| 1. |
- El-Alti, Mohammad, 1981, et al.
(author)
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Computations and full-scale tests of active flow control applied on a Volvo truck-trailer
- 2016
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In: Lecture Notes in Applied and Computational Mechanics. - Cham : Springer International Publishing. - 1860-0816 .- 1613-7736. ; 79, s. 253-267
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Conference paper (peer-reviewed)abstract
- Large-eddy simulations and full-scale investigations were carried out that aimed to reduce the aerodynamic drag and thus the fuel consumption of truck-trailers. The computational model is a relevant generic truck-trailer combination, and the fullscale is a corresponding Volvo prototype vehicle. Passive and active flow control (AFC) approaches were adopted in this work and applied at the rear end of the trailer. Flaps were mounted at an angle that induces separation, and synthetic jet actuators were placed close to the corner of the rear end and the flaps. The drag reduction obtained is in the order of 30%. The flow was analyzed by comparing the phase-averaged and time-averaged flow field of the unforced and the forced cases. The full-scale prototype is a Volvo truck-trailer. The trailer is mounted by three flaps at the rear sides and top end. The actuators consist of loudspeakers in sealed cavities, connected to amplifiers that are supplied with a frequency generator controlled by LabVIEW. The full-scale test includes passive and active flow control investigations by varying the flap angle, with and without AFC, investigating different frequency and slot angle configurations. The fuel flux was measured during the full-scale test. The test shows a fuel reduction of about 4% in a comparison of two flap angles. The test of active flow control shows a reduction of 5.3%compared to the corresponding unforced case. Compared with the baseline case, the passive flow control fails to reduce the total fuel consumption.
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| 2. |
- Gerolymatou, Eleni, 1981, et al.
(author)
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In Situ Stress Assessment Based on Width and Depth of Brittle Borehole Breakouts
- 2020
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In: Lecture Notes in Applied and Computational Mechanics. - Cham : Springer International Publishing. - 1860-0816 .- 1613-7736. ; 91, s. 297-319
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Book chapter (other academic/artistic)abstract
- Borehole breakouts, as well as breakouts in tunnels and shafts, are a common occurrence, especially under high in situ stresses or stress states with high deviatoric component. Though they can pose a risk to stability, often they are of use, especially in deep boreholes, as they can help to determine to a certain extent the primary in situ stress. Observations have shown that while their depth evolves, their width remains constant. Currently the width only is used in conjunction with the Kirsch analytical solution to establish a linear relationship between the two in plane principal primary stress components. The stress state cannot be fully determined since one equation is available (failure criterion) for two unknowns. A recently proposed numerical tool based on conformal mapping is used in this work to simulate the formation of shear breakouts and investigate the feasibility of the determination of both principal primary in situ stress components, by making use of both the depth and the width of the breakout. Concluding, recommendations are provided for the use of the proposed methodology and limitations of its applicability are discussed.
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| 3. |
- Hino, Takanori, et al.
(author)
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Introduction, conclusions and recommendations
- 2021
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In: Lecture Notes in Applied and Computational Mechanics. - Cham : Springer International Publishing. - 1860-0816 .- 1613-7736. ; 94, s. 1-21
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Book chapter (other academic/artistic)abstract
- The Tokyo 2015 Workshop on CFD in Hydrodynamics was the seventh in a series started in 1980. The purpose of the Workshops is to regularly assess the state of the art in Numerical Hydrodynamics and to provide guidelines for further developments in the area. The 2015 Workshop offered 16 test cases for three ship hulls. A total of 36 participating groups of CFD specialists submitted their computed results during the fall of 2015. The results were compiled by the organizers and discussed at a meeting in Tokyo in December 2015. In this chapter the background and development of the Workshops since the start are presented. The three hulls used in the 2015 Workshop are introduced and the computations requested from the participants are specified. Based on a questionnaire sent to all participants the details of their CFD methods are listed, and finally the general conclusions from each chapter and recommendations for future Workshops are presented. The detailed results of the computations are discussed in subsequent Chapters.
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| 4. |
- Krajnovic, Sinisa, 1970, et al.
(author)
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Exploring the Flow Around a Simplified Bus with Large Eddy Simulation and Topological Tools
- 2004
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In: Lecture Notes in Applied and Computational Mechanics. - 1860-0816 .- 1613-7736. ; , s. 49-64
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Conference paper (peer-reviewed)abstract
- The results of the large eddy simulation of the flow around a simplified bus presented in Krajnovic and Davidson (Journal of Fluids Engineering,125, pages 500-509, 2002) are used to describe this flow in detail. Using time-averaged trace lines on the surface of the body, the patterns of the shear-stress lines are revealed and used to identify bifurcation lines and critical points (zero-shear-stress points) in the flow. This information is then used to establish a complete picture of the flow on the surface of the body that can be used for understanding soiling and accumulation of water on the surface or in determinations of aeroacoustic noise sources. Kinematical investigations of the flow in two symmetry planes were done to reveal the critical points in the flow. With this it was proven that the flow resulting from numerical simulation is kinematically possible.
