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| 2. |
- Gullberg, Peter, 1983, et al.
(author)
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3D fan modelling strategies for heavy duty vehicle cooling installations - CFD with experimental validation
- 2008
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In: 32nd FISITA World Automotive Congress 2008; Munich; Germany; 14 September 2008 through 19 September 2008. ; , s. 275-284
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Conference paper (peer-reviewed)abstract
- The need for low fuel consumption and lower emissions is for every automotive OEM a reality. With a cooling fan in today’s trucks that typically consumes of the order of magnitude 50bHp fully engaged – reducing this loss is very important. In addition a lot of the new after treatment systems requires a higher airflow through the engine bay, and new legislations requires quieter fans, i.e. today there is a need for fans with higher efficiency. To reach these needs CFD offers great potential. However since computer power is still limited for resolving transient Navier-Stokes equations without any turbulence models and in a mesh-independent domain - one relies heavily on the performance of simplified assumptions and models. This is also what is addressed in this paper – an investigation of different fan modelling strategies and how these interfere with turbulence models and mesh-size. Main focus is on modelling the fan with MRF (Multiple Reference Frames, stationary) and its behaviour compared to resolving the fan rotation in a rigid body rotation (transient). The turbulence models investigated is a number of the standard two equation models. In the work comprised by this paper it was found that it is very difficult to get the fan MRF model to perform well in a complete vehicle installation, this due to a limited space for fitting a valid rotational domain for the fan – independent of choice of turbulence model and mesh size. Fully transient (URANS) sliding mesh approach performs well, even for small case sizes. It was found that a small transient case could outperform a well resolved stationary simulation, still consuming less CPU hours then the stationary.Referring to the context of this work, the authors do not claim to deliver the final answer to fan modelling techniques. For the sliding mesh runs, a 2% discrepancy of measured pressure for a fixed air-flow was achieved in working points close to the fan’s design point. This would typically convert to a 1% error in mass flow in a case where the flow is not fixed by the boundary conditions, .i.e in a typical full vehicle under hood environment. In the fan stalling and fan transition regions, though, discrepancy was larger. However these areas are, to the authors’ knowledge and experience, hard to measure with good repetition, so a numerical issue in these regions is to be expected as well. More effort needs still to be made on producing more elaborate experimental data, not just measured for the system, but also component data such as radiator coefficients, larger meshes and more turbulence models should be evaluated in transient mode in order to predict these regions better. In conclusion, though, this paper gives a clear hint on what type of fan modelling strategy can be worth considering for UTM simulations in the upcoming future.
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| 3. |
- Kounenis, Charlampos, et al.
(author)
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Investigations of the Rear-End Flow Structures on a Sedan Car
- 2016
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In: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627.
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Journal article (peer-reviewed)abstract
- The aerodynamic drag, fuel consumption and hence CO2 emissions, of a road vehicle depend strongly on its flow structures and the pressure drag generated. The rear end flow which is an area of complex three-dimensional flow structures, contributes to the wake development and the overall aerodynamic performance of the vehicle. This paper seeks to provide improved insight into this flow region to better inform future drag reduction strategies. Using experimental and numerical techniques, two vehicle shapes have been studied; a 30% scale model of a Volvo S60 representing a 2003MY vehicle and a full scale 2010MY S60. First the surface topology of the rear end (rear window and trunk deck) of both configurations is analysed, using paint to visualise the skin friction pattern. By means of critical points, the pattern is characterized and changes are identified studying the location and type of the occurring singularities. The flow field away from the surface is then analysed using PIV measurements and CFD for the scale model and CFD simulations for the full scale vehicle. The flow field is investigated regarding its singular points in cross-planes and the correlation between the patterns for the two geometries is analysed. Furthermore, it is discussed how the occurring structures can be described in more generalized terms to be able to compare different vehicle geometries regarding their flow field properties. The results show the extent to which detailed flow structures on similar but distinct vehicles are comparable; as well as providing insight into the complex 3D wake flow.
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| 4. |
- Minovski, Blago, 1986, et al.
(author)
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A numerical investigation of thermal engine encapsulation concept for a passenger vehicle and its effect on fuel consumption
- 2019
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In: Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering. - : SAGE Publications. - 2041-2991 .- 0954-4070. ; 233:3, s. 557-571
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Journal article (peer-reviewed)abstract
- Increasingly tough regulations for emission levels and a growing demand for an environmentally clean motor industry impose high requirements in modern automotive development. During recent decades, carmakers have been utilizing various strategies to minimize energy losses in the powertrain to meet legislative and market demands. A great part of research efforts has been focused on improving engine performance during cold starts characterized by increased friction losses. Thermal engine encapsulation is an effective design choice to reduce engine friction in applications with frequent cold starts. In the present work, a coupled 1-D–3-D system-level approach is used to investigate the effects of a novel engine-mounted encapsulation concept featuring air shutters on fuel consumption in a Volvo S80 passenger vehicle. Simulations are performed for sequences of the Worldwide harmonized light vehicles test cycle (WLTC) drive cycle, which include different time intervals of engine inactivity when the car is parked in air of an quiescent ambient temperature. The results show that engine encapsulation with high area coverage (97%) can retain engine oil temperature above 19°C for up to 16 h after engine shutdown at an ambient temperature of 5°C, leading to 2.5% fuel saving during engine warm-up when cold starts occur between 2 and 8 h after key-off. Encapsulations with a lower area coverage (90%) have proven to be less effective, with fuel saving of 1.25% as the temperatures of the oil and engine structures decrease more quickly after key-off compared to the fully enclosed encapsulation.
