The Experts below are selected from a list of 195 Experts worldwide ranked by ideXlab platform
Christian Oliver Paschereit - One of the best experts on this subject based on the ideXlab platform.
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Wake Structures and Surface Patterns of the DrivAer Notchback Car Model under Side Wind Conditions
Energies, 2020Co-Authors: Dirk Wieser, Christian Navid Nayeri, Christian Oliver PaschereitAbstract:The flow field topology of passenger cars considerably changes under side wind conditions. This changes the surface pressure, aerodynamic force, and drag and performance of a vehicle. In this study, the flow field of a generic passenger vehicle is investigated based on three different side wind angles. The study aimed to identify vortical structures causing changes in the rear pressure distribution. The Notchback section of the DrivAer model is evaluated on a scale of 1:4. The wind tunnel tests are conducted in a closed section with a splitter plate at a Reynolds number of 3 million. The side wind angles are 0 ∘ , 5 ∘ , and 10 ∘ . The three-dimensional and time-averaged flow field downstream direction of the model is captured by a stereoscopic particle image velocimetry system performed at several measurement planes. These flow field data are complemented by surface flow visualizations performed on the entire model. The combined approaches provide a comprehensive insight into the flow field at the frontal and side wind inflows. The flow without side wind is almost symmetrical. Longitudinal vortices are evident along the downstream direction of the A-pillar, the C-pillars, the middle part of the rear window, and the base surface. In addition, there is a ring vortex downstream of the vehicle base. The side wind completely changes the flow field. The asymmetric topology is dominated by the windward C-pillar vortex, the leeward A-pillar vortex, and other base vortices. Based on the location of the vortices and the pressure distributions measured in earlier studies, it can be concluded that the vortices identified in the wake are responsible for the local minima of pressure, increasing the vehicle drag.
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Experiments with Vortex Generators applied to a Notchback Car Model
53rd AIAA Aerospace Sciences Meeting, 2015Co-Authors: Dirk Wieser, Christian Navid Nayeri, Christian Oliver PaschereitAbstract:An experimental study on a realistic 1:4 scale car model with a Notchback is conducted. Vortex generators are attached to the roof at variable positions in order to analyze their effect on the aerodynamic drag. The experiments are conducted at a Reynolds number of three million. The effects of the vortex generators are evaluated by comparing the aerodynamic forces and the surface pressures. Furthermore, the flow field is investigated using stereo particle image velocimetry. In general the vortex generators increase the pressure level on the back light and trunk of the car. This results from the suppression of a recirculation bubble. The pressure increase depends on the position of the the vortex generators as well as their geometrical characteristics. The maximal achieved pressure coefficient with vortex generators is approximately CP = +0.15, which corresponds to an increment of ∆CP,max = +0.2. The increased pressure leads to a growth in the downward force of around 33%. However, the base pressure, which is mainly responsible for the aerodynamic drag, is only marginally affected about ∆CP ≈ −1%. Consequently, the force measurements show an increase in drag of about 1-4%. The PIV measurements show further, that the VGs suppress the recirculation bubble at the rear window and the upper trunk. Furthermore, the center of the spanwise counter-rotating vortices in the near wake behind the car are shifted further downstream and the off-surface stagnation point is stable but shifted upwards.
Dirk Wieser - One of the best experts on this subject based on the ideXlab platform.
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Wake Structures and Surface Patterns of the DrivAer Notchback Car Model under Side Wind Conditions
Energies, 2020Co-Authors: Dirk Wieser, Christian Navid Nayeri, Christian Oliver PaschereitAbstract:The flow field topology of passenger cars considerably changes under side wind conditions. This changes the surface pressure, aerodynamic force, and drag and performance of a vehicle. In this study, the flow field of a generic passenger vehicle is investigated based on three different side wind angles. The study aimed to identify vortical structures causing changes in the rear pressure distribution. The Notchback section of the DrivAer model is evaluated on a scale of 1:4. The wind tunnel tests are conducted in a closed section with a splitter plate at a Reynolds number of 3 million. The side wind angles are 0 ∘ , 5 ∘ , and 10 ∘ . The three-dimensional and time-averaged flow field downstream direction of the model is captured by a stereoscopic particle image velocimetry system performed at several measurement planes. These flow field data are complemented by surface flow visualizations performed on the entire model. The combined approaches provide a comprehensive insight into the flow field at the frontal and side wind inflows. The flow without side wind is almost symmetrical. Longitudinal vortices are evident along the downstream direction of the A-pillar, the C-pillars, the middle part of the rear window, and the base surface. In addition, there is a ring vortex downstream of the vehicle base. The side wind completely changes the flow field. The asymmetric topology is dominated by the windward C-pillar vortex, the leeward A-pillar vortex, and other base vortices. Based on the location of the vortices and the pressure distributions measured in earlier studies, it can be concluded that the vortices identified in the wake are responsible for the local minima of pressure, increasing the vehicle drag.
