Research Of Guide Blade Impingement Cooling Structure Design And Heat Transfer Characteristics

It is important to improve aero turbine engine thermal efficiency and thrust-to-weightratio by increasing turbine inlet temperature, which also brings a series of serious problemsfor the normal operation of the engine. Now the inlet temperature increases much faster thanthe development of the temperature resistance of the blade material. The efficient coolingtechnology and the thermal protective measures must be taken into consideration to ensure theturbine blades working safely and reliably at a high temperature, in addition to continuing toimprove high temperature materials resistance. The precise heat transfer analysis of turbineblades is essential to improve the cooling efficiency and extend the operating life of the blades.With the incessant maturity of computational fluid dynamics, the conjugate heat transfermethodology has gradually become a prevailing tools in the design process of aero turbineengine. With the help of numerical simulation of conjugate heat transfer methodology, theimpingement cooling structure which is focused on the small size high pressure turbine guideblade, has been designed, and then the three-dimensional aerodynamics analysis and the heattransfer coupled analysis of this structure have been completed, which can provide referencefor the cooling structure design of the actual engine guide blades.The boundary layer transition flow is widespread in turbo machinery, and it directlyaffects the heat transfer process of the turbine blade near the wall. The problem of how toaccurately predict the boundary layer transition flow was firstly studied, then the Transitionk-kl-model was selected to simulate boundary layer transition on the flat plate, and then theflow state before and after the boundary layer transition was in-depth studied. The resultsshow that: Transition k-kl-model has a good performance on the plate bypass transitionwith or without pressure gradient, and the pressure gradient has influence to the boundarylayer transition flow. The favor pressure gradient can stabilize boundary layer flow, postponethe onset location of transition. Otherwise the adverse pressure gradient can induce theboundary layer separation, and pre-act transition occurs.The conjugate heat transfer methodology has been employed to NASA-MarkII turbineguide vane in this dissertation. By discussing the calculation characteristics of the turbulencemodel and the ability to identifying transitional flows, the influence of the blade surfaceboundary layer flow on turbine blade heat transfer was analyzed and corrected. Compared to all the other turbulence models, the transition model can predict the separation transition stateof the boundary layer more accurately. As the transition model uses laminar kinetic energy todescribe the development of the disturbance, so this model can avoid the errors introduced bythe empirical formula, which is related with the inflow turbulence intensity. This modelintroduces the "split system" to describe the interaction between the laminar and the turbulentfluctuation, besides Tollmien-Schlichting wave is added into the bypass transition and thenatural transition source term. The result of temperature calculation behind the strong shock ismore consistent with the experimental value, compared to that of the common models withthe intermittent transition factor. Finally, the mutative turbulent Prandtl number method isadded to correct the thermal eddy diffusion coefficient term of the transition model, which canguarantee the smooth transition of the turbulent Prandtl number from the boundary layer intothe mainstream area, and furthermore, the heat transfer coefficient is closer to the actualexperiment value.The above-mentioned transition model was selected to carry out the numericalsimulation of the single-hole cooling. By comparing the analytical solution ofthree-dimensional impingement cooling with the theoretical and experimental solutions, thegrid independence was calculated to verify the accuracy of the numerical results. Thecorresponding law of the single-hole impingement cooling has a great help in understandingthe impact of the flow structure and the cooling mechanism. The identified numericalmethods were used to analyze the influence of the different geometrical and physicalparameters on the array jet impingement cooling heat transfer and flow. Compared with theexperimental correlations, the laws of the plat array jet heat transfer was determined toprovide the basis for the design of the next deflector impingement cooling holes.With aid of the numerical simulation technology, the detail investigation of the enginerealistic operating conditions has a great significance in aero turbine engine design process.Lab environment can not totally realize the realistic operating conditions of the aero turbineengine. Then the guide blade impingement cooling structure was designed. Firstly the leaftemperature distribution with no-cooling is calculated, and it is found that the maximumtemperature of the leaves exists at the central surface of the leading edge. The air-cooledstructure was designed to complete the analysis of the three-dimensional aerodynamic andheat transfer coupled, to achieve a goal of enhancing the cooling effect and reducing the performance requirements of the material under a condition of the fixed cooling gas flow rate.When the number of holes and diameter along blade height satisfy the relationship（4n-1）D=h,the temperature can meet the cooling requirements. When each column of the jet hole X/d=5~7in the axial direction to the principle of simple structure, it can meet the coolingrequirements of the leaves chord region. In order to meet the cooling requirements of theleading edge, there shall be arranged in two cooling holes at least. In the small impact spacing,the impact spacing has little effect on the variation of the average temperature of the inner andouter surfaces, the maximum temperature will lower and the minimum temperature will riserwith smaller spacing. Just from the view of the cooling effect, the use of small spacing isappropriate. Compared with the cutout exhaust structure, the split seam structure of thetrailing edge can improve the cooling effect of the trailing edge and reduce the total pressureloss effectively.Finally, the thermal stress was analyzed with temperature load and impact forceconditions on the blade by applying the thermoplastic coupling, and the influence of gridnumber was discussed. The results show that: the total maximum deformation exists in theblade central location with lower structural strength. The maximum thermal stress exists inthe blade root and the tip position, and it is due to the end wall which is given the constraintsof a fixed support. The deformation will be delivered to the two end walls producingcompression effect due to thermal stress generated in the guide blade.