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This dissertation applies a commercial flow simulation software package together with common signal processing techniques to the task of accurately detecting leakage in a large commercial gas pipeline. The techniques developed significantly improved the ability to produce accurate, reliable and stable leak detection predictions for the gas transmission pipeline studied and can be applied generally to other pipelines as well. Recommendations for minimum pipeline requirements to implement successful leak detection are also detailed. There are several commercial software packages available that perform some form of leak detection via system modelling. However, due to the commercial aspects of these products, vendors do not publish the detailed methods of leak detection. This thesis identifies the fundamental techniques required to have accurate and reliable leak detection on a gas transmission pipeline, whilst taking into account the lack of measurement data typically encountered on most gas pipelines. The investigation confirmed that a mass balance technique could be successfully used to produce stable leak detection results for compressible flow in gas transmission pipelines. This leak detection [using mass balance] can be achieved without flow measurement along the pipeline, instead, using only pressure and temperature measurements. Although it is recognized that flow measurement data will greatly improve the ability to detect leaks, the focus of this work is on pipelines where this flow measurement data at intermediate points along the pipeline is not available. It was also demonstrated the reliability of the leak detection was improved by the application of on-line signal processing techniques at various stages of the data processing. / It was clear early into the investigation that the majority of the errors within the leak detection model were created by random errors from the input field data. These non-systematic errors from the measurement data that included pressure and temperature, produced interference with model output. This interference resembled random “white” noise that was removed by a combination of well established data filtering techniques. The most appropriate process of calculating leak detection flow was determined after analysing the results of different techniques applied to large quantities of actual pipeline operating data. The validation of the on-line techniques developed provides a valuable resource for those wishing to implement similar leak detection schemes elsewhere. Furthermore a software environment was chosen which incorporated an open input and output platform for data that could be interfaced with any operating system. Therefore these techniques can be applied to the numerous Supervisory Control and Data Acquisition (SCADA) systems in operation throughout the gas transmission industry, to provide a low cost solution to leak monitoring.

<p>  </p> <p>The focus of this work was to characterize the overall performance effects due to altering the stagger angle of a variable inlet guide vane (VIGV) on a multistage axial compressor. Data were collected from the Purdue three-stage axial compressor (P3S). The stagger angle from the VIGV was varied thrice from the baseline configuration in increments of 5 degrees resulting in four configurations with angles of 4 deg, 9 deg, 14 deg, and 19, where the baseline configuration was 9 degrees. </p> <p>Compressor performance data were collected and analyzed for each stagger angle configuration along three corrected speeds (68%, 80%, 100%). Each speedline consisted of approximately six loading conditions for which the corrected mass flow rate was matched for each configuration to allow for a basis of comparison among the configurations. Stalling mass flow rates and stall inception were also investigated. Total pressure and total temperature rakes were installed throughout the compressor to investigate the performance at interstage locations for each loading condition. In addition to the rakes, static pressure taps were distributed along the compressor and unsteady pressure measurements were distributed circumferentially. Capacitance probes were installed over each of the three rotors to evaluate rotor tip clearance measurements during the tests. The effects of the stagger angle on the stability margin of the compressor were also characterized. Each speedline presented, thus, includes a representative stall point in addition to the six loading conditions where detailed flow field traverses were conducted. </p> <p>The results of this investigation showed that while the total