Analysis of conjugated heat transfer, stress and failure in a gas turbine blade with circular cooling passages

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Abstract

Prediction of heat transfer coefficients and stresses on blade surfaces keys a role in thermal design of a gas turbine blade. The present study investigates heat transfer and stress in a gas turbine blade with 10 circular internal cooling passages. 3D-numerical conjugated simulations using a FVM and FEM commercial codes, CFX and ANSYS are performed to calculate distributions of the heat transfer coefficients and the stresses, respectively. The heat transfer coefficient is the highest on the stagnation point of leading edge due to impingement of incoming gas flow. It is the lowest at the trailing edge on both pressure and suction sides due to development of thermal boundary layer. However, the maximum material temperature and the maximum thermal stress occur at the trailing edge near the mid-span. Therefore, the failure of turbine blade should be predicted by total stress resulted from the combination of thermal load and cooling.

Introduction

Hot components in a recent gas turbine engine have been operated over conditions of maximum material temperature for enhancing energy efficiency. Because of these environments, various cooling schemes have been used and investigated. Moreover, accurate prediction of heat transfer coefficients on external and internal blade surface is important in gas turbine cooling design and optimization [1], [2]. In the last years, therefore, there have been many studies of problem including: (1) Freestream turbulence intensity [3], [4]; (2) Reynolds number and Mach number [5], [6]; (3) boundary layer transition [7], [8]; (4) surface curvature [9]; (5) surface roughness [10], [11]; (6) unsteady wake [12], [13]; (7) rotational effects [14], [15]; and (8) tip and platform shapes [16], [17].

As well as above experimental studies many numerical studies have been carried out using CFD (computational fluid dynamics) codes [18], [19], which are developed by solving Navier–Stokes equations using boundary layer modeling. Among them, TEXTAN [20] had been widely used in the industry. With developing computer technology and turbulence models, CFD has become a powerful design tool. Many researchers performed CFD prediction and compared with the test data obtained in the turbine cascade. In this paper, we have conducted an analysis to obtain the conjugated heat transfer data from analysis of thermal and mechanical characteristics using a commercial code, CFX-11 with the operating conditions in an actual gas turbine blade.

In addition, we calculated the thermal stress using a commercial code, ANSYS-11. If unsuitable cooling method is used, cracks and failures are caused by the thermal and mechanical stresses. Furthermore, the temperature gradient in hot component increases with the turbine inlet temperature increasing, and it generates thermal damage by high thermal stresses [21], [22]. We have attempted a thermal analysis in hot components of gas turbines and the thermal damage was predicted [23], [24], [25], [26], [27], [28]. It has been shown that the computational results are useful for inspecting the thermal environment of the gas turbine and defining the factors that contribute to advanced maintenance and operation.

In the present paper, the heat transfer and the stresses are calculated and discussed for a gas turbine blade used in an industrial power generation system. The objectives of the present investigation are: (1) to understand heat transfer characteristics in the vicinity of a gas turbine blade; (2) to obtain pressure, temperature, and heat transfer data simultaneously in order to analyze thermal stresses and design internal cooling passages in this turbine blade; and (3) to predict stresses and deformations in the turbine blade. This blade has a shroud tip, twist shapes, and 10 circular cooling passages which are 7 rib-roughened and 3 smooth channels.

Section snippets

Research methods

Traditionally, turbine designers solved the fluid flow and heat transfer problems separately from the structural problem, relying on the field experiences with earlier designs. However, in recent years, engineers should design the hot components with high performance from limited operating history and limited experience. Moreover, to maintain a balance between internal and external flow and heat transfer, the hot components design processes are required using the thermal analysis and

Fluid flow analysis

Fig. 5 presents the pressure distributions obtained by using modeling in Fig. 2a. The calculation is conducted in order to use pressure and temperature as boundary conditions for an accurate prediction of heat transfer coefficients. The static pressure distributions by difference in flow velocity between suction and pressure sides are shown in Fig. 5a. At each section, the highest pressure value occurs on stagnation points near the leading edge. In general, in the stationary blade, the high

Conclusions

In order to predict the weak points of hot components, the prediction of deformation and stresses in the blade is required. The deformation and stresses greatly depend on the heat transfer on external and internal blade surfaces. The present paper investigated heat transfer and stress distributions on a gas turbine blade in an industry power generation system. The main conclusions are summarized as follows:

  • (1)

    The highest heat transfer coefficients occur on the stagnation point of the leading edge.

Acknowledgment

This work was supported by the Power Generation & Electricity Delivery of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea Government Ministry of Knowledge Economy.

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