This thesis experimentally investigates the phenomenon of ingress through gas turbine rim seals. The work focuses on developing experimental and numerical techniques for measuring the required sealing flow levels to purge the wheel-space against ingress and the effect of externally-induced ingress on the surface temperature as well as heat transfer to the rotor. Ingress is driven by a pressure difference between the mainstream annulus and wheel-space cavity resulting from the asymmetric external pressure profile in the annulus and/or the rotation of fluid in the rotor-stator wheel-space cavity. It can be prevented by pressurising the wheel-space through the supply of sealant flow. The University of Bath had measured and shown, for the first time, the thermal effects of ingress on the rotor in the wheel-space for a datum seal (axial-clearance seal) using thermo-chromic liquid crystal. However, as the previously used experimental technique with thermo-chromic liquid crystal was prone to large uncertainties, a non-intrusive temperature measurement technique using an infrared (IR) temperature sensor was developed. The new technique was successfully applied to the Bath one-stage gas turbine test facility and provided a full temperature history of the rotor surface in a transient heat transfer experiment. Moreover, a data analysis method appropriate for transient experiments using the IR temperature measurement technique was developed. The method was used to accurately calculate the heat transfer coefficient and the adiabatic surface temperature based on the full temperature history. A series of numerical experiments was carried out to develop the analysis method and the results from the numerical experiments were used to design new heat transfer experiments for both the 1 and 1.5-stage ingestion rigs of the University of Bath. Gas concentration measurements were made on the stator of the Bath one-stage gas turbine test rig to determine the variation of sealing effectiveness with sealant flow rate for four different seal geometries at design operational conditions. The IR temperature measurement technique was used to determine the effect of ingress on the heat transfer coefficient and the adiabatic wall temperature on the rotor of the ingestion test facility. Concurrent gas concentration measurements were made on the stator to compare the effects of ingress on the two discs (stator and rotor). Comparison between the adiabatic effectiveness on the rotor and the concentration effectiveness on the stator showed that the rotor was protected against the effects of ingress relative to the stator. The sealing air, which was drawn into the rotor boundary layer from the source region, thermally buffered the rotor against the ingested fluid in the core. Subsequently, a thermal buffer ratio hypothesis was developed and shown to be in good agreement with the experimental data. A previously published orifice model was modified so that the sealing effectiveness determined from the concentration measurements in a rig could be used to determine the effectiveness based on pressure measurements in an engine. There was good agreement between the effectiveness acquired from pressure measurement determined using the theoretical model and the sealing effectiveness determined from concentration measurements. It was also shown how parameters obtained from measurements of pressure and concentration in a rig could be used to calculate the sealing effectiveness in an engine.

abstract: Gas turbine efficiency has improved over the years due to increases in compressor pressure ratio and turbine entry temperature (TET) of main combustion gas, made viable through advancements in material science and cooling techniques. Ingestion of main combustion gas into the turbine rotor-stator disk cavities can cause major damage to the gas turbine. To counter this ingestion, rim seals are installed at the periphery of turbine disks, and purge air extracted from the compressor discharge is supplied to the disk cavities. Optimum usage of purge air is essential as purge air extraction imparts a penalty on turbine efficiency and specific fuel consumption. In the present work, experiments were conducted in a newly constructed 1.5-stage axial flow air turbine featuring vanes and blades to study main gas ingestion. The disk cavity upstream of the rotor, the 'front cavity', features a double seal with radial clearance and axial overlap at its rim. The disk cavity downstream of the rotor, the 'aft cavity', features a double seal at its rim but with axial gap. Both cavities contain a labyrinth seal radially inboard; this divides each disk cavity into an 'inner cavity' and a 'rim cavity'. Time-averaged static pressure at various locations in the main gas path and disk cavities, and tracer gas (CO2) concentration at different locations in the cavities were measured. Three sets of experiments were carried out; each set is defined by the main air flow rate and rotor speed. Each of the three sets comprises of four different purge air flow rates, low to high. The mass flow rate of ingested main gas into the front and aft rim cavities is reported at the different purge air flow rates, for the three experiment sets. For the present stage configuration, it appears that some ingestion persisted into both the front and aft rim cavities even at high purge air flow rates. On the other hand, the front and aft inner cavity were completely sealed at all purge flows. / Dissertation/Thesis / Masters Thesis Engineering 2015

Afin de faire face aux fortes températures rencontrées par les composantsen aval de la chambre de combustion, des prélèvements d’air plus frais sont réalisésau niveau du compresseur. Cet air alimente les cavités en pied de turbine et refroidiles disques rotor permettant d’assurer le bon fonctionnement de la turbine.Ce manuscrit présente une étude numérique de l’effet de ces écoulements de cavitéau pied de la turbine sur ses performances aérodynamiques. Les phénomènesd’interaction entre l’air de cavité en pied de turbine et l’air de veine principal est unphénomène encore difficilement compris. L’étude de ces phénomènes est réalisée autravers de différentes approches numériques (RANS, LES et LES-LBM) appliquéesà deux configurations pour lesquelles des résultats expérimentaux s ont disponibles.Une première configuration en grille d’aube linéaire en amont de laquelle différentesgéométries d’entrefer (interface entre plateforme rotor et stator) et débits de cavitépouvaient être variés. Une seconde configuration annulaire composée de deux étagesde turbine comprenant les cavités en pied et plus proche d’une configuration industrielle.Les pertes additionnelles associées à l’écoulement de cavité sont mesurées etétudiées à l’aide d’une méthode basée sur l’exergie (bilans d’énergie dans l’objectifde générer du travail). / In order to deal with high temperatures faced by the components downstreamof the combustion chamber, some relatively cold air is bled at the compressor.This air feeds the cavities under the turbine main annulus and cool down the rotordisks ensuring a proper and safe operation of the turbine. This thesis manuscriptintroduces a numerical study of the effect of the cavity flow close to the turbine hubon its aerodynamic performance. The interaction phenomena between the cav-ity andmain annulus flow are not currently fully understood. The study of these phenomenais performed based on different numerical approaches (RANS, LES and LES-LBM)applied to two configurations for which experimental results are avail-able. A linearcascade configuration with an upstream cavity and various rim seal geometries(interface between rotor and stator platform) and cavity flow rate avail-able. Arotating configuration that is a two stage turbine including cavities close to realisticindustrial configurations. Additional losses incurred by the cavity flow are measuredand studied using a method based on exergy (energy balance in the purpose togenerate work).

