| 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. |
- Laumert, Björn, 1972-, et al.
(författare)
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Investigation of unsteady aerodynamic blade excitation mechanisms in a transonic turbine stage - Part I : Phenomenological identification and classification
- 2002
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Ingår i: Journal of turbomachinery. - : ASME International. - 0889-504X .- 1528-8900. ; 124:3, s. 410-418
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Tidskriftsartikel (refereegranskat)abstract
- Based on the results of time-dependent 3-D viscous computations the aerodynamic mechanisms that cause the unsteady pressure fluctuations on the vane and rotor blade surface of a high-pressure transonic turbine are identified and separately classified in a phenomenological manner. In order to be able to describe separately the influence of wake, potential and shock distortions on the blade surface pressure tit design operation conditions, the stator exit Mach number is increased as to enhance the shock distortions and lowered as to enhance potential anti wake distortions, In a comprehensive approach the observations from the off-design conditions are utilized to classify every major perturbation observed in the perturbation space-time maps tit design operation conditions. The spanwise variations caused by the inherent 3-D nature of the flow field and promoted by the 3-D shape of the rotor blade are addressed.
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| 3. |
- Laumert, Björn, 1972-, et al.
(författare)
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Investigation of unsteady aerodynamic blade excitation mechanisms in a transonic turbine stage - Part II : Analytical description and quantification
- 2002
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Ingår i: Journal of turbomachinery. - : ASME International. - 0889-504X .- 1528-8900. ; 124:3, s. 419-428
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a study of the blade pressure perturbation levels and the resulting blade forces in a high-pressure transonic turbine stage based on 3-D time dependent viscous computations. Globally, the blade pressure unsteadiness is quantified with the RMS of the pressure perturbations integrated in both time and along the blade surface. Operation point as well as spanwise variations are addressed. Locally, the relative strength of the pressure perturbation events on the vane and rotor blade surface is investigated. To obtain information about the relative strength of events related to the blade passing frequency and higher harmonics, the pressure field is Fourier decomposed in time at different radial positions along the blade arc-length. The amplitude peaks are then related to the pressure events in space-time maps. With the help of the observations and results from the blade pressure study, the radial variations of the unsteady blade force and torque acting on a constant span blade profile section are investigated. The connection between the first and second vane passing frequency pressure amplitudes on the rotor blade surface and the resulting force and the torque amplitudes for three selected blade modes was investigated in detail. In this investigation the pressure was integrated over defined rotor blade regions to quanti,, local force contributions. Spanwise as well as operation point variations are addressed.
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| 4. |
- Mayorca, María A., et al.
(författare)
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A New Reduced Order Modeling for Stability and Forced Response Analysis of Aero-Coupled Blades Considering Various Mode Families
- 2012
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Ingår i: Journal of turbomachinery. - : ASME International. - 0889-504X .- 1528-8900. ; 134:5, s. 051008-
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the description and application of a new method for stability and forced response analyses of aerodynamically coupled blades considering the interaction of various mode families. The method, here referred as multimode least square, considers the unsteady forces due to the blade motion at different modes shape families and calculates the aerodynamic matrixes by means of a least square (L2) approximations. This approach permits the prediction of mode families' interaction with capabilities of structural, aerodynamic and force mistuning. A projection technique is implemented in order to reduce the computational domain. Application of the method on tuned and structural mistuned forced response and stability analyses is presented on a highly loaded transonic compressor blade. When considering structural mistuning the forced response amplitude magnification is highly affected by the change in aerodynamic damping due to mistuning. Analyses of structural mistuning without aerodynamic coupling might result in over-estimated or under-estimated response when the source of damping is mainly aerodynamic. The frequency split due to mistuning can cause that mode families' interact due to reducing their frequencies separation. The advantage of the present method is that the effect of mode family interaction on aerodynamic damping and forced response is captured not being restricted to single mode families.
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| 5. |
- Mayorca, Maria Angelica, et al.
(författare)
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Prediction of Turbomachinery Aeroelastic Behavior From a Set of Representative Modes
- 2013
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Ingår i: Journal of turbomachinery. - : ASME International. - 0889-504X .- 1528-8900. ; 135:1, s. 011032-
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Tidskriftsartikel (refereegranskat)abstract
- A method is proposed for the determination of the aeroelastic behavior of a system responding to mode-shapes which are different from the tuned in vacuo ones, due to mistuning, mode family interaction, or any other source of mode-shape perturbation. The method is based on the generation of a data base of unsteady aerodynamic forces arising from the motion of arbitrary modes and uses least square approximations for the prediction of any responding mode. The use of a reduced order technique allows for mistuning analyses and is also applied for the selection of a limited number of arbitrary modes. The application of this method on a transonic compressor blade shows that the method captures the aeroelastic properties well in a wide frequency range. A discussion of the influence of the mode-shapes and frequency on the final stability response is also provided.
