Mark R. Woike

Testing of a Microwave Blade Tip Clearance Sensor at the NASA Glenn Research Center

Abstract The development of new active tip clearance control and structural health monitoring schemes in turbine engines and other types of rotating machinery requires sensors that are highly accurate and can operate in a high-temperature environment. The use of a microwave sensor to acquire blade tip clearance and tip timing measurements is being explored at the NASA Glenn Research Center. The microwave blade tip clearance sensor works on principles that are very similar to a short-range radar system. The sensor sends a continuous microwave signal towards a target and measures the reflected signal. The phase difference of the reflected signal is directly proportional to the distance between the sensor and the target being measured. This type of sensor is beneficial in that it has the ability to operate at extremely high temperatures and is unaffected by contaminants that may be present in turbine engines. The use of microwave sensors for this application is a new concept. Techniques on calibrating the sensors along with installation effects are not well quantified as they are for other sensor technologies. Developing calibration techniques and evaluating installation effects are essential in using these sensors to make tip clearance and tip timing measurements. As a means of better understanding these issues, the microwave sensors were used on a benchtop calibration rig, a large axial vane fan, and a turbofan. Background on the microwave tip clearance sensor, an overview of their calibration, and the results from their use on the axial vane fan and the turbofan will be presented in this paper.

NDE using sensor based approach to propulsion health monitoring of a turbine engine disk

Rotor health monitoring and on-line damage detection have been increasingly gaining interest to manufacturers of aircraft engines, primarily to increase safety of operation and lower the high maintenance costs. But health monitoring in the presence of scatter in the loading conditions, crack size, disk geometry, and material property is rather challenging. However, detection factors that cause fractures and hidden internal cracks can be implemented via noninvasive types of health monitoring and or nondestructive evaluation techniques. These evaluations go further to inspect materials discontinuities and other anomalies that have grown to become critical defects that can lead to failure. To address the bulk of these concerning issues and understand the technical aspects leading to these outcomes, a combined analytical and experimental study is being thought. Results produced from the experiments such as blade tip displacement and other data collected from tests conducted at the NASA Glenn Research Centers Rotordynamics Laboratory, a high precision spin rig, are evaluated, discussed and compared with data predicted from finite element analysis simulating the engine rotor disk spinning at various rotational speeds. Further computations using the progressive failure analysis (PFA) approach with GENOA code [6] to additionally assess the structural response, damage initiation, propagation, and failure criterion are also performed. This study presents an inclusive evaluation of an on-line health monitoring of a rotating disk and an examination for the capability of the in-house spin system in support of ongoing research under the NASA Integrated Vehicle Health Management (IVHM) program.

Demonstration of a reheat combustor for power production with CO2 sequestration

Concerns about climate change have encouraged significant interest in concepts for ultralow or “zero”-emissions power generation systems. In a concept proposed by Clean Energy Systems, Inc., nitrogen is removed from the combustion air and replaced with steam diluent. In this way, formation of nitrogen oxides is prevented, and the exhaust stream can be separated into concentrated CO2 and water streams. The concentrated CO2 stream could then serve as input to a CO2 sequestration process. In this study, experimental data are reported from a full-scale combustion test using steam as the diluent in oxy-fuel combustion. This combustor represents the “reheat” combustion system in a steam cycle that uses a high and low-pressure steam expansion. The reheat combustor serves to raise the temperature of the low-pressure steam turbine inlet, similar to the reheat stage of a conventional steam power cycle. Unlike a conventional steam cycle, the reheat enthalpy is actually generated by oxy-fuel combustion in the steam flow. This paper reports on the unique design aspects of this combustor, as well as initial emissions and operating performance.

A Microwave Blade Tip Clearance Sensor for Propulsion Health Monitoring

The NASA Glenn Research Center has investigated a microwave blade tip clearance system for the structural health monitoring of gas turbine engines. This presentation describes the sensors and the experiments that have been conducted to evaluate their performance along with future plans for their use on an engine ground test.

