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| 2. |
- Aghaali, Habib, 1981-, et al.
(författare)
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Turbocharged SI-Engine Simulation with Cold and Hot-Measured Turbocharger Performance Maps
- 2012
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Ingår i: Proceedings of ASME Turbo Expo 2012. - ASME.
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Konferensbidrag (refereegranskat)abstract
- Heat transfer within the turbocharger is an issue in engine simulation based on zero and one-dimensional gas dynamics. Turbocharged engine simulation is often done without taking into account the heat transfer in the turbocharger. In the simulation, using multipliers is the common way of adjusting turbocharger speed and parameters downstream of the compressor and upstream of the turbine. However, they do not represent the physical reality. The multipliers change the maps and need often to be different for different load points. The aim of this paper is to simulate a turbocharged engine and also consider heat transfer in the turbocharger. To be able to consider heat transfer in the turbine and compressor, heat is transferred from the turbine volute and into the compressor scroll. Additionally, the engine simulation was done by using two different turbocharger performance maps of a turbocharger measured under cold and hot conditions. The turbine inlet temperatures were 100 and 600°C, respectively. The turbocharged engine experiment was performed on a water-oil-cooled turbocharger (closed waste-gate), which was installed on a 2-liter gasoline direct-injected engine with variable valve timing, for different load points of the engine. In the work described in this paper, the difference between cold and hot-measured turbocharger performance maps is discussed and the quantified heat transfers from the turbine and to/from the compressor are interpreted and related to the maps.
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| 3. |
- Malla, Bhupatindra, et al.
(författare)
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Proper Orthogonal Decomposition on LES and PIV Data Sets from a Mach 0.9 Jet.
- 2012
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Ingår i: 50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition. - AIAA. ; s. 12
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Konferensbidrag (refereegranskat)abstract
- This paper contains the complementary analysis of the results obtained through computational and experimental methods using the technique of Proper Orthogonal Decomposition (POD). A detailed study of the experimentally obtained flow field data using the method of POD has already been accomplished. The experimental data consists of the 2D visualization of the velocity field obtained using Particle Image Velocimetry (PIV). The computational process is initialized with the simulation of the 3D flow field using a steady state RANS flow solver. RANS is used as a platform to proceed towards capturing the unsteadiness of the flow field which is accomplished using the Large Eddy Simulation (LES). A significant match in the characteristics of the mode shapes has been observed, in both the axial and radial components of the velocity field, however, there is difference in the distribution of the energies over the modes. The LES predicts the energies to be higher at the lowest modes and the energy drop off rate is higher. On the contrary, PIV predicts lower energies at the first few modes, in comparison to the LES results, however the energy drop off rate is smaller.
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| 4. |
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Chalmers Environmental Initiative Progress Report 2001
- 2001
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Samlingsverk (redaktörskap) (övrigt vetenskapligt)abstract
- The Board of the Chalmers University of Technology Foundation decided in 1999 to invest SEK 100 million in a strategic investment in the environment with a special focus on environmental systems analysis. This investment was entitled The Chalmers Environmental Initiative (CEI). Through this environmental initiative Chalmers has acquired a prominent international position within environmental systems analysis. CEI is the result of the active research and education that has taken place at Chalmers over the past 10 years. A broad base in combination with leading edge technology presented the opportunity to create a very strong research programme based on interaction between the various schools at Chalmers. As CEI is integrated into undergraduate and doctoral programmes at Chalmers, engineers, architects and doctoral students have access, within the framework of their studies, to research-based environmental education with a focus on a sustainable society. CEI also co-operates with other parties, such as industry, politicians, various organisations and the general public, as a further means of contributing to sustainable development in society. Within CEI, seven new professors have been appointed within the following areas: Management for Sustainability Rolf Wolff, 1 June 2000 Environmental Systems Technology Anne-Marie Tillman, 1 September 2000 Sustainable Industrial Metabolism Christian Azar, 1 September 2000 Global Environmental Measurements Donal Murtagh, 1 November 2000 Green Chemistry William J. Frederick Jr, 1 August 2001 Sustainable Energy Systems Filip Johnsson, preliminary 1 October 2001 Design for Sustainable Urban Development Vacant: interviews during April 2001 The four professors appointed in 2000 are presented in this report as well as their declaration of intent for the next few years. At present, the CEI professors are involved with approximately 40 universities, institutes and industrial partners in the form of project co-operation and joint publications. The four professors have the greater proportion of their environmental research funded through external grants, compared to CEI. The proportion of faculty funds and other internal Chalmers funds is at present very low. A summary of the financing structure is also included in this report. During 2001, various forms of co-operation were initiated between the professors, such as joint project plans, doctoral students, courses and graduate schools. During autumn 2001, a residential seminar is planned for discussions within CEI as well as an open presentation of the project and the professors. This major in-house focus on environmental research has attracted attention externally and contributed to the opening up of new potential in combination with increased expectations. Since May 1, 2000, Chalmers has been a member of the Alliance for Global Sustainability (AGS), an association of some of the world’s foremost universities in the environmental field. AGS and other platforms form the basis for international research collaboration. CEI and other environmental activities have led to spin-off effects and contributed to increased interest in Chalmers as an environmental university. Chalmers and Göteborg University were, for example, jointly awarded the King Carl XVI Gustaf visiting professorship in environmental science for 2001-2002 and Margot Wallström received an honorary doctorate from Chalmers in 2001. A large number of well-known environmental researchers have also visited Chalmers to take part in conferences and seminars, including the winners of the Volvo Environmental Award for 2000 and the winner of the City of Göteborg International Environmental Award for 2000.