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| 6. |
- Abeywecra, Ruchira, et al.
(författare)
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A Remote Mode High Quality International Master Degree Program in Environomical Pathways for Sustainable Energy Systems (SELECT) -Pilot Program Experiences During First Year of Studies
- 2018
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Ingår i: PROCEEDINGS OF 2018 IEEE GLOBAL ENGINEERING EDUCATION CONFERENCE (EDUCON) - EMERGING TRENDS AND CHALLENGES OF ENGINEERING EDUCATION. - : IEEE. - 9781538629574 ; , s. 276-284
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Konferensbidrag (refereegranskat)abstract
- Remote mode study programs at master degree level are becoming more popular than undergraduate level programs. Students after graduation with Bachelors degree very often are employed and the most appropriate mode for them to pursue higher studies is the remote mode. Postgraduate programs with one or two year duration mostly focus on specific areas of research based industrial application. Traditional remote education is thought to be more centered on web based on-line programs with a little opportunity for teacher student interaction and interaction with peers. In such programs motivation for studies has been a problem and as a result many students drop off and also those remain in the program for prolonged periods do not show good performance. One of the reasons for failures of students in remote studies is the isolation leading to discouragement for the completion studies. A remote mode Master Degree Program in Environomical Pathways for Sustainable Energy Systems (MSc-SELECT), consisting of a number of innovative features aimed at improved student engagement, motivation, exposure to experiences in multi-national setting and team work, was developed and implemented by the Master School of the EIT-InnoEnergy, as a pilot project. The program was offered, collaboratively and simultaneously to students in three locations, Royal Institute of Technology in Sweden, Universitat Politecnica de Catalunya in Spain and the Open University of Sri Lanka. The students in Sweden and Spain each followed 50% of the courses on-campus and 50% in remote mode depending upon the university they registered with. The students in Sri Lanka followed the entire 1st year fully remotely. All the students (from KTH, OUSL and UPC) will spend the 2nd year on-campus at another university in the consortium. This paper discusses, from the perspective of the fully remote site, the remote program with its innovative aspects, student performance and experience together with future tasks for making the program viable and beneficial to all partner countries.
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| 7. |
- Abeyweera, Ruchira, et al.
(författare)
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Capacity Building Through a Web Based Master Degree Programme in Sustainable Energy Engineering
- 2017
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Ingår i: PROCEEDINGS OF 2017 IEEE GLOBAL ENGINEERING EDUCATION CONFERENCE (EDUCON2017). - : IEEE. - 9781509054671 ; , s. 800-805
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Konferensbidrag (refereegranskat)abstract
- Open Distance Learning is gaining popularity as a successful alternative for on-campus higher education especially with the emergence of web based platforms which enable the online delivery of courses worldwide. This emerging educational pedagogy can successfully be employed as means of capacity building of the people living in the less fortunate parts of the world where higher education especially at master level are scarce. This paper presents a two-year collaborative master study programme in sustainable energy engineering offered in synchronous with an on-campus study programme conducted by the KTH Royal Institute of Technology of Sweden, to students of Sri Lanka, which was facilitated by the Open University of Sri Lanka. The paper describes the need of such a programme, the format of course delivery and assessment thereof, plus the benefits gained. This programme has produced 72 post graduates in Sri Lanka alone and more than 200 distant postgraduates worldwide in the field of sustainable energy engineering during last 10 years period. In terms of capacity building in the energy sector in Sri Lanka this is considered a great achievement. The experience gained by the local staff in the role of local facilitators who engaged in some of the academic related activities such as evaluation of students' presentation and co-supervision of thesis projects have been greatly appreciated as being additional benefits to the staff in terms of their own academic development and capacity building. Finally, conclusions are made on how remote programmes of study could successfully be delivered to places where such know-how is scarce by adapting appropriate technologies in training personnel at postgraduate level to meet the needs of the industry.
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| 8. |
- Allégret-Bourdon, Davy, et al.
