Investigations On Flow And Heat Transfer Characteristics Of Internal Cooling For Turbine Blade In Rotating Condition

With the development of high-efficiency gas turbine technology,the temperature standard of turbine inlet gas is continuously increasing.In the case that the hightemperature resistant material is not sufficient to withstand the gas temperature,only effective thermal protection measures can meet the design requirements.Typical turbine blade cooling structures contain external film cooling and internal turbulent flow cooling,impingement cooling,etc.Modern turbine blades often combine a variety of structures to achieve composite cooling.In addition,turbine blades are exposed to high temperatures and are working in a high-speed environment.In an internal cooling design scheme,the influence of additional forces such as Coriolis forces on the heat transfer must be considered.This dissertation focuses on the research of internal cooling of turbine blades in a rotating state.The numerical simulation method is employed to study the flow and heat transfer mechanisms of three typical internal cooling structures under rotating conditions,which are ribbed channels,impinging jets and pin-fin cooling.An internal cooling design that promotes internal cooling performance and improves heat transfer uniformity is proposed.In this paper,the internal heat transfer of a rotating channel with an aspect ratio of 0.5 is studied,and the angle between the plane of symmetry of the leading and trailing edge and the rotation axis is 45°.It is found that by the effect of the Coriolis force,the opposite heat transfer result will be found in the the continuous rib cases which have the same inclination angle but with different directions.When the component force of Coriolis force along the rib direction is same as the the rib direction,the vortex generated by the Coriolis force can effectively promote the vortex induced by this oblique rib scheme and make the heat transfer on leading side recuperative to the level that is comparable to trailing side.On the other hand,the superimposed effect of Coriolis force and the ribs diminish the heat transfer on the leading and trailing sides the component force of Coriolis force along the rib direction is opposite to the the rib direction.In the study of the discrete rib scheme,it was found that the appropriate discrete rib scheme can significantly enhance the heat transfer on the inner-half-front wall.When the stremwise gap between the ribs increases,the heat transfer performance gradually decreases;When the angle of the inner-half ribs increases from 30° to 90°,the flow resistance in the channel and the heat transfer on the leading edge surface witness a increase before decrease;The increase of the spanwise gap leads to a decrease in both flow resistance and heat transfer.In this paper,it is found that the circumferential Coriolis force generated by the rotation effect drives the radial crossflow toward the trailing side,so that the target surface heat exchange is gradually reduced;The radial and circumferential direction of the jet orifice is an effective parameter to offset the effects of the radial crossflow and the circumferential Coriolis force,which contributes to the improvement of the heat transfer uniformity but does not obviously help the heat transfer enhancement;It is beneficial to modify the shape of the jet hole to a racetrack shape,which helps offset the radial crossflow and promote the jet to penetrate the crossflow to improve the impingement effect on the target surface;The use of Double Swirling Chamber(DSC)can significantly enhance the heat transfer on the target surface,and the area of the high heat transfer area is enlarged due to the vortex formed in the channel which effectively counteracts the disadvantage of Coriolis force.In this paper,the pin-fin cooling in the rotating trailing edge channel is studied.It is found that the inclined pin-fins can increase the secondary flow intensity at the wake of pin-fins,and improve the mixing between the heated gas in the boundary layer and the low temperature core gas,and the thermal resistance increase caused by over development of the thermal boundary layer is prevented.Choosing a proper oblique direction could offset the adverse effects of Coriolis force.The use of the cylindrical convex scheme also increases the secondary flow intensity in the wake region.The study of the circular truncated cone scheme shows that the obtuse-angle at the root of the cone enhances the horseshoe eddy which enhances the local heat transfer.Therefore,it is appropriate to arrange the obtuse-angle side on the suction side,on which the heat transfer is suppressed by Coriolis force,to uniformly increase the heat transfer of the two side walls.Finally,the cooling structure units in each part of the study are applied to a typical turbine rotor blade and the 3D aerodynamic-thermal coupled calculation is performed.In general,the distribution of heat transfer in the blade obeys the rule in each basic unit: the heat transfer in discrete rib scheme with dimensionless streamwise rib gap m/P = 0.2 is higher than the corresponding continuous rib scheme;The jet path in DSC channel is shorter than that in semicircular channel,and the high velocity area of the cross flow is far away from the target surface.Besides that,the heat transfer on pressure side shows a significant improvement,to some extent the adverse effect of Coriolis force is counteracted;In the trailing edge,only from the view of enhancing the heat transfer,the performance of the inclined cylindrical convex scheme is the best.