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| 5. |
- Dadfar, Reza, 1978-
(författare)
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Active Control and Reduced-Order Modeling ofTransition in Shear Flows
- 2013
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Licentiatavhandling (övrigt vetenskapligt)abstract
- In this thesis direct numerical simulation is used to investigate the possibilityto delay the transition from laminar to turbulent in boundary layer flows.Furthermore, modal analysis is used to reveal the coherent structures in highdimensional dynamical systems arising in the flow problems.Among different transition scenarios, the classical transition scenario isanalysed. In this scenario, the laminar-turbulent transition occurs when Tollmien-Schlichting waves are triggered inside the boundary layer and grow exponentiallyas they move downstream in the domain. The aim is to attenuate the amplitudeof these waves using active control strategy based on a row of spatiallylocalised sensors and actuators distributed near the wall inside the boundarylayer. To avoid the high dimensional system arises from discretisation of theNavier Stokes equation, a reduced order model (ROM) based on EigensystemRealisation Algorithm (ERA) is obtained and a linear controller is designed.A plasma actuator is modelled and implemented as an external forcing on theflow. To account for the limitation of the plasma actuators and to further reducethe complexity of the controller several control strategies are examinedand compared. The outcomes reveal successful performance in mitigating theenergy of the disturbances inside the boundary layer.To extract coherent features of the wind turbine wakes, modal decompositiontechnique is employed where a large scale dynamical system is reduced toa fewer number of degrees of freedom. Two decomposition techniques are employed:proper orthogonal decomposition and dynamic mode decomposition.In the former procedure, the flow is decomposed into a set of uncorrelated structureswhich are rank according to their energy. In the latter, the eigenvaluesand eigenvectors of the underlying approximate linear operator is computedwhere each mode is associated with a specific frequency and growth rate. Theresults revealed the structures which are dynamically significant to the onsetof instability in the wind turbine wakes.
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| 6. |
- Favre, Tristan
(författare)
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Aerodynamics simulations of ground vehicles in unsteady crosswind
- 2011
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Doktorsavhandling (övrigt vetenskapligt)abstract
- Ground vehicles, both on roads or on rail, are sensitive to crosswinds and the handling, travelling speeds or in some cases, safety can be affected. Full modelling of the crosswind stability of a vehicle is a demanding task as the nature of the disturbance, the wind gust, is complex and the aerodynamics, vehicle dynamics and driver reactions interact with each other. One of the objectives of this thesis, is to assess the aerodynamic response of simplified ground vehicles under sudden strong crosswind disturbances by using an advanced turbulence model. In the aerodynamic simulations, time-dependant boundary data have been used to introduce a deterministic wind gust model into the computational domain. This thesis covers the implementation of such gust models into Detached-Eddy Simulations (DES) and assesses the overall accuracy. Different type of grids, numerical setups and refinements are considered. Although the overall use of DES is seen suitable, further investigations can be foreseen on more challenging geometries. Two families of vehicle models have been studied. The first one, a box-like geometry, has been used to characterize the influence of the radius of curvature and benefited from unsteady experimental data for comparison. The second one, the Windsor model, has been used to understand the impact of the different rear designs. Noticeably, the different geometries tested have exhibited strong transients in the loads that can not be represented in pure steady crosswind conditions.The static coupling between aerodynamics and vehicle dynamics simulations enhances the comparisons of the aerodynamic designs. Also, it shows that the motion of the centre of pressure with respect the locations of the centre of gravity and the neutral steer point, is of prime interest to design vehicles that are less crosswind sensitive. Recommendations on the future work on crosswind sensitivity for ground vehicles are proposed at the end of this thesis.
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| 7. |
- Grönstedt, Tomas, 1970-, et al.
