Trailing Edge Film Cooling of Gas Turbine Airfoils: External Cooling Performance of Various Internal Pin Fin Configurations

Abstract

The present paper describes an experimental study on trailing edge film cooling of modern high-pressure turbine blades using coolant ejection through planar slots on a pressure side cutback. The experimental test section consists of a generic scaled-up trailing edge model in an atmospheric open loop wind tunnel, which has been used in earlier studies by Martini et al. (e.g. [1]). An infrared thermographic measurement technique is employed, which allows for the application of engine-realistic density ratios around 1.6 by increasing the main flow temperature. The effects of different geometric configurations on the structure and performance of the cooling film are investigated in terms of film cooling effectiveness, heat transfer, and discharge behavior. Among other issues, the interaction between internal turbulators, namely an array of pin fins, with the ejection slot lip is of major interest. Therefore, different designs of the coolant ejection lip are studied. Four different ratios of lip thickness to ejection slot height (t/H = 0.2, 0.5, 1.0, 1.5) are investigated as well as three different lip profiles representing typical manufacturing imperfections and wear. Other geometric variations comprise elliptic pin fins with spanwise and streamwise orientation and the application of land extensions from the internal coolant cavity onto the cut-back surface. The blowing ratio is varied between 0.2 < M < 1.25. In terms of film cooling effectiveness the results show a strong dependency on ejection lip thickness and minor improvements are obtained with a rounded ejection lip profile. Significant improvements are achieved using land extensions. The elliptic pin fins have a strong effect on discharge behavior as well as on film cooling effectiveness and heat transfer. Except for the elliptic pin fins, the geometric variations have only a minor influence on heat transfer.

DES study of blade trailing edge cutback cooling performance with various lip thicknesses

“…After the verification of the modelling procedures and boundary conditions, the SST k-ω turbulence model based DES is employed for the simulations and the experimental measurements of Martini et al [21] [22] [28] [29] and Horbach et al [6] are used for validation. Two blowing ratios (M = 0.5, 1.1) are considered for this purpose.…”

“…Figure 9 provides the quantitative comparison of the averaged film-cooling effectiveness for four different t/H ratios, at two blowing ratios of 0.5 and 1.1. The DES predictions are compared with experimental measurements by Martini et al [28] [29] and Horbach et al [6], respectively.…”

“…Due to this reason, modern gas turbines often operate at high blade inlet temperatures up to 1,200 -1,500°C [1][2] [3]. Recent developments in gas turbine engines for aero-propulsion applications require much higher turbine inlet temperatures in excess of 1,727°C [4][5] [6], and an overall compressor pressure ratio of greater than 50 [6]. These extreme conditions and requirements will however cause serious aero-thermodynamic problems for key engine components such as liners, vanes and blades as the engine operation temperature is far beyond the critical working temperature of the materials used [3].…”

“…In recent experiments of Horbach et al [6][19] on a blade trailing-edge cutback cooling configuration, four different t/H ratios ranging from 0.2 to 1.5 have been carefully examined. It was found that the decrease of the t/H ratio has the potential to improve the adiabatic filmcooling effectiveness to unity, while an increase of the t/H ratio will cause the fast decay of the film-cooling effectiveness in the vicinity of the trailing-edge cutback region.…”

Scrutiny of the Structural Stability of CMSX-4 and NIMONIC 901 made Gas Turbine Fixed blades with Showerhead Cooling

“…In some specific cases like aerospace applications as much high as 1,727°C [4][5][6], the pressure ratio also high at compressor about 50 [6]. In Such situations the components often encounter the thermal damages as well as other damages like melting, corrosion, oxidation and erosion [7], the degradation of local or global structural strengths of blades, vanes and other components and it was estimated that half of the lifespan of the blades gets reduced due to small temperature difference by improper cooling [3,6,9]. The specific damages are: blade trailing-edge cracks [8], buckling and risk of blade failure [11], thermal-fatigue [8,10,11].…”