(författare)
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Study of shock movement and unsteady pressure on 2D generic model
- 2006
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Ingår i: Unsteady Aerodynamics, Aeroacoustics and Aeroelasticity of Turbomachines. - Dordrecht : Kluwer Academic Publishers. - 1402042671 ; , s. 409-421
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Konferensbidrag (refereegranskat)abstract
- A flexible generic model has been developed at the Chair of Heat and Power Technology in order to perform fatter experiments in a more fundamental fashion. It is made of engineered flexible material and oscillate in a controlled way at non-uniform amplitude and variable frequencies. Time-resolved measurements of the unsteady surface pressures, the instantaneous model geometry as well as unsteady Schlieren visualizations are performed in order to study the shock wave motion and the aerodynamic load acting over this flexible generic bump. The model oscillates at reduced frequencies from 0.015 to 0.294 at transonic flow condition. The mode shapes of such a flexible bump strongly depends on the excitation frequency of the generic model. Schlieren pictures are obtained for an operating point characterized by an inlet Mach number of 0.63. Moreover, the presented results demonstrate that the phase of shock wave movement towards bump local motion shows a decreasing trend for the third bending mode shapes at reduced frequency higher than k=0.074. At the pressure taps located after the shock wave formation, the phase of pressure fluctuations towards bump local motion presents the same decreasing trend.
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| 9. |
- Andrinopoulos, Nikos, et al.
(författare)
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Design And Testing Of A Vibrating Test Object For Investigating Fluid-Structure Interaction
- 2008
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Ingår i: PROCEEDINGS OF THE ASME TURBO EXPO 2008, VOL 5, PT A. - NEW YORK : AMER SOC MECHANICAL ENGINEERS. - 9780791843154 ; , s. 415-424
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Konferensbidrag (refereegranskat)abstract
- In this study the vibration properties of a deforming test object are presented. The test object is bump shaped and is integrated into the wall of a transonic wind tunnel. The purpose for using such a test object is to study, in a generic manner, the unsteady aerodynamic phenomena occurring due to the presence of a vibrating structure in the flow. The setup is part of an ongoing study to address the phenomena of fluid-structure interaction and shock-boundary layer interaction. The design objective for the test object is to assimilate a IF vibration mode at a given section of atypical compressor blade. Finite element (FE) analyses have been used to predict the frequency response of the test object prior to manufacturing. The design objectives have been verified experimentally by time-resolved laser measurements. It has been found that the FE predictions are in good agreement with experimental data. Furthermore it has been shown that the present test object allows for the achievement of the targeted vibration properties up to a frequency of 250Hz, corresponding to a reduced frequency above 0.8.
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| 10. |
- Araoz Ramos, Joseph A., et al.
(författare)
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Numerical simulation for the design analysis of kinematic Stirling engines
- 2015
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 159, s. 633-650
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Tidskriftsartikel (refereegranskat)abstract
- The Stirling engine is a closed-cycle regenerative system that presents good theoretical properties. These include a high thermodynamic efficiency, low emissions levels thanks to a controlled external heat source, and multi-fuel capability among others. However, the performance of actual prototypes largely differs from the mentioned theoretical potential. Actual engine prototypes present low electrical power outputs and high energy losses. These are mainly attributed to the complex interaction between the different components of the engine, and the challenging heat transfer and fluid dynamics requirements. Furthermore, the integration of the engine into decentralized energy systems such as the Combined Heat and Power systems (CHP) entails additional complications. These has increased the need for engineering tools that could assess design improvements, considering a broader range of parameters that would influence the engine performance when integrated within overall systems. Following this trend, the current work aimed to implement an analysis that could integrate the thermodynamics, and the thermal and mechanical interactions that influence the performance of kinematic Stirling engines. In particular for their use in Combined Heat and Power systems. The mentioned analysis was applied for the study of an engine prototype that presented very low experimental performance. The numerical methodology was selected for the identification of possible causes that limited the performance. This analysis is based on a second order Stirling engine model that was previously developed and validated. The simulation allowed to evaluate the effect that different design and operational parameters have on the engine performance, and consequently different performance curves were obtained. These curves allowed to identify ranges for the charged pressure, temperature ratio, heat exchangers dimensions, crank phase angle and crank mechanical effectiveness, where the engine performance was improved. In addition, the curves also permitted to recognise ranges were the design parameters could drastically reduce the brake power and efficiency. The results also showed that the design of the engine is affected by the conditions imposed by the CHP interactions, and that the engine could reach a brake power closer to 832 W with a corresponding brake efficiency of 26% when the adequate design parameters were considered. On the other hand, the performance could also be very low; as the reported in experimental tests, with brake power measurements ranging 52-120W.
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