Key-Phase-Free Blade Tip-Timing for Nonstationary Test Conditions: An Improved Algorithm for the Vibration Monitoring of a SAFRAN Turbomachine from the Surveillance 9 International Conference Contest

A turbomachine is a fundamental engineering apparatus meant to transfer energy between a rotor and a fluid. Turbomachines are the core of power generation in many engineering applications such as electric power generation plants, aerospace, marine power, automotive etc. Their relevance makes them both mission critical and safety critical in many fields. To foster reliability and safety, then, continuous monitoring of the rotor is more than desirable. One promising monitoring technique is, with no doubt, the Blade Tip-Timing, which, being simple and non-invasive, can be easily implemented on many different rotors. Blade Tip-Timing is based on the recording of the time of arrival of the blades passing in front of a probe located at a fixed angular position. The non-contact nature of the measurement prevents influences on the measured vibration, that can be recovered for all the blades simultaneously, possibly even online. In this regard, a novel algorithm is presented in this paper for obtaining a good estimate of the vibration of the blades with minimum system complexity (i.e., only one Blade Tip-Timing probe) and minimum computational effort, so to create a simple vibration monitoring system, potentially implementable online. The methodology was tested on a dataset from a SAFRAN turbomachine made available during the Surveillance 9 international conference for a diagnostic contest

Experimental testing of tip-timing methods used for blade vibration measurement in the aero-engine

An important component within the jet engine in terms of vibration and high cycle fatigue (HCF) is the blade. This is the component where continuously higher demands on weight and loading are being made. As a consequence of this, there has been a growing interest in developing both numerical methods and instrument technology for blade HCF measurement. This growing interest has also been attributed to changing attitude within the military and aerospace industry, which has tended towards driving down costs and lengthening the engine's life span. Many development technologies have been reported. One of which, is the development of a non-intrusive system for measuring blade vibratory stress. Research in non-intrusive techniques for the measurement of blade vibration has been ongoing since the early 1970' s. The aim of which, has been to replace the conventional method, using strain gauges and slip rings, with an improved system based upon non-intrusive type instrumentation such as optical or capacitance probes. One such approach is known as tip-timing. Tip-timing is a technique used to measure blade vibration using non-contact probes located around the engine casing. Many tip-timing techniques have been developed over the years, but there still remain significant problems associated with the approach. Such problems include sensitivity to noise and the high number of probes required. The development of two tip-timing methods known as the Autoregressive (AR) method and the Two Parameter Plot (2PP) method has recently been published in the open literature. This thesis describes the work done to experimentally test these two techniques. During the course of this work, an experimental optical tip-timing test facility was built. This included purpose-built optical tip-timing instrumentation, a tip-timing data acquisition system, and a post processing system incorporated into the Cranfield University low speed compressor facility. Experimental testing of the Autoregressive method and the Two Parameter Plot method was carried out using a controlled test environment, representative of a real engine. An analysis of the two methods was conducted using data from a comprehensive range of frequencies and RPM speeds. The results were then compared with previously published numerical results and the two algorithms were evaluated in terms of replacing the conventional strain gauge method. Testing of the AR method presented some interesting findings, with acceptable results produced at low rotational RPM speeds. However, as the rotational speed was increased, the accuracy of the results deteriorated. This type of result had not be highlighted in previous work. The 2PP method performed relatively well when using data sampled from the smaller 16 Engine Order (EO) response. However, this was not repeated when using the larger 72EO data. Additionally, this type of result had not been shown in previously published work. Overall, it was concluded that the issues associated with the frequency measurements should be remedied and a technique for measuring Multiple-Degree-of-Freedom responses should be explored before tip-timing techniques can be considered as a replacement to the strain gauge approach.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

VSCE technology definition study

Refined design definition of the variable stream control engine (VSCE) concept for advanced supersonic transports is presented. Operating and performance features of the VSCE are discussed, including the engine components, thrust specific fuel consumption, weight, noise, and emission system. A preliminary engine design is presented

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

Unsteady Aerodynamics and Blade-Row Interactions in the Embedded Stage of an Axial Compressor

