| 1. |
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| 2. |
- Lingfors, David, 1987-, et al.
(författare)
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Maximizing PV hosting capacity by smart allocation of PV : A case study on a Swedish distribution grid
- 2015
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Ingår i: Proceedings of ASES Solar 2015, Pennsylvania State University, Pennsylvania, USA, July 28-30, 2015.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Detailed simulations of large amounts of PV production in Swedish rural power grids show that as module and system prices keep declining and thus increasing the profitability and demand for solar power, current grid performance will limit the potential. Simulations have been made on a case distribution grid (10 kV) with actual hourly load data for 2014 and calculated hourly production with respect to building roof area, tilt and azimuth together with irradiation data. At high production, especially voltage rises along cables in the outer part of the grid is problematic, but also currents in cables close to transformer buses increases substantially at these conditions. Resulting hosting capacity for the case grid is 32%, as of annual production compared to annual demand. What is limiting the hosting capacity is the tolerated voltage rise, which is set to 5% of nominal grid voltage. Through smart allocation of PV systems to the strongest nodes in the grid the hosting capacity of the same grid can be increased to 74%.
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| 3. |
- Lingfors, David, 1987-, et al.
(författare)
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Photovoltaics in Swedish agriculture : Technical potential, grid integration and profitability
- 2015
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Ingår i: ISES Solar World Congress 2015, Conference Proceedings. - Freiburg, Germany : International Solar Energy Society. - 9783981465952 ; , s. 259-267
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Konferensbidrag (refereegranskat)abstract
- This paper investigates the realizable potential for photovoltaic (PV) systems in Swedish agriculture. Marginal lands and available building areas for PV systems are quantified, and factors limiting the potential are analyzed. It is shown that the potential for PV in Swedish agriculture is high, but what is fully realizable is limited by the capacity of the rural power grid. A case study in the rural municipality of Herrljunga was conducted and scaled to national level. The study shows that the risk of surges in the medium voltage grid (10 kV) in rural areas are small in case where all roof surfaces with an annual solar irradiance of over 950 kWh/m2 are used for solar power. The total electricity production from the Swedish agriculture, if all roof areas with this irradiance level were used, is estimated to 4 TWh annually. With solar power on all roof surfaces with an annual irradiance of at least 900 kWh per m2 problems with voltage rise and overloads in the electricity grid might occur. The electrical grid capacities thus substantially limit how much solar power can be installed. Our results also show that the profitability limits the potential to 0.2 TWh on a national level, but that it could increase if more optimistic economic conditions are assumed.
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| 4. |
- Marklund, Ture Jesper, 1970, et al.
(författare)
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Aerodynamics of passenger vehicles - bluff bodies
- 2012
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Ingår i: The Vehicle Component. - 1652-862X. ; 2012:1
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Vehicle manufacturers are today struggling to develop more energy efficient vehicles that will meet future emissions targets of CO2 (Carbon Dioxide). To do so it is essential to improve both efficiency of driveline and reduce resistance forces of all kind. The aerodynamic drag force is the single biggest resistance force for a passenger car to overcome at highway speeds and it is a significant part of the total resistance forces that the vehicle has to overcome in average use, city and highway driving. Since a reduction in fuel consumption directly will lead to a reduction of CO2 the best way is to reduce the energy required for propulsion of the system. Aerodynamic drag force can be divided into two parts, pressure and friction. Pressure forces on the exterior body of a passenger car dominate the total drag force. A rule of thumb says that 80-90% of the aerodynamics drag forces of a passenger car are pressure forces and the rest is friction. For a finite wing for instance we will have the opposite, about 95% friction and 5% pressure forces. When the pressure forces are the dominating part of the aerodynamic drag we use to call the body bluff, and if the friction forces are dominating we call it a streamlined body. This then, classifies a passenger car aerodynamically as a bluff body. The biggest pressure forces are associated to wake formations at the rear end of a bluff body.
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| 5. |
- Marklund, Ture Jesper, 1970, et al.
(författare)
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DRAG AND LIFT MEASUREMENTS OF FOUR BLUFF BODIES
- 2010
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Ingår i: General Motors Vehicle Development Research Lab, May 2010, Detroit, USA.
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Konferensbidrag (refereegranskat)abstract
- This report summarizes the detailed experimental study of drag and lift for four different bluff bodies. The experiments are compared with the numerical CFD simulations. Special attention is paid to the rear end shape and experiments as well as simulations are conducted using a stationary ground. The measurements are performed in the wind tunnel at Chalmers University of Technology. All force measurements are performed with an external balance mounted under the wind tunnel floor. The models are simplified vehicle like bluff bodies that are classified as square-back, fastback and boat-tailed rear ends. The main objective with the measurements was to get accurate results of lift forces to be used as reference data for CFD validations. The measurement results presented here will be followed up with similar experiments based on a moving ground boundary condition.
