HIGH-SPEED ROTOR TIP CLEARANCE MEASUREMENTS IN A TRANSONIC COMPRESSOR

Performance of a gas turbine compressor is directly dependent on the size of the region between the rotor blade’s tips and the surrounding casing, the tip clearance, which dynamically changes with rising rotor speed due to rotor blade radial growth from centrifugal loading. Too large a tip clearance introduces disruptive air flow that will lower compressor efficiency and lead to stall conditions, whereas too small a tip clearance will increase the risk of blade tip rubbing with the casing inner wall and may lead to catastrophic failure. This experiment is a part of a program of research that characterizes the Naval Postgraduate School Military Fan (NPSMF) in the Turbopropulsion Lab’s (TPL) Transonic Compressor Rig (TCR). This study involves the design, creation, and use of two benchtop rigs with a capacitive proximity probe blade tip clearance measurement system to develop mathematical methods to post-process capacitive probe output signals for calibration and tip clearance measurements. The mathematical methods developed in this study are validated against the tip clearance measurement system manufacturer’s method, showing improvement. A comparison of the different calibration rigs’ resulting calibration curves is discussed. The post-process method is then applied to high-speed tip clearance measurements of the NPSMF in the TCR and the results are compared to a model.Office of Naval Research, Arlington, VAOutstanding ThesisLieutenant, United States NavyApproved for public release. Distribution is unlimited

A probabilistic approach to analyse Blade Tip Timing data of non-synchronous vibrations under constant rotor speed

Blades are among the most critical components of turbomachines, their monitoring and characterization undergoing working conditions are fundamental for the insiders, both for preventing eventual breakage and for optimising future development. Two approaches are possible for monitoring rotor blade vibrations: a traditional one based on the use of strain gauges and another one called Blade Tip Timing (BTT). BTT is an indirect, non-intrusive simple and robust measurement method, but the processing of such data is not easy because they are often subsampled with respect to the Nyquist limit and the ordering of the samples is not unique. In this work the focus is on multi component non-synchronous vibrations, typical for example of flutter, measured at constant rotor speed by a BTT system. These data are organized into batches of fixed length called snapshots and they are interpreted as members of a random vector. When the signal contains only one harmonic component the frequency can be determined using a method here described and called Harmonic Matching (HM). While for the analyses of multi harmonic component vibrations a probabilistic approach capable of separating and identify the components using Principal Component Analysis (PCA) and Independent Component Analysis (ICA) is proposed. For the development of data processing methods, the possibility of having controllable and repeatable data is fundamental, for this reason two test rigs of increasing complexity have been developed and are here described

Capacitance tip timing techniques in gas turbines

The vibration of turbomachinery blades is an important phenomenon to understand, observe and predict and is the reason for developing a tip timing measurement system. Vibration leads to High Cycle Fatigue (HCF), which limits blade durability and life. HCF can result in blade failure, having expensive consequences for the engine involved. The traditional method for monitoring blade vibration under test conditions is to use blade mounted strain gauges. However, strain gauges are costly and time consuming to install. They have a limited operating life as they are subjected to the harsh on-engine conditions. Only a limited number of blades can be monitored with strain gauges as the number that can be used is limited by the number of channels in the slip ring or telemetry. They can also interfere with the assembly aerodynamics. Consequently non-intrusive alternative techniques such as tip timing are sought. Capacitance probe based clearance measurement systems see widespread use in turbomachinery applications to establish rotor blade tip clearance. This thesis reports investigations into an alternative and additional use in aero-engine rotor blade tip timing measurement for these commercially available systems. Tip clearance is of great importance in the gas turbine industry; this is clear from the fact that gas turbine efficiency has an inverse relationship with tip clearance. Large tip clearance leads to large leakage flows, hence low efficiency, thus the common use of the capacitance probe clearance measurement technique in monitoring turbomachinery. Optical systems have been successfully used to measure rotor blade tip timing on test rigs with several optical probes mounted equally spaced around the turbomachine casing. However, there are practical problems associated with mounting such monitoring systems on in-service jet engines. Optical probes require high maintenance to keep the lenses clean, probably incorporating a purge air system to keep the lenses from fouling. Such impracticalities and added weight make it unlikely that an optical probe based tip timing system will be fitted on an in-service engine in the foreseeable future. In this thesis the scope for a dual use sensor to measure both turbomachinery tip clearance and tip timing is investigated. Since it is impractical to measure blade tip clearance with an optical probe, then the obvious choice for such a sensor is a capacitance probe. Therefore, a commercially available FM capacitance probe based blade tip clearance measurement system is used in a series of tip timing practical investigations. The equipment and instrumentation designed, assembled and produced to facilitate this investigation is documented. These include the development of an optical once per revolution sensor and the design of an independent vibration measurement system based on blade mounted strain gauges. Through an extensive body of experimental work the practicalities in this alternate use of the tip clearance measurement equipment have been assessed. System responses pertaining to tip timing measurement have been investigated, characterised and quantified. The accuracy by which tip timing can be measured using the system has been reported through the findings of an experimental programme carried out on a full-sized, low-speed compressor. Specifically, dual capacitance probe tip timing derived vibration amplitudes have been compared to those derived from blade mounted strain gauge signals. Sources of error have been identified and quantified. Amplitudes were found to agree within the calculated error bands. Instantaneous resonant blade vibrations measured through single capacitance probe tip timing have been correlated with strain gauge derived vibration levels. This has also been done as the rotor traverses blade resonant speed. In this case the vibration phase change across resonance expected from theory was successfully detected through tip timing. Also, the accuracy by which blade time of arrival can be determined by using capacitance probe tip timing has been assessed using a precision OPR sensor and a non-vibrating compressor rotor blade. The characteristics of a DC capacitance probe based clearance measurement system's response to movement in 3D space in proximity to a blade tip have been mapped. Detection of small vibrations have also been investigated in a series of static impulse tests.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Arquitectura para la medida del Tip Clearance y el Time of Arrival en motores aeronáuticos