Crack-Detection Experiments on Simulated Turbine Engine Disks in NASA Glenn Research Center's Rotordynamics Laboratory

The development of new health-monitoring techniques requires the use of theoretical and experimental tools to allow new concepts to be demonstrated and validated prior to use on more complicated and expensive engine hardware. In order to meet this need, significant upgrades were made to NASA Glenn Research Center’s Rotordynamics Laboratory and a series of tests were conducted on simulated turbine engine disks as a means of demonstrating potential crack-detection techniques. The Rotordynamics Laboratory consists of a highprecision spin rig that can rotate subscale engine disks at speeds up to 12 000 rpm. The crack-detection experiment involved introducing a notch on a subscale engine disk and measuring its vibration response using externally mounted blade-tip-clearance sensors as the disk was operated at speeds up to 12 000 rpm. Testing was accomplished on both a clean baseline disk and a disk with an artificial crack: a 50.8-mm- (2-in.-) long introduced notch. The disk’s vibration responses were compared and evaluated against theoretical models to investigate their applicability to and success of detecting cracks. This paper presents the capabilities of the Rotordynamics Laboratory, the baseline theory and experimental setup for the crack-detection experiments, and the associated results from the latest test campaign. I. Introduction HE development of fault-detection techniques for the in situ health monitoring of gas turbine engines is of high interest to NASA’s Aviation Safety Program (AVSP). The rotating components of modern gas turbine engines operate in severe environmental conditions and are exposed to high thermal and mechanical loads. The cumulative effects of these loads over time lead to high stresses, structural deformity, and eventual component failure. Current risk-mitigation practices involve periodic inspections and schedule-based maintenance of engine components to ensure their integrity over the lifetime of the engine. However, these methods have their limitations, and failures are experienced leading to unscheduled maintenance and unplanned engine shutdowns. To prevent these failures and enhance aviation safety, the NASA Integrated Vehicle Health Management (IVHM) Project, as part of the overall AVSP, is investigating new types of sensor technologies and methods for the in situ structural health monitoring and detection of flaws in gas turbine engines. The successful development and implementation of such technology and health-monitoring techniques requires the use of both theoretical and experimental tools to allow new concepts to be investigated and demonstrated prior to use on more complicated and expensive hardware. In order to meet this need, research has been conducted at the NASA Glenn Research Center to develop both global and local approaches for monitoring critical rotor components. 1-6

New Sensors and Techniques for the Structural Health Monitoring of Propulsion Systems

The ability to monitor the structural health of the rotating components, especially in the hot sections of turbine engines, is of major interest to aero community in improving engine safety and reliability. The use of instrumentation for these applications remains very challenging. It requires sensors and techniques that are highly accurate, are able to operate in a high temperature environment, and can detect minute changes and hidden flaws before catastrophic events occur. The National Aeronautics and Space Administration (NASA), through the Aviation Safety Program (AVSP), has taken a lead role in the development of new sensor technologies and techniques for the in situ structural health monitoring of gas turbine engines. This paper presents a summary of key results and findings obtained from three different structural health monitoring approaches that have been investigated. This includes evaluating the performance of a novel microwave blade tip clearance sensor; a vibration based crack detection technique using an externally mounted capacitive blade tip clearance sensor; and lastly the results of using data driven anomaly detection algorithms for detecting cracks in a rotating disk.

Rotor health monitoring combining spin tests and data-driven anomaly detection methods

Health monitoring is highly dependent on sensor systems that are capable of performing in various engine environmental conditions and able to transmit a signal upon a predetermined crack length, while acting in a neutral form upon the overall performance of the engine system. Efforts are under way at NASA Glenn Research Center through support of the Intelligent Vehicle Health Management Project (IVHM) to develop and implement such sensor technology for a wide variety of applications. These efforts are focused on developing high temperature, wireless, low cost, and durable products. In an effort to address technical issues concerning health monitoring, this article considers data collected from an experimental study using high frequency capacitive sensor technology to capture blade tip clearance and tip timing measurements in a rotating turbine engine-like-disk to detect the disk faults and assess its structural integrity. The experimental results composed at a range of rotational speeds from tests conducted at the NASA Glenn Research Center’s Rotordynamics Laboratory are evaluated and integrated into multiple data-driven anomaly detection techniques to identify faults and anomalies in the disk. In summary, this study presents a select evaluation of online health monitoring of a rotating disk using high caliber capacitive sensors and demonstrates the capability of the in-house spin system.

