The effects of a wake generated by a stationary upstream strut on surface heat transfer to turbine blades were measured experimentally. Time-resolved and unsteady heat flux measurements were made with Heat Flux Microsensors (HFM) at three positions on the suction surface and one position on the pressure surface of a turbine blade. The experiments were conducted on a stationary cascade of blades for heated runs at transonic conditions Methods for determining the adiabatic wall temperature and heat transfer coefficient are presented and the results are compared to computer predictions for these blades. Heat transfer measurements were taken with new HFM-6 insert gages. A strong influence on the heat transfer coefficient was seen from the relative position of the strut with respect to the leading edge of the test blades. As the strut approached the leading edge of the blade the heat transfer increased by 15% at gage location 2 on the suction surface. The largest increase in .the heat transfer coefficient was seen on the pressure surface. Results at this location show a 24% increase in the overall heat transfer coefficient for one of the strut locations. The values obtained for the heat transfer coefficients for the no strut case did not compare well with computer predictions. The results did support the experimental results of other researchers, however. The fast time response of the HFM illustrated graphically an increase in the frequency energy between the 0-10 kHz range when the strut was located near the leading edge of the instrumented blade. The heat flux turbulence intensity (Tuq) was defined as another physical quantity important to turbine blade heat transfer, but no conclusions could be drawn from the results as to how this value compares to the turbulence intensity. / Master of Science

Large-Eddy Simulations (LES or wall-resolved LES, WRLES) has been used extensively in capturing the physics of anisotropic turbulent flows. However, near wall turbulent scales in the inner layer in wall bounded flows makes it unfeasible for large Reynolds numbers due to grid requirements. This study evaluates the use of a wall model for LES (WMLES) on a channel with rotation at ã Reã _b = 34,000 from ã Roã _b = 0 to 0.38, non-staggered 90° ribbed duct with rotation at ã Reã _b = 20,000 from ã Roã _b = 0 to 0.70, stationary 45° staggered ribbed duct at ã Reã _b = 49,000, and two-pass smooth duct with a U-bend at ã Reã _b = 25,000 for ã Roã _b = 0 to 0.238 against WRLES and experimental data. In addition, for the two-pass smooth duct with a U-bend simulations, the synthetic eddy method (SEM) is used to artificially generate eddies at the inlet based on given flow characteristics. It is presented that WMLES captures the effects of Coriolis forces and predicts mean heat transfer augmentation ratios reasonably well for all simulations. The alleviated grid resolution for these simulations indicates significant reductions in resources, specifically, by a factor of 10-20 in non-staggered 90° ribbed duct simulations. The combined effects of density ratio, Coriolis forces, with SEM for the inlet turbulence, capture the general trends in heat transfer in and after the bend. / Master of Science

In this study, the cooling of a simulated blade under increasing pitch between holes was examined. The change in non-dimensional surface temperature, phi, was measured experimentally to quantify this performance loss. This critical quantification of the sensitivity of cooling to pitch between holes has not been studied previously. A range of blowing ratios and angles of attack were tested. Data are presented in terms of the laterally averaged phi, and in terms of the minimum phi, arguably more important from a design perspective. Increasing the pitch 13% produced no measureable change using either parameter. An increase of 26% in pitch produced only a 4% loss in lateral averages, while some hot points dropped by 10%. These small changes are due to compensating effects of increased internal and through-hole convective cooling. A limit to these effects was shown when increasing pitch 53%. While performance loss in the average was still relatively small at 15%, the minimum phi decreased by 27%. Heat flux gauges were used to gather data on the internal and external surface. The internal impingement used in this study represents a more accurate representation of internal cooling for an actual engine part than has been previously studied, providing a starting point for exploring the differences between engine configurations and those generally investigated in the literature. External heat flux measurements were used to measure the ratio of heat flux with and without film cooling. These results call into question the use of the net heat flux reduction parameter, which is commonly used to quantify overall film cooling performance. / text

