Electrical Resistance and Acoustic Emission During Fatigue Testing of Pristine and High Velocity Impact SiC/SiC Composites at Room and Elevated Temperature

Electrical resistance (ER) is a relatively new approach for real-time monitoring and evaluating damage in SiC/SiC composites for a variety of loading conditions. In this study, ER of woven silicon carbide fiber-reinforced silicon carbide composite systems in their pristine and impacted state were measured under cyclic loading conditions at room and high temperature (1200C). In addition, modal acoustic emission (AE) was also monitored, which can reveal the occasion of matrix cracks and fiber. ER measurement and AE technique are shown in this study to be useful methods to monitor damage and indicate the failure under cyclic loading. Based on the slope of the ER evolution, an initial attempt has been made to develop a method allowing a critical damage phase to be identified. While the physical meaning of the critical point is not yet clear, it has the potential to allow the failure to be indicated at its early stage.

Evaluation of Measurement Uncertainties for Pneumatic Multi-Hole Probes Using a Monte Carlo Method

The subject of this paper is a statistical method for the accurate evaluation of the uncertainties for pneumatic multi-hole probe measurements. The method can be applied to different types of evaluation algorithms and is suitable for steady flowfield measurements in compressible flows. The evaluation of uncertainties is performed by a Monte Carlo method (MCM), which is based on the statistical law of large numbers. Each input quantity, including calibration and measurement quantities, is randomly varied on the basis of its corresponding probability density function (PDF) and propagated through the deterministic parameter evaluation algorithm. Other than linear Taylor series based uncertainty evaluation methods, MCM features several advantages. On the one hand, MCM does not suffer from lower-order expansion errors and can therefore reproduce nonlinearity effects. On the other hand, different types of PDFs can be assumed for the input quantities and the corresponding coverage intervals can be calculated for any coverage probability. To demonstrate the uncertainty evaluation, a calibration and subsequent measurements in the wake of an airfoil with a 5-hole probe are performed. MCM is applied to different parameter evaluation algorithms. It is found that the MCM approach presented cannot be applied to polynomial curve fits, if the differences between the calibration data and the polynomial curve fits are of the same order of magnitude compared to the calibration uncertainty. Since this method has not yet been used for the evaluation of measurement uncertainties for pneumatic multi-hole probes, the aim of the paper is to present a highly accurate and easy-to-implement uncertainty evaluation method.

Establishment of a Competitive Additive Manufacturing Workshop

Compared to conventional manufacturing processes, additive manufacturing offers a degree of freedom that has the potential to revolutionize the turbine components supply chain. Additive manufacturing facilitates the design and manufacture of highly complex components in high performance materials with features that cannot currently be realized with other processes. In addition, shorter development and manufacturing lead-times are possible due to the flexibility of 3D based processing and the absence of expensive, complicated molds or dies. Having been confined for many years to rapid prototyping or R&D applications, additive manufacturing is now making the move to the factory floor. However, a dearth of manufacturing experience makes the development effort and risk of costly mistakes a deterrent for many organizations that would otherwise be interested in exploring the benefits of additive manufacturing. A former manufacturer of industrial gas turbines recently established an additive manufacturing workshop designed to deliver highly complex engine-ready components that can contribute to increased performance of the gas turbine. A strong emphasis on process validation and implementation of the organization’s best practice Lean and Quality methodologies has laid solid foundations for a highly capable manufacturing environment. This paper describes the approach taken to ensure that the workshop achieves a high level of operational excellence. Process development topics explored in the paper include the following: • Planning of process flow and cell layout to permit the maximum lean performance • Strategy used to determine machine specification and selection method. • Assessment of process capability • Influence of design for manufacture on process efficiency and product quality • Experience gained during actual production of first commercial components

