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.

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This paper presents an experimental investigation on the performances of a new film cooling structure design, in which a ramp is placed upstream of a cylindrical film hole and a cylindrical cavity with two diagonal impingement holes is set at the inlet of the film hole to generate a swirling coolant flow entering the film hole. The experiments are carried out by two undisturbed measurement techniques, planar laser induced fluorescence (PLIF) and time-resolved particle image velocimetry (TR-PIV) in a water tunnel. The effects of the upstream ramp angle, blowing ratio (BR), and coolant impingement angle on the film cooling performances of a flat plate are studied at three ramp angles (0 deg, 15 deg, and 25 deg), two coolant swirling directions (clockwise and counterclockwise), two impingement angles (15 deg and 30 deg), and three BRs (0.6, 1.0, and 1.4). The experimental results show that at high BRs, the combination structures of the upstream ramp with the swirling coolant flow generated by the impingement angles can significantly improve film cooling performances; the best combination is at a 30 deg impingement angle and a 25 deg ramp angle. This can be explained by the fact that the swirling flow is significantly pressed on to the wall by means of the upstream ramp. Using the analogous analysis of heat and mass transfer, the adiabatic film effectiveness averaged over a cross section is obtained; the analysis indicates that at high BRs, the combined effect of a ramp with a large angle of 25 deg with 30 deg impingement angle can increase the film effectiveness up to 30% when compared to the test case without a ramp at the exit of the film hole. The images captured by PLIF exhibit an interesting phenomenon, i.e., the swirling of the coolant in different directions can influence the counter vortex pair (CVP) in rotating layers, and the coolant swirling in a clockwise direction enhances the right mixing of the CVP with coolant ejection, whereas the coolant swirling in a counterclockwise direction enhances the left-mixing of the CVP with coolant ejection.

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.

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Models simplified from real annular turbine cascades into linear cascades have been widely used in the experimental investigations on the cooling performances of turbine blade and endwall (including hub and shroud), but errors caused by the simplifications are seldom considered and discussed. This paper presents a numerical comparison of film cooled endwall between real annular and linear cascade. The model used in this work is derived from a real gas turbine stator, which consists of 46 vanes. Numerical simulations are carried out by the commercial software ANSYS CFX 15.0 and ICEM 15.0. Conjugate Heat Transfer (CHT) analysis is used to solve pressure field and temperature field through a fully implicit multi-grid coupling algorithm, and the two-equation turbulence model, Shear Stress Transport (SST) k-ω, is selected as closed equations. To validate the numerical strategy, a series of experiments is conducted by a flat endwall model, in the hot gas wind tunnel at University of Science and Technology of China (USTC). Using the validated numerical strategy, the fluid flow and heat transfer characteristics of the real annular and flat endwalls models are simulated and compared. The differences in static pressure, temperature and overall cooling effectiveness between the two models are exhibited, and the reliability and reasonability of the simplification from a real annular cascade to a linear cascade are discussed. The results show the following important conclusion: If the pressure problems of hub endwall are considered only, the flat endwall simplification is acceptable, but at experimental conditions, the cooling effectiveness of the flat endwall could be 10% higher than that of the real annular endwall, while at realistic condition, the difference decreases obviously.

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