The objectives of this study are (1) to develop an accurate and efficient fatigue analysis procedure that can be used in reliability analysis and reliability-based design optimization (RBDO) of composite wind turbine blades; (2) to develop a wind load uncertainty model that provides realistic uncertain wind load for the reliability analysis and the RBDO process; and (3) to obtain an optimal composite wind turbine blade that satisfies target reliability for durability under the uncertain wind load. The current research effort involves: (1) developing an aerodynamic analysis method that can effectively calculate detailed wind pressure on the blade surface for stress analysis; (2) developing a fatigue failure criterion that can cope with non-proportional multi-axial stress states in composite wind turbine blades; (3) developing a wind load uncertainty model that represents realistic uncertain wind load for fatigue reliability of wind turbine systems; (4) applying the wind load uncertainty model into a composite wind turbine blade and obtaining an RBDO optimum design that satisfies a target probability of failure for a lifespan of 20 years under wind load uncertainty. In blade fatigue analysis, resultant aerodynamic forces are usually applied at the aerodynamic centers of the airfoils of a blade to calculate stress/strain. However, in reality the wind pressures are applied on the blade surface. A wind turbine blade is often treated as a typical beam-like structure for which fatigue life calculations are limited in the edge-wise and/or flap-wise direction(s). Using the beam-like structure, existing fatigue analysis methods for composite wind turbine blades cannot cope with the non-proportional multi-axial stress states that are endured by wind turbine blades during operation. Therefore, it is desirable to develop a fatigue analysis procedure that utilizes detailed wind pressures as wind loads and considers non-proportional multi-axial stress states in fatigue damage calculation. In this study, a 10-minute wind field realization, determined by a 10-minute mean wind speed V10 and a 10-minute turbulence intensity I10, is first simulated using Veers’ method. The simulated wind field is used for aerodynamic analysis. An aerodynamic analysis method, which could efficiently generate detailed quasi-physical blade surface pressures, has been developed. The generated pressures are then applied on a high-fidelity 3-D finite element blade model for stress and fatigue analysis. The fatigue damage calculation considers the non-proportional multi-axial complex stress states. A detailed fatigue damage contour, which indicates the fatigue failure locally, can be obtained using the developed fatigue analysis procedure. As the 10-minute fatigue analysis procedure is deterministic in this study, the calculated 10-minute fatigue damage is determined by V10 and I10. It is necessary to clarify that the rotational speed of the wind turbine blade is assumed to be constant (12.1 rpm) and the pitch angle is fixed to be 0 degree for different wind conditions, since the rotational speed control and pitch angle control have not been considered in this study. For predicting the fatigue life of a wind turbine, a fixed Weibull distribution is widely used to determine the percentage of time the wind turbine experiences different mean wind speeds during its life-cycle. Meanwhile, fixed turbulence intensities are often used based on the designed wind turbine types. These simplifications, i.e., fixed Weibull distribution and fixed turbulence intensities, ignore the realistic uncertain wind load when designing a reliable wind turbine system. In the real world, both the mean wind speed and turbulence intensity vary constantly over one year, and their annual distributions are different at different locations and in different years. Thus, it is necessary to develop a wind load uncertainty model that can provide a realistic uncertain wind load for designing reliable wind turbine systems. In this study, 249 groups of measured wind data, collected at different locations and in different years, are used to develop a dynamic wind load uncertainty model. The dynamic wind load uncertainty model consists of annual wind load variation and wind load variation in a large spatiotemporal range, i.e., at different locations and in different years. The annual wind load variation is represented by the joint probability density function of V10 and I10. The wind load variation in a large spatiotemporal range is represented by the probability density functions of five parameters, C, k, a, b, and τ, which determine the joint probability density function of V10 and I10. In order to obtain the RBDO optimum design efficiently, a deterministic design optimization (DDO) procedure of a composite wind turbine blade has been first carried out using averaged percentage of time (probability) for each wind condition. A wind condition is specified by two terms: 10-minute mean wind speed and 10-minute turbulence intensity. In this research, a probability table, which consists of averaged probabilities corresponding to different wind conditions, is referred as a mean wind load. The mean wind load is generated using the dynamic wind load uncertainty model. During the DDO process, the laminate thickness design variables are tailored to minimize the total cost of composite materials while satisfying the target fatigue lifespan of 20 years. It is found that, under the mean wind load condition, the fatigue life of the initial design is only 0.0004 year. After the DDO process, even though the cost at the DDO optimum design is increased by 31.5% compared to that at the initial design, the predicted fatigue life at the DDO optimum design is significantly increased to 19.9995 years. Reliability analyses of the initial design and the DDO optimum design have been carried out using the wind load uncertainty model and Monte Carlo simulation. The reliability analysis results show that the DDO procedure reduces the probability of failure from 100% at the initial design to 49.9% at the DDO optimum design considering only wind load uncertainty. In order to satisfy the target 2.275% probability of failure, it is necessary to further improve the fatigue reliability of the composite wind turbine blade by RBDO. Reliability-based design optimization of the composite wind turbine blade has been carried out starting at the DDO optimum design. Fatigue hotspots for RBDO are identified among the laminate section points, which are selected from the DDO optimum design. Local surrogate models for 10-minute fatigue damage have been created at the selected hotspots. Using the local surrogate models, both the wind load uncertainty and manufacturing variability has been included in the RBDO process. It is found that the probability of failure is 50.06% at the RBDO initial design (DDO optimum design) considering both wind load uncertainty and manufacturing variability. During the RBDO process, the normalized laminate thickness design variables are tailored to minimize the total cost of composite materials while satisfying the target 2.275% probability of failure. The obtained RBDO optimum design reduces the probability of failure from 50.06% at the DDO optimum design to 2.28%, while increasing the cost by 3.01%.

