This work presents a numerical investigation of the combined effects of thermal barrier coating (TBC) with mainstream turbulence intensity (Tu) on a modified vane of the real film-cooled nozzle guide vane (NGV) reported by Timko (NASA CR-168289). Using a 3D conjugate heat transfer (CHT) analysis, the NGVs with and without TBC are simulated at three Tus (Tu = 3.3%, 10% and 20%). The overall cooling effectiveness, TBC effectiveness and heat transfer coefficient are analyzed and discussed. The results indicate the following three interesting phenomena: (1) TBC on the pressure side (PS) is more effective than that on the suction side (SS) due to a fewer number of film holes on the SS; (2) for all three Tus, the variation trends of the overall cooling effectiveness are similar, and TBC plays the positive and negative roles in heat flux at the same time, and significantly increases the overall cooling effectiveness in regions cooled ineffectively by cooling air; (3) when Tu increases, the TBC effect is more significant, for example, at the highest Tu (Tu = 20%) the overall cooling effectiveness can increase as much as 24% in the film cooling ineffective regions, but near the trailing edge (TE) and the exits and downstream of film holes on the SS, this phenomenon is slight.

This paper presents a numerical investigation of the conjugate heat transfer (CHT) to calculate the steady state aerodynamic and thermal characteristics of a film cooled gas turbine vane. The commercial code ANSYS FLUENT 15.0 is applied as the numerical tool. The turbine configuration selected from NASA Energy Efficient Engine program consists of 46 vanes with two impingement baffles in forward and aft cavities. The periodic boundary condition is used to reduce the calculation cost while maintaining a reasonable accuracy of the numerical results. Using the commercial software ANSYS ICEM 15.0, steady simulations are based on a structured grid method with the finite volume technique. In the numerical simulations, two two-equation turbulence models, i.e. the Realizable k-epsilon (k-ε) and Shear Stress Transport k-omega (SST k-ω), and a four-equation turbulence model, i.e. the V2-F model, are used. To estimate the numerical strategy, the calculated results of the Mach number distributions obtained by the three turbulence models are compared with the experimental data of Timko (NASA CR-168289). Then the detailed flow and heat transfer characteristics, including the cooling effectiveness, heat transfer coefficient distributions on the vane’s surfaces, static pressure distributions along three span-wise lines and total pressure distributions in the cascade passage are predicted. Through the comparison of the numerical results obtained under adiabatic and CHT conditions, the influences of heat conduction on vane cooling effect are discussed.

No abstract

Abstract:The aim of this paper is to numerically investigate cooling performances of a non-film-cooled turbine vane coated with a thermal barrier coating (TBC) at two turbulence intensities (Tu = 8.3% and 16.6%). Computational fluid dynamics (CFD) with conjugate heat transfer (CHT) analysis is used to predict the surface heat transfer coefficient, overall and TBC effectiveness, as well as internal and average temperatures under a condition of a NASA report provided by Hylton et al. [NASA CR-168015]. The following interesting phenomena are observed: (1) At each Tu, the TBC slightly dampens the heat transfer coefficient in general, and results in the quantitative increment of overall cooling effectiveness about 16-20%, but about 8% at the trailing edge (TE). (2) The protective ability of the TBC increases with Tu in many regions, that is, the leading edge (LE) and its neighborhoods on the suction side (SS), as well as the region from the LE to the front of the TE on the pressure side (PS), because the TBC causes the lower enhancement of the heat transfer coefficient in general at the higher Tu. (3) Considering the internal and average temperatures of the vane coated with two different TBCs, although the vane with the lower thermal conductivity protects more effectively, its role in the TE region reduces more significantly. (4) For both TBCs, the increment of Tu has a relatively small effect on the reduction of the average temperature of the vane.

This is a numerical study of thermal barrier coating (TBC) and turbulence on leading edge (LE) cooling of a guide vane. Numerical results were carried out using 3D CFD with conjugate heat transfer analysis. Important phenomena were revealed. (1) TBC is effective in the LE region especially when free stream turbulence (Tu) increases. (2) At each Tu, TBC near the hub of the vane provides the most effective protection and at the highest Tu, TBC improves overall cooling effectiveness there by about 25%. (3) Near the exits of film hole, TBC may have negative effect, because of heat transfer impedance from the solid structure into the mixing fluid between mainstream and cooling air emitted from film holes.

The thermal efficiency of gas turbine engines increases with turbine inlet temperature (TIT) directly. However, the TIT is limited by the allowable temperature of current blade materials. Film cooling technique is an effective method to maintain turbine vane working smoothly under high TIT conditions. The adiabatic film effectiveness has been widely employed to understand film cooling mechanism. Therefore, the prediction of the adiabatic effectiveness of gas turbine engines under real operating conditions is essential. The showerhead film cooled turbine vane reported by L. P. Timko (NASA CR-168289) is adopted in the present study. There are two rows of film holes on the leading edge, three rows on the pressure side, and two rows on the suction side. All holes are cylindrical, which are placed at an angle of 45 degrees to the vane surface in the span-wise direction. This numerical investigation discusses the influences of free stream turbulence intensity on the adiabatic film effectiveness in the vane leading edge region and its vicinity. Five two-equation turbulence models based on Reynolds Averaged Navier-Stokes (RANS) are employed to predict the adiabatic film effectiveness under real operating conditions at a blowing ratio (BR) of 1.41 and three free stream turbulence intensities (Tu=3.3, 10, and 20%). The adiabatic film effectiveness on the vane surface at 8, 52.5, and 89% span in an x/C range between −0.4 and 0.4 is presented. Obviously, the numerical results predicted by all five models show that on the suction side, the increasing free stream turbulence intensity can reduce film effectiveness except at 8% span. On the pressure side, the RNG k-ε, Realizable k-ε and SST k-ω models predict the same trend of the adiabatic film effectiveness, especially the RNG k-ε and SST k-ω models. Those three models predict that the locally adiabatic film effectiveness (especially near film holes) can be improved when turbulence intensity increases. However, at a span of 89% within the x/C range between −0.4 and −0.2, all k-ε models and SST k-ω model predict that the increase of turbulence intensity can reduce the adiabatic film effectiveness. In addition, the film effectiveness contours show a significant variation of film effectiveness predicted by the five turbulence models on the leading edge when turbulence intensity increases. For the near-pressure side, all models except the Standard k-ω model predict that the high turbulence intensity can reduce the film spreading from film holes dramatically.

No abstract

This paper presents a numerical approach to study the fluid-thermal-structure coupling problems of laminated film cooling configurations. The SST k-ω turbulence model, T-grid technology, and SIMPLEC algorithm in the commercial tool Fluent 6.3 were employed to solve the coupling problems of flowing fluid and heat transfer within the solid configurations. The numerical method and program were validated with the experimental date obtained by an infrared thermal imaging system in the first part of this work. The validated method and program were applied to analyze the coupling effects of variant solid structure devices, and the influences of film-hole angles and rib-arrangements on cooling effectiveness were compared. The temperature fields obtained by the validated program were input into another commercial tool, Ansys 11, to estimate the thermal stress profiles within the configurations. The fluid-thermal-structure characteristics of the laminated cooling configurations were synthetically discussed.