The Application of Ceramic Matrix Composite to Low Pressure Turbine Blade

The structural reliability of composite parts for aircraft is established through the “building block” approach, which is a series of tests that are conducted using specimens of various levels of complexity. In this approach, the failure modes and criteria are validated step by step with tests and analysis at coupon, element, sub-component, and component levels. IHI is developing ceramic matrix composite (CMC) components for aircraft engines to realize performance improvement and weight reduction. We conducted the concept design of CMC low pressure turbine (LPT) blade with the building block approach. In this paper, we present the processes and results of the design, which was supported by a series of tests. Typical low pressure turbine blade has dovetail, airfoil and tip shroud. Each element has different function and characteristic shape. In order to select the configuration of CMC LPT blade, we conducted screening tests for each element. The function of dovetail is to sustain the connection with blade and disk against centrifugal force. The failure modes and strength of dovetail elements were examined by static load tests and cyclic load tests. The configuration of airfoil was selected by modal tests. The function of tip shroud is forming gas passage and reducing the leakage flow, therefore this portion needs to sustain the shape against the centrifugal force and the rubbing force. The feasibility of tip shroud was verified by spin tests and rubbing tests. The initial CMC LPT blades were designed as combination of the selected elements by these screening tests. Prototype parts were made and tested to check the manufacturability and the structural feasibility. The static strength to the centrifugal force was examined by spin test. The durability to vibration was examined by HCF test.

Defect Detection in an Annular Swirl-Burner-Array by Optical Measuring Exhaust Gases

Defects in combustion chambers of aircraft engines might have an impact on the reliability of the downstream turbine and the machine’s performance. Detecting failures in the combustion chamber of an aircraft engine during operation may improve the resource management and the availability of the system. Aim of the ongoing research project is to find an approach to evaluate the state of the jet engine by analyzing the temperature and emissions field in the exhaust jet. This investigation is part of the collaborative research center SFB 871. The SFB 871 deals with the improvement of the regeneration process of complex capital goods such as aircraft engines. Maintenance, repair, and overhaul processes would be more efficient if the internal status of the engine would be known while still on the wing before it is disassembled. The feasibility of this approach is investigated for a pilot scaled model combustor, which provides optical access and allows the selection of “defined errors” in the combustor. It consists of an atmospheric tubular combustor with an array of eight premixed swirl burners with a maximum output of 160 kW. The operating conditions of one of the eight burners concerning power and air-fuel ratio, can be controlled. A power distribution between the burners is typical fault in an aircraft combustor and will be investigated in this study. It is observed that it is possible to determine small deviations by measuring density profiles applying a tomographic background-oriented schlieren (BOS) technique behind the combustor. Additionally, particle image velocimetry is used to measure differences in the velocity field of the exhaust gases. This study shows that a minimum power deviation of one burner in an array of a total of eight burners is detectable in the exhaust plane with the above mentioned measurement techniques.

A Damage Evaluation Model of Turbine Blade for Gas Turbine

Current maintenance, having a great impact on the safety, reliability and economics of gas turbine, becomes the major obstacle of the application of gas turbine in energy field. An effective solution is to process Condition based Maintenance (CBM) thoroughly for gas turbine. Maintenance of high temperature blade, accounting for most of the maintenance cost and time, is the crucial section of gas turbine maintenance. The suggested life of high temperature blade by Original Equipment Manufacturer (OEM) is based on several certain operating conditions, which is used for Time based Maintenance (TBM). Thus, for the requirement of gas turbine CBM, a damage evaluation model is demanded to estimate the life consumption in real time. A physics-based model is built, consisting of thermodynamic performance simulation model, mechanical stress estimation model, thermal estimation model, creep damage analysis model and fatigue damage analysis model. Unmeasured parameters are simulated by the thermodynamic performance simulation model, as the input of the mechanical stress estimation model and the thermal estimation model. Then the stress and temperature distribution of blades will be got as the input of the creep damage analysis model and the fatigue damage analysis model. The real-time damage of blades will be evaluated based on the creep and fatigue analysis results. To validate this physics-based model, it is used to calculate the lifes of high temperature blade under several certain operating conditions. And the results are compared to the suggestion value of OEM. An application case is designed to evaluate the application effect of this model. The result shows that the relative error of this model is less than 10.4% in selected cases. And it can cut overhaul costs and increase the availability of gas turbine significantly. Therefore, the physical-based damage evaluation model proposed in this paper, is found to be a useful tool to tracing the real-time life consumption of high temperature blade, to support the implementation of CBM for gas turbine, and to guarantee the reliability of gas turbine with lowest maintenance costs.

