Investigation On Flow Integration-Obstruction Reduction Mechanism And Heat Transfer Performance In A Serpentine Channel Of Turbine Blade

The serpentine channels in turbine blade can enhance the cooling effect by efficiently utilizing the cooling air,which is of great significance for increasing the turbine inlet temperature and then improving the engine efficiency.In this paper,the typical U-shaped channel in a blade is selected as the research object.The characteristics of flow integration-obstruction reduction and heat transfer enhancement of various turning vanes in the bend are studied by numerical and experimental methods.In addition,the sensitive parameters of structures for reducing pressure drop are extracted and combined to explore the effects between each other.Numerical methods and experimental measurements using transient liquid crystal are introduced firstly,and their accuracies are verified respectively.The flow characteristics and heat transfer of the U-shaped channels which are designed with guide vanes of seven circumferential lengths and without guide vanes are numerically investigated at Re=30000,40000,50000,60000.Typical channels among them are experimentally studied at Re=30000.The results show that,guide vanes can significantly reduce the collision loss of the coolant to the outer wall of the channel and effectively limit the size of separation bubble over the bend,change the secondary flow structure to reduce the channel pressure loss.Besides,the heat transfer of the bend is enhanced and the non-uniform distribution of heat transfer performance in bend exit region is improved.For the channels with guide vanes of 90deg,135deg and 180deg,increasing the angle is beneficial to play the role of flow integration,then the friction factor ratio of the channel decreases and heat transfer enhancement of the bend becomes more uniform.The tail extension of guide vanes further limit the development of the separation vortex,thereby significantly reducing the pressure loss.In the channels with four extension lengths(P/d=0.1,0.25,0.5,1),as the length increases,the friction factor ratio decreases firstly and then increases,while the change in thermal performance factor is completely opposite.Compared to the smooth channel,a maximum decrease of the fiction factor ratio is up to nearly 60%and a maximum increase of the overall thermal performance factor is up to 26%in the channels with guide vanes.For the eight channels in this study,the Reynolds number has little effects on the flow field and the distribution trend of heat transfer.With the Reynolds number increasing,the friction factor ratio increases while the thermal performance factor decreases.On this basis,multiple cross-combination schemes of three divider thickness(T/d=0.2,0.5,1),two bend geometries(circular turn,square turn)and three radial distance(W_r/W=0.2,0.33,0.5)of guide vane are numerically studied at Re=30000.The results show that,increasing the thickness can suppress the flow separation over the bend and reduce the pressure loss,but the overall heat transfer performance also decreases.For the two bend geometries,when the divider is thin,the friction factor ratio of the square turn is slightly higher than that of the circular turn;as the thickness increases,the difference between the two cases is increasing and the maximum is about 8%.The influence of the radial distance on the friction factor ratio is related to the divider thickness,the guide vanes with small radial distance show good performance of pressure drop reduction,which is opposite when the divider gets thicker.