scholarly journals Assessment of conventional and air-jet wheel deflectors for drag reduction of the DrivAer model

2021 ◽  
Vol 3 (1) ◽  
Author(s):  
Kaloki L. Nabutola ◽  
Sandra K. S. Boetcher
Keyword(s):  
Aerodynamic Drag ◽  
Resistance Force ◽  
Passenger Vehicle ◽  
Air Jet ◽  
Baseline Case ◽  
Vehicle Aerodynamics ◽  
Computational Fluid Dynamics Simulations ◽  
Vehicle Motion ◽  
Dynamics Simulations ◽  
Flow Deflection

AbstractAerodynamic drag is a large resistance force to vehicle motion, particularly at highway speeds. Conventional wheel deflectors were designed to reduce the wheel drag and, consequently, the overall vehicle drag; however, they may actually be detrimental to vehicle aerodynamics in modern designs. In the present study, computational fluid dynamics simulations were conducted on the notchback DrivAer model—a simplified, yet realistic, open-source vehicle model that incorporates features of a modern passenger vehicle. Conventional and air-jet wheel deflectors upstream of the front wheels were introduced to assess the effect of underbody-flow deflection on the vehicle drag. Conventional wheel-deflector designs with varying heights were observed and compared to 45∘ and 90∘ air-jet wheel deflectors. The conventional wheel deflectors reduced wheel drag but resulted in an overall drag increase of up to 10%. For the cases studied, the 90∘ air jet did not reduce the overall drag compared to the baseline case; the 45∘ air jet presented drag benefits of up to 1.5% at 35 m/s and above. Compared to conventional wheel deflectors, air-jet wheel deflectors have the potential to reduce vehicle drag to a greater extent and present the benefit of being turned off at lower speeds when flow deflection is undesirable, thus improving efficiency and reducing emissions.

scholarly journals Aerodynamic optimisation of the rear wheel fairing of the land speed record vehicle BLOODHOUND SSC

2016 ◽  
Vol 120 (1228) ◽  
pp. 930-955
Author(s):  
J. Townsend ◽  
B. Evans ◽  
T. Tudor
Keyword(s):  
Design Space ◽  
Aerodynamic Drag ◽  
Ground Plane ◽  
Rear Wheel ◽  
Navier Stokes ◽  
High Dimensional ◽  
Aerodynamic Properties ◽  
Function Design ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations

ABSTRACTThis paper describes the design optimisation study used to aerodynamically optimise the fairings that cover the rear wheels of the Land Speed Record vehicle, BLOODHOUND SuperSonic Car (SSC). Initially, using a Design of Experiments approach, a series of Computational Fluid Dynamics simulations were performed on a set of parametric geometries, with the goal of identifying a fairing geometry that was aerodynamically optimised for the target speed of 1,000 mph. Several aerodynamic properties were considered when deciding what design objectives the fairings would be optimised to achieve; chief amongst these was the minimisation of aerodynamic drag. A parallel, finite-volume Navier–Stokes solver was used on unstructured meshes in order to simulate the complex aerodynamic behaviour of the flow around the vehicle’s rear wheel structure, which involved a rotating wheel, and shockwaves generated close to a supersonic rolling ground plane. It was found that the simple response surface fitting approach did not sufficiently capture the complexities of the optimisation objective function across the high-dimensional design space. As a result, a Nelder–Mead optimisation approach was implemented, coupled with Radial Basis Function design space interpolation to find the final optimised fairing design. This paper presents the results of the optimisation study as well as indicating the likely impact this optimisation will have on the ultimate top speed of this unique vehicle.

scholarly journals Impact of wheel rotation on the aerodynamic drag of a time trial cyclist

2021 ◽  
Vol 24 (1) ◽  
Author(s):  
Fabio Malizia ◽  
T. van Druenen ◽  
B. Blocken
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Wind Tunnel ◽  
Aerodynamic Drag ◽  
Front Wheel ◽  
Wind Tunnel Tests ◽  
Wheel Rotation ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations ◽  
Drag Area