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| 5. |
- Krajnovic, Sinisa, 1970
(author)
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Optimization of the aerodynamic properties of high-speed train with CFD and response surface models
- 2007
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In: Lecture Notes in Applied and Computational Mechanics. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 1860-0816 .- 1613-7736. ; 41, s. 197-211
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Conference paper (peer-reviewed)abstract
- The aerodynamic properties of high-speed trains have in past been optimized through trial and error design process. Such an approach relies on the experience and skills of the engineer to suggest changes in the design that will lead to an improvement of the aerodynamic performance of the train. Although this process leads to an improvement of the design there is no guarantee that the best design will be identified. A more rigorous numerical optimization methodology that allows the best design to be identified is required. The majority of numerical design optimization procedures in fluid machinery uses gradient-based search algorithms. These methods work iteratively through the design space until the optimal design is reached. Such an approach is impractical in optimization of vehicle aerodynamics due to computational effort required for such a large number of CFD simulations. The present work presents the use of a surrogate model in form of response surface approximation (RSA) for multi-objective optimization of train aerodynamics. The design problem of vehicle aerodynamics has multiple objectives, i.e. drag, lift force, cross-wind stability, aeroacoustics etc. An optimal solution of such a problem is called the Pareto optimal front and can help the designers to visualize the trade-offs between different objectives and select an compromise design. In this paper we use an example of optimization of aerodynamic properties of the front of a generic high-speed train to demonstrate an efficient multi-objective optimization procedure. Two object functions are chosen and the response surfaces are produced as a result of Reynolds-Averaged Navier-Stokes simulations (RANS) using simple two-equation turbulence model. The Pareto optimal front is obtained using an evolutionary algorithm (NSGA-II). The present work shows that our approach is very efficient in terms of optimization time and computational requirements. Instead of large number of CFD simulations (several hundreds ) required in traditional gradient-based search algorithms only small number of CFD simulations were required to find an optimal design of the front of the high-speed train.
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| 6. |
- Krajnovic, Sinisa, 1970
(author)
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What can LES do in vehicle aerodynamics?
- 2016
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In: Lecture Notes in Applied and Computational Mechanics. - Cham : Springer International Publishing. - 1860-0816 .- 1613-7736. ; 79, s. 311-326
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Conference paper (peer-reviewed)abstract
- The paper discusses an appropriate usage of large eddy simulation (LES) in external vehicle aerodynamics. Three different applications including wheelhouse flow, gusty flow and active flow control, are used to demonstrate how LES can be used to obtain new knowledge about vehicle flows. The three examples illustrate the information that can be extracted using LES in vehicle aerodynamics.
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| 7. |
- Larsson, Lars, 1945
(author)
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Evaluation of resistance, sinkage, trim and wave pattern predictions for JBC
- 2021
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In: Lecture Notes in Applied and Computational Mechanics. - Cham : Springer International Publishing. - 1860-0816 .- 1613-7736. ; 94, s. 139-157
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Book chapter (other academic/artistic)abstract
- JBC predictions are presented for four cases: towed and self-propulsion for the bare hull and a hull with an Energy Saving Device (ESD). A statistical evaluation is made based on the 88 resistance predictions submitted. The comparison error is defined as the difference between the measured data and the numerically predicted value. This error is analyzed in different ways. It is seen that the mean signed error is as small as the measurement accuracy, while the mean absolute error is about twice as large. This represents the typical error in the prediction. A similar accuracy was found in the 2010 Workshop. The number of grid cells has increased since 2010 and the required grid size for a given uncertainty of 4% has increased from 3 M cells to 10 M cells. Reasons for this are discussed. As in the previous workshop the two-equation turbulence models produce more accurate results than the more advanced models, although the more and more popular Explicit Algebraic Stress Model (EASM) is close. A surprising result of the analysis is that methods with wall-functions give significantly smaller resistance errors than those with a wall-resolved flow. Grid convergence is discussed and it is shown that the vast majority of results converge with grid refinement, but that the achieved order of accuracy is often far from the theoretical one. Sinkage is much better predicted than in 2010 and the trim results are also improved. Finally, the wave pattern prediction is discussed. The best methods in 2010 predicted the waves extremely well, in fact better than in the present workshop. A consistent shift in the predicted wave phase relative to the data could indicate a measurement error.