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| 5. |
- Sterken, Lennert, 1984, et al.
(author)
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Connection between rear-end extensions and yaw response of a passenger vehicle
- 2020
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In: International Journal of Aerodynamics. - 1743-5447. ; 7:1, s. 1-17
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Journal article (peer-reviewed)abstract
- This paper aims to investigate the sensitivity of the rear-end design to the yaw response of a passenger vehicle. To accomplish this, rear-end extensions are attached to the base perimeter of a sport utility vehicle (SUV). The intention of the extensions is to improve and to smooth out the pressure recovery such that a more stable wake is created. The extensions facilitate the implementation of configuration changes with respect to design, inclination angle and length. To control the separation conditions of the flow entering the near-wake, two different designs are studied. The yaw response is analysed through the global forces and flow field measurements presented as surface pressure distributions and wake plane measurements of local drag. The results show that the rear-end can be designed as to control the yaw response so the aerodynamic drag is minimised and passenger vehicle stability is maintained.
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| 7. |
- Wieser, D., et al.
(author)
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Surface Flow Visualization on a Full-Scale Passenger Car with Quantitative Tuft Image Processing
- 2016
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In: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627. ; 2016-April:April
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Journal article (peer-reviewed)abstract
- Flow visualization techniques are widely used in aerodynamics to investigate the surface trace pattern. In this experimental investigation, the surface flow pattern over the rear end of a full-scale passenger car is studied using tufts. The movement of the tufts is recorded with a DSLR still camera, which continuously takes pictures. A novel and efficient tuft image processing algorithm has been developed to extract the tuft orientations in each image. This allows the extraction of the mean tuft angle and other such statistics. From the extracted tuft angles, streamline plots are created to identify points of interest, such as saddle points as well as separation and reattachment lines. Furthermore, the information about the tuft orientation in each time step allows studying steady and unsteady flow phenomena. Hence, the tuft image processing algorithm provides more detailed information about the surface flow than the traditional tuft method. The main advantages over other flow visualization methods, such as oil paint, is that experimental facilities are not contaminated and statistical data can be extracted. The investigated surface pattern shows a symmetric flow on the entire rear end section of the passenger car. The flow field on the roof, backlight, and upper trunk deck is attached almost everywhere. However, two small regions indicate the presence of two counter-rotating vortices at the lower edge of the backlight (rear window). Those vortices are also detectable in the distribution of the tuft angle standard deviation. A bifurcation line is present at each side of the trunk due to the streamwise vortices originating at the C-pillars. The tuft streamlines created with this novel tuft method are compared to a standard oil paint flow visualization to validate the calculated tuft flow pattern. A critical comparison between the methods confirms that the flow tuft analysis algorithm functions flawlessly as a highly detailed flow analysis tool without the mess of oil paint.
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| 8. |
- Martini, Helena, 1984, et al.