AbstractAerodynamic drag is the main resistive force in cycling at high speeds and on flat terrain. In wind tunnel tests or computational fluid dynamics simulations, the aerodynamic drag of cycling wheels is often investigated isolated from the rest of the bicycle, and sometimes in static rather than rotating conditions. It is not yet clear how these testing and simulating conditions influence the wheel aerodynamic performance and how the inclusion of wheel rotation influences the overall measured or computed cyclist drag. This study presents computational fluid dynamics simulations, validated with wind tunnel tests, that indicate that an isolated static spoked front wheel has a 2.2% larger drag area than the same wheel when rotating, and that a non-isolated static spoked front wheel has a 7.1% larger drag area than its rotating counterpart. However, rotating wheels are also subjected to the rotational moment, which increases the total power required to rotate and translate the wheel compared to static conditions where only translation is considered. The interaction with the bicycle frame and forks lowers the drag area of the front wheel by 8.8% for static and by 12.9% for the rotating condition, compared to the drag area of the isolated wheels. A different flow behavior is also found for static versus rotating wheels: large low-pressure regions develop from the hub for rotating wheels, together with a lower streamwise velocity region inside the circumference of the wheel compared to static wheels. The results are intended to help in the selection of testing/simulating methodologies for cycling spoked wheels.

scholarly journals Experimental and numerical investigations of cooling drag

2017 ◽  
Vol 231 (9) ◽  
pp. 1203-1210
Author(s):  
Teddy Hobeika ◽  
Simone Sebben ◽  
Lennart Löfdahl
Keyword(s):  
Velocity Distribution ◽  
Aerodynamic Drag ◽  
Cooling System ◽  
Good Prediction ◽  
Test Results ◽  
Cooling Flow ◽  
Computational Fluid Dynamics Simulations ◽  
Flow Through ◽  
Mass Flows ◽  
Dynamics Simulations

As the target figures for CO2 emissions are reduced every year, vehicle manufacturers seek to exploit all possible gains in the different vehicle attributes. Aerodynamic drag is an important factor that affects the vehicle’s fuel consumption, and its importance rises with the shift from the New European Driving Cycle to the Worldwide harmonized Light vehicles Test Cycle which has a higher average speed. In order to reduce vehicle drag, car manufacturers employ the use of grill/spoiler shutters which reduces the amount of air going through the vehicle’s cooling system, also known as cooling flow, thus reducing both its cooling capability and the resultant cooling drag. This paper investigates the influence of different grill blockages on the cooling flow through the radiator of a Volvo S60. By modifying the engine bay and radiator, load cells are used to measure the force acting on the radiator core while the velocity distribution across the radiator core is measured using pressure probes. These values are analyzed and compared to different vehicle configurations and grill inlet designs. A number of test configurations are reproduced in Computational Fluid Dynamics simulations and compared to the test results. For some grill configurations, the simulations provide a good prediction of mass flow and velocity distribution; however a clear discrepancy is present as the grill blockages increase. On the other hand, the force acting on the radiator core was well predicted for all configurations. This paper discusses the different parameters affecting cooling flow predictions such as wind tunnel blockage and measurement grid discretization by comparing radiator forces and mass flows. In addition, the changes on overall vehicle forces are discussed with the radiator force put in context with cooling drag.

Design and development of a climatic wind tunnel for physiological sports experimentation

2018 ◽  
Vol 233 (1) ◽  
pp. 86-100 ◽  
Author(s):  
Mats Ainegren ◽  
Simon Tuplin ◽  
Peter Carlsson ◽  
Peter Render
Keyword(s):  
Wind Tunnel ◽  
Human Performance ◽  
Aerodynamic Drag ◽  
Flow Conditions ◽  
Worst Case ◽  
Overall Design ◽  
Double Poling ◽  
Frictional Forces ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations

The aim of this project was to develop a wind tunnel that enables the study of human performance during various types of sports and physical activities by examining the influence of aerodynamic drag, precipitation, frictional forces and gravitational forces on uphill and downhill travel on a moving substrate. An overall design for a wind tunnel and working section containing a large treadmill was drafted, followed by computational fluid dynamics simulations of flow conditions to assess the design’s feasibility and select from different geometries prior to its construction. The flow conditions in the completed wind tunnel were validated using different flows, speeds and treadmill inclinations. Pilot experiments were carried out using a cross-country skier to investigate the effect of aerodynamic drag on oxygen uptake during double poling and the maximal achieved speed when rolling on a declined treadmill. The purpose was to validate the usefulness of the tunnel. The results showed that flow conditions are acceptable for experiments even in worst-case scenarios with maximal inclined and declined treadmill. Results also showed that aerodynamic drag has a significant impact on the skier’s energy expenditure.

scholarly journals Impact of a motorcycle on cyclist aerodynamic drag in parallel and staggered arrangements

