| 1. |
- Jöcker, Markus, et al.
(författare)
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Comparison of models to predict low engine order excitation in a high pressure turbine stage
- 2006
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Ingår i: Unsteady Aerodynamics, Aeroacoustics and Aeroelasticity of Turbomachines. - Dordrecht : Kluwer Academic Publishers. - 1402042671 ; , s. 145-159
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Konferensbidrag (refereegranskat)abstract
- The paper compares three numerical strategies to predict the aerodynamic rotor excitation sources of "Low Engine Order" (LEO) in a high-pressure turbine stage. Main focus is laid on methods to compute the stator exit flow. The aim is to evaluate computationally cheap approaches to avoid modeling the whole circumference of the stator. A single passage viscous strategy, a single passage inviscid linear blade movement strategy, and a viscous multi-passage sector strategy are compared and evaluated. The assessment of the prediction quality is made by comparison of the computed stator exit flow to experimental data. The main result is that only the global behavior of the stator exit flow is estimated right, both the level and amplitude of Mach number and pressure are computed with poor agreement to experiments. Future evaluations of the resulting rotor excitation pressure are needed to estimate the level of necessary agreement to give acceptable predictions of the low engine order forced response.
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| 2. |
- Jöcker, Markus, 1969-
(författare)
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Numerical Investigation of the Aerodynamic Vibration Excitation of High-Pressure Turbine Rotors
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The design parameters axial gap and stator count of highpressure turbine stages are evaluated numerically towards theirinfluence on the unsteady aerodynamic excitation of rotorblades. Of particular interest is if and how unsteadyaerodynamic considerations in the design could reduce the riskofhigh cycle fatigue (HCF) failures of the turbine rotor.A well-documented 2D/Q3D non-linear unsteady code (UNSFLO)is chosen to perform the stage flow analyses. The evaluatedresults are interpreted as aerodynamic excitation mechanisms onstream sheets neglecting 3D effects. Mesh studies andvalidations against measurements and 3D computations provideconfidence in the unsteady results. Three test cases areanalysed. First, a typical aero-engine high pressure turbinestage is studied at subsonic and transonic flow conditions,with four axial gaps (37% - 52% of cax,rotor) and two statorconfigurations (43 and 70 NGV). Operating conditions areaccording to the resonant conditions of the blades used inaccompanied experiments. Second, a subsonic high pressureturbine intended to drive the turbopump of a rocket engine isinvestigated. Four axial gap variations (10% - 29% ofcax,rotor) and three stator geometry variations are analysed toextend and generalise the findings made on the first study.Third, a transonic low pressure turbine rotor, known as theInternational Standard Configuration 11, has been modelled tocompute the unsteady flow due to blade vibration and comparedto available experimental data.Excitation mechanisms due to shock, potential waves andwakes are described and related to the work found in the openliterature. The strength of shock excitation leads to increasedpressure excitation levels by a factor 2 to 3 compared tosubsonic cases. Potential excitations are of a typical wavetype in all cases, differences in the propagation direction ofthe waves and the wave reflection pattern in the rotor passagelead to modifications in the time and space resolved unsteadypressures on the blade surface. The significant influence ofoperating conditions, axial gap and stator size on the wavepropagation is discussed on chosen cases. The wake influence onthe rotorblade unsteady pressure is small in the presentevaluations, which is explicitly demonstrated on the turbopumpturbine by a parametric study of wake and potentialexcitations. A reduction in stator size (towards R≈1)reduces the potential excitation part so that wake andpotential excitation approach in their magnitude.Potentials to reduce the risk of HCF excitation in transonicflow are the decrease of stator exit Mach number and themodification of temporal relations between shock and potentialexcitation events. A similar temporal tuning of wake excitationto shock excitation appears not efficient because of the smallwake excitation contribution. The increase of axial gap doesnot necessarily decrease the shock excitation strength neitherdoes the decrease of vane size because the shock excitation mayremain strong even behind a smaller stator. The evaluation ofthe aerodynamic excitation towards a HCF risk reduction shouldonly be done with regard to the excited mode shape, asdemonstrated with parametric studies of the mode shapeinfluence on excitability.Keywords:Aeroelasticity, Aerodynamics, Stator-RotorInteraction, Excitation Mechanism, Unsteady Flow Computation,Forced Response, High Cycle Fatigue, Turbomachinery,Gas-Turbine, High-Pressure Turbine, Turbopump, CFD, Design
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| 3. |
- Kessar, Alexandros, et al.
