Browsing by Author "Ivey, Paul C."
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Item Open Access Abradable stator gas turbine labyrinth seals(Cranfield University, 1999-03) Allcock, D. C. J.; Ivey, Paul C.This is a detailed study into the internal aerodynamics of labyrinth seals, with pmic| reference to the effects of abradable honeycomb stators on labyrinth seal leakage.- A extensive experimental programme established tables of friction factor for three different grades of honeycomb used by industry, and examined the effect of both Reynolds number and clearance on these friction factors. The friction factor associated with a aerodynamically smooth surface was also experimentally determined in order to establish the experimental method. The experimental data was used to model the different grades of honeycomb used as stator material in numerical simulations of a number labyrinth seals, and allowed for comparison of the leakage associated with both smooth and abradable stator straight through labyrinth seals. Step-up and step-down seal geometries were also considered, and the effects of pressure ratio, clearance and rotation on labyrinth seal leakage was examined on all modelled seal types. This numerically generated leakage data was comprehensive enough to allow for the creation of a second-generation one-dimensional labyrinth seal leakage predictor tool of the type used by design engineers in network models. This tool accounts for stator material, seal clearance, overall pressure ratio, rotation and seal geometry, and the accuracy associated with this tool allows labyrinth seal leakage to b predicted to within 10%. Functions of discharge coefficient and carry-over factor obtained from the numerical predictions are used by this tool, and as such it is capable of dealing with a large number of different operating conditions for all the seal types modelled.Item Open Access The application of a new research and development project selection model in SMEs.(Elsevier Science B.V., Amsterdam., 2006-02-01T00:00:00Z) Lawson, Craig P.; Longhurst, Philip J.; Ivey, Paul C.The work reported in this paper investigates Research and Development (R&D) project selection models, focusing on the application of a new hybrid project selection model in a UK based engineering Small to Medium-sized Enterprise (SME). Work is done to enable the new project selection model to be applied in an SME and the model is then field tested. Field test results provide insight into the barriers to the adoption of such a model in an SME, either as a decision support tool or as a knowledge acquisition and learning tool. Insights are gained into the suitability and limits that exist within SMEs for the use of such decision support models. As an outcome of the field test results a simple R&D project portfolio cash-flow tracking method is proposed.Item Open Access The aquisition of three dimensional flow measurements through a muli stage high speed axial flow compressor(Cranfield University, 2003-02) Lippett, D. A.; Ivey, Paul C.The focus of the thesis is research based around Cranfield University's 3-stage high speed axial compressor test rig. This newly built rig supported by European Commission funding has tested a set of conventionally stacked 2D rotor and stator blades. The results will be used to evaluate the CFD codes; a advanced three dimensional blade set will then be designed by a collaboration of companies. The aim of which is to prove a 2% efficiency gain for the advanced blade set. Due to the limited axial spacing between the measurement planes a unique seven probe assembly and traverse mechanism has been designed. The assembly has the ability to yaw the probes and control the insertion depths. This takes a number of different probes such as cobra probes, fast response (pneumatic) probes and temperature probes. A computer program has been written that completely automates the control of the probes and the data acquisition. This has allowed full area traversing of the compressor between rotor and stator blade rows. Due to the unique design of the seven probes, a high-speed wind turmel section has also been designed and manufactured. This has enabled the probes to be calibrated for mach numbers up to 0.78 as well as for both pitch and yaw. Due to the representative size, blade count and high flow forces of the high-speed compressor, instrumentation to capture the three-dimensional flow field in a high-speed environment has been researched. A small four-hole probe has been designed and used to take three dimensional steady state pneumatic measurements. This combined with a post processing program has provided very detailed results downstream of the stators through the compressor. This includes the complex three-dimensional flow structure and secondary flows associated with tip leakage, end wall boundary layer, wake transportation and blade row interactions. A fast response probe was designed and evaluated to capture the flow field downstream of the rotors but found to be insensitive to yaw angle. The results taken in a high-speed environment at full scale and engine representative speed supports some of the findings taken in a low speed environment. The author considers that the higher turbulence and speeds leads to increased mixing in the blade rows. This leads to almost all the ow being three dimensional in nature, this is not apparent in a low speed representation. The upstream wakes and their interaction with the downstream rows can be clearly seen. This is further demonstrated by the insertion of an upstream probe. The effects of this probe being transported axially downstream through a blade row. The results show the effectiveness and importance of a rigorous mapping procedure. This is particularly useful where the wake thicknesses are small and pressure gradients are high in comparison to the probe size. The size and extent of the areas of loss become more pronounced as results are taken through the compressor. This is true both at peak efficiency as well as near surge. The higher loading at the near surge condition increases these areas of loss still further.Item Open Access Capacitance Tip Timing Techniques in Gas Turbines(Cranfield University, 2003-11) Lawson, Craig P.; Ivey, Paul C.