Steady State Detection in Industrial Gas Turbines for Condition Monitoring and Diagnostics Applications

This work describes the development and implementation of a signal analysis module which allows the reliable detection of operating regimes in industrial gas turbines. Its use is intended for steady state-based condition monitoring and diagnostics systems. This type of systems requires the determination of the operating regime of the equipment, in this particular case, of the industrial gas turbine. After a brief introduction the context in which the signal analysis module is developed is highlighted. Next the state of the art of the different methodologies used for steady state detection in equipment is summarized. A detailed description of the signal analysis module developed, including its different sub systems and the main hypotheses considered during its development, is shown to follow. Finally the main results obtained through the use of the module developed are presented and discussed. The results obtained emphasize the adequacy of this type of procedures for the determination of operating regimes in industrial gas turbines.

Investigation of Filtered Rayleigh Scattering Techniques for Rig Testing Diagnostics

A laboratory investigation of Filtered Rayleigh Scattering (FRS) techniques for high-resolution and high-accuracy temperature measurements in rig tests with high pressures and temperatures and combustion is presented. Imaging techniques based on filtered Rayleigh scattering have the potential for two-dimensional (2D) and near wall measurement of gas velocity and temperature fields among other properties. For gas temperature measurements, laser Rayleigh scattering from gas molecules are typically captured with an ICCD camera and temperature can be inferred from the number density measured from the image intensities. The accuracy challenges associated with property spatial variations, gas composition, and pressure and temperature conditions are investigated for the rig test environments. Representative examples including mixing layer, jet and vortex flows and flame and combustion tests are presented.

Hybrid Modeling of Heavy Duty Gas Turbines for On-Line Performance Monitoring

Due to their complex physics, accurate modeling of modern heavy duty gas turbines can be both challenging and time consuming. For online performance monitoring, the purpose of modeling is to predict operational parameters to assess the current performance and identify any possible deviation between the model’s expected performance parameters and the actual performance. In this paper, a method is presented to tune a physical model to a specific gas turbine by applying a data-driven approach to correct for the differences between the real gas turbine operation and the performance model prediction of the same. The first step in this process is to generate a surrogate model of the 1st principle performance model through the use of a neural network. A second “correction model” is then developed from selected operational data to correct the differences between the surrogate model and the real gas turbine. This corrects for the inaccuracies between the performance model and the real operation. The methodology is described and the results from its application to a heavy duty gas turbine are presented in this paper.

Mullite Whisker Reinforced Zirconia Toughened Alumina for High Temperature Applications

Particulate enhanced oxide ceramics are an attractive class of materials for high temperature applications because they possess many of the high temperature capabilities of monolithic ceramics but also have enhanced mechanical properties due to their multi-phase structure. High temperature structural ceramics have the potential to operate above at higher temperatures than current super alloys; however, processing costs and lack of reliability has prevented their commercialization. In this work a particulate reinforced ceramic composed entirely of oxides is proposed as a more oxidation resistant and cost effective structural ceramic which will have potentially improved resistance to environmental degradation. Zirconia Toughened Alumina (ZTA), as the matrix, has enhanced toughness, strength, and creep resistance over single phase alumina or zirconia. ZTA can further be strengthened by the incorporation of SiC type whiskers; however, these whiskers are prone to deterioration at temperatures above 1000°C through oxidation. In this work Mullite, in whisker form, is proposed as the reinforcement to ZTA due to its stability in oxidizing atmospheres at high temperatures. Mullite whiskers are grown through the molten salt method and incorporated into the ZTA matrix using a colloidal processing route in this study. The composition of the ZTA matrix is 15wt% Yttria stabilized Zirconia (YSZ), 85 wt% α-Alumina. The Mullite whiskers make up 20 vol% of the composite, yielding a final composition of 71.6 wt% Alumina, 12.7 wt% YSZ, and 15.6 wt% Mullite. The green compacts are fired in a two stage sintering process incorporating atmospheric pressure sintering to 92% density (seal the pore channels) and then hot isostatic pressure pressing (HIP) to increase the density. Samples have been tested for room temperature flexural strength using a three point bend test and fracture toughness through Gong’s Vickers indentation method. The results of microstructure study and mechanical tests are reported in this paper.

An Approximate Method to Obtain Thermodynamic Gas Properties for Use in Gas Turbines

The calculation of the performance of gas turbines, turbochargers, compressors and turbines requires the thermodynamic properties of the gases. Tables of properties exist which are effectively exact, but using these tables is tedious and far from practical in computer-based calculations. Representing tabulated results with polynomial approximations is inconvenient and prone to error in implementation. For teaching and simple calculations simple approximations, such as γ = 1.4 for unburned air and γ = 1.3 for combustion products, are sometimes used, but this is far from wholly satisfactory. This paper describes and discusses a simple empirical approach which will give adequate accuracy for many purposes but is simple enough to be used as part of an educational course.

Fuel System With Variable Speed Pump to Improve Thermal Management Ability for Aircraft Engines

Now, fuel systems on aircrafts/engines are required to rapidly improve thermal management technology. The proposed variable speed pump systems are a unique solution to improve the thermal management of aircrafts/engines without requiring a major change in the conventional interface between a jet engine and a fuel system. Concurrently, the proposed systems have the possibility to improve SFC by about 0.25% during cruise on a small turbofan engine due to reducing inefficient energy consumption. These systems lead to minimize the conventional cooling mechanisms and contribute to the additional improvement of SFC. The purpose of this paper is to show the characteristics of the proposed systems.