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| 8. |
- Nayeri Navid, Christian, 1978, et al.
(author)
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Experimental Investigations of the Drag Reduction on a Generic Tractor-Trailer Configuration Using Active Flow Control in Combination with Solid Flaps
- 2009
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In: Lecture Notes in Applied and Computational Mechanics. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 1860-0816 .- 1613-7736. ; 41, s. 179-191
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Conference paper (peer-reviewed)abstract
- An experimental investigation was carried out to assess the drag reducing potential of active flow control in conjunction with flat panel flaps attached to the trailer of a generic tractor-trailer model. The experiments were carried out in a wind tunnel with a 1/10th scale generic tractor-trailer model at Reynolds numbers up to 640,000 based on the model width. Active flow control was achieved by means of constant blowing, constant suction and oscillatory blowing and suction. A secondary objective was to make short base flaps with active flow control as effective as long flaps with no active flow control. Measurement techniques such as flow visualizations, loads by means of a 6-component balance, LDA and PIV were employed. The results show that constant blowing at a momentum coefficient of 11.13% is able to achieve higher drag reduction than long flaps with no active flow control. The analysis of the flow field in the wake showed that constant blowing deflects the shear layer between the free stream and the wake region downward and hence reduces the size of the wake. The flaps at the side of the truck did not appear to have any substantial drag reducing effect.
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| 9. |
- Söderblom, David, 1983, et al.
(author)
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Wheel housing aerodynamics on heavy trucks
- 2016
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In: Lecture Notes in Applied and Computational Mechanics. - Cham : Springer International Publishing. - 1860-0816 .- 1613-7736. ; 79, s. 211-223
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Conference paper (peer-reviewed)abstract
- © Springer International Publishing Switzerland 2016. Modern trucks have a reasonably optimised cab shape, and there exist several OEM and aftermarket devices for drag reduction for heavy trucks as well. To further reduce the aerodynamic drag major changes to the current layout of the vehicle are required, or the focus must be shifted from the cab and tractor trailer gap to other regions of the vehicle. The drag of the underbody, including wheel housings, wheels and engine compartment, represents a significant proportion of the aerodynamic drag and there has not been much investigation in this specific area on heavy trucks. To be able to reduce the fuel consumption and to fulfil the legislated emission standards for heavy trucks it is important to take all areas of the vehicle under consideration, and even though the individual improvements may be small, the total drag reduction will be substantial. In order to study the flowclose to the vehicle underbody it is important to utilise the correct boundary conditions, that is,moving ground and rotatingwheels. This work has focused on the flow in the front wheel housings. The flow field around the front wheels under the influence of ground simulation on a heavy truck of standard European configuration was investigated using numerical simulations. The in- and outflow to the wheel housing was located and the vortices originating from the front wheels were identified. This information was then used to identify which areas of the wheel housing having the greatest potential for aerodynamic improvements by changing the front wheel housing design. Furthermore, several wheel housing design parameters were defined, and their influence on the flow field and aerodynamic drag were investigated. Examples of these parameters are the shape of the wheel housing opening and implementation of wheel housing ventilation. It was found that there is potential for reducing the aerodynamic drag by applying these geometric changes to the wheel housing, and several of the configurations could be implemented on current production vehicles.
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| 10. |
- Östh, Jan, 1985, et al.
(author)
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A LES study of a simplified Tractor-Trailer model
- 2016
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In: Lecture Notes in Applied and Computational Mechanics. - Cham : Springer International Publishing. - 1860-0816 .- 1613-7736. - 9783319201214 ; 79, s. 327-342
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Conference paper (peer-reviewed)abstract
- Large-eddy simulation (LES) was used to study the flow around a simplified tractor-trailer model. The model consists of two boxes placed in tandem. The front box represents the cab of a tractor-trailer road vehicle and the rear box represents the trailer. The LES was made at the Reynolds number of 0.51×106 based on the height of the rear box and the inlet air velocity. Two variants of the model were studied, one where the leading edges on the front box are sharp and one where the edges are rounded. One small and one large gap width between the two boxes were studied for both variants. Two computational grids were used in the LES simulations and a comparison was made with available experimental force measurements. The results of the LES simulations were used to analyze the flow field around the cab and in the gap between the two boxes of the tractor-trailer model. Large vortical structures around the front box and in the gap were identified. The flow field analysis showed how these large vortical structures are responsible for the difference in the drag force for the model that arises when the leading edges on the front box are rounded and the gap width is varied.
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