Turbomachinery forms the principal prime mover in the energy and aviation industries. Due to its size, improvements to this fleet of machines have the potential of significant impact on global emissions. Due to high gas temperatures in stationary gas turbines and jet engines, areas of flow mixing and cooling are identified to benefit from continued research. Here, sensitive areas are cooled through cold air injection, but with the cost of power to compress the coolant to appropriate pressure. Further, the injection itself reduces output due to mixing losses.A turbine testing facility is center to the study, allowing measurement of cooling impact on a rotating low degree of reaction high pressure axial turbine. General performance, flow details, and cooling performance is quantified by output torque, pneumatic probes, and gas concentration measurement respectively. The methodology of simultaneously investigating the beneficial cooling and the detrimental mixing is aimed at the cavity purge flow, used to purge the wheelspace upstream of the rotor from hot main flow gas.Results show the tradeoff between turbine efficiency and cooling performance, with an efficiency penalty of 1.2 %-points for each percentage point of massflow ratio of purge. The simultaneous cooling effectiveness increase is about 40 %-points, and local impact on flow parameters downstream of the rotor is of the order of 2° altered turning and a Mach number delta of 0.01. It has also been showed that flow bypassing the rotor blading may be beneficial for cooling downstream.The results may be used to design turbines with less cooling. Detrimental effects of the remaining cooling may be minimized with the flow field knowledge. Stage performance is then optimized aerodynamically, mixing losses are reduced, and the cycle output is maximized due to the reduced compression work. The combination may be used to provide a significant benefit to the turbomachinery industry and reduced associated emissions. / Strömningsmaskinen i dess olika variationer bildar den främsta drivmotorn inom kraftproduktion och flygindustrin. En förbättring av denna väldiga maskinpark har potentialen till betydande inverkan på globala utsläpp. Områden som identifierats kunna dra nytta av vidare forskning är ombandningsprocesser och kylning. Dessa områden är inneboende i stationära gasturbiner och jetmotorer på grund av de heta gaser som används. Kylning uppnås genom injektion av kall luft i kritiska områden och försäkrar därmed säker drift. Kylningen kommer dock till en kostnad. På cykelnivå krävs arbete för att komprimera flödet till korrekt tryck. Dessutom medför injektionen i sig förluster som kan härledas till omblandningsprocessen. Syftet med detta arbete är att samtidigt undersöka de fördelaktiga kylegenskaperna som nackdelarna med inblandning för att på så sätt bestämma den uppoffring som måste göras för en viss kylning. Alla förbättringar tros dock inte behöva föregås av en uppoffring. Om påverkan av kylningen på huvudflödet är välförstådd kan designen justeras för att ta hänsyn till denna förändring och minimera inverkan. Denna metodologi riktar sig mot ett särskilt kylflöde, kavitetsrensningsflödet, som har till uppgift att avlägsna het luft från den kavitet som uppkommer uppströms rotorskivan i ett högtrycksturbinsteg. Studien kretsar kring en turbinprovanläggning som möjliggör detaljerade strömningsmätningar i ett roterande turbinsteg under inverkan av kavitetsrensningsflödet. Högtrycksturbinsteget som används för undersökningen är av låg reaktionsgrad. Här kvantifieras generell prestanda genom mätning av vridmomentet på utgående axel. Flödesfältet kvantifieras med pneumatiska sonder, och kylningsprestandan predikteras genom gaskoncentrationsmätningar. Resultaten visar avvägningen och sambandet mellan turbinverkningsgrad och kylning i kavitet samt huvudkanal. Flödet mäts i detalj, och de effekter som kan förväntas uppkomma då ett turbinsteg utsätts för en viss mängd av kylflödet kvantifieras. De kvantitativa resultaten för det undersökta steget visar på en förlust i verkningsgrad på 1.2 procentenheter för varje procentenhet av kavitetsrensningsflödet i termer om massflödesförhållande. Samtidigt ses kyleffektiviteten öka med 40 procentenheter. Den lokala inverkan på flödesfältet nedströms rotorn för det undersökta steget är 2° i flödesvinken och en ändring på 0.01 i Machnummer för varje procentenhet av kylflödet. Dessa ändringar ses i form av ökad omlänkning och reducerad hastighet nära hubben, och vice versa omkring halva spännvidden. Inverkan av aktuell driftpunkt understryks genom arbetet. Det har också visats att ett läckage som kringgår rotorbladen i vissa kan fall ge fördelaktig kylning i områden nedströms. Denna kombinerade kunskap kan användas för design av turbiner med så låg mängd kylning som möjligt samtidigt som säker drift bibehålls. Den negativa inverkan av den återstående kylningen kan minimeras genom kunskapen om hur flödesfältet påverkas. Genom detta optimeras stegverkningsgraden aerodynamiskt, omblandningsförluster minimeras, och cykeleffekten maximeras genom det minskade kompressionsarbetet till följd av de reducerade kylmängderna. Kombinationen kan ge en betydande förbättring för turbinindustrin och minskade utsläpp. / <p>QC 20171129</p>