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Technical Paper

Wake and Unsteady Surface-Pressure Measurements on an SUV with Rear-End Extensions

2015-04-14
2015-01-1545
Previous research on both small-scale and full-scale vehicles shows that base extensions are an effective method to increase the base pressure, enhancing pressure recovery and reducing the wake size. These extensions decrease drag at zero yaw, but show an even larger improvement at small yaw angles. In this paper, rear extensions are investigated on an SUV in the Volvo Cars Aerodynamic Wind Tunnel with focus on the wake flow and on the unsteady behavior of the surface pressures near the base perimeter. To increase the effect of the extensions on the wake flow, the investigated configurations have a closed upper- and lower grille (closed-cooling) and the underbody has been smoothed with additional panels. This paper aims to analyze differences in flow characteristics on the wake of an SUV at 0° and 2.5° yaw, caused by different sets of extensions attached to the base perimeter. Extensions with several lengths are investigated with and without a kick.
Technical Paper

Uncertainty Quantification of Flow Uniformity Measurements in a Slotted Wall Wind Tunnel

2019-04-02
2019-01-0656
The need for a more complete understanding of the flow behavior in aerodynamic wind tunnels has increased as they have become vital tools not only for vehicle development, but also for vehicle certification. One important aspect of the behavior is the empty test section flow, which in a conventional tunnel should be as uniform as possible. In order to assess the uniformity and ensure consistent behavior over time, accurate measurements need to be performed regularly. Furthermore, the uncertainties and errors of the measurements need to be minimized in order to resolve small non-uniformities. In this work, the quantification of the measurement uncertainties from the full measurement chain of the new flow uniformity measurement rig for the Volvo Cars aerodynamic wind tunnel is presented. The simulation based method used to account for flow interference of the probe mount is also discussed.
Journal Article

Tyre Pattern Features and Their Effects on Passenger Vehicle Drag

2018-04-03
2018-01-0710
In light of the drive for energy efficiency and low CO2 emissions, extensive research is performed to reduce vehicle aerodynamic drag. The wheels are relatively shielded from the main flow compared to the exterior of the passenger car; however, they are typically responsible for around 25% of the overall vehicle drag. This contribution is large as the wheels and tyres protrude into the flow and change the flow structure around the vehicle underbody. Given that the tyre is the first part of the wheel to get in contact with the oncoming flow, its shape and features have a significant impact on the flow pattern that develops. This study aims at identifying the general effects of two main tyre features, the longitudinal rain grooves and lateral pattern grooves, using both Computational Fluid Dynamics (CFD) and wind tunnel tests. This is performed by cutting generic representations of these details into identical slick tyres.
Journal Article

On the Effects of Wind Tunnel Floor Tangential Blowing on the Aerodynamic Forces of Passenger Vehicles

2017-03-28
2017-01-1518
Many aerodynamic wind tunnels used for testing of ground vehicles have advanced ground simulation systems to account for the relative motion between the ground and the vehicle. One commonly used approach for ground simulation is a five belt system, where moving belts are used, often in conjunction with distributed suction and tangential blowing that reduces the displacement thickness of the boundary layer along the wind tunnel floor. This paper investigates the effects from aft-belt tangential blowing in the Volvo Cars Aerodynamic wind tunnel. First the uniformity of the boundary layer thickness downstream of the blowing slots is examined in the empty tunnel. This is followed by investigations of how the measured performance of different vehicle types in several configurations, typically tested in routine aerodynamic development work, depends on whether the tangential blowing system is active or not.
Technical Paper

Numerical Simulations of a Car Underbody: Effect of Front-Wheel Deflectors

2004-03-08
2004-01-1307
Numerical simulations of a detailed car underbody have been carried out using a commercial code. The objective of the present study was to decrease vehicle aerodynamic drag by placing front-wheel deflectors and to understand the influence of these extra details on the underbody flow. A base-model and five different configurations have been investigated and analyzed. The results are presented in terms of drag and front and rear lift values. In addition, the drag contribution of individual parts/areas of the underbody is also presented, which helps a great deal the understanding of the effect of front-wheels deflectors on the underbody of a vehicle. The results show that, in most cases, front-wheel deflectors are very effective in reducing overall aerodynamic drag (values around dCd = −0.010 were calculated, which correspond to a 4% reduction in drag).
Technical Paper

Numerical Flow Simulations of a Detailed Car Underbody

2001-03-05
2001-01-0703
The airflow around a detailed car underbody has been simulated using a commercial CFD software. Moving ground and rotating-wheel boundary conditions were applied in order to allow comparisons of Cd and dCd values with experimental data from a wind tunnel fitted with moving ground facilities. The calculated Cd and dCd figures compared very well with the available experimental results. Four configurations were tested and the maximum difference between experimental and numerical Cd values was 0.009. The individual contribution of different parts of the vehicle to the total drag was calculated and is discussed in this paper. This paper also describes in detail the numerical technique used to perform the computations.
Technical Paper

Numerical Analysis of Aerodynamic Impact on Passenger Vehicles during Cornering

2018-05-30
2018-37-0014
Governmental regulations and increased consumer awareness of the negative effects of green-house gases has led the automotive industry to massive invest in the energy efficiency of its fleet. One way towards accomplishing reduced fuel consumption is minimizing the drag of vehicles by improving its aerodynamics. Fuel consumption is measured by standardized driving cycles which do not consider aerodynamic losses during cornering. It is uncertain whether cornering has a significant impact on the drag, and the present study intends to investigate this numerically, using a generic vehicle model called the DrivAer. The model is considered in two different configurations: the notchback and the squareback. Cornering in various radiuses is modelled using a Moving Reference Frame approach which provides the correct flow conditions when simulating a stationary vehicle where the wind and ground are moving instead.
Technical Paper