(author)
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Aerodynamic Analysis of Cooling Airflow for Different Front-End Designs of a Heavy-Duty Cab-Over-Engine Truck
- 2018
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In: SAE International Journal of Commercial Vehicles. - : SAE International. - 1946-3928 .- 1946-391X. ; 11:1, s. 31-44
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Journal article (peer-reviewed)abstract
- Improving the aerodynamics of heavy trucks is an important consideration in the strive for more energy-efficient vehicles. Cooling drag is one part of the total aerodynamic resistance acting on a vehicle, which arises as a consequence of air flowing through the grille area, the heat exchangers, and the irregular under-hood area. Today cooling packages of heavy trucks are dimensioned for a critical cooling case, typically when the vehicle is driving fully laden, at low speed up a steep hill. However, for long-haul trucks, mostly operating at highway speeds on mostly level roads, it may not be necessary to have all the cooling airflow from an open-grille configuration. It can therefore be desirable for fuel consumption purposes, to shut off the entire cooling airflow, or a portion of it, under certain driving conditions dictated by the cooling demands. In Europe, most trucks operating on the roads are of cab-over-engine type, as a consequence of the length legislations present. However, there are new directions from the European Union, which would permit slightly longer vehicles to improve aerodynamics and also to allow for a safer, more environmentally friendly vehicle. The truck design, where a cab-over-engine cab has an elongated front, is often referred to as a Soft Nose, where, as the name implies, the nose should be “soft” to improve the safety for pedestrians and also for car occupants in the event of a collision. This paper deals with the analysis of cooling airflow for two different front-end designs of a heavy truck. The first design is a cab-over-engine cab; the second is a Soft Nose cab, which in this case is basically an elongation of the grille area of the cab-over-engine cab to obtain a smoother shape of the cab. The Soft Nose model used in this investigation was extended 200 mm from the cab-over-engine front. Computational Fluid Dynamics was used as the tool for examining the aerodynamic properties of the vehicle models. A steady RANS-based approach was conducted, based on the method evaluated in previous work performed by the authors. The cab-over-engine and Soft Nose models were evaluated in an open-road environment. The configurations were evaluated both with inactive and active heat exchangers, in order to examine the effect of heating the air on the drag co-efficient and also to determine the cooling capacity of the different models. A sub- study was performed where different opening percentages of the grille area was investigated to determine the minimum percentage opening that would be needed to achieve a radiator Top Tank Temperature value below a target limit of 100 °C. The results show that there was potential for drag reductions for the Soft Nose model used. The cooling airflow was different for the cab-over-engine and Soft Nose models; as a consequence of the longer distance between the grille and cooling package, less air entered the cooling module for the Soft Nose model. A large portion of the airflow entering the grille leaked around the cooling module for the Soft Nose model. Also, following on from the reduced airflow through the cooling package, the radiator Top Tank Temperature values were considerably increased with the Soft Nose model. It was also shown that for the specific driving condition simulated here, an opening of 17.5% of the grille area was required to ensure sufficient cooling capacity. An interesting continuation of the cooling airflow analysis of the Soft Nose model would be to add ducts, guiding the air from the grille to the cooling module, to investigate if leakage could be reduced and cooling capacity increased.
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| 9. |
- Christoffersen, Lasse Malmkjaer, 1979, et al.
(author)
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Wing-diffuser interaction on a sports car
- 2011
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In: SAE Technical Papers. - 0148-7191 .- 2688-3627.
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Journal article (peer-reviewed)abstract
- Amongst the aerodynamic devices often found on race cars, the diffuser is one of the most important items. The diffuser can work both to reduce drag and also to increase downforce. It has been shown in previously published studies, that the efficiency of the diffuser is a function of the diffuser angle, ground clearance and most importantly, the base pressure. The base pressure of a car is defined by the shape of the car and in particular the shape at the rear end, including the rear wheels. Furthermore, on most race cars, a wing is mounted at the rear end. Since the rear wheels and wing will influence the base pressure it is believed that, for a modern race car, there could be a strong interaction between these items and the diffuser. This work aims to systematically study the interaction between the rear wheels and wing; and the diffuser of a contemporary, sports car type, race vehicle. The work was carried out using computational fluid dynamics and the geometry, that the study was based on, was the Lotus Evora Type 124 CUP car. The car carried detailed chassis components and a complete cooling system. In the study, the diffuser angle was varied over several inclinations, ranging from 3 to 12 degrees. Furthermore, the height of the wing over the "rear deck" of the car was also varied. It was found from the study that the vertical position of the wing over the rear deck of the car had no significant influence on the flow through the diffuser, at the wing heights tested and vice versa, the diffuser showed only little influence on the flow past the rear wing. The diffuser however, had an influence on the base pressure and most importantly; on the downforce generation. At increasing diffuser angles the base pressure was reduced and consequently the downforce was increased. Copyright © 2011 SAE International.
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| 10. |
- Astaneh, Majid, 1990, et al.
(author)
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Lithium-ion Battery Pack Design for Electric Vehicles Using GT-AutoLion: Multi-Physics Simulation and Multi-Criteria Optimization Approach
- 2021
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In: Global Gamma Technologies Virtual Conference.
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Conference paper (other academic/artistic)abstract
- High specific energy battery systems with improved thermal performance are required for large-scale introduction of electric vehicles (EVs) into the market. This study presents a comprehensive multi-physics simulation and multi-criteria optimization framework for Lithium-ion (Li-ion) battery pack design for EV applications. The battery cells are modeled by electrochemical thermally coupled approach using GT-AutoLion. Multi-objective optimization using genetic algorithm is employed to explore energy and thermally efficient cell design alternatives. The performances of the optimally designed cells are then evaluated under pack environment to account for inhomogeneities in large traction battery packs under realistic working scenarios. It is observed that considering the thermal efficiency of battery cells is crucial for obtaining improved battery pack performance. The integrated framework developed in this work provides systematic pack-aware guidelines for manufacturers already at the initial cell design stage. Moreover, the proposed design optimization methodology is generic, handing over valuable knowledge for future cell and pack designs for various applications.
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