(författare)
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Flow Measurements for Low Engine order Excitations in a High Pressure Turbine stage
- 2005
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Konferensbidrag (refereegranskat)abstract
- This paper demonstrates and evaluates unique flow measurement results obtained in a high pressure test turbine, in order to analyze the effect of Low Engine Order (LEO) excitations. A stator was modified to induce LEO flow variations by either imposing a throat width variation or a blockage of the trailing edge cooling flow from some of the vanes. Laser Two Focus (L2F) and pressure probe measurements were performed at subsonic and transonic flow conditions, without and with the rotor installed and operated. Time resolved velocity data was obtained in front and inside of rotor passages covering the Low Engine Order variation period. The presented results evaluation focuses only on L2F measurements and show that the LEO variation of flow velocity and turbulence intensity is most visible in the gap between stator and rotor and at the first measurement location inside the rotor passage. The overall trend is that stator exit flow Mach numbers are higher behind the passages with smaller pitch and vice versa.
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| 4. |
- Lindborg, Jenny, et al.
(författare)
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Systemperspektiv för effektiv produktion och användning av vätgas viakoppling till fjärrvärme
- 2023
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Detta projekt har analyserat sektorkopplingars möjligheter att ta vara på restflöden som genereras vid produktion av vätgas genom elektrolys samt hur dessa flöden kan generera ekonomiska och systemmässiga fördelar. Förutsättningen har varit att all el köps in externt för spotpris. Projektet har redovisat i detalj hur restvärmen, som uppstår i elektrolysen, kan tillgodogöras som fjärrvärme och därigenom öka processens verkningsgrad från cirka 66 till 95 %. EU:s mål om produktion av 10 miljoner ton vätgas per år till 2030 innebär att det bildas 230 TWh restvärme, motsvarande fyra gånger Sveriges totala fjärrvärmeenergi. Det visar potentialen och vikten av att värmeöverskottet nyttjas i framtida investeringar. För varje kilo vätgas som produceras bildas åtta kilo syrgas, som kan användas i för att förbättra förbränningen i en avfallspanna. Alternativt kan syrgasen transporteras till ett närliggande vattenreningsverk, vilket minskar elanvändningen för de pumpar som idag cirkulerar luft i de biologiska reningsstegen. Svenska kraftnät har skapat flera olika marknader för systemtjänster. Vätgasproduktion har goda förutsättningar att delta, särskilt med FCR-D. Analyserna visar att intäkterna från dessa tjänster kan vara större än både restvärmen och syrgasen, förutsatt att restvärmen inte ersätter bränslen som har en högre kostnadsprofil, som exempelvis bio-olja eller pellets. I dessa fall får restvärmen ett betydligt högre värde. Sektorkopplingen mot fjärrvärme skapar ett resurseffektivt energisystem där alla restflöden kan komma till nytta. Vätgaslager kan också bidra till ett mer robust och resilient energisystem, med möjligheter att förse kritiska verksamheter med reservkraft eller för att starta lokala elnät i ö-drift. För bästa lönsamhet, utifrån befintliga data om elpriser och vätgasens värde, bör vätgasen säljas vidare som bränsle till tunga transport eller som råvara till industrier istället för att lagras för senare omvandling tillbaka till el. I en framtid, där behov av elgenerering för balanskraft kan öka och samtidigt krävas vara koldioxidneutral, kan dock situationen bli annorlunda. Baserat på indata och förutsättningar från omvärldsanalyserna visar att kostnaden för att producera vätgas (kr/kg) minimeras när elektrolysen är i drift cirka 80 % av årets timmar eftersom avskrivningskostnaderna annars blir högre i relation till producerad mängd vätgas. Förutsatt avsättning för vätgasen bör produktionen dras ner enbart vid de allra högsta elpriserna. Scenariot ”gas-to-power” har inte visat sig lönsamt, baserat på de förutsättningar som använts. Historiska elpriser har inte varit tillräckligt höga, tillräckligt ofta för att en extra investering i en gasturbin eller bränslecell ska betala sig. Samtidigt kan det vara missvisande att jämföra priser där dagens fossila bränslen ingår eftersom dessa bränslen på sikt inte är något alternativ. Även om sektorkopplingen till fjärrvärme ökar intäktsmöjligheterna för vätgasproduktion så finns fortfarande ett antal osäkra parametrar som påverkar lönsamheten och investeringsviljan. Dessa specificeras och diskuteras i denna och dess underliggande rapporter.