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.Item Open Access Experimental studies on volute-impeller interactions pf centrifugal compressors having vaned diffusers(Cranfield University, 2003) Georgakis, C.; Ivey, Paul C.It is well recognised that the volute plays a important role on the stage performance of a turbo machine in terms of pressure recovery, losses, efficiency and flow range, in addition to influencing stability and radial loads. Although there is a demand for further improvements in efficiency and operating range of compressor components, less attention has been paid to the effect of volute design. The goal of the present study was to experimentally measure the flow through a high pressure ratio 5:1 centrifugal compressor incorporating a vaned diffuser and a volute as part of a fully representative, production version turbocharger test facility. By running the unit as in a gas turbine cycle' (that is with the compressor flow passed through the combustors and then through the hot axial turbine of the turbocharger) it was possible to generate the 1.2MW of power that the test compressor required at its design point. This approach allowed the compressor to be tested at a duty that was relevant to todays industrial needs. The present study shows that the source of the circumferential pressure distortion at the impeller tip was the non-axisymmetric volute. The vaned diffuser did not fully attenuate this distortion, and consequently some of this distortion was measured at the impeller tip. The impeller tip pressure distortion varied as the operating point moved on the compressor characteristic and it was seen to be greatest at the surge point. The performance duties of the compressor components were examined in detail. The radial vaned diffuser had a major influence on both the stage and volute performance, and imposed a very narrow operating range on the test volute. The volute had a nearly constant loss coefficient and the pressure recovery therefore mainly depended on the dynamic head at the volute inlet at the duty points encountered on the tests. The test volute was modified to have a cutback° tongue which gave a better compressor matching at high flows. The flow pattern at the impeller exit was seen to comprise two distinct regions, firstly a wake° or accumulation of low relative energy fluid which occupied most of the shroud surface and extended towards the suction side, and secondly a lower loss flow which was present at the hub pressure comer. The survey also investigated the structure of the flow in the test volute. The volute did not operate as a constant pressure collector° and there was a swirling flow within it. This Vortex distribution was seen to depend on the radial velocity distribution at the volute inlet. Larger radial velocities contributed to stronger swirling flows. The lowest total pressure showed itself in the core of the Vortex over the volute cross sections. There was a radial decrease of the tangential velocities from the inner to the outer radius of the volute cross sections. The flow into the test volute is not uniform. Additional insight into the nature of the compressor flows was derived from a complimentary CFD analysis which is also described.Item Open Access Experimental Testing of Tip-Timing Methods used for Blade Vibration Measurement in the Aero-Engine(Cranfield University, 2004-10) Grant, Kelly; Ivey, Paul C.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.Item Open Access Influence of blade row aerodynamics on pneumatic gas turbine instrumentation(Cranfield University, 2003-04) Coldrick , S.; Ivey, Paul C.Steady state, inter row measurements in multistage axial compressors are relevant to the current design process. The objective in obtaining such data is for evaluation of compressor blading as well as validation for the computer programmes used in compressor design. Multi-hole pressure probes are a reliable and economical method of collecting detailed flowfield data in compressors for these purposes. These probes are calibrated in a uniform flow in a wind tunnel prior to use, to determine their response to a range of flow angles and speeds. When the probe is subsequently used for measurements in the compressor, often the small inter row spacing means that the probe has to be close to the downstream stator passage and upstream rotor. The result is that the probe is no longer situated in the uniform flow in which it was calibrated, in terms of influences from both the upstream rotor and downstream stator. This project presents the investigation of these two effects on steady state pressure probe measurements. The effects of blockage on a probe positioned in front of a stator row in a high speed compressor were studied using CFD. This was also carried out on a large scale probe in a low speed compressor. It was found that the blockage effect caused a reduced mass flow in the downstream stator passage which in turn lead to an altered flow angle and a small reduction in measured total pressure. Experimental in rig calibrations showed that the change in flow angle was due to an angular offset of the pressure distribution about the probe. These calibrations also showed that the wind tunnel calibration was valid in the compressor within a small angular range. The influence of the upstream rotor passing was studied using an unsteady CFD model. Responses of the individual probe ports and the deduced flow angle and total pressure indicated that the steady state blockage effect is present throughout the wake passing. The wake passing was found to be a largely two dimensional effect in that the radial flow component changes in the low speed compressor wakes had little influence. The Total Technology thesis incorporates a management project on the relevant