Surge Margin Tracking for Active Control of Quick Windmill Relighting

Surge margin tracking logic is developed for use in the control of quick windmill relighting (QWR) at sub-idle. Using existing high pressure compressor (HPC) characteristics (but without any gas turbine engine model), the surge margin can be calculated and used to approximate the air flow which is currently not measured in flight. During the QWR flight test, only limited measurements excluding the airflow measurement are available. Based on the fact that a beta value is equivalent to the position of the throttle valve in a compressor test rig, the role of the beta value is here to interrelate between the PRC (pressure ratio of compressor) and NDMF (non-dimensional mass flow) values for the measured CNH (corrected high pressure spool speed) and PRC values. Using the proposed scaling factors (SFs), the HPC map in terms of PRC is adaptively scaled with the engine parameters to cover the operating pressure ratio of the HPC. These account qualitatively for the effects of heat soakage and stability aids such as bleed and VSV (variable stator vane) on the compressor map. The simulation results show that the variable SF approach is more realistic in estimation of the surge margin, compared to the fixed SF approach. As a result of this proposed surge margin tracking logic, an active control for QWR may be possible using an estimated surge margin to adjust the fuel flow. This improves the pull-away time to reach idle power without danger of stall or surge during QWR.

Development and Evaluation of Environmental Barrier Coatings for Si-Based Ceramics

Environmental barrier coatings (EBCs) are being developed for silicon carbide (SiC) based composites and monolithic silicon nitride (Si3N4) to protect against the accelerated oxidation and subsequent silica volatilization in high temperature, high-pressure steam environments encountered in gas turbine engines. While EBCs for silicon carbide (EBCSiC) have been demonstrated in combustor liner applications, efforts are ongoing in the development of EBC systems for silicon nitride (EBCSiN). The challenges of adapting EBCSiC to monolithic Si3N4 are discussed in this paper. Progress in the area of EBCSiN including development and performance during field tests and tests simulating engine conditions are reviewed.

Cumulative Damage Mechanics: Characterization, Modeling, and Interpretation of Progressive Failure in Ceramics and Composites

Ceramic matrix composites (CMCs) have evolved to exhibit inherent damage tolerance through nonlinear energy absorption mechanisms while retaining the desirable attributes of their monolithic structural ceramic counterparts. Mathematical (analytic and numeric) models together with experimental measurements of this damage absorption have aided in understanding the thermomechanical behavior of CMCs. This understanding has led to improved test methods, better predictive modeling of material behavior, appropriate processing methods, and finally novel design methodologies for implementing CMCs. In this paper, background on CMC damage is presented, damage measurement and damage models are discussed and finally probabilistic aspects of constituent materials that can be used to illustrate the cumulative damage behavior of CMCs are described.

High Temperature Stability of MGCs Gas Turbine Components in Air and Combustion Gas Flow Environments

Melt growth composites (MGCs) have a unique microstructure, in which continuous networks of single-crystal phases interpenetrate without grain boundaries. Therefore, the MGCs have excellent high-temperature strength characteristics, creep resistance, oxidation resistance and thermal stability in an air atmosphere at very high temperature. To achieve ultra-high thermal efficiency and low NOx emission for gas turbine systems, non-cooled turbine nozzle vanes and heat shield panels of combustor liners has been fabricated on an experimental basis. These components are thermally stable after heat treatment at 1700°C for 1000 hours in an air atmosphere. In addition, we have just started the exposure tests to evaluate the influence of combustion gas flow environment on MGCs.

Multi-Fidelity Simulation of a Turbofan Engine With Results Zoomed Into Mini-Maps for a Zero-D Cycle Simulation

A Zero-D cycle simulation of the GE90-94B high bypass turbofan engine has been achieved utilizing mini-maps generated from a high-fidelity simulation. The simulation utilizes the Numerical Propulsion System Simulation (NPSS) thermodynamic cycle modeling system coupled to a high-fidelity full-engine model represented by a set of coupled 3D computational fluid dynamic (CFD) component models. Boundary conditions from the balanced, steady-state cycle model are used to define component boundary conditions in the full-engine model. Operating characteristics of the 3D component models are integrated into the cycle model via partial performance maps generated from the CFD flow solutions using one-dimensional meanline turbomachinery programs. This paper high-lights the generation of the highpressure compressor, booster, and fan partial performance maps, as well as turbine maps for the high pressure and low pressure turbine. These are actually “mini-maps” in the sense that they are developed only for a narrow operating range of the component. Results are compared between actual cycle data at a take-off condition and the comparable condition utilizing these mini-maps. The mini-maps are also presented with comparison to actual component data where possible.

Aero-Gasturbine Emission Reduction and Simulation Technology: Philosophy and Approach

Aircraft engine technology has gained major advances in the past 40–50 years, steadily bringing significant gains in the reduction of exhaust emissions at the source. However, with the projected increase in air traffic, the cumulative amount of aircraft emissions will still increase. This maintains the need for further progress in developing analytical methods to predict the amount and composition of exhaust gases from aircraft engines to better assess the alternatives for reducing emissions and better inform decision-makers, manufacturers and operators. The Research Project “Aero-Gasturbine Emission Reduction and Simulation Technology”, started at the Delft University of Technology in collaboration with the Dutch National Aerospace Laboratory (NLR) and the Netherlands Ministry of Traffic, is aimed to contribute to the efforts to solve the problem. With the limitations, complexity and costs of emission measurements at operational conditions, the ability to predict engine exhaust emissions by means of analytical tools becomes more urgent for minimizing aircraft engine exhaust gas emissions. This paper presents a philosophy and approach to develop such tools.