Development of a Flaw Detection/Health Monitoring Scheme for Turbine Engine Rotating Components

The hot section components of jet engines undergo severe environmental operating conditions where combined thermal and mechanical loading is the dominant factor in affecting their durability and performance. Minimizing the impact of these loads and inventing a flaw detection technology to monitor the health of these components is of utmost importance to the NASA Aviation Safety Program (AVSP). Work is underway through the AVSP’s Integrated Vehicle Health Management (IVHM) Project to conduct research on ways to improve the safety, structural durability of critical hot engine section components, reduce cost, and improve performance in every aircraft class. Therefore, it is NASA’s goal to develop a robust health monitoring technique via utilizing means of in-situ and wireless detection technology by expanding on sensor systems that are capable of functioning in severe environments, transmitting a signal upon detecting a predetermined crack length, and acting in an impartial fashion with respect to the overall performance of the engine system. Development and implementation of such sensor technology and diagnostic capabilities is possible only by conducting combined analytical and experimental studies (coupon and sub-scale levels) to determine their applicability and success. As a result, ongoing research at NASA GRC has aimed at investigating both global and local approaches for monitoring critical rotor components 1-4 . This paper is focused on presenting current ongoing research activities concerning health monitoringflaw detection systems of turbine engine rotating components and their relevance on meeting the IVHM program goals and millstones. Test data obtained under various operating conditions of a rotor disk with and without an artificially induced notch rotated at a rotational speed up to 12000 Rpm are presented, discussed and evaluated for health monitoring applications. Disk flaw observations and related assessments from the collected data are reported. Lastly, parallel analytical results of disk spinning at a range of rotational speeds showing the disk modal shapes and notch influence on damage initiation and crack propagation are also included.

Structural Health Monitoring on Turbine Engines Using Microwave Blade Tip Clearance Sensors

The ability to monitor the structural health of the rotating components, especially in the hot sections of turbine engines, is of major interest to the aero community in improving engine safety and reliability. The use of instrumentation for these applications remains very challenging. It requires sensors and techniques that are highly accurate, are able to operate in a high temperature environment, and can detect minute changes and hidden flaws before catastrophic events occur. The National Aeronautics and Space Administration (NASA) has taken a lead role in the investigation of new sensor technologies and techniques for the in situ structural health monitoring of gas turbine engines. As part of this effort, microwave sensor technology has been investigated as a means of making high temperature non-contact blade tip clearance, blade tip timing, and blade vibration measurements for use in gas turbine engines. This paper presents a summary of key results and findings obtained from the evaluation of two different types of microwave sensors that have been investigated for possible use in structural health monitoring applications. The first is a microwave blade tip clearance sensor that has been evaluated on a large scale Axial Vane Fan, a subscale Turbofan, and more recently on sub-scale turbine engine like disks. The second is a novel microwave based blade vibration sensor that was also used in parallel with the microwave blade tip clearance sensors on the same experiments with the sub-scale turbine engine disks.

Investigation of a Moire Based Crack Detection Technique for Propulsion Health Monitoring

The development of techniques for the health monitoring of the rotating components in gas turbine engines is of major interest to NASAs Aviation Safety Program. As part of this on-going effort several experiments utilizing a novel optical Moiré based concept along with external blade tip clearance and shaft displacement instrumentation were conducted on a simulated turbine engine disk as a means of demonstrating a potential optical crack detection technique. A Moiré pattern results from the overlap of two repetitive patterns with slightly different periods. With this technique, it is possible to detect very small differences in spacing and hence radial growth in a rotating disk due to a flaw such as a crack. The experiment involved etching a circular reference pattern on a subscale engine disk that had a 50.8 mm (2 in.) long notch machined into it to simulate a crack. The disk was operated at speeds up to 12 000 RPM and the Moiré pattern due to the shift with respect to the reference pattern was monitored as a means of detecting the radial growth of the disk due to the defect. In addition, blade displacement data were acquired using external blade tip clearance and shaft displacement sensors as a means of confirming the data obtained from the optical technique. The results of the crack detection experiments and its associated analysis are presented in this paper.