Comparative analysis of steady state heat transfer in a TBC and functionally graded air cooled gas turbine blade

Abstract

Internal cooling passages and thermal barrier coatings (TBCs) are presently used to control metal temperatures in gas turbine blades. Functionally graded materials (FGMs), which are typically mixtures of ceramic and metal, have been proposed for use in turbine blades because they possess smooth property gradients thereby rendering them more durable under thermal loads. In the present work, a functionally graded model of an air-cooled turbine blade with airfoil geometry conforming to the NACA0012 is developed which is then used in a finite element algorithm to obtain a non-linear steady state solution to the heat equation for the blade under convection and radiation boundary conditions. The effects of external gas temperature, coolant temperature, surface emissivity changes and different average ceramic/metal content of the blade on the temperature distributions are examined. Simulations are also carried out to compare cooling effectiveness of functionally graded blades with that of blades having TBC. The results highlight the effect of including radiation in the simulation and also indicate that external gas temperature influences the blade heat transfer more strongly. It is also seen that graded blades with about 70% ceramic content can deliver better cooling effectiveness than conventional blades with TBC.

Functionally graded materials classifications and development trends from industrial point of view

“…[22,151,152]. According to area of application, FGMs can be classified into biomaterial [125,[153][154][155], aerospace [156][157][158], automotive [159,160], defense [161,162], cutting tools [163], nuclear reactor [164], smart structure [165], turbine blades [166] and sports equipment [167]. Figure 10 represent an overview of the classification according to the major fields of applications.…”

Colour changing material for the estimation of flue gas radiation on the miniature gas turbine surface

“…When the hot flame flows over the surface of the turbine blade, heat transfer takes place between the blade and hot flue gases. 4 Firstly, heat transfer to the blade occurs due to convection from the free stream hot gases. 5 The second heat transfer mechanism on both the external pressure and suction airfoil surfaces that must be taken into account is the radiation from the hot gases and the other surfaces.…”

“…One side of the blade has been exposed to flue gases as these gases impinge on one surface of the blade, whereas the annulus air flows over the other side of the blade, thereby cooling the blade. 4 The heat transferred on the blade surface can be estimated based on the temperature recorded on the blade surface. The surface temperature of the blade can be recorded by any one of the techniques described in Table 1.…”

“…9 The radiation plays a secondary role in heat transfer between blade surface and hot gas in motion. 4,5 Around 70–80% of total radiation absorbed by the blade painted with TIP is emitted at different locations on the surface of the turbine blade. The amount of emitted radiation has been calculated based on the wavelength of the colour obtained, and the temperature detected during experimentation.…”

Numerical simulation of thermal fracture in functionally graded materials using element-free Galerkin method

“…For example, the toughness of a metal can be mated with the refractoriness of a ceramic, without any compromise in the toughness of the metal side or the refractoriness of the ceramic side. FGMs and FGM coating are used in wide variety of applications [2][3][4][5]. FGMs offer great promise in applications where the operating conditions are quite severe, e.g., wear-resistant linings for handling large heavy abrasive ore particles, rocket heat shields, heat exchanger tubes, thermoelectric generators, heat-engine components, plasma facings for fusion reactors, piezoelectric devices, graded refractive index materials, thermionic converters, dental and other implants, fireretardant doors, solid oxide fuel cell and electrically insulating metal-ceramic joints.…”