pressure ratio (TPR) increased as the stagger angle decreased, the stability margin was reduced. The opposite trend was observed with a decrease in overall TPR across the compressor and an increase in stability margin for increased stagger angles. Based on findings from previous authors, this trend was anticipated. A similar metric for monitoring compressor performance is isentropic efficiency. This investigation utilized both temperature-based and torque-based isentropic efficiency. The greatest effect of the VIGV stagger angle on compressor isentropic efficiency occurred at the lowest loading conditions, and there was no discernible impact on isentropic efficiency at high loading conditions for this case. As VIGVs typically have the greatest impact on off-design conditions, this trend was expected. The varied stagger angle configurations had no discernible effect on the type of stall inception mechanism experienced by the compressor. The primary effect on stall that was consistent across the configurations was a noticeable increase in the duration and strength of modal oscillations present throughout the compressor with increased stagger angles, indicating an increase in stability. </p> <p>The data collected and presented herein provide a unique, robust dataset to improve understanding of the effects of changing stagger angles on variable inlet guide vanes on multistage axial compressors. These data correspondingly provide a unique training set and validation method for predictive technology. </p>

Thesis (PhD)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The aims of this thesis are to identify all possible modes of operaton for a multi-stage axial flow compressor; then to characterise the performance, attempt to numerically model operation, and determine the main flow field features for each mode. Four quadrant axial flow compressor operation occurs when the direction of flow through the compressor or the sign of the pressure difference across the compressor reverses, or any combination of these. Depending on the direction of rotation of the compressor, six modes of operation are possible in the four quadrants of the performance map. The rotor rotates in the design direction for three modes, and in the opposite direction for the other three. The stationary-rotor pressure characteristic is S-shaped and passes through the second and fourth quadrants. A three-stage axial flow compressor operating in the incompressible flow regime was used for the experimental investigation. Flow through the compressor was reversed or augmented by means of an auxiliary axial flow fan. Compressor performance was measured by means of static pressure tappings, a turbine anemometer calibrated to measure forward and reversed volumetric flow and a load cell for torque measurement. The inter-blade row flow fields were measured with pneumatic probes and 50 μm cylindrical hot film probes. Three dimensional single blade-passage Navier-Stokes simulations were performed using the Numeca FineTurbo package. Steady state simulations used a mixing plane approach. A nonlinear harmonic approximation was used for time-unsteady simulations. Unstalled first quadrant operation was unremarkable, and good agreement was obtained between experimental and numerical data. A single stall cell was detected experimentally during stalled operation, which was not modelled numerically. In the fourth quadrant for positive rotation, (windmilling), the compressor acts as an inefficient turbine. Flow separates from the pressure surface of the blade, rendering the steady-state mixing plane approach unsuitable. The performance characteristic curves for second quadrant for positive rotation, are discontinuous with those of first quadrant operation. The temperature rise in the working fluid is significantly higher than at design point. Periodic flow structures occurring across two blade passages were detected at all flow coefficients investigated, invalidating numerical modelling assumptions. Better agreement was obtained between experimental and numerical data from a case found in literature. If the compressor operates as a compressor in reverse (third quadrant operation), significant separation occurs on the pressure surface of all blades, and flow conditions resemble severe first quadrant stall. Separation becomes less severe at larger flow rates, allowing numerical simulation, though this is sensitive to the initial flow field. In the the part of the second quadrant, where the compressor rotates in reverse, it operates as a turbine. The blade angles and the direction of curvature match the flow angles and turning well, leading to high turbine