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Experiments with Vortex Generators applied to a Notchback Car Model
53rd AIAA Aerospace Sciences Meeting, 2015Co-Authors: Dirk Wieser, Christian Navid Nayeri, Christian Oliver PaschereitAbstract:An experimental study on a realistic 1:4 scale car model with a Notchback is conducted. Vortex generators are attached to the roof at variable positions in order to analyze their effect on the aerodynamic drag. The experiments are conducted at a Reynolds number of three million. The effects of the vortex generators are evaluated by comparing the aerodynamic forces and the surface pressures. Furthermore, the flow field is investigated using stereo particle image velocimetry. In general the vortex generators increase the pressure level on the back light and trunk of the car. This results from the suppression of a recirculation bubble. The pressure increase depends on the position of the the vortex generators as well as their geometrical characteristics. The maximal achieved pressure coefficient with vortex generators is approximately CP = +0.15, which corresponds to an increment of ∆CP,max = +0.2. The increased pressure leads to a growth in the downward force of around 33%. However, the base pressure, which is mainly responsible for the aerodynamic drag, is only marginally affected about ∆CP ≈ −1%. Consequently, the force measurements show an increase in drag of about 1-4%. The PIV measurements show further, that the VGs suppress the recirculation bubble at the rear window and the upper trunk. Furthermore, the center of the spanwise counter-rotating vortices in the near wake behind the car are shifted further downstream and the off-surface stagnation point is stable but shifted upwards.
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Experiments on the influence of yaw on the aerodynamic behaviour of realistic car geometries
The International Vehicle Aerodynamics Conference, 2014Co-Authors: C.n. Nayer, Dirk Wieser, Hanns-joachim Schmidt, Christoph Strangfeld, O. PaschereitAbstract:ABSTRACT Static wind tunnel experiments with a 1:4 scale realistic passenger car model called DrivAer were carried out under variation of yaw angle β between 0° and ± 10°. The investigation considered fastback and Notchback geometries. The flow field behaviour was examined through force measurements, time resolved surface pressure measurements, and surface flow visualizations. At zero yaw angle the fastback’s drag coefficient is CD = 0.254 and for the Notchback CD = 0.258. The Notchback exhibits a large and asymmetrical separated flow field whereas the fastback shows a symmetrical flow field. The separated regions shift leeward for increasing yaw angles. In general, higher pressure fluctuations are observed at the lower windward and the upper leeward base for yawed conditions.
Jochen Wiedemann - One of the best experts on this subject based on the ideXlab platform.
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Aerodynamic study on the vehicle rear shape parameters with respect to ground simulation
Proceedings, 2019Co-Authors: Chenyi Zhang, Daniel Stoll, Timo Kuthada, Jochen WiedemannAbstract:The automotive market today is being divided into more detailed segments than before to meet the diverse demand of customers. Correspondingly, the vehicle basic shape especially the rear end shape becomes more numerous. In addition to the three typical rear end shapes – Notchback, fastback and squareback – some new concepts are derived from a mixture of those classic rear end shapes. For example, as demonstrated in Figure 1, an SUV-coupe like vehicle has a much higher trunk and a more raised trunk lid slope angle than a normal limousine or coupe. On some limousine models like the Porsche Panamera Sport, the rear end shape is designed as a fastback. Its rear screen angle is smaller than a station wagon. Moreover, the rear underbody diffuser is often equipped to improve the vehicle road behavior.
Daniel Wood - One of the best experts on this subject based on the ideXlab platform.
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The effect of rear geometry changes on the Notchback flow field
2015Co-Authors: Daniel WoodAbstract:An experimental investigation into the form of the Notchback wake topology, its temporal behaviour, and how this changes with the underlying geometry has been undertaken to further understanding of this flow regime pertaining to a popular automotive body type. Whilst this work has been performed at model scale on a simplified body a sufficiently complex design of backlight header and trailing pillar have been utilised. Thereby allowing the systematic study of the wake structure of a family of production representative geometries to be undertaken enabling the flow topology across bodies with parameters representative of vehicles produced from the 1960s to the present day to be investigated. Body force measurements showed both drag and rear lift to increase with backlight angle in a manner which was largely expected due to these designs being representative of older production Notchback vehicles. Manufacturers knowledge and understanding of how drag changes with this parameter, combined with on going shape optimisation studies, have led to the shallower backlight angles common to modern designs. Detailed flow field measurements were subsequently used to determine the form and temporal behaviour of the flow topologies responsible for this force behaviour. Across the range of geometries tested, the in-notch structures were shown to undergo significant variation, both their time-averaged form and time-variant behaviour changing. Common to all configurations were the presence of a pair of strong trailing vortex structures which flanked the edges of the backlight and bootdeck. However, flow in the centre of the backlight underwent the greatest variation. This region was shown to develop from a largely attached form at shallower backlight angles before developing into an increasingly strong hairpin like structure. As backlight angle increased further the topology ultimately took a highly asymmetric form. With these changes of the flow topology also came changes of the temporal behaviour which revealed vortex shedding, flow structure oscillation and the switching of bi-stable structures as backlight angle increased. It is hoped that in thoroughly understanding the range of Notchback flow topologies typically generated by production vehicles that this work will form the vital foundation upon which future investigations looking to reduced drag can be based.