A Comparative Study of Genetic Algorithms and Gradient Methods for RM12 Turbofan Engine Diagnostics and Performance Estimation

Recent work on gas turbine diagnostics based on optimisation techniques advocates two different approaches: 1) Stochastic optimisation, including Genetic Algorithm techniques, for its robustness when optimising objective functions with many local optima and 2) Gradient based methods mainly for their computational efficiency. For smooth and single optimum functions, gradient methods are known to provide superior numerical performance. This paper addresses the key issue for method selection, i.e. whether multiple local optima may occur when the optimisation approach is applied to real engine testing. Two performance test data sets for the RM12 low bypass ratio turbofan engine, powering the Swedish Fighter Gripen, have been analysed. One set of data was recorded during performance testing of a highly degraded engine. This engine has been subjected to Accelerated Mission Testing (AMT) cycles corresponding to more than 4000 hours of run time. The other data set was recorded for a development engine with less than 200 hours of operation. The search for multiple optima was performed starting from more than 100 extreme points. Not a single case of multi-modality was encountered, i.e. one unique solution for each of the two data sets was consistently obtained. The RM12 engine cycle is typical for a modern fighter engine, implying that the obtained results can be transferred to, at least, most low bypass ratio turbofan engines. The paper goes on to describe the numerical difficulties that had to be resolved to obtain efficient and robust performance by the gradient solvers. Ill conditioning and noise may, as illustrated on a model problem, introduce local optima without a correspondence in the gas turbine physics. Numerical methods exploiting the special problem structure represented by a non-linear least squares formulation is given special attention. Finally, a mixed norm allowing for both robustness and numerical efficiency is suggested.

Ongoing Development and Recent Results of the Research in the Swedish Gas Turbine Centre (GTC)

This paper describes a way of co-operation between industries, universities and government that has proven to be very fruitful. The Swedish Gas Turbine Centre (GTC) is constituted as a research consortium between technical universities and gas turbine industry. The overall goal of the centre, that was founded in 1996 on a governmental initiative, is to build up a basis of knowledge at Swedish universities to support the industrial development in Sweden of gas turbines of the future with expected requirements on low emissions, high efficiencies, high availability, and low costs. Since the start the research has had a focus on high temperature components of gas turbines (combustion chamber and turbine). This is also reflected in the on-going development phase where the research program consists of four project areas: cooling technology, combustion technology, aeroelasticity, and life time prediction of hot components. The projects are aiming at developing design tools and calculation and verification methods within these fields. A total of eleven research students (among them one industrial PhD student) are active in the centre at present. Numerical analysis as well as experimental verification in test rigs are included. The program has so far produced eleven Licentiate of Engineering and five PhD. On-going activities and recent results of the research in the four research areas are presented: • A new test rig for investigation of time-dependent pressures of three-dimensional features on a vibrating turbine blade at realistic Mach, Reynolds and Strouhal numbers and first experimental results. • Results of numerical simulations of heat loads on turbine blades and vanes, especially platform cooling. • First results of numerical investigations of combustion and thermo-acoustic instabilities in gas turbine chambers. • Experimental investigation of crack propagation in gas turbine materials using the scanning electron microscope (SEM).

Engine Test and Post Engine Test Characterization of Self-Sealing Ceramic Matrix Composites for Nozzle Applications in Gas Turbine Engines

The advancement of self-sealing ceramic matrix composites offers durability improvements in hot section components of gas turbine engines. These durability improvements come with no need for internal cooling and with reduced weight. Building on past material efforts, ceramic matrix composites based on either a carbon fiber or a SiC fiber with a sequenced self-sealing matrix have been developed for gas turbine applications. The specific application being pursued on this effort is an F100-PW-229 nozzle seal. Full design life ground engine testing has been accomplished with both material systems. The ground testing has demonstrated a significant durability improvement from the baseline metal design. Residual properties are being determined for both systems by extracting tensile and microstructural coupons from the ceramic matrix composite seal. Nondestructive interrogation showed no material degradation and was used as a guide in setting cutting diagrams. The results from this effort will be presented along with documentation from flight test efforts.

Exposure Test Results of Lu2Si2O7 in Combustion Gas Flow at High Temperature and High Speed

In order to understand recession behavior and the amount of recession of Lu2Si2O7 in the combustion gas flow, sintered Lu2Si2O7 specimens were manufactured by hot pressing and exposed under various combustion gas flow conditions (T = 1300–1500 °C, P = 0.3 MPa, V = 150 m/s, PH2O = 27–69 kPa, t = 10h). After the exposure tests, etch pits, which are assumed to form due to volatilization of SiO2 in the grain boundary phase, were observed at the surface of specimen. The amount of Lu2SiO5 phase at the surface of specimen increased with the increase of gas temperature or water vapor partial pressure. A corresponding decrease in the amount of Lu2Si2O7 phase was observed. Furthermore, by using the average weight loss rate for exposure times of ten hours, the influence of gas temperature and water vapor partial pressure on weight loss rate was examined, and the amount of recession under gas turbine conditions was calculated.