In a mature engineering field like compressor aerodynamics, the most accessible advances in machine technology, translating to performance and efficiency, have been discovered and have found industry design applications. As the community continues to make progress, increasingly challenging aspects of the involved physics must be exploited. Modern turbomachinery operates with larger bypass ratios, smaller cores, and lighter, thinner, and more flexible materials resulting in the maintenance of higher operating pressures and temperatures. As the performance and efficiency of these machines continues to climb, the same technological advances reinforce challenges like forced-response vibration, high-cycle fatigue of engine components, and large relative tip clearances in an engine core. Accounting for these challenges increasingly depends on the investigation of the unsteady domain for solutions. Tools at the disposal of the designer include progressively improving computational simulations through both computational resources and attainable model fidelity. As essential as these tools are for modern turbomachinery design, the confidence in their results is only as good as the experimental data used to validate them. The objective of this research is the experimental investigation and characterization of the transient aerodynamics and blade-row interactions near forced-response resonant vibratory operating conditions in a multi-stage environment. Experimental methods are focused on fast-response pressure transducers with the high frequency response capable of capturing the unsteady pressure fluctuations associated with the high-speed rotation and blade-pass frequency of a modern high-pressure core axial compressor. Investigation is centered on an engine-representative embedded rear stage, with adjacent stages establishing realistic flow conditions and resulting boundary conditions for model comparison. Aerodynamic characterization of several flow conditions and the examination of the effect of a reduced vane-count stator configuration upstream of the embedded stage are performed with measurements of the embedded rotor at the casing endwall and rotor exit plane, as well as within a passage of the embedded stator. Circumferential vane traverse around stationary instrumentation provide a full vane passage of phase-locked, time-resolved pressure measurements of the rotor aerodynamics and the unsteady loading of the embedded stator is distinguished for a single vane position. Results from this investigation identify and describe the inception and trajectory of tip clearance flows, including the tip leakage vortex and double-leakage tip clearance flow. Evidence of an upstream vane wake interaction with the rotor occurs for limited regions of vane passage positions. Spectral analyses and pressure unsteadiness provide further insight into the blade-row interactions

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

Performance and preliminary design of nutating disc engine topping cycles for civil aero-engine applications.

Within the next thirty years evolutionary approaches to aero engine development will struggle to keep abreast with ever stringent environmental targets. A key component of the environmental targets stipulated by the SRIA is to reduce mission fuel burn by 75% by the year 2050, when compared to a year 2000 baseline. If the mission fuel burn benefits attributed to flight path optimization are excluded, a fuel burn target of 68% is postulated. Therefore, radical approaches to aero-engine development in terms of thermal and propulsive efficiency improvements need to be considered. One particular concept involves the inclusion of an un-ducted contra rotating propeller array to increase the propulsive efficiency of an aero-engine, for a short range aircraft, by the 2050 time frame. Concurrently a pressure-rise combustion system, called the nutating disc engine system, can increase the thermal efficiency of the year 2050 short-haul engine. The nutating disc engine system concept is a strong contender due to its power density. The feasibility of the nutating disc engine system has been previously investigated for unmanned vehicle applications. However, this work investigates the performance benefits of incorporating a nutating disc engine system in a geared open rotor engine for the year 2050. According to the investigated literature, a methodology to size the nutating disc engine system and predict its potential fuel burn performance benefit in a geared open rotor configuration is lacking. In addition, there is a lack of knowledge regarding the impact synergetic technologies such as intercooling and secondary combustion affect the performance of a nutating disc engine system coupled to an un-ducted contra rotating propeller array. Hence, the primary contribution of this work is to determine a methodology to predict the size and turbo-charged performance of a nutating disc engine system. An outcome of this contribution determines whether a geared open rotor engine with a nutating disc engine system can meet the fuel burn target of 68%, when compared to a year 2000 baseline engine. This investigation is furthered with an uncertainty analysis, to show the variability of potential 2050 fuel burn estimates. The derived nutating disc engine system sizing methodology shows confluence with known prototype dimensions and CAD based sizing approaches. The used thermodynamic model also shows reasonable levels of confluence with published literature. Another outcome of the primary contribution to knowledge, is to determine whether synergetic technologies such as intercooling and secondary combustion can meet the 68% fuel burn target in conjunction with a nutating disc engine system in a geared open rotor engine architecture. These investigations are furthered by an uncertainty analysis. The secondary contribution of this work is to provide preliminary performance and mass estimates of Y2050 engine configurations that can meet the 68% fuel burn target. An engine specification for a year 2000 baseline engine and a reference year 2050 geared open rotor engine are proposed to benchmark the relative fuel burn benefit achieved by a perceived year 2050 nutating disc engine system engine configurations. The reference 2050 geared open rotor engine, on a short range aircraft, determines engine technology levels for further radical engine configurations in this work. The reference year 2050 engine, geared open rotor, produces a fuel-burn benefit of 58.9% relative to a comparable year 2000 baseline. Since it falls short of the 68% target fuel-burn benefit, the viability of a nutating disc engine system is considered. A geared open rotor with a nutating disc engine system can provide fuel burn benefits of 63% relative to a year 2000 baseline. An uncertainty study indicates, that the proposed engine configuration can provide relative fuel burn benefits from 37% to 71%, when compared to a year 2000 baseline. The inclusion of intercooling, secondary combustion and a combination of the two with a nutating disc engine system produced fuel burn benefits of 64%, 71% and 65% respectively relative to year 2000 baseline, as a consequence of a targeted search optimization. The design variables that influence the uncertainty the most in all the investigated nutating disc engine variants are the heat flux through the casing and the ratio of constant volume combustion to constant pressure combustion. A like for like analysis, for the four investigated engine configurations indicate that a geared open rotor with only a nutating disc engine system provides the highest potential fuel burn benefit. However, when aspects such as NOx and noise emissions are considered qualitatively it is postulated that a nutating disc engine system with intercooling and secondary combustion technologies is desirable. Due to the high degree of uncertainty in the perceived fuel burn values, for the proposed engine configurations, a roadmap to progress the nutating disc engine system technology to higher TRL are further detailed.PhD in Aerospac