topic of project selection within companies. An existing project selection model was applied to a sample group of projects to determine the applicability of such models. The main findings were that these models can generate useful information for further selection decisions and that the applicability is towards lower budget projects where a structured approach is often not used.Item Open Access Low speed axial compressor design and evaluation : High speed representation and endwall flow control studies(Cranfield University, 1999-01-28) Lyes, Peter A.; Elder, R. L.; Ivey, Paul C.; Ginder, R. B.This Thesis reports the design, build and test of two sets of blading for the Cranfield University low speed research compressor. The first of these was a datum low speed design based on the fourth stage of the DERA high speed research compressor C 147. The emphasis of this datum design was on the high-to-low speed transformation process and the evaluation of such a process through comparing detailed flow measurements from both compressors. Area traverse measurements in both the stationary and rotating frame of reference were taken at Cranfield along with overall performance, blade surface static pressure and flow visualisation measurements. These compare favourably with traverse and performance measurements taken on C147 before commencement of the PhD work. They show that despite the compromises made during the transformation process, due to both geometric and aerodynamic considerations, both the primary and secondary flow features can be successfully reproduced in the low speed environment. The aim of the second design was to improve on the performance of the datum blading through the use of advanced '3D' design concepts such as lean and sweep. The blading used nominally the same blade sections as the datum, and parametric studies were conducted into various lean/sweep configurations to try to optimise the blade performance. The final blade geometry also incorporated leading edge recambering towards the fixed endwalls of both the rotor and stator. The '3D' blading demonstrated a 1.5% increase in efficiency (over the datum blading) at design flow rising to around 3% at near stall along with an improvement in stall margin and pressure rise characteristic. The design work was completed using the TRANSCode flow solver for both the blade-to-blade solutions (used in the SI-S2 datum design calculation) and the fully 3D solutions (for the advanced design and post datum design appraisal). The 3D solutions gave a reasonable representation of the mid-span and main 3D flow features but failed to model the corner and tip clearance flow accurately. An interesting feature of the low speed flowfield was the circumferential variation in total pressure observed at exit from all rotors for both designs. This was not present at high speed and represents one of the main differences between the high and low speed flow. Unsteady modelling of mid- height sections from the first stage indicate that part of this variation is due to the potential interaction of the rotor with the downstream stator while the remainder is due to the wake structure from the upstream stator convecting through the rotor passage. Finally, the implications for a high speed design based on the success of the 3D low speed design are considered.Item Open Access The measurement of near wall flows using pneumatic wedge probes.(Cranfield University, 1995-01) Smout, Peter David; Ivey, Paul C.; Loftus, P.The three hole, wedge-type pneumatic pressure probe represents a robust traverse probe design which is widely used for total and static pressure and yaw angle measurements in turbomachinery. However, unsteady flows are incorrectly averaged due to pneumatic meaning errors in the pressure pipes. Wedge probes also fail to measure the correct static pressure when operating in close proximity to a wall through which the probe is inserted. Thirdly, the aerodynamic calibration obtained for a wedge-type probe in a closed wind tunnel differs appreciably from that obtained in an open jet. If not corrected, these errors will corrupt any calculation of turbomachinery blade row performance. In this investigation, the second and third effects described above have been addressed. A factorial experiment was completed in which the influence of seven variables on the wall proximity effect was quantified. Flow visualisation studies were performed to understand the responsible flow mechanisms. Two regions of re-circulating flow were identified in the probe wake, the structure of which depended on the probe immersion. Similar re-circulatory flows were resolved from three-dimensional computational fluid dynamics (CFD) calculations of the flow over a wedge probe. A link between the probe wake re-circulations and flow over the wedge faces was established. Based on this understanding of the flow structures, a model was developed from which the wall proximity effect could be predicted for a given set of conditions. Wedge probe calibrations were completed in a closed wind tunnel and in two open jets. Discrepancies in the static pressure coefficient and yaw angle sensitivity results were found. These were partially explained in terms of modifications to the probe wake structure which occurred when the probes were calibrated in the open jet facilities. Procedures for correcting the wall proximity effect and for avoiding the facility dependence of wedge probe calibrations were developed from this understanding of the flow mechanisms involved. Based on the findings of this investigation, a novel wedge probe was designed to minimise the wall proximity effect. This probe demonstrated a reduction in the wall proximity effect, from 20% dynamic head with current designs, to 3% dynamic head at flows typical of high speed turbomachinery.Item Open Access Modelling, imaging and measurement of distortion, drag and break-up of aircraft- icing droplets(2005-01-01T00:00:00Z) Luxford, Geoffrey; Hammond, David W.; Ivey, Paul C.The distortion, drag