To decrease the computational cost of genetic algorithm optimizations, surrogate models are used during optimization. Online update of surrogate models and repeated exchange of surrogate models with exact model during genetic optimization converts static optimization problems to dynamic ones. However, genetic algorithms fail to converge to the global optimum in dynamic optimization problems. To address these problems, a multiploid genetic algorithm optimization method is proposed. Multi-fidelity surrogate models are assigned to corresponding levels of fitness values to sustain the static optimization problem. Low fidelity fitness values are used to decrease the computational cost. The exact/highest-fidelity model fitness value is used for converging to the global optimum. The algorithm is applied to single and multi-objective turbine blade aerodynamic optimization problems. The design objectives are selected as maximizing the adiabatic efficiency and torque so as to reduce the weight, size and the cost of the gas turbine engine. A 3-D steady Reynolds-Averaged Navier-Stokes solver is coupled with an automated unstructured grid generation tool. The solver is validated by using two well known test cases. Blade geometry is modelled by 37 design variables. Fine and coarse grid solutions are respected as high and low fidelity surrogate models, respectively. One of the test cases is selected as the baseline and is modified in the design process. The effects of input parameters on the performance of the multiploid genetic algorithm are studied. It is demonstrated that the proposed algorithm accelerates the optimization cycle while providing convergence to the global optimum for single and multi-objective problems.

The required useful service lives of gas turbine components and parts are naturally one of the major design constraints limiting the gas turbine design space. For example, the required service life of a turbine blade limits the firing temperature in the combustor, which in turn limits the performance of the gas turbine. For a cooled turbine blade, it also determines the necessary cooling flow, which has a strong impact on the turbine efficiency. In most gas turbine design practices, the life prediction is only emphasized during or after the detailed design has been completed. Limited life prediction efforts have been made in the early design stages, but these efforts capture only a few of the necessary key factors, such as centrifugal stress. Furthermore, the early stage prediction methods are usually hard coded in the gas turbine system design tools and hidden from the system designer s view. The common failure mechanisms affecting the service life, such as creep, fatigue and oxidation, are highly sensitive to the material temperatures and/or stresses. Calculation of these temperatures and stresses requires that the geometry, material properties, and operating conditions be known; information not typically available in early stages of design. Even without awareness of the errors, the resulting inaccuracy in the life prediction may mislead the system designers when examining a design space which is bounded indirectly by the inaccurate required life constraints. Furthermore, because intensive creep lifing analysis is possible only towards the end of the design process, any errors or changes will cost the engine manufacturer significant money; money that could be saved if more comprehensive creep lifing predictions were possible in the early stages of design. A rapid, physics-based life prediction method could address this problem by enabling the system designer to investigate the design space more thoroughly and accurately. Although not meant as a final decision method, the realistic trends will help to reduce risk, by providing greater insight into the bounded space at an earlier stage of the design. The method proposed by this thesis was developed by first identifying the missing pieces in the system design tools. Then, by bringing some key features from later stages of design and analysis forward through 0/1/2Ds dimensional modeling and simulation, the method allows estimation of the geometry, material selection, and the loading stemming from the operating conditions. Finally, after integration with a system design platform, the method provides a rapid and more complete way to allow system designers to better investigate the required life constraints. It also extracts the creep life as a system level metric to allow the designers to see the impact of their design decisions on life. The method is to be first applied to a cooled gas turbine blade and could be further development for other critical parts. These new developments are integrated to allow the system designers to better capture the blade creep life as well as its impact on the overall design.

Vibration is an inherent phenomenon in dynamic mechanical systems. The work undertaken in this thesis is to identify natural frequencies of a variable length blade. Therefore designers can ensure that natural frequencies will not be close to the frequency (or integer multiples) of the main excitation forces in order to avoid resonance. For a wind turbine blade, the frequency range between 0.5 Hz and 30 Hz is relevant. The turbine blade is approximated by a cantilever, therefore, it is fully constrained where attached to a turbine shaft/hub. Flap-wise, edge-wise and torsional natural frequencies are calculated. The MATLAB program “BEAMANALYSIS.m” has been developed for the finite element analysis of a one dimensional model of the beam. Similarly, a three dimensional model of the beam has been developed in a finite element program Unigraphics NX5. The results found using the MATLAB program are compared with those found with NX5. Satisfactory agreement between the results is found for frequencies up to almost 500 Hz. Additionally, the frequencies one might expect in an experiment are identified. Experimental modal analysis has been performed on a uniform and stepped beam made of mild steel to extract the first five flap-wise natural frequencies. The results found have been compared to numerical results and the exact solution of an Euler-Bernoulli beam. Concurrence is found for the frequency range of interest. Although, some discrepancies exist at higher frequencies (above 500 Hz), finite element analysis proves to be reliable for calculating natural frequencies. Finally, the fixed portion and moveable portion of the variable length blade are approximated respectively by a hollow and a solid beam which can be slid in and out. Ten different configurations of the variable length blade, representing ten different positions of the moveable portion are investigated. A MATLAB program named VARIBLADEANALYSIS.m was developed to predict natural frequencies. Similarly three dimensional models of the variable length blade have been developed in the finite element program Unigraphics NX5. / This work was supported by the Research office of CPUT.