An improved key-phase-free blade tip-timing technique for nonstationary test conditions and its application on large-scale centrifugal compressor blades

7partially_openopenHe, Changbo; Antoni, Jerome; Daga, Alessandro Paolo; Li, Hongkun; Chu, Ning; Lu, Siliang; Li, ZhixiongHe, Changbo; Antoni, Jerome; Daga, Alessandro Paolo; Li, Hongkun; Chu, Ning; Lu, Siliang; Li, Zhixion

Constant speed tip deflection determination using the instantaneous phase of blade tip timing data

Blade Tip Timing (BTT) is a non-intrusive measurement technique that can be used to estimate the vibration characteristics of rotor blades during turbomachine operation. BTT uses proximity probes mounted into the turbomachine casing to measure the Time-of-Arrival (ToA) of rotor blades at these proximity probes. The ToAs are determined using a triggering criterion on the proximity probe signal. Rotor blade tip displacements are then calculated from these ToAs. It is therefore imperative that the triggering criterion be as accurate as possible. This article proposes a new method to determine the tip displacement of rotor blades from a proximity probe signal. The method first converts the signal into the angular domain and then obtains the tip deflection through manipulation of the instantaneous phase in the signal. Three experimental tests are conducted where existing triggering criteria are compared to the proposed method. It is found that the proposed method is highly accurate in determining the tip deflections for a constant rotor speedA Skye Foundation Scholarship and the Eskom Power Plant Engineering Institute (EPPEI).http://www.elsevier.com/locate/ymssp2022-09-10hj2022Mechanical and Aeronautical Engineerin

Investigation of the flow field around a propeller-rudder configuration: on-surface pressure measurements and velocity-pressure-phase-locked correlations

The present paper deals with the problem of the propeller induced perturbation on the rudder . The study aims at providing insights on the key mechanisms governing the complex interaction between the propeller wake structures and the rudder. In this regard, a wide experimental activity that concerned PIV and LDV velocity measurements and wall-pressure-measurements on the two faces of the rudder was performed in a cavitation tunnel. The major flow features that distinguish the flow field around a rudder operating in the race of a propeller, were highlighted, such as the complex dynamics of the propeller tip votices and the re-storing mechanism of the tip vortex downstream of the rudder. Wall-pressure signals were Fourier decomposed and, then, reconstructed isolating the contributions of the more energetic harmonics when both the propeller phase and the rudder deflection change