(författare)
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First and Second Law Analysis of Future Aircraft Engines
- 2013
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Ingår i: ASME Turbo Expo, 2013. ; :GT2013-95516
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Konferensbidrag (refereegranskat)abstract
- An optimal baseline turbofan cycle designed for a performance level expected to be available around year 2050 is established. Detailed performance data are given in take-off, top of climb and cruise to support the analysis. Losses are analyzed based on a combined use of the first and second law of thermodynamics, to establish a basis for discussion on future radical engine concepts and to quantify loss levels of very high performance engines. In the light of the performance of the future baseline engine, three radical cycles designed to reduce the observed major loss sources are introduced. The combined use of a first and second law analysis of an open rotor engine, an intercooled recuperated engine and an engine working with a pulse detonation combustion core is presented. In the past, virtually no attention has been paid to the systematic quantification of the irreversibility rates of such radical concepts. Previous research on this topic has concentrated on the analysis of the turbojet and the turbofan engine. In the framework developed, the irreversibility rates are quantified through the calculation of the exergy destruction per unit time. A striking strength of the analysis is that it establishes a common currency for comparing losses originating from very different physical sources of irreversibility. This substantially reduces the complexity of analyzing and comparing losses in aero engines. In particular, the analysis sheds new light on how the intercooled recuperated engine establishes its performance benefits.
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| 8. |
- Grönstedt, Tomas, 1970-
(författare)
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Propulsion Systems Modeling
- 2012
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Ingår i: Physics-Based Modeling & Simulation for Aerospace Systems, VKI lecture series. - 978-2-87516-038-6
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Bokkapitel (övrigt vetenskapligt)abstract
- The present text draws attention to three interrelated topics; aero engine system simulation, evaluation of losses through exergy analysis and the search for more energy efficient power plants. The first chapter reviews the historical development of simulation tools, with an emphasis on generic programs, and discusses efficient numerical solution techniques and suitable solvers. A short discussion on multidisciplinary optimization tools is given. The chapter also briefly reviews the state of the art in terms of commercially available software for aero engine simulation and discusses the needs and uses in industrial applications. The second chapter introduces the concept of exergy analysis and develops the necessary equations for applying the theory to evaluate losses in aero engines. The third chapter pursues future ultra efficient engines designed for an estimated 2050 technology level. The analysis is based on mission optimization starting with a conventional three shaft engine. The concept of exergy analysis is then used to show where in the cycle that major efficiency improvements of such an engine can be accomplished. This is followed by a discussion on a number of cycle innovations that can target the observed losses. Optimization is used to quantify the improvement potential.
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| 9. |
- Gupta, Mohit, 1986-, et al.
(författare)
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Design of Low Thermal Conductivity Thermal Barrier Coatings by Finite Element Modelling
- 2011
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Ingår i: Surface Modification Technologies XXIV : SMT24, Dresden, September 7-9, 2010. ; s. 353-365
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Konferensbidrag (refereegranskat)abstract
- Fundamental understanding of relationships between coating microstructure and thermal conductivity is important to be able to understand the influence of coating defects, such as delaminations and pores, on heat insulation in thermal barrier coatings (TBC). Object Oriented Finite element analysis (OOF) has recently been shown as an effective tool for evaluating thermo-mechanical material behaviour as this method is capable of incorporating the inherent material microstructure as an input to the model. The objective of this work was to evaluate a procedure where this technique is combined with Tbctool, a plasma-sprayed TBC like morphology generator, thus enabling development of low thermal conductivity coatings by simulation. Input parameters for Tbctool were computed from SEM images of sprayed microstructures using the image analysis software, Aphelion. Microstructures for as-sprayed as well as heat treated samples were evaluated. The thermal conductivities of the artificially generated microstructures were determined using OOF. Verification of the modelling procedure was performed by comparing predicted values by OOF with corresponding measured values using the laser flash technique. The results, although tentative in nature, indicate that the proposed simulation approach can be a powerful tool in the development of new low conductivity coatings.
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| 10. |
- Gupta, Mohit, 1986-, et al.
(författare)
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Structure-property Relationships in Thermal Barrier Coatings by Finite Element Modelling
- 2012
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Ingår i: Surface Modification Technologies XXV : proceedings of the Twenty Fifth International Conference on Surface Modification Technologies : SMT25, Trollhättan, June 20-22, 2011. - 978-81-910571-4-0 ; s. 175-184
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Konferensbidrag (refereegranskat)abstract
- The thermal and mechanical properties of Thermal Barrier Coating systems (TBCs) are strongly influenced by coating defects, such as delaminations and pores, thus making it essential to have a fundamental understanding of microstructure-property relationships in TBCs, to produce a desired coating. Object-Oriented Finite element analysis (OOF) has been shown previously as an effective tool for evaluating thermal and mechanical material behaviour, as this method is capable of incorporating the inherent material microstructure as an input to the model. In this work, OOF was used to predict the thermal conductivity and effective Young’s modulus of TBC topcoats. A Design of Experiments (DoE) was conducted by varying selected spray parameters for spraying Yttria Partially Stabilized Zirconia (YPSZ) topcoat. Characterisation of the coatings included microstructure, porosity and crack content and thermal conductivity measurements. The relationships between microstructural features, thermal conductivity and Young’s modulus are discussed.
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