Les aubes de turbines haute pression des turboréacteurs sont soumises à des chargements thermomécaniques sévères en service. Elles sont actuellement fabriquées par solidification dirigée sous forme de monocristaux orientés suivant la direction <001> le long de la direction principale de l'aube. La solidification peut entrainer dans certains cas l'apparition de défauts, notamment la formation de deux grains : l'aube est alors constituée de deux grains d'orientations différentes. L'objectif de cette thèse est d'étudier l'influence de la présence d'un joint de grains sur la durée de vie de l'aube en superalliage AM1. Dans un premier temps, nous avons réalisé une étude expérimentale sur aubes réelles afin de déterminer l'influence du joint de grains sur la rupture par fatigue en flexion à différentes températures. Pour cela, des entailles ont été usinées dans les aubes pour solliciter de façon préférentielle le joint de grains au sein de l'aube dans des essais de type flexion. Cette étude a permis de mettre en évidence le rôle du joint de grains sur la durée de vie de l'aube selon la température d'essai, l'orientation cristallographique relative des grains, la position du joint de grains et le type de sollicitation. Parallèlement, une étude exprimentale sur éprouvettes bi-cristallines de type fatigue oligocyclique a été conduite en traction compression, avec une contrainte principale de traction suivant la normale au plan moyen du joint. Ces essais ont permis de quantifier la réduction de durée de vie induite par la présence du joint de grains par rapport à une éprouvette monocristalline. Un critère de rupture a été ainsi introduit dans la loi d'endommagement développée par l'Onera pour le superalliage monocristallin d'AM1. Ce critère de durée de vie a été appliqué dans les simulations numériques des aubes remaillées et permet de faire une première estimation de la nocivité du joint de grains dans les aubes. / The high pressure turbine blade of aeroengine are submitted to severe thermomechanical loading in service. The turbine blade are curently manufactured by directionnal solidification with oriented single crystal on the direction <001>, along the principal direction of the blade.The solidification process can induce different defects in the structure.This study is focused on a particular defect: the formation of two crystals in a blade. Defective turbine blades are composed of two grains with different orientation.The aim of this present thesis is to study the influence of the grain boundary on AM1 superalloy blade fatigue life. First, experimental investigations have been performed to understand at different temperatures, the influence of grain boundaries on fatigue fracture due to bending loadings. Notches have been introduced on turbine blades in order to accentuate solicitations on grain boundary. These experiments have evidenced the major role of grain boundary and grains orientations on turbine blade fatigue life.Then another experimental investigation has been carried out under low cycle fatigue on bicrystal specimens with tension/compression loading; the tensile principal stress is along the normal direction of the grain boundary mean plane. These tests allowed quantification of the fatigue life decrease due to the presence of grain boundary compared to the fatigue life of single crystal specimens.A failure criterion have been introduced in the damage constitutive behavior of single crystal AM1 developped by the Onera. This lifetime prediction model have been implemented in FE simulations. It allows the evaluation of the sensivity of grain boundary on turbine blade.

This master thesis deals with steam turbine blade attachment. Main goal is to perform strength analysis of the given geometry under static and cyclic loads by FEM and software ANSYS. Every particular model is described separately with mentioning of the problems which had to be solved. To create model of material, the tensile tests has been performed and results has been evaluate. There were planned and performed the low cycle fatigue tests to create a model of ultimate states which is used to evaluate the fatigue life of the attachment. Results of the nonlinear FEM analysis is discussed and some improvements of the geometry has been proposed to achieve better state of stress. Finally, the plan of future work has been proposed.

This diploma thesis continues to the Ing. Damborský work and deals with strain-stress and dynamic analysis of the steam turbine blade. This blade is part of the last row of low pressure level of steam turbine. Computational analysis has been performed in first part using FEM. After that follows a modal analysis for the blade without residual stress as well as for the blade affected by heat treatment. Main goal is to obtain whether the state of stress is in the crack initiation area is influenced by thermal treatment. This problem was solved by computational simulation in commercial software Ansys 11.0.