Investigation On Conjugate Heat Transfer Of Combined Cooling And Dimple Cooling

Turbine inlet temperature is one of the most important factors affecting gas turbine performance.The development of turbine cooling technology lays a foundation for further increase of turbine inlet temperature.Currently,cooling schemes including external cooling(film cooling,effusion cooling)and internal cooling(convection cooling,impingement cooling,etc.)have been applied in the turbine turbine blades.For turbine blades in real engine,multiple cooling units are combined to meet the challenge of high temperature and high thermal load.The film and impingement combined cooling scheme is widely used to the region of leading edge,middle chord,endwall and other positions of the blade.Conjugate heat transfer between multiple cooling units is not the superposition of all simple cooling units.In this paper,the internal flow and heat transfer characteristics of combined cooling are analyzed by using the conjugate heat transfer numerical method.In addition,a concave vortex generator is introduced into the composite structure.The cooling characteristics of various combined cooling schemes are summarized,and the overall cooling effectiveness is measured in the conjugate heat transfer experiments.The influences imposed by the factors of geometrics,flow conditions and thermal conductivity on the cooling efficiency of combined structures were studied.The results show that film hole exit shapes and the diameter of impingement holes play an important roles in the overall cooling performance for the composite structure.But the impact of impingement spacing is slight.Among all the cooling schemes presented in this paper,fan-shaped film holes combined impingement cooling own the best cooling performance.The flow coefficients studied in this paper includes blowing ratio,impingement Reynolds number and mass flow ratio.The blowing ratio influences both the cooling performance of the impinging cooling and the film cooling.With the increase of the blowing ratio,the local convective heat transfer coefficient at the target surface for impinging cooling improves,but the coolant ejection from the film cooling hole trends to lift off and leads to a poor coolant coverage over the wall surface on the hot gas side.The improvement amplitude of the laterally-averaged overall cooling effectiveness is reduced with the increase of the blowing ratio.There is a maximum overall cooling effectiveness for a specific cooling scheme.For a specific combine cooling scheme and a given BR,the Biot number(i.e.the thermal conductivity of the film cooling plate in present study)decides the contribution proportion of impingement cooling and film cooling to the overall cooling effectiveness.The cooling potential of the coolant should be reasonably allocated to the internal and the external cooling to achieve the optimal overall cooling effectiveness.For the dimple combined with film and impingement cooling scheme,the effects of dimple layout,depth to diameter ratio and impingement Reynolds number on overall cooling effectiveness were studied.The results show that under the condition of high impingement Reynolds number,the staggered arrangement of dimple and impingement holes trend to improve the effect of internal convection heat transfer,which results in an improvement of the overall cooling effectiveness.The cooling effectiveness of shallow dimple is higher for that of other different depth-diameter ratio of dimple.The conjugate heat transfer experiment was performed and an image acquisition and processing system based on TSP technique was built for overall cooling effectiveness measurement.The numerical results are verified by experimental data.