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| 5. |
- Saha, Ranjan, 1984-
(författare)
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Aerodynamic Investigations of a High Pressure Turbine Vane with Leading Edge Contouring at Endwall in a Transonic Annular Sector Cascade
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Efficiency improvement is an important aspect to reduce the use of fossil-based fuel in order to achieve a sustainable future. Gas turbines are mainly fossil-fuel based turbomachines, and, therefore, efficiency improvement is still the subject of many on-going research activities in the gas turbine community. This study is incorporated into a research project that investigates design possibilities of efficiency improvement at the high pressure turbine (HPT) stage. In the search for HPT-stage efficiency gains, leading edge (LE) contouring near the endwall is one of the methods found in the published literature that has shown a potential to increase the efficiency by decreasing the amount of secondary losses. The overall objective of the thesis is to contribute to the development of gas turbine efficiency improvements in relation to the HPT stage. Particularly, the influence of the LE fillet on losses and flow structure is investigated concentrating on the secondary flow. The core investigation is of an experimental nature. Detailed investigations of the flow field in an annular sector cascade (ASC) are presented with and without the LE fillet, using a geometric replica of a modern gas turbine nozzle guide vane (NGV) with a contoured tip endwall. Furthermore, a separate investigation is performed on a hub-cooled NGV, which focuses on endwalls, specifically the interaction between the hub film cooling and the mainstream (MS). The experimental investigations indicate that the LE fillet has no significant effect on the flow and energy losses of the investigated NGV. The reason why the LE fillet does not affect the losses might be due to the use of a three-dimensional vane with an existing typical fillet over the full hub and tip profile. Findings also reveal that the complex secondary flow depends heavily on the incoming boundary layer. Oil flow visualisation for the baseline case displays a clear saddle point, with a separation line where the horseshoe (HS) vortex separates into the suction side (SS) and the pressure side (PS), whereas for the filleted case, the saddle point is not noticeable. The investigation of a cooled vane, using a tracer gas carbon dioxide (CO2), reveals that the upstream platform film coolant is concentrated along the SS surfaces and does not reach the PS of the hub surface, leaving it less protected from the hot gas.
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| 6. |
- Spelling, James, 1987-, et al.
(författare)
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Annual performance improvement for solar steam turbines through the use of temperature-maintaining modifications
- 2012
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Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 86:1, s. 496-504
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Tidskriftsartikel (refereegranskat)abstract
- Steam turbines in solar thermal power plants experience a much greater number of starts than those operating in base-load plants. By maintaining higher internal temperature during idle periods, faster start-up times can be achieved, increasing the flexibility of the plant as well as increasing net electrical production. Prior work by the authors identified a number of methods for achieving this, with strong increases in daily production predicted; only two specific start-up cases were studied however. In order to obtain a more representative evaluation of the performance increase that can be achieved through increased dispatchability of the turbine, the annual improvement needs to be studied. Building on the existing results, a dynamic system model of a parabolic trough power plant has been established and used to determine the distribution of different cool-down times experienced throughout the year, with a view to evaluating the potential annual production increase. A modification of the start-up curves allows an increase in annual electrical production between 6.4% and 2.4% depending upon the operating mode (free operation versus day-time operation). Through application of a combination of heat blankets and an increase in gland steam temperature, further annual production increases between 2.2% and 3.1% are predicted.
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| 7. |
- Spelling, James, 1987-, et al.
(författare)
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Thermal modeling of a solar steam turbine with a focus on start-up time reduction
- 2012
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Ingår i: Proceedings of the ASME Turbo Expo 2011, Vol 3. - 9780791854631 ; , s. 1021-1030
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Konferensbidrag (refereegranskat)abstract
- Steam turbines in solar thermal power plants experience a much greater number of starts than those operating in base-load plants. In order to preserve the lifetime of the turbine whilst still allowing fast starts, it is of great interest to find ways to maintain the turbine temperature during idle periods. A dynamic model of a solar steam turbine has been elaborated, simulating both the heat conduction within the body and the heat exchange with the gland steam, main steam and the environment, allowing prediction of the temperatures within the turbine during off-design operation and standby. The model has been validated against 96h of measured data from the Andasol 1 power plant, giving an average error of 1.2% for key temperature measurements. The validated model was then used to evaluate a number of modifications that can be made to maintain the turbine temperature during idle periods. Heat blankets were shown to be the most effective measure for keeping the turbine casing warm, whereas increasing the gland steam temperature was most effective in maintaining the temperature of the rotor. By applying a combination of these measures the dispatchability of the turbine can be improved significantly: electrical output can be increased by up to 9.5% after a long cool-down and up to 9.8% after a short cool-down.
