Development of the Functional-Gradient Turbine Wheel With Cooled Blades Without Lock Connection

Wheels of high-temperature turbines are traditionally produced in the form of detachable joints of the disk and blades made from different materials. The blades, which are under the influence of high gas temperatures, are made with internal channels by air cooling. The disk is subject to significant centrifugal loads, but lower temperatures. The locking connection of the blades to the disk is a stress concentrator, which leads to resource limitation. One of the solutions is the wheel of the turbine type blisk consisting of cast-cooled blades of heat-resistant alloys and a disk of granulated nickel alloys, interconnected by hot isostatic pressing. The disk can be made of granules of different sizes in different parts. This approach is based on the fact that during operation, the disk is also subject to uneven heating and loading along the radius. The blisk design of the wheel with cooled blades is developed on the basis of the turbine wheel with a detachable connection of the blades with the disk. The blades of the blisk are produced from casting heat-resistant nickel alloy. The disk portion is created from granulated alloy with different grain sizes along the disk radius. The system of supplying cooling air in the blades of the wheel is developed. The technology of manufacturing a disk consisting of granules of various sizes and technology of connection of a disk with cooled cast blades is developed. To determine the mechanical characteristics of the zones of connection of dissimilar materials samples were tested. The combined samples were made of a granulated alloy with different sizes of granules. The bimetallic samples were made of a casting blade alloy and a granulated disk alloy. Multi-parameter optimization of the blisk was carried out. The mass of the designed wheel was reduced by more than 40% compared to the original wheel with lock connection when the strength and service life conditions were satisfied.

Untwist Creep Analysis of Gas Turbine First Stage Blade

During operation, turbine blades subjected to high temperatures will experience permanent geometric distortion due to creep. The principal form of this distortion is blade elongation due to the centrifugal load, but the blade can also straighten or ‘untwist’. The magnitude of the untwist can be used to track the accumulated creep strain damage in a blade, and so measurements of blade untwist over time are often recorded. If the relationship between untwist and creep strain damage can be expressed, then it will be possible to make more informed maintenance decisions. This study describes a finite element creep analysis of a first stage turbine blade using a calibrated creep material model, and compares the calculated untwist to records kept by the operator. The creep model used in this study is a physics based model using the microstructural properties of the blade alloy, and is calibrated using a single creep test at representative stress and temperature. An important objective of this study is to demonstrate that application of the creep model in a component with non-uniform stress and temperature will lead to representative results. The analysis was repeated with two materials that correspond to different blade versions. The material with superior high temperature properties exhibited less untwist, and the analysis of both variants were comparable to the recorded blade measurements.

Numerical Simulation and Experimental Investigation of the Failure of a Gas Turbine Compressor Blade

This paper is concerned with the premature failures occurred in the high pressure compressor section of the gas turbine of HESA power plant in Iran. Metallurgical and mechanical properties of the blade alloy were evaluated. Fractography investigations were carried out on the fracture surface of the blade roots using scanning electron microscopy. Stress and fracture simulations were conducted using ANSYS software in both 2D and 3D dimensions under centrifugal, aerodynamic and contact forces. The aerodynamic forces were evaluated using FLUENT software. The results showed no metallurgical and mechanical deviations for the blade material from standards. SEM fractography showed different aspects of fretting fatigue including multiple crack initiation sites, fatigue beach marks, debris particles, and a high surface roughness on the edge of contact (EOC). The simulation results showed that there was a high stress gradient at the EOC of the blade which is one of the most significant characteristics of the fretting fatigue. Another analysis was performed to simulate the fracture by creating an initial crack on the EOC. The stress fields and stress intensity factors for modes I, II and III were evaluated along the crack front. The results indicated a strong stress intensity factor for mode I at the EOC.

An Investigation on Failure Analysis of Titanium Gas Turbine Compressor Blades

Several premature failures were occurred in the high-pressure section of an industrial gas turbine compressor due to the fracture of Titanium blade roots. In this work, the failure process of the compressor blades was investigated based on the experimental characterisation. Macro/microfractographic studies were carried out on the fracture surfaces. Optical and scanning electron microscopy of the blade airfoil and root were performed. Mechanical properties of the blade alloy were also evaluated and compared with the standard specifications. The experimental results showed no metallurgical and mechanical defects for the blade materials. Microstructures of the blade root and airfoil as well as the hardness and tensile properties were all comparable with those reported in the standard specification AMS 4928Q. Fractography experiments showed clearly multiple crack initiation sites and fatigue beach marks. Debris particles were observed on the fracture surface of samples and in the mouth of initiated cracks. The blade surface in contact to the disc in the dovetail region showed a higher surface roughness than the other surfaces. Based on the results obtained, the fretting fatigue mechanism was proposed for the premature failures. It was concluded that the stress concentration has been caused by either unsuitable curvature ratio of the disk dovetail, incorrect design of the blade or insufficient distance between the blade root and the disk in dovetail region.

Measured Adiabatic Effectiveness and Heat Transfer for Blowing From the Tip of a Turbine Blade

The clearance gap between the tip of a turbine blade and the shroud has an inherent leakage flow from the pressure side to the suction side of the blade. This leakage flow of combustion gas and air mixtures leads to severe heat transfer rates on the blade tip of the high-pressure turbine. As the thermal load to the blade increases, blade alloy oxidation and erosion rates increase thereby adversely affecting component life. The subject of this paper is the cooling effectiveness levels and heat transfer coefficients that result from blowing through two holes placed in the forward region of a blade tip. These holes are referred to as dirt purge holes and are generally required for manufacturing purposes and expelling dirt from the coolant flow when operating in sandy environments. Experiments were performed in a linear blade cascade for two tip-gap heights over a range of blowing ratios. Results indicated that the cooling effectiveness was highly dependent on the tip-gap clearance with better cooling achieved at smaller clearances. Also, heat transfer was found to increase with blowing. In considering an overall benefit of cooling from the dirt purge blowing, a large benefit was realized for a smaller tip gap as compared with a larger tip gap.

Measured Adiabatic Effectiveness and Heat Transfer for Blowing From the Tip of a Turbine Blade

The clearance gap between the tip of a turbine blade and the shroud has an inherent leakage flow from the pressure side to the suction side of the blade. This leakage flow of combustion gas and air mixtures leads to severe heat transfer rates on the blade tip of the high pressure turbine. As the thermal load to the blade increases, blade alloy oxidation and erosion rates increase thereby adversely affecting component life. The subject of this paper is the cooling effectiveness levels and heat transfer coefficients that result from blowing through two holes placed in the forward region of a blade tip. These holes are referred to as dirt purge holes and are generally required for manufacturing purposes and expelling dirt from the coolant flow when operating in sandy environments. Experiments were performed in a linear blade cascade for two tip gap heights over a range of blowing ratios. Results indicated that the cooling effectiveness was highly dependent upon the tip gap clearance with better cooling achieved at smaller clearances. Also, heat transfer was found to increase with blowing. In considering an overall benefit of cooling from the dirt purge blowing, a large benefit was realized for a smaller tip gap as compared with a larger tip gap.