165 p.Esta tesis propone una arquitectura para la medición de dos parámetros que caracterizan elfuncionamiento de un motor aeronáutico: el Tip Clearance y el Time of Arrival. El primero representa ladistancia desde la punta de álabe a la carcasa del motor. El segundo representa el instante en que el álabepasa frente al sensor. Ambos parámetros son el punto de partida para realizar un análisis del estado devibración que sufre ese motor.La arquitectura propuesta para le medida del Tip Clearance y del Time of Arrival consigue podermonitorizar cada álabe de forma individual realizando las medidas en tiempo real. La arquitectura sepuede adaptar a las formas de onda de diversos sensores de los que se emplean habitualmente en estecampo. También permite configurar diversos aspectos de la medida o del ensayo. La arquitectura esescalable y establece un medio de sincronización que permite que se puedan medir simultáneamentevarios sensores instalados en diferentes puntos de la carcasa de motor.La validación de la arquitectura se ha realizado con las formas de onda de un sensor óptico trifurcadoprobado en ensayos reales de una etapa compresora en un túnel de viento. En la implementación se hanpropuesto algoritmos para la determinación de los dos parámetros que se adaptan al procesadoconcurrente y secuencial de una FPGA

Arquitectura para la medida del Tip Clearance y el Time of Arrival en motores aeronáuticos

165 p.Esta tesis propone una arquitectura para la medición de dos parámetros que caracterizan elfuncionamiento de un motor aeronáutico: el Tip Clearance y el Time of Arrival. El primero representa ladistancia desde la punta de álabe a la carcasa del motor. El segundo representa el instante en que el álabepasa frente al sensor. Ambos parámetros son el punto de partida para realizar un análisis del estado devibración que sufre ese motor.La arquitectura propuesta para le medida del Tip Clearance y del Time of Arrival consigue podermonitorizar cada álabe de forma individual realizando las medidas en tiempo real. La arquitectura sepuede adaptar a las formas de onda de diversos sensores de los que se emplean habitualmente en estecampo. También permite configurar diversos aspectos de la medida o del ensayo. La arquitectura esescalable y establece un medio de sincronización que permite que se puedan medir simultáneamentevarios sensores instalados en diferentes puntos de la carcasa de motor.La validación de la arquitectura se ha realizado con las formas de onda de un sensor óptico trifurcadoprobado en ensayos reales de una etapa compresora en un túnel de viento. En la implementación se hanpropuesto algoritmos para la determinación de los dos parámetros que se adaptan al procesadoconcurrente y secuencial de una FPGA

Desarrollo de un sensor de fibra óptica para la medida del tip clearance y tip timing en motores aeronáuticos