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| 6. |
- Marklund, Ture Jesper, 1970, et al.
(författare)
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Drag Reduction of a Simple Bluff Body by Changing The Rear End
- 2009
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Ingår i: 2009 ASME Fluids Engineering Division Summer Conference, FEDSM2009; Vail, CO; United States; 2 August 2009 through 6 August 2009. - 9780791843734 ; , s. 291-296
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Konferensbidrag (refereegranskat)abstract
- The flow field around bluff bodies constitutes a classic areawithin fluid dynamics and has been the topic for much researchthrough the years. However, in the use for road vehicles withthe effect of the ground, the behavior is changed very muchfrom more classical aviation usage. In this paper we areinvestigating the drag force reduction on a vehicle likesimplified model with rear open diffuser when stationaryground simulation is considered.The objective with this work was to study the rear end of abluff body and optimize it for drag with ground vehicle likeboundaries. Here the testing contains two common bodyvariants, square back, boat tailed/fastback in generic forms.Scale model testing combined with simulations is used toexplain behavior and flow field. The model testing isperformed in the L2 scale model wind tunnel at ChalmersUniversity of Technology in Gothenburg, Sweden. Simulationsare done with the commercial CFD code Fluent.A diffuser on a car is normally used to create down forcebut here it is tested to see if the energy in the flow can be usedto optimize reduction of drag. One part of the study is to showthe potential in optimizing the rear end underbody for drag, byvarying the diffuser angle.The results show a potential in drag reduction by using adiffuser and varying effect depending on other rear endgeometries.
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| 7. |
- Marklund, Ture Jesper, 1970, et al.
(författare)
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FLOW FIELD AROUND AND IN A SAAB 9-3 CONVERTIBLE
- 2009
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Ingår i: EUROMECH COLLOQUIUM 509,External aerodynamics of Railway Vehicles Trucks Buses and Cars, Berlin, Germany, March 24--25, 2009. ; , s. 144-157
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Konferensbidrag (refereegranskat)abstract
- The aerodynamic comfort in a four seated convertible with open roof is not as goodas many would like it to be. This job was initiated to look at what should be done to improvethis. The car used for this study was a Saab 9-3 convertible. Most of the work was done inCFD in the commercial code Fluent.The flow field in the cockpit was first of all analyzed and evaluated. The problem with convertiblesis the large recirculation bubble that occurs around the passenger compartment. Therear seat passengers are located in an area of this zone with very high wind speeds comparedto the front seat passengers. The flow field was analyzed by several pressure and velocityplots and a method to evaluate comfort grading was developed. The selected main variable tocompare cases was the mean velocity that the passengers head is exposed to. This was foundto be the most affecting parameter because it affects not only the dynamic pressure, but alsothe temperature discomfort. Geometry optimizations of windows, wind shield and wind blockershave been simulated and evaluated. Height and length of the side windows and a numberof different wind deflectors on the wind shield, plus wind blockers inside and behind cockpitwas tested. The results show that the biggest potential of improvement is the wind deflector onthe windshield and some of the wind blockers.
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| 8. |
- Marklund, Ture Jesper, 1970, et al.
(författare)
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Fordonsaerodynamik - trubbig kropp
- 2012
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Ingår i: Fordonskomponenten. - 1652-862X. ; 2012:1, s. 20-23
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Fordonstillverkare lägger idag ned mycket utvecklingsarbete på att skapa mer energieffektiva fordon som möter framtida CO2 (koldioxid) krav. För att klara detta krävs både förbättring av drivlinor och minimering av motståndskrafter. Det aerodynamiska motståndet är det särklass största motståndet, i motorvägsfart, för ett passagerarfordon och det står för en betydande del av motståndskrafterna som måste övervinnas vid en normal användning, stads och landsvägskörning. Eftersom en minskning av motståndet innebär en minskad energiåtgång för framdrivningen av fordonet, blir detta en direkt minskning av bränsleförbrukningen. Det aerodynamiska motståndet kan delas upp i två delar, friktion och tryckkrafter. Tryckkrafterna är de dominerande krafterna för ett passagerarfordon. Man brukar säga att 80-90% av det aerodynamiska motståndet är tryckkrafter och resten är friktion. För en vingprofil är 95% friktionskrafter och resten tryck. När friktionskrafterna är de dominerande kallar vi kroppen strömlinjeformad och när tryckkrafterna dominerar kallar vi den trubbig. Ett passagerarfordon klassas vanligen som en trubbig kropp. De största tryckkrafterna kommer från vaken, vid bakdelen på en trubbig kropp.
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| 9. |
- Marklund, Ture Jesper, 1970, et al.