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Experimental data for the validation of numerical methods: SAE reference Notchback model
SAE International Journal of Passenger Cars - Mechanical Systems, 2014Co-Authors: Daniel Wood, Martin A. Passmore, A. E. PerryAbstract:The use of simulation tools by vehicle manufacturers to design, optimize and validate their vehicles is essential if they are to respond to the demands of their customers, to meet legislative requirements and deliver new vehicles ever more quickly. The use of such tools in the aerodynamics community is already widespread, but they remain some way from replacing physical testing completely. Further advances in simulation capabilities depend on the availability of high quality validation data so that simulation code developers can ensure that they are capturing the physics of the problems in all the important areas of the flow-field. This paper reports on an experimental program to generate such high quality validation data for a SAE 20 degree backlight angle Notchback reference model. This geometry is selected as a particularly powerful test case for the development and validation of numerical tools because the flow exhibits a realistic impingement and A pillar regime, significant three dimensional structures and the backlight/boot-deck exhibits a local separation and reattachment. The paper includes force and moment data, surface pressures for the centerline, slant, boot-deck and base and detailed PIV data for the impingement region, model centerline, A pillar and multiple planes on the slant and boot-deck. Time averaged, statistical and instantaneous data are presented. Results are discussed with regard to the overall flow features, the correlation between the different data sets and the accuracy and limitations of each of the experimental techniques in this particular application. Example data is included throughout the paper and full data sets are freely available in the Loughborough University Institutional Repository as a resource for future code development. © 2014 SAE International.
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SAE reference model: 20 degree Notchback validation dataset (reference SAE paper 2014-01-0590)
2013Co-Authors: Martin A. Passmore, Anna K. Perry, Daniel WoodAbstract:The data is freely available for further analysis and use in computational validation subject to the terms of the licence. The data is available under a Creative Commons Attribution Licence CC-BY-NC 3.0 The authors of this dataset would like to encourage all users of the data to publish their results.
Christian Navid Nayeri - One of the best experts on this subject based on the ideXlab platform.
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Wake Structures and Surface Patterns of the DrivAer Notchback Car Model under Side Wind Conditions
Energies, 2020Co-Authors: Dirk Wieser, Christian Navid Nayeri, Christian Oliver PaschereitAbstract:The flow field topology of passenger cars considerably changes under side wind conditions. This changes the surface pressure, aerodynamic force, and drag and performance of a vehicle. In this study, the flow field of a generic passenger vehicle is investigated based on three different side wind angles. The study aimed to identify vortical structures causing changes in the rear pressure distribution. The Notchback section of the DrivAer model is evaluated on a scale of 1:4. The wind tunnel tests are conducted in a closed section with a splitter plate at a Reynolds number of 3 million. The side wind angles are 0 ∘ , 5 ∘ , and 10 ∘ . The three-dimensional and time-averaged flow field downstream direction of the model is captured by a stereoscopic particle image velocimetry system performed at several measurement planes. These flow field data are complemented by surface flow visualizations performed on the entire model. The combined approaches provide a comprehensive insight into the flow field at the frontal and side wind inflows. The flow without side wind is almost symmetrical. Longitudinal vortices are evident along the downstream direction of the A-pillar, the C-pillars, the middle part of the rear window, and the base surface. In addition, there is a ring vortex downstream of the vehicle base. The side wind completely changes the flow field. The asymmetric topology is dominated by the windward C-pillar vortex, the leeward A-pillar vortex, and other base vortices. Based on the location of the vortices and the pressure distributions measured in earlier studies, it can be concluded that the vortices identified in the wake are responsible for the local minima of pressure, increasing the vehicle drag.
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Experiments with Vortex Generators applied to a Notchback Car Model
53rd AIAA Aerospace Sciences Meeting, 2015Co-Authors: Dirk Wieser, Christian Navid Nayeri, Christian Oliver PaschereitAbstract:An experimental study on a realistic 1:4 scale car model with a Notchback is conducted. Vortex generators are attached to the roof at variable positions in order to analyze their effect on the aerodynamic drag. The experiments are conducted at a Reynolds number of three million. The effects of the vortex generators are evaluated by comparing the aerodynamic forces and the surface pressures. Furthermore, the flow field is investigated using stereo particle image velocimetry. In general the vortex generators increase the pressure level on the back light and trunk of the car. This results from the suppression of a recirculation bubble. The pressure increase depends on the position of the the vortex generators as well as their geometrical characteristics. The maximal achieved pressure coefficient with vortex generators is approximately CP = +0.15, which corresponds to an increment of ∆CP,max = +0.2. The increased pressure leads to a growth in the downward force of around 33%. However, the base pressure, which is mainly responsible for the aerodynamic drag, is only marginally affected about ∆CP ≈ −1%. Consequently, the force measurements show an increase in drag of about 1-4%. The PIV measurements show further, that the VGs suppress the recirculation bubble at the rear window and the upper trunk. Furthermore, the center of the spanwise counter-rotating vortices in the near wake behind the car are shifted further downstream and the off-surface stagnation point is stable but shifted upwards.
