Misalignment in Gas Foil Journal Bearings: An Experimental Study

As gas foil journal bearings become more prevalent in production machines, such as small gas turbine propulsion systems and microturbines, system level performance issues must be identified and quantified in order to provide for successful design practices. Several examples of system level design parameters that are not fully understood in foil bearing systems are thermal management schemes, alignment requirements, balance requirements, thrust load balancing, and others. In order to address some of these deficiencies and begin to develop guidelines, this paper presents a preliminary experimental investigation of the misalignment tolerance of gas foil journal bearing systems. Using a notional gas foil bearing supported rotor and a laser-based shaft alignment system, increasing levels of misalignment are imparted to the bearing supports while monitoring temperature at the bearing edges. The amount of misalignment that induces bearing failure is identified and compared to other conventional bearing types such as cylindrical roller bearings and angular contact ball bearings. Additionally, the dynamic response of the rotor indicates that the gas foil bearing force coefficients may be affected by misalignment.

Thermodynamic Equilibrium Analysis of Rice Husk Pyrolysis

Pyrolysis of biomass materials can implement the efficient conversion of biomass to gaseous, liquid and solid energy products. Compared with experimental research which needs massive apparatus and funds and also takes long time, the computer simulation of biomass pyrolysis is more convenient and flexible to achieve the main characteristics of the process. Simulation of thermodynamic equilibrium for the pyrolysis of rice husk was studied in this paper. Based on the minimization of Gibbs free energy, MATLAB was used to calculate thermodynamic equilibrium for the pyrolysis of rice husk in the temperatures ranges from 523 K to 1723 K at intervals of 100 K. The results showed that the contents of H2 and CO increased rapidly with the temperature from 723 K to 1223 K, while the contents of H2O, CH4, CO2 and C decreased sharply. When the temperature was higher than 1223 K, the yields of H2 and CO reached the maximum of 51 mol% and 48 mol% respectively, and then kept stable. In order to be closer to experimental results, the constrain conditions of element C in tar was introduced in the calculations. The results indicated that, in the main components of tar from 523 K to 1223 K, the contents of naphthalene and toluene both decreased and then toluene vanished gradually. However, the content of benzene increased with increasing temperature and finally became the dominant product when the temperature was above 1300 K.

Ceramic Gas Turbine Development: Need for a 10-Year Plan

Ceramic gas turbine development that started in the 1950s has slowed considerably since most of the large-scale ceramic gas turbine development programs of the 1970s–1990s ended. While component durability still does not meet expectations, the prospect of significant energy savings and emissions reductions, potentially achievable with ceramic gas turbines, continues to justify development efforts. Four gas turbine applications have been identified that could be commercially attractive: a small recuperated gas turbine (microturbine) with ∼35% electrical efficiency, a recuperated gas turbine for transportation applications with ∼40% electrical efficiency with potential applications for efficient small engine cogeneration, a ∼40% efficient mid-size industrial gas turbine and a ∼63% (combined cycle) efficient utility turbine. Key technologies have been identified to ensure performance and component durability targets can be met over the expected life cycle for these applications. These technologies include: a Si3N4 or SiC with high fracture toughness, durable EBCs for Si3N4 and SiC, an effective EBC/TBC for SiC/SiC, a durable Oxide/Oxide CMC with thermally insulating coating, and the Next Generation CMCs with high strength that can be used as structural materials for turbine components for small engines and for rotating components in engines of various sizes. The programs will require integrated partnerships between government, national laboratories, universities and industry. The overall cost of the proposed development programs is estimated at U.S. $100M over ten-years, i.e. an annual average of U.S. $10M.