(författare)
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Influence of a Diffuser to the Wake Flow of a Passenger Car
- 2012
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Ingår i: American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FEDSM. - 0888-8116. - 9780791844755 ; :PARTS A AND B, s. 53-62
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Konferensbidrag (refereegranskat)abstract
- To achieve more energy efficient transportation we have to reduce losses and resistance forces all over the vehicle. Aerodynamic drag is one of the primary resistance forces a passenger vehicle has to overcome and the force increases exponentially with increased speed. The under-body and rear-end geometry of a passenger car is a significant contributor to the overall aerodynamic drag and the shape of it is normally a compromise between styling, cost and other properties. To reduce the aerodynamic drag it is very important to have a good pressure recovery at the rear-end; to end up with a base pressure as high as possible. It is not necessarily the case that an optimized lower part of the rear-end for a square-back car has the same performance as a notch-back or fast-back car.This work investigates the rear-end flow and aerodynamic performance of a sedan and wagon car with varying rear-end under-body design parameters. The study is a numerical analysis using a standard CFD approach commonly used in the automotive industry. A parameter study of under-body covers with varying rear angles, making the rear floor act like a diffuser. The function of the rear floor working as a diffuser is similar regardless of the upper geometry, but its function as a drag reduction device can be very different. Results from this study show a potential to reduce aerodynamic drag of the sedan car approximately 10%, with the best diffuser angle and cover plates over the floor. The best drag reduction for the wagon car was 2-3 % and the optimum was at a smaller diffuser angle. Flow analysis of the wake shows how important it is the wake is balanced.
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| 10. |
- Marklund, Ture Jesper, 1970
(författare)
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Minimize Vortex Drag of a Passenger Car
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aerodynamic drag force is the single biggest resistance force for a passenger car toovercome at highway speeds. Since all driving resistance forces can be directly linked tofuel consumption this has become a significant priority in recent years. Increasing fuelprices and environmental issues are strong drivers for reducing these resistance forces.Vehicle manufacturers are today struggling to develop more energy efficient vehicles thatwill meet future emissions targets of CO2 (carbon dioxide). To do so it is essential toimprove both efficiency of driveline and reduce resistance such as inertia and drag forces.Pressure forces from the exterior body of a passenger car are the dominating forces of thetotal drag force. This will classify a passenger car aerodynamically as a bluff body. Thebiggest pressure forces are associated to wake formations at the rear end of a bluff body.This is the reason for this study of simplified vehicle like bluff bodies focusing on therear end.Detailed flow field investigations of wake flows behind the models and boundary layerflows close to the surfaces have been performed. The measurements were carried outwith stationary ground simulation in the L2 scale model wind tunnel at ChalmersUniversity of Technology in Gothenburg. The wake flow was measured with a smallscale 12-hole omniprobe that is capable of capturing almost reversed flows. The purposewas to measure the wake flow of small vehicle-like bodies in ground proximity todetermine preferred rear end bodywork geometries. The testing was carried out on fourdifferent rear end type of models labeled boat-tailed, fastback and square-back rear end.It is important to have a small and balanced wake to reduce drag. It is preferable to have ahigh pressure recovery to the rear part of the body and minimum vortices. The drag forceis due to the pressure difference between the front and rear of the body.Computational Fluid Dynamics (CFD) simulations have been performed on the samebodies with the same boundary conditions as the wind tunnel tests. The numericalsettings were selected to compare standard simulation methods generally used forexternal vehicle aerodynamics.
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| 11. |
- Marklund, Ture Jesper, 1970, et al.
(författare)
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Performance of an Automotive Under-Body Diffuser Applied to a Sedan and a Wagon Vehicle
- 2013
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Ingår i: SAE International Journal of Passenger Cars - Mechanical Systems. - : SAE International. - 1946-3995 .- 1946-4002. ; 6:1, s. 293-307
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Tidskriftsartikel (refereegranskat)abstract
- Reducing resistance forces all over the vehicle is the most sustainable way to reduce fuel consumption. Aerodynamicdrag is the dominating resistance force at highway speeds, and the power required to overcome this force increases by the power three of speed. The exterior body and especially the under-body and rear-end geometry of a passenger car aresignificant contributors to the overall aerodynamic drag. To reduce the aerodynamic drag it is of great importance to have a good pressure recovery at the rear. Since pressure drag is the dominating aerodynamic drag force for a passenger vehicle,the drag force will be a measure of the difference between the pressure in front and at the rear. There is high stagnationpressure at the front which requires a base pressure as high as possible. The pressure will recover from the sides by a taperangle, from the top by the rear wind screen, and from the bottom, by a diffuser. It is not necessarily the case that anoptimized lower part of the rear end for a wagon-type car has the same performance as for a sedan or hatch-back car. Thisstudy focused on the function of an under-body diffuser applied to a sedan and wagon car. The diffuser geometry waschosen from a feasibility stand-point of a production vehicle such as a passenger car. The fluid dynamic function andtheory of the automotive under-body diffuser working as a drag reduction device is discussed. The flow physics of theunder-body and the wake was analyzed to understand the diffuser behaviour in its application to lift and drag forces on avehicle in ground proximity. This work is mainly a numerical analysis that uses the traditional CFD approach from theautomotive industry. Results from this study show a potential to reduce aerodynamic drag of the sedan car approximately10%, and the wagon car by 2-3 %. The possible gain was much bigger for the sedan vehicle and the optimum occurs at ahigher diffuser angle. This was most likely due to the fact that the sedan car in its original shape produced more lift force than the wagon, a wagon usually produces very little lift or even down-force. Lift forces were also reduced with the use of under-body covers with diffuser. The down-force increased, or lift force decreased, linearly with increased diffuser angle, and the trend was the same for both sedan and wagon rear ends. Flow analysis of the wake showed the importance of how the wake is balanced.