163 p.Los sensores basados en fibra óptica son cada vez más utilizados en aeronáutica debido a las ventajas que presentan frente a sensores más tradicionales. En esta tesis se presenta el diseño y desarrollo de un sensor de fibra óptica para la medida del tip clearance y del tip timing en motores aeronáuticos. Este sensor está basado en la modulación de la luz reflejada por parte de los álabes de un motor aeronáutico en función de la distancia a la que se encuentran.En el capítulo 1 se realiza una introducción a los sensores de fibra óptica dedicando especial atención a que utilizan la modulación de la intensidad como principio de funcionamiento, y se explican los parámetros que serán objeto de medida por el sensor desarrollado en la presente tesis.En el segundo capítulo se presenta la metodología seguida en el diseño y desarrollo del sensor. Se definen los objetivos y requisitos iniciales que el sensor debe cumplir y los pasos seguidos hasta conseguirlo.En el tercer capítulo se muestran los resultados obtenidos para aplicaciones reales de funcionamiento del sensor diseñado. Se presentan los resultados conseguidos en dos entornos reales de trabajo. Por un lado, el túnel de viento que el Centro de Tecnologías Aeronáuticas posee en sus instalaciones de Zamudio (Vizcaya), y por el otro, el banco de ensayos con el que cuenta el Instituto Tecnológico de las Fuerzas Aéreas polacas en Varsovia (Polonia).Este documento concluye con un capítulo en el que se recogen las conclusiones del trabajo, así como las líneas futuras del mismo. También se enumeran los artículos (incluidos en un apéndice) en los que se basa la tesis, así como las conferencias y otras publicaciones realizadas durante este periodo

Experimental Investigation of Inlet Distortion in a Multistage Axial Compressor

The primary objective of this research is to present results and methodologies used to study total pressure inlet distortion in a multi-stage axial compressor environment. The study was performed at the Purdue 3-Stage Axial Compressor Facility (P3S) which models the final three stages of a production turbofan engine’s high-pressure compressor (HPC). The goal of this study was twofold; first, to design, implement, and validate a circumferentially traversable total pressure inlet distortion generation system, and second, to demonstrate data acquisition methods to characterize the inter-stage total pressure flow fields to study the propagation and attenuation of a one-per-rev total pressure distortion. The datasets acquired for this study are intended to support the development and validation of novel computational tools and flow physics models for turbomachinery flow analysis. Total pressure inlet distortion was generated using a series of low-porosity wire gauze screens placed upstream of the compressor in the inlet duct. The screens are mounted to a rotatable duct section that can be precisely controlled. The P3S compressor features fixed instrumentation stations located at the aerodynamic interface plane (AIP) and downstream and upstream of each vane row. Furthermore, the compressor features individually indexable stator vanes which can be traverse by up to two vane passages. Using a series of coordinated distortion and vane traverses, the total pressure flow field at the AIP and subsequent inter-stage stations was characterized with a high circumferential resolution. The uniformity of the honeycomb carrier was demonstrated by characterizing the flow field at the AIP while no distortion screens where installed. Next, the distortion screen used for this study was selected following three iterations of porosity reduction. The selected screen consisted of a series of layered screens with a 100% radial extent and a 120° circumferential extent. A detailed total pressure flow field characterization of the AIP was performed using the selected screen at nominal, low, and high compressor loading. Thermal anemometry was used to characterize the spatial variation in turbulence intensity at the AIP in an effort to further define inlet boundary conditions for future computational investigations. Two data acquisition methods for the study of distortion propagation and attenuation were utilized in this study. The first method approximated the bulk flow through each vane passage using a single rake measurement positioned near the center of the passage. All vane passages were measured virtually by rotating the distortion upstream by an increment equal to one vane passage. This method proved successful in tracking the distortion propagation and attenuation from the AIP up until the compressor exit. A second, more detailed, inter-stage flow field characterization method was used that generated a total pressure field with a circumferential resolution of 880 increments, or one every 0.41°. The resulting fields demonstrated the importance of secondary flows in the propagation of a total pressure distortion at the different loading conditions investigated. A second objective of this research was to document proposals and design efforts to outfit the existing P3S research compressor with a strain gage telemetry system. The purpose of this system is to validate and supplement existing blade tip timing data on the embedded rotor stage to support the development and validation of novel aeromechanical analysis tools. Integration strategies and telemetry considerations are discussed based on proposals and consultation provided by suppliers