Large Eddy Simulation on the Underbody Flow of the Vehicle with Semi-Complex Underbody Configuration

2007-04-16
2007-01-0103
To effectively process CFD works in early stage of aerodynamic developments of vehicles, simple but semi-complex configurations of the vehicle underbody should be pursued. Large eddy simulation (LES) was performed on the flow around the vehicle with a semi-complex underbody configuration designed at Volvo Car. Computations with CFD code “FrontFlow-red” were performed for both flat and semi-complex underbody configurations. Unstructured meshes of approximately 22 and 23 millions were used respectively. Differences in the flow fields with flat and semi-complex underbody configurations and rotational effects of the wheels are discussed. LES results are also compared with those with Reynolds averaged Navier-Stokes (RANS) computations.
Technical Paper

Investigations of the Rear-End Flow Structures on a Sedan Car

2016-04-05
2016-01-1606
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.
Journal Article

Investigation of the Influence of Tyre Geometry on the Aerodynamics of Passenger Cars

2013-04-08
2013-01-0955
It is well known that wheels are responsible for a significant amount of the total aerodynamic drag of passenger vehicles. Tyres, and mostly rims, have been the subject of research in the automotive industry for the past years, but their effect and interaction with each other and with the car exterior is still not completely understood. This paper focuses on the use of CFD to study the effects of tyre geometry (tyre profile and tyre tread) on road vehicle aerodynamics. Whenever possible, results of the numerical computations are compared with experiments. More than sixty configurations were simulated. These simulations combined different tyre profiles, treads, rim designs and spoke orientation on two car types: a sedan and a sports wagon. Two tyre geometries were obtained directly from the tyre manufacturer, while a third geometry was obtained from our database and represents a generic tyre which covers different profiles of a given tyre size.
Journal Article

Investigation of Wheel Aerodynamic Resistance of Passenger Cars

2014-04-01
2014-01-0606
There are a number of numerical and experimental studies of the aerodynamic performance of wheels that have been published. They show that wheels and wheel-housing flows are responsible for a substantial part of the total aerodynamic drag on passenger vehicles. Previous investigations have also shown that aerodynamic resistance moment acting on rotating wheels, sometimes referred to as ventilation resistance or ventilation torque is a significant contributor to the total aerodynamic resistance of the vehicle; therefore it should not be neglected when designing the wheel-housing area. This work presents a numerical study of the wheel ventilation resistance moment and factors that affect it, using computational fluid dynamics (CFD). It is demonstrated how pressure and shear forces acting on different rotating parts of the wheel affect the ventilation torque. It is also shown how a simple change of rim design can lead to a significant decrease in power consumption of the vehicle.
Technical Paper

Experimental and Numerical Investigations of the Base Wake on an SUV

2013-04-08
2013-01-0464
With the increase in fuel prices and the increasingly strict environmental legislations regarding CO₂ emissions, reduction of the total energy consumption of our society becomes more important. Passenger vehicles are partly responsible for this consumption due to their strong presence in the daily life of most people. Therefore reducing the impact of cars on the environment can assist in decreasing the overall energy consumption. Even though several fields have an impact on a passenger car's performance, this paper will focus on the aerodynamic part and more specifically, the wake behind a vehicle. By definition a car is a bluff body on which the air resistance is for the most part driven by pressure drag. This is caused by the wake these bodies create. Therefore analyzing the wake characteristics behind a vehicle is crucial if one would like to reduce drag.
Technical Paper

Effect of Rear-End Extensions on the Aerodynamic Forces of an SUV

2014-04-01
2014-01-0602
Under a global impulse for less man-made emissions, the automotive manufacturers search for innovative methods to reduce the fuel consumption and hence the CO2-emissions. Aerodynamics has great potential to aid the emission reduction since aerodynamic drag is an important parameter in the overall driving resistance force. As vehicles are considered bluff bodies, the main drag source is pressure drag, caused by the difference between front and rear pressure. Therefore increasing the base pressure is a key parameter to reduce the aerodynamic drag. From previous research on small-scale and full-scale vehicles, rear-end extensions are known to have a positive effect on the base pressure, enhancing pressure recovery and reducing the wake area. This paper investigates the effect of several parameters of these extensions on the forces, on the surface pressures of an SUV in the Volvo Cars Aerodynamic Wind Tunnel and compares them with numerical results.
Technical Paper

A CFD Approach via Large Eddy Simulation to the Flow Field with Complex Geometrical Configurations: A Study Case of Vehicle Underbody Flows

2009-04-20
2009-01-0332
CFD is becoming an inevitable modern engineering tool in the vehicle aerodynamics. A LES based CFD approach is proposed for analysis for flows with complex geometrical configurations to which detailed experiments, high grid-density LES or DNS cannot be applicable. How CFD results should be evaluated for cases in which the related experiments are not available. The procedure proposed consists of four stages, i.e., inspections of solutions with coarse and fine meshes, reconfirmation of energy spectrum, references to the similar experiments, explanations of results obtained. The procedures are applied to the underbody flows with a semi-complex underbody configuration.
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