and break-up of supercooled drizzle droplets in aircraft icing was investigated in ambient conditions. An effective efficient computer procedure was developed for the distortion and drag of small droplets, < 1mm, at low Reynolds numbers, < 1000, and high Weber numbers, > 10. High-speed videos and photographs were obtained with an improved high-intensity LED strobe. Experimental measurements validated the drag model for droplets distorted by a rapidly accelerating airflow in a convergent wind tunnel. To prevent droplet coalescence, due to wake interactions, droplets were generated with a steady jet impinging of a rotating slotted disk.Item Open Access Role of droplet distortion and break-up in large droplet aircraft icing(2004-01-01T00:00:00Z) Luxford, Geoffrey; Hammond, David W.; Ivey, Paul C.Experimental and analytical evidence is presented to illustrate droplet distortion and potential break-up in the flow conditions similar those of a drizzle droplet in the vicinity of an aerofoil. The droplet size range considered is 100u m to 500u m. The current research is at ambient temperature but with equivalent parametric conditions to SLD icing. While the results support the contention that smaller droplets, <100u m, remain essentially spherical, the larger droplets become sufficiently distorted to affect their drag characteristics and can break up due to the transient aerodynamic forces.Item Open Access Turbomachinery blade vibration amplitude measurement through tip timing with capacitance tip clearance probes(Elsevier Science B.V., Amsterdam., 2005-01-01T00:00:00Z) Lawson, Craig P.; Ivey, Paul C.Turbomachinery blade vibrations can cause High Cycle Fatigue, which reduces blade life. In order to observe this vibration a nonintrusive monitoring system is sought. The vibration can be detected by measuring blade tip timing since in the presence of vibration the blade timing will differ slightly from the passing time calculated from rotor speed. Much research and development has gone into investigating the ability of optical probes to achieve this. However, this paper looks at the potential for a dual use capacitance probe sensor to measure both tip timing and tip clearance. This paper provides new insights into the ability of a commercially available capacitance probe tip clearance measurement system for application as a non-intrusive turbomachinery blade tip timing measurement device. This is done by correlating capacitance probe tip timing results with simultaneously measured blade-mounted strain gauge vibration results and precise rotational speeds. Blade tip vibration amplitudes are measured using capacitance probes and compared to strain derived vibration levels. Thus the characterisation and quantification of the performance of the capacitance probe system when measuring blade vibration on a full-sized low-speed research compressor is analysed and reported.Item Open Access Unsteadiness In An Embedded Axial Compressor Stage(Cranfield University, 2008-02) Naylor, Edward; Ivey, Paul C.; Amaral Teixeira, JoaoPrevious research on blade boundary layers in turbomachinery have been recognised to crucially influence the stability and performance of the gas turbine components. The interactions between rotating and stationary blade rows inevitably make the flow environment within a multistage axial compressor unsteady. Research conducted at midspan in Low Pressure turbines has shown that patches of transitional flow can withstand higher levels of deceleration, helping the boundary layer stay attached. An experimental investigation into unsteadiness in a embedded stage was conducted in the third-stage of the Cranfield four-stage Low Speed Research Compressor at two operating points: peak efficiency and near stall. This build of the Cranfield Rig was equipped with three-dimensional blading. A three-hole pressure probe was traversed at the exit of Rotor 3 in the rotating frame of reference and at the exit of Stator 3 in the stationary frame of reference. In addition measurements were made at the exit of both Rotor and Stator 3 using a slanted hotwire rotated about its axis. This measurement technique gave time-resolved three-dimensional velocities. Coupled to the exit traverses a series of boundary layer traverses were performed along Stator 3 suction surface covering the midchord region at midspan and close to the casing endwall. To aid in the understanding and interpretation of the experimental campaign, three-dimensional computations of Stator 3 were made at the two operating points using the commercial Computational Fluid Dynamics code ANSYS-CFX . A two-dimensional unsteady calculation of Rotor 3, Stator 3 and Rotator 4 at midspan and peak efficiency was also performed. The time-resolved measurements downstream of Rotor 3 showed that the rotor wake was characterised by high levels of random unsteadiness and increased incidence onto the stator row. The increase in incidence across the wake was two to three times that experienced with change in flow coefficient. Therefore the increased incidence and turbulence in a rotor wake will have a significant influence on the unsteady development of a downstream boundary layer. Measurements of the boundary layer at design condition at midspan show evidence of laminar and transitional flow up to 50% of the suction surface length. The boundary layer flow periodically undergoes transition due to the convection of the wake-induced strip that was generated close to the leading edge. Towards the casing the picture is altered slightly due to the stator-casing separation region. Boundary layer transition is completed farther forward and the transition length reduced. At off-design the picture is completely altered. Transition is completed upstream of 25% suction surface length and the flow shows only a modulating variation with blade passing. The stator-casing separation region grows in spanwise extent and the boundary layer flow on the stator surface is completely separated aft of 50% of suction surface length.