Derivative Design of Axial Fan Range: From Academia to Industry

The work presented in this paper concerns a useful method for axial fans preliminary design based on the “Derivative Design” concept. The emphasis is, on one side, on education and, on the other, on the practical help that such method can provide in the early preliminary design process. A complete data set of an axial fan measured with ISO 5801 standards is the start point for the investigation and the prediction of the multiple possible performance that different fan configurations can provide, in terms of dimensionless duty coefficients. In particular, configurations with different number of blades, and hence of solidity, are studied. The typical options of derivative design are explored and relations for performance prediction are presented. A detailed description of the derivative design methodology is followed by tests and validation. The tools employed are a fully three dimensional code, the Advanceded Actuator Disk Mode (AADM), and two other in-house codes, the Meanline Axisymmetric Calculation (MAC) and Axisymmetric Laboratory (AXLAB). Results of the derivative design method are reported, showing a good accuracy against the AADM data. The MAC and AXLAB ensure still acceptable results when increasing the solidity of the machine. On the contrary, a decrease of solidity leads to higher relative errors in the prediction of the load coefficient. In conclusion, an exploration of the possible fields of operation of a blade profile can be carried out by a correct prediction of the stage diffusion factor.

Development and Test of Oxide/Oxide CMC Combustor Liner Demonstrators for Aero Engines

Ceramic matrix composites (CMC) offer the potential of increased service temperatures and are thus an interesting alternative to conventional combustor alloys. Tubular combustor liner demonstrators made of an oxide/oxide CMC were developed for a lean combustor in a future aero-engine in the medium thrust range and tested at engine conditions. During the design various aspects like protective coating, thermo-mechanical design, development of a failure model for the CMC as well as design and test of an attachment system were taken into account. The tests of the two liners were conducted at conditions up to 80% take-off. A new protective coating was tested successfully with a coating thickness of up to t=1 mm. Different inspection criteria were derived in order to detect crack initiation at an early stage for a validation of the failure model. With the help of detailed pre- and post-test computer tomography scans to account for the micro structure of the CMC the findings of the failure model were in reasonable agreement with the test results.

Advanced High Temperature Erosion Tunnel for Testing TBC and New Turbine Blade Materials

Current elevated turbine inlet temperatures were made possible by the development of blade thermal barrier coatings (TBCs). However the effectiveness of these coatings could be compromised by erosive particles ingested into the engine with the incoming air or generated by the combustion of heavy and synthetic fuels. Reliable test facilities are essential to characterize their erosion resistance in increased test temperatures. This paper provides a detailed description of an advanced high temperature erosion tunnel capable of testing at temperature of 1370 °C (2500 °F) that has been recently constructed and installed in the University of Cincinnati Gas Turbine Erosion Lab. The paper also presents an overview of both theoretical and experimental investigations dealing with the new high temperature erosion tunnel design optimization and validation with comparisons to our legacy erosion tunnels. Results are presented for tested standard plasma sprayed 7 wt% Yttria stabilized Zirconia (7YSZ) TBC coated samples’ erosion rates at different temperatures, particle impact velocities and impingement angles.

The Use of Eddy Current Sensors for the Measurement of Rotor Blade Tip Timing: Development of a New Method Based on Integration

The advent of tip-timing systems makes it possible to assess turbomachinery blade vibration using non-contact systems. The most widely used systems in industry are optical. However, these systems are still only used on developmental gas turbine engines, largely because of contamination problems from dust, dirt, oil, water etc. Further development of these systems for in-service use is problematic because of the difficulty of eliminating contamination of the optics. Eddy current sensors are found to be a good alternative and are already being used for gas turbine health monitoring in power plants. Experimental measurements have been carried out on three different rotors using an eddy current sensor developed in a series of laboratory and engine tests in-house to measure rotor blade arrival times. A new tip-timing algorithm for eddy current sensors based on integration has been developed and is compared with two existing tip-timing algorithms: peak-to-peak and peak-and-trough. Among the three, the integration method provided the most promising results in the presence of electrical noise interference. The main aim of this work is to develop an algorithm that can be used to build a simple, robust, real-time and low cost analogue electronic circuit for use in-service health monitoring of engines.