Desarrollo de un sensor de fibra óptica para la medida del tip clearance y tip timing en motores aeronáuticos

163 p.Los sensores basados en fibra óptica son cada vez más utilizados en aeronáutica debido a las ventajas que presentan frente a sensores más tradicionales. En esta tesis se presenta el diseño y desarrollo de un sensor de fibra óptica para la medida del tip clearance y del tip timing en motores aeronáuticos. Este sensor está basado en la modulación de la luz reflejada por parte de los álabes de un motor aeronáutico en función de la distancia a la que se encuentran.En el capítulo 1 se realiza una introducción a los sensores de fibra óptica dedicando especial atención a que utilizan la modulación de la intensidad como principio de funcionamiento, y se explican los parámetros que serán objeto de medida por el sensor desarrollado en la presente tesis.En el segundo capítulo se presenta la metodología seguida en el diseño y desarrollo del sensor. Se definen los objetivos y requisitos iniciales que el sensor debe cumplir y los pasos seguidos hasta conseguirlo.En el tercer capítulo se muestran los resultados obtenidos para aplicaciones reales de funcionamiento del sensor diseñado. Se presentan los resultados conseguidos en dos entornos reales de trabajo. Por un lado, el túnel de viento que el Centro de Tecnologías Aeronáuticas posee en sus instalaciones de Zamudio (Vizcaya), y por el otro, el banco de ensayos con el que cuenta el Instituto Tecnológico de las Fuerzas Aéreas polacas en Varsovia (Polonia).Este documento concluye con un capítulo en el que se recogen las conclusiones del trabajo, así como las líneas futuras del mismo. También se enumeran los artículos (incluidos en un apéndice) en los que se basa la tesis, así como las conferencias y otras publicaciones realizadas durante este periodo

An Experimental Study of Gas Lubricated Foil Journal Bearings Using an Instrumented Rotor with Wireless Telemetry

In order to increase their efficiency and power-density, turbomachines are continuously pushed to run faster, and hotter rotors. These requirements create enormous engineering challenges that affect the design of turbomachines down to the component level. Among these challenges is the choice of an adequate bearing technology. Gas lubricated foil bearings showed competency to support several high-speed turbomachinery applications. The foil bearing performance is governed by the properties of the gas film and the underlying compliant structure. A significant amount of research is dedicated to analyze the latter. However, the gas film was addressed only once in the experimental research efforts on foil bearings extending from the 1960s. This gap in the literature is due to the complexity of the foil bearing structure that hinders the placement of sensors through the bearing surface. As a consequence, the pressure profile inside the gas film of compliant foil journal bearings were never measured. The lack of such experimental data is hampering the conclusive validation of foil bearing models using pressure as the fundamental variable. The goal of this thesis is to provide pressure profile measurements within the gas film of compliant foil journal bearings at different rotational speeds. The experimental data will be a step towards the validation of foil bearing models using gas film measurements. An instrumented rotor with embedded pressure probes and a wireless telemetry is used to execute that mission. The designed rotor is capable of measuring the pressure profile at two different axial planes inside the bearing. The developed embedded pressure probes consisted of pressure transducers, and pneumatic channels to connect them to the measurement point on the surface of the rotor. Such layout required a special calibration procedure in order to account for the dynamics of the pneumatic channel that influences the pressure signal. A Siren Disk was designed and manufactured to produce periodic pressure signals with a controlled frequency and amplitude. Such signal was used to excite the pressure probes, and consequently identity their transfer functions, which are used to correct the pressure signals afterwards. As a proof of concept, the instrumented rotor was tested on externally pressurized gas journal bearings up to a speed of 37.5 krpm. The test bearings were equipped with pressure taps to measure the spatially sampled pressure profiles from the bearing side. The two measurements were compared and were in good agreement at quasi-static conditions. The bearing side measurement was considered as a reference signal (input), and once compared to the rotor side measurement (output), an in-situ calibration and system identification is performed. The pressure measurements were used to validate an externally pressurized bearing model based on the compressible Reynolds equation at different rotational speeds and supply pressures. The developed transfer function was subjected to several fitness tests before placing the instrumented rotor on foil bearings and measuring the pressure profiles at different rotational speeds. The developed transfer functions were used to correct the measured signal within the gas film of the foil bearing. Finally, the pressure profiles were compared to a foil bearing model based on the compressible Reynolds equation