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| 12. |
- Marklund, Ture Jesper, 1970
(författare)
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Under-body and Diffuser Flows of Passenger Vehicles
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Energy efficient vehicles will be required to meet future emission and fuel consumption requirements. Customers require reduced fuel consumption due to increasing fuel prices and the environmental issues, are drivers to reduce CO2. It is essential to improve the drivelines, but improving resistance forces of the vehicle is also an efficient and sustainable way to improve energy efficiency. Aerodynamic drag is the dominating resistance force for passenger and commercial vehicles at highway speeds.A passenger car is a bluff body aerodynamically, with pressure forces at the rear that dominate the aerodynamic drag. This is due to a relatively square shape, with a length / height ratio of approximately three, and a truncated rear-end that generates a wake. About 60 % of the aerodynamic drag forces of a passenger vehicle are related to the exterior body, upper and under-body; the rest being related to wheel, wheel house and cooling drag.This work focuses on the aerodynamics of the rear-end and under-body of bluff bodies in general, but also applied to passenger cars. Firstly, simplified bluff bodies, that represent different vehicle types, were used to study and map the general behaviour of the bodies. The findings were then tested and applied to full–size vehicles, with the focus on under-body flows and the effect of under-body diffusers. Both experimental and numerical tools were used, and scale model as well as full-size test bodies have been investigated.A unique feature with road vehicle aerodynamics are the boundary conditions: ground proximity and moving ground; relative the body. Also, rotating wheels and a cooling flow that re-distributes the flow around the body have to be considered. The Chalmers L2 wind tunnel is equipped with a moving ground system, and the simulations were set up with moving ground, rotating wheels and a cooling flow. The rotating wheels were simulated with the MRF approach and the cooling flow was tuned by measuring the cooling flow of a full-sized car and using this data in the simulations.A significant difference in the flow in an under-body diffuser, depending on upper body, was noticed in the bluff body experiments. In particular, drag was reduced more for a sedan or fastback upper body, compare to a wagon or square-back. This difference was confirmed in simulations of full–size vehicles, under road-vehicle boundary conditions, with under-body diffusers applied. It was found that it is very important to have flow symmetry around the vehicle and especially at the wake, to optimize pressure recovery at the rear end and reduce drag.
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| 13. |
- Marklund, Ture Jesper, 1970, et al.
(författare)
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WAKE MEASUREMENT OF A SIMPLE BLUFF BODY WITH VARYING REAR END DESIGN AND CLOSE PROXIMITY TO GROUND
- 2010
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Ingår i: ASME, FEDSM2010, August 1-5, 2010, Montreal, CANADA.
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Konferensbidrag (refereegranskat)abstract
- The flow field around simplified bluff bodies constitutes a classic area within vehicle aerodynamics. In this study we are looking at the wake flow of a vehicle-like simplified model with and without a rear open diffuser in close proximity to ground. The measurements were done with stationary ground simulation in the L2 scale model wind tunnel at Chalmers University of Technology in Gothenburg, Sweden. The wake flow was measured with a 12-hole omniprobe that has a spherical probe head of 6.35 mm. The purpose was to test how well this probe suits wake measurements of small vehicle-like bodies in ground proximity. The testing was done to a boat tailed/fast back model of small scale. Reynolds number for the experiments was about 1,01 million based on the model length and will be considered low compared to a full scale passenger vehicle. Since the main objective was to test the measurement method, the result is still valid. Measurements are compared to simulations done in the commercial CFD code Fluent. The task was to study the rear end of a simplified bluff body by measuring the close wake of a model with and without a diffuser. A diffuser reduces the drag of this model significantly, and the flow measurements show the difference in wake size and vortex formations.
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