2021 ◽  
Vol 24 (1) ◽  
Author(s):  
Bert Blocken ◽  
Stefanie Gillmeier ◽  
Fabio Malizia ◽  
Thijs van Druenen
Keyword(s):  
Aerodynamic Drag ◽  
Television Broadcasting ◽  
Close Proximity ◽  
Parallel Arrangement ◽  
Staggered Arrangement ◽  
Computational Fluid Dynamics Simulations ◽  
Calm Weather ◽  
Dynamics Simulations ◽  
The Impact ◽  
Insight Into

AbstractCycling races contain a multitude of motorcycles for various activities including television broadcasting. During parts of the race, these motorcycles can ride in close proximity of cyclists. Earlier studies focused on the impact of a nearby motorcycle on cyclist drag for in-line arrangements. It was shown that not only a motorcycle in front of a cyclist but also a motorcycle closely behind a cyclist can substantially reduce cyclist drag. However, there appears to be no information in the scientific literature about the impact of the motorcycle on cyclist drag for parallel and staggered arrangements. This paper presents wind tunnel measurements of cyclist drag for 32 different parallel and staggered cyclist-motorcycle arrangements. It is shown that the parallel arrangement leads to a drag increase for the cyclist, in the range of 5 to about 10% for a lateral distance of 2 to 1 m. The staggered arrangement can lead to either a drag increase or a drag decrease, where the latter is about 2% for most positions analyzed. For one of the parallel arrangements, computational fluid dynamics simulations were performed to provide insight into the reasons for the drag increase. A cyclist power model was used to convert the drag changes into potential time gains or losses. Compared to a lone cyclist riding at a speed of 46.8 km/h (13 m/s) on level road in calm weather, the time loss by a drag increase of 10%, 4% and − 2% was 2.16, 0.76 s and − 0.80 s per km, respectively. These time differences are large enough to influence the outcome of cycling races.

scholarly journals Aerodynamic analysis of uphill drafting in cycling

2021 ◽  
Vol 24 (1) ◽  
Author(s):  
T. van Druenen ◽  
B. Blocken
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
High Speed ◽  
Scientific Literature ◽  
Sensitivity Analyses ◽  
Air Resistance ◽  
Wind Tunnel Measurements ◽  
Aerodynamic Effect ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations

AbstractSome teams aiming for victory in a mountain stage in cycling take control in the uphill sections of the stage. While drafting, the team imposes a high speed at the front of the peloton defending their team leader from opponent’s attacks. Drafting is a well-known strategy on flat or descending sections and has been studied before in this context. However, there are no systematic and extensive studies in the scientific literature on the aerodynamic effect of uphill drafting. Some studies even suggested that for gradients above 7.2% the speeds drop to 17 km/h and the air resistance can be neglected. In this paper, uphill drafting is analyzed and quantified by means of drag reductions and power reductions obtained by computational fluid dynamics simulations validated with wind tunnel measurements. It is shown that even for gradients above 7.2%, drafting can yield substantial benefits. Drafting allows cyclists to save over 7% of power on a slope of 7.5% at a speed of 6 m/s. At a speed of 8 m/s, this reduction can exceed 16%. Sensitivity analyses indicate that significant power savings can be achieved, also with varying bicycle, cyclist, road and environmental characteristics.

scholarly journals Evaluation of Active Heat Sinks Design under Forced Convection—Effect of Geometric and Boundary Parameters

Materials ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2041
Author(s):  
Eva C. Silva ◽  
Álvaro M. Sampaio ◽  
António J. Pontes
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Additive Manufacturing ◽  
Pressure Drop ◽  
Forced Convection ◽  
Thermal Performance ◽  
Heat Sinks ◽  
Trapezoidal Shape ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations

This study shows the performance of heat sinks (HS) with different designs under forced convection, varying geometric and boundary parameters, via computational fluid dynamics simulations. Initially, a complete and detailed analysis of the thermal performance of various conventional HS designs was taken. Afterwards, HS designs were modified following some additive manufacturing approaches. The HS performance was compared by measuring their temperatures and pressure drop after 15 s. Smaller diameters/thicknesses and larger fins/pins spacing provided better results. For fins HS, the use of radial fins, with an inverted trapezoidal shape and with larger holes was advantageous. Regarding pins HS, the best option contemplated circular pins in combination with frontal holes in their structure. Additionally, lattice HS, only possible to be produced by additive manufacturing, was also studied. Lower temperatures were obtained with a hexagon unit cell. Lastly, a comparison between the best HS in each category showed a lower thermal resistance for lattice HS. Despite the increase of at least 38% in pressure drop, a consequence of its frontal area, the temperature was 26% and 56% lower when compared to conventional pins and fins HS, respectively, and 9% and 28% lower when compared to the best pins and best fins of this study.

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