake; the rotational speed of rotor and the heat flux supplied on the cylinder surface.For fully understanding of the heat transfer effect on rotating flow field, a wind tunnel with a rotating rotor was built to the heat transfer study on the rotating cylinder with or without film cooling. The procedure of this experiment in the following steps: At first, adjusting the various Reynolds number to measure the heat transfer and turbulence intensity distribution with different geometric location of rod of wake generator. Subsequently, for simulating the thermal behavior of turbine blade, the heat transfer on rotating cylinder was carried out to determine the rotational effect with or without wake generator. Finally, to understand the effect of film cooling, one designed the test cylinder with film holes were inclined outwards at an injection angle of 35o, and the secondary air was injected though four rows of inclined holes locating at ±15o and ±40o from the stagnation line.In general, the results display that the higher wake passing frequency produces more frequent instantaneous velocity fluctuations, more broad velocity profiles, and more stronger degree of turbulence intensity created by the upstream wake generator to enhance the heat transfer. Because of the phenomenon of wake superimposition by neighboring rod, the wake interaction is more violent and complex in dense configuration of the wake generator. The combined effects of Coriolis force and unsteady wake improve the heat transfer coefficient due to the mixing behavior of flow conditions. It is evident that an increase in blowing ratio causes larger interactions between injected air and free-stream flow, and produces an augmentation in the turbulence at the exit of the film holes to enhance the heat transfer.