Performance Comparison of More Electric Engine Configurations

An analytical study was undertaken to investigate the fuel burn potential of More Electric Engine (MEE) configurations using the performance model of a 2-shaft high BPR 20–30 klbf turbofan in revenue service. The 3 following power off-take configurations were compared: an HP-generator, an LP-generator, and a split-power generator (small HP starter/generator and a main LP generator). For this study, because of the small performance differences, high accuracy steady-state and transient performance models must be used. For steady-state operating conditions, the design point was modified and the off-design redline margins were calculated; ground and flight idle settings were adjusted to yield both the lowest possible fuel burn and residual thrust within the surge margin of the compressor, and the resulting short range mission fuel burn was calculated. For transient conditions, the thrust response, as well as both HPC and LPC surge margin lapse during engine acceleration and deceleration, had to maintain those of the baseline engine and fulfill certification requirements. This was achieved by modifying the idle settings and acceleration/deceleration schedules. Subsequently, the resulting short range mission fuel burn was calculated. Lastly, an introduction to the business case is provided with a simple cost-effectiveness calculation. This study was an initial investigation into MEE’s that focused primarily on the propulsion unit. For further in-depth studies, it is recommended to consider in detail the business model, aircraft weight issues, and the interaction propulsion performance and aircraft performance.

Damage Evolution and Failure Mechanisms for APS-TBCS

Thermal barrier coatings (TBC-s) have been utilized in gas turbine engines for over two decades, primarily to protect the existing materials under the demands for higher temperatures and greater engine efficiency. Atmospheric Plasma Sprayed TBC, commonly used for hot combustion chamber components of advanced gas turbines, are exposed to thermo-mechanical loads, which may lead to failure in form of macroscopic spallations from the metallic component. The durability of TBC is limited by the interaction of different processes and parameters, such as bond coat oxidation, cyclic strains, visco-plastic and relaxation properties, interface roughness and others. In this work, the spallation failure mechanisms and damage evolution of APS-TBC system are investigated on samples aged by isothermal and thermal cycle tests using different time and temperatures exposures. Several parameters have been analyzed by SEM and a life prediction model approach for APS-TBC is being developed focusing on oxidation kinetics, identifying the parameters such as rumpling, bond coat oxidation, TGO thickness and interdiffusion of base metal elements which drive the oxide formation and TBC spallation mechanisms.

Three-Dimensional Stress Analysis and Configuration Optimization of Cross Wavy Primary Surface Recuperator for Microturbine System

Recuperator in a microturbine system, which has to work under a high temperature and high pressure condition, is a key component to improve the electricity efficiency of the system. High temperature and pressure may cause high stress inside the Cross-Wavy Primary Surface (CWPS) sheet, and it is essential to analyze the stress distribution to ensure the security while the recuperator is working. In this paper the combined thermomechanical design of a CWPS recuperator for a 100kW microturbine system is presented. With the ANSYS Parametric Design Language (APDL), calculation procedures for heat transfer and stress analysis are combined in order to perform a reliable strength prediction of the recuperator. A program has been generated, which allows the automatic generation of the numerical model, the mesh and the boundary conditions. Also with the energy minimum principle, an optimal configuration of the air and gas passages is obtained. The results show that the material of the primary sheet (0Cr18Ni11Nb) is reliable. The stress distribution changes with the different configuration of the passages. Since the air pressure is much higher than that of the exhaust gas, the configuration of the primary sheet is much better when the sectional area of the gas passage is larger than that of the air passage. If the pitch of the sheet is maintained at 2mm, the best configuration is obtained when the dimension of passage is at r = 0.35–0.42mm, R = 0.55–0.48mm.

Fischer-Tropsch Fuel Characterization via Microturbine Testing and Fundamental Combustion Measurements

Synthetic fuels such as Fischer-Tropsch (FT) fuels are of interest as a replacement for aviation, diesel, and other petroleum-based fuels, and the present paper outlines a joint program to study the combustion behavior of FT synthetic fuels. To this end, shock-tube spray and high-recirculation combustion rig experiments are being utilized to study the ignition delay times, formation of soot, and emissions of FT jet fuels. Undiluted shock tube spray experiments were conducted using a recently developed heterogeneous technique wherein the fuel is sprayed directly into the test region of a shock tube. The high recirculation combustion rig is a complete gas turbine system where Syntroleum FT jet fuel was combusted, and soot formation and emission characteristics were observed. Reduction of soot volume fraction and unchanged emissions were observed, in agreement with previous investigations. The fundamental shock tube results were found to be consistent with the observations made in the experimental engine.