Development of the Electric Fuel System for the More Electric Engine

This paper describes the experimental rig test result of the electric motor-driven fuel pump system for the MEE (More Electric Engine). The MEE is an aircraft engine system concept, which replaces conventional mechanical/hydraulic driven components with electric motor-driven components. Various MEE approaches have been studied since the early 2000s and one of its key concepts is an electric motor-driven fuel pump [1–4]. The authors commenced a feasibility study of the electric motor-driven gear pump system for what was assumed to be a small-sized turbofan engine. The concept study and system design were conducted, whereupon technical issues for the electric fuel pump system, which both supplies and meters fuel via the motor speed control, were clarified [5, 6]. Since one of the key issues is fuel-metering accuracy, the electric fuel system, including a flow feedback closed-loop control, was designed to ensure accurate fuel-flow metering for aircraft engine applications. To verify the rig system, an experimental model of the electric fuel pump system is assumed for a small-sized turbofan engine. The hardware of the motor-driven fuel pump and flow measurement mechanism, including an FPV (Fuel-Pressurizing Valve) and orifice, were designed, manufactured and fabricated and a differential pressure sensor for flow feedback was selected. Other equipment was also prepared, including a motor controller, power source and measurement devices, and the entire rig set-up was constructed. A bench test using the rig test set-up was conducted to verify the fuel-metering accuracy, response and system stability. Data, including the static performance and frequency response, were obtained for the electric motor, motor-driven fuel pump and entire fuel system respectively. The rig test results indicate the feasibility of the system, which will provide an accurate engine fuel flow (Wf) measurement and frequency response required for actual engine operation, via an electric motor speed control and fuel-flow feedback system, as proposed in the MEE electric fuel system.

Synchrotron XRD Measurements Mapping Internal Strains of Thermal Barrier Coatings During Thermal Gradient Mechanical Fatigue Loading

An understanding of the high temperature mechanics experienced in Thermal Barrier Coatings (TBC) during cycling conditions would be highly beneficial to extending the lifespan of the coatings. This study will present results obtained using synchrotron x-rays to measure depth resolved strains in the various layers of TBCs under thermal mechanical loading and a superposed thermal gradient. Tubular specimens, coated with Yttria Stabilized Zirconia (YSZ) and an aluminum containing nickel alloy as a bond coat both through Electron Beam - Physical Vapor Deposition (EBPVD), were subjected to external heating and controlled internal cooling generating a thermal gradient across the specimen’s wall. Temperatures at the external surface were in excess of 1000 °C. Throughout high temperature testing, 2-D high-resolution XRD strain measurements are taken at various locations through the entire depth of the coating layers. Across the YSZ a strain gradient was observed showing higher compressive strain at the interface to the bond coat than towards the surface. This behavior can be attributed to the specific microstructure of the EB-PVD-coating, which reveals higher porosity at the outer surface than at the interface to the bond coat, resulting in a lower in plane modulus near the surface. This location at the interface displays the most significant variation due to applied load at room temperature with this effect diminishing at elevated uniform temperatures. During thermal cycling with a thermal gradient and mechanical loading, the bond coat strain moves from a highly tensile state at room temperature to an initially compressive state at high temperature before relaxing to zero during the high temperature hold. The results of these experiments give insight into previously unseen material behavior at high temperature which can be used to develop an increased understanding of various failure modes and their causes.

Development of a Course on Gas and Steam Turbines Supported by Cost-Efficient Turbomachinery Experiments

Based on a voice-of-the-industry survey covering major turbine manufactures as well as power plant owners and operators an undergraduate course on gas and steam turbines was developed at Muenster University of Applied Sciences. This course is also supported by cost-efficient experiments. The experimental investigations on laboratory test rigs are making the students more familiar with turbomachinery phenomena like gas turbine cycle performance, fundamental rotordynamics, blade vibrations, and flow through turbine cascades and loss correlations. The experiments and test rigs were developed in great part by students as part of their Bachelor or Master theses. Furthermore, the experiments did not require tremendous efforts or an expensive infrastructure; they were operated in typical University laboratory environments.

High Velocity Impact Damage Assessment in SiC/SiC Composites

Foreign object damage in gas turbines presents serious safety and financial concerns. As the aerospace industry draws closer to implementing ceramic matrix composites (CMCs) in gas turbines, the corresponding behavior in these materials after such events needs to be understood. To address this requirement, several silicon infiltrated fiber reinforced SiC/SiC coupons were impacted with high speed projectiles with velocities up to 360 m/s with an impact rig built at the University of Akron and NAVAIR. The resulting damage states were assessed using several non-destructive evaluation (NDE) techniques and compared to actual damage condition observed through the sectioning of impacted coupons. Ultimately, the true consequence of the damage was revealed by measuring the post-impact, residual strengths via uniaxial tensile tests to failure at both room and elevated temperatures. Lastly, the NDE results revealed a complicated damage morphology consisting of in-and-out-of plane damage that significantly affected the retained mechanical properties.