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| 8. |
- Spelling, James, et al.
(författare)
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Thermal Modeling of a Solar Steam Turbine With a Focus on Start-Up Time Reduction
- 2012
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Ingår i: Journal of engineering for gas turbines and power. - : ASME International. - 0742-4795 .- 1528-8919. ; 134:1, s. 013001-
-
Tidskriftsartikel (refereegranskat)abstract
- Steam turbines in solar thermal power plants experience a much greater number of starts than those operating in baseload plants. In order to preserve the lifetime of the turbine while still allowing fast starts, it is of great interest to find ways to maintain the turbine temperature during idle periods. A dynamic model of a solar steam turbine has been elaborated, simulating both the heat conduction within the body and the heat exchange with the gland steam, main steam and the environment, allowing prediction of the temperatures within the turbine during off-design operation and standby. The model has been validated against 96 h of measured data from the Andasol 1 power plant, giving an average error of 1.2% for key temperature measurements. The validated model was then used to evaluate a number of modifications that can be made to maintain the turbine temperature during idle periods. Heat blankets were shown to be the most effective measure for keeping the turbine casing warm, whereas increasing the gland steam temperature was most effective in maintaining the temperature of the rotor. By applying a combination of these measures the dispatchability of the turbine can be improved significantly: electrical output can be increased by up to 9.5% after a long cooldown and up to 9.8% after a short cooldown.
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| 9. |
- Topel, Monika, et al.
(författare)
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Geometric Modularity in the Thermal Modeling of Solar Steam Turbines
- 2014
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Ingår i: Proceedings of the SolarPACES 2013 International Conference. - : Elsevier. ; , s. 1737-1746
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Konferensbidrag (refereegranskat)abstract
- To optimize the start-up schedules of steam turbines operating in concentrating solar power plants, accurate predictions of the temperatures within the turbine are required. In previous work by the authors, thermal models of steam turbines have been developed and validated for parabolic trough solar power plant applications. Building on these results, there is an interest to increase the adaptability of the models with respect to different turbine geometries due to the growing trend of having larger steam turbines in parabolic trough and solar tower power plants. In this work, a modular geometric approach has been developed and compared against both the previous modeling approach and 96h of measured data from an operational parabolic trough power plant. Results show a large degree of agreement with respect to the measured data in spite of the different detail levels. The new model allows for simple and fast prediction of the thermal behavior of different steam turbine sizes and geometries, which is expected to be of significant importance for future concentrating solar power plants.
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| 10. |
- Topel, Monika, 1988-
(författare)
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Improving Concentrating Solar Power Plant Performance through Steam Turbine Flexibility
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The amount of incoming solar energy to earth is greater than any other source. Among existing technologies to harness solar energy there is concentrating solar power (CSP). One advantage of CSP is that is dispatchable, meaning that it can provide power even when the sun is not shining. However, CSP is undergoing challenges which hinder its development such as operating variabilities caused by the fluctuations of the sun or the fact that these systems are not yet cost competitive with respect to other technologies. One way of improving the performance of CSP plants (CSPPs) is by increasing their operational flexibility, specifically their capability for fast starts. In this way it is possible for the CSPP to harness the solar energy as soon as possible, thus producing more energy and increasing its profitability. Over 90% of CSPPs use a steam turbine to generate electricity. Steam turbines are not currently designed with the flexibility required by the CSP application. Steam turbine start-up is limited by thermal stress and differential expansion. If not carefully controlled, these phenomena either consume lifetime or even result in machine failure.The aim of this work was to understand the improvement potential of steam turbine start-up and quantify this in terms of CSPP performance indicators. For this, a thermo-mechanical steam turbine model was developed and validated. The model was then used to analyze potential improvements and thermal constraints to steam turbine start-up operation. Furthermore, a CSP plant techno-economic model was developed including steam turbine details. This modeling approach including two levels of detail allowed for the particularities of the component to be included within the dynamics of the plant and thus be able to connect the perspectives of the equipment manufacturer with those of the plant operator. Reductions of up to 11.4% in the cost of electricity were found in the studies carried out.
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