High Temperature Radiation Heat Transfer Performance of Thermal Barrier Coatings With Multiple Layered Structures

Meeting the demands for ever increasing operating temperatures in gas turbines requires concurrent development in cooling technologies, new generations of superalloys, and thermal barrier coatings (TBCs) with increased insulation capability. In the case of the latter, considerable research continues to focus on new coating material compositions, alloying/doping existing yttria stabilized zirconia ceramics, and the development of improved coating microstructures. The advent of the EB-PVD coating process has made it possible to consider the creation of multiple layered coating structures to meet specific performance requirements. In this paper, the advantages of layered structures are first reviewed in terms of their functions in impeding thermal conduction (via phonons) and thermal radiation (via photons). Subsequently, the design and performance of new multiple layered coating structures based on multiple layered stacks will be detailed. Designed with the primary objective to reduce thermal radiation transport through TBC systems, the multiple layered structures consist of several highly reflective multiple layered stacks, with each stack used to reflect a targeted radiation wavelength range. Two ceramic materials with alternating high and low refractive indices are used in the stacks to provide multiple-beam interference. A broadband reflection of the required wavelength range is obtained using a sufficient number of stacks. In order to achieve 80% reflectance to thermal radiation in the wavelength range of 0.3 ∼ 5.3 μm, 12 stacks, each containing 12 layers, are needed, resulting in a total thickness of 44.9 μm. Using a one dimensional heat transfer model, steady state heat transfer through the multiple layered TBC system is computed. Various coating configurations combining multiple layered stacks along with a single layer are evaluated in terms of the temperature profile in the TBC system. When compared to a baseline single layered coating structure of the same thickness, it is estimated that the temperature on the metal surface can be reduced by as much as 90°C due to the use of multiple layered coating configurations. This reduction in metal surface temperature, however, diminishes with increasing scattering coefficient of the coating and total coating thickness. It is also apparent that using a multiple layered structure throughout the coating thickness may not offer the best thermal insulation; rather, placing multiple layered stacks on top of a single layer can provide a more efficient approach to reduce the heat transport of the TBC system.

Assessing of Hot Gas Parts Using Advanced Eddy Current Testing Methods

The turbine section of state-of-the-art industrial gas turbines is exposed to the most severe conditions such as high temperatures, corrosive environments and high mechanical stresses for several tens of thousands of hours. To withstand these conditions, turbine blades and vanes have become the most sophisticated parts. This, together with advanced manufacturing technologies, strict quality requirements and maximum reliability demands, affects costs. Different design features have been realized in the past to meet the ambitious requirements, and are also under constant development. Blades and vanes made of superalloys with directionally-solidified or single-crystal structure are used to provide highest strengths at temperatures as near as possible to the hot gas temperature. The high integrity and conformity of the parts are required to realize the material potential. Different advanced diagnostic methods are applied to ensure these over time. Another way to increase the operating temperatures of gas turbines is the application of corrosion and thermal protection coatings for one or several rows of the blades and vanes. Deviations in the specified coating thickness tend to reduce the lifetime of such coatings significantly. Hence, the monitoring of this property during the manufacturing requires special nondestructive diagnostic measures. Service exposed parts, which need to be refurbished when the protective coatings are spent, offer a significant operation potential after refurbishment. To guarantee the design parameters during the next service interval, several nondestructive material evaluation methods are available for the necessary part property assessment. Multifrequency Eddy Current has proven itself as an appropriate NDE technique to accomplish the above diagnostic requirements. The paper will give an overview of results gained at Siemens with model based Eddy Current methods using measurement systems developed by Jentek Sensors Inc., USA, and CESI, Italy. Potential applications and limitations of the method also will be discussed.

Advanced Modeling of Fluid Thermodynamic Properties for Gas Turbine Performance Simulation

This paper describes the structure of an advanced fluid thermodynamic model which has been developed for a novel advanced gas turbine simulation environment called PROOSIS. PROOSIS (PRopulsion Object Oriented SImulation Software) is part of the VIVACE-ECP (Value Improvement through a Virtual Aeronautical Collaborative Enterprise - European Cycle Programme) project. The main objective of the paper is to determine a way to achieve an accurate, robust and reliable fluid model. The results obtained demonstrate that accurate modeling of the working fluid is essential to avoid convergence problems of the thermodynamic functions thereby increasing the accuracy of calculated fluid properties. Additionally, the impact of accurately modeling fuel thermodynamic properties, at the point of the injection, is discussed.