efficiencies. Numerical simulations yielded good agreement with measured results, but were again sensitive to the initial flow field. Fourth quadrant operation with negative rotation occurs when flow is forced through the compressor in the design direction. Large separation bubbles are attached to the pressure surfaces of rotor and stator blades, so virtually all throughflow occurs near the hub and casing / AFRIKAANSE OPSOMMING: Die doelwitte van hierdie tesis is om al die moontlike werkmodusse vir ’n bestaande multi-stadium aksiaalvloei kompressor uit te ken; om dan die gedrag te gekarakteriseer, ’n poging aan te wend om die werking numeries te modelleer, en die belangrikste vloeiveldkenmerke vir elke modus te bepaal. Vier-kwadrant aksiaalvloei kompressor werking vind plaas as die rigting van die vloei deur die kompressor, of die teken van die drukverskil oor die kompressor omkeer, of enige kombinasie daarvan. Afhangende van die rigting van rotasie van die kompressor is ses operasionele modusse moontlik in die vier kwadrante van die kompressorkaart. Die rotor draai in die ontwerprigting vir drie van die modes, en in die teenoorgestelde rigting vir die ander drie. Die stilstaande-rotor drukkarakteristiek is S-vormig gaan deur die tweede en vierde kwadrante. ’n Drie-stadium onsamedrukbare vloei aksiaalvloei kompressor is vir die eksperimentele ondersoek gebruik. Vloei deur die kompressor is omgekeer of aangehelp deur middel van ’n aksiaalvloei hulpwaaier. Kompressor werking is gemeet deur middel van statiese druk meetpunte in die omhulsel, ’n turbine anemometer wat gekalibreer is om vorentoe en omgekeerde volumetriese vloei te meet, en ’n lassel vir wringmoment meting. Interlemryvloeivelde is opgemeet met pneumatiese sensors en 50-μm silindriese warm film sensors. Drie-dimensionele Navier-Stokes simulasies is uitgevoer vir ’n enkele lem van elke lemry, met behulp van die Numeca FineTurbo sagtewarepakket. ’n Mengvlakbenadering is gebruik vir bestendige toestand simulasies, terwyl ’n nie-linere harmoniese benadering gebruik is vir die tyd-afhanklike simulasies. Ongestaakte eerste kwadrant werking was alledaags, en goeie ooreenkoms is gevind tussen die eksperimentele en numeriese data. ’n Enkele staak-sel is eksperimenteel ontdek tydens gestaakte werking. Gestaakte werking is nie numeries gemodelleer nie. In die vierde kwadrant vir positiewe rotasie, (”windmeulwerking”), werk die kompressor as ’n ondoeltreffende turbine. Vloei-wegbrekinging op die lem drukoppervlaktes maak die bestendige toestand mengvlakbenadering ongeskik. In die kenlyne vir tweede kwadrant positiewe rotasie, is daar ’n diskontinu¨ıteit in die prestasie karakteristiekkrommes vir die eerste en tweede kwadrant werking. Die temperatuurstyging in die werk- vloeistof is beduidend ho¨er as as by die ontwerppunt. Periodiese vloeistrukture wat oor twee lemme plaasvind is gevind by alle vloei ko¨effisi¨ente wat ondersoek is, en dit maak die numeriese modellering aannames ongeldig. Beter ooreenkoms tussen die eksperimentele en numeriese data iss verkry met ’n geval wat uit die literatuur gevind is. Indien die kompressor werk as ’n kompressor in omgekeerde (derde kwadrant weking), vind beduidende wegbreking op die drukoppervlak van al die lemme plaas, wat lyk soos ernstige gestaakte eerste kwadrant werking. Die vloeiskeiding raak minder ernstig by ’n groter vloeitempo, wat numeriese nabootsing toelaat, maar die nabootsings is sensitief vir die aanvanklike vloeiveld. In die tweede kwadrant, by omgekeerde rotasie, werk die kompressor as ’n turbine. Die lemhoeke en die rigting van lemkromming stem ooreen met die vloeihoeke en verwringing, wat lei tot ho¨er turbine doeltreffendheid. Numeriese nabootsings stem goed ooreen met gemete resultate, maar is weereens sensitief vir die keuse van die aanvanklike vloeiveld. Vierde kwadrant werking met negatiewe rotasie vind plaas wanneer die lug gedwing word om deur die kompressor in die ontwerprigting te vloei. Groot skeidingborrels sit vas aan die drukoppervlaktes van alle lemme, sodat meeste deurvloei naby die naaf en die omhulsel plaas vind.

This work will be focused on issue of a jet engine. The thesis will be divided into search retrieval part and computational part. In the search retrieval part it will focus on different configurations of jet engines as well as areas of their use. The main part of the thesis will however focus on a calculations where a turbine, compressor and an exhaust nozzle will be designed in order to give a thrust of approximately 1kN. Next step will be determination of an engine charcteristic that will give us a preview on how the engine performance will look like in off-design modes.