Accuracy and Speed for Scale-Resolving Simulations of the DrivAer Reference Model

Ekman, Petter; Larsson, Torbjörn; Virdung, Torbjörn; Karlsson, Matts

doi:10.4271/2019-01-0639

Cited by 13 publications

(3 citation statements)

References 17 publications

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“…A second-order implicit temporal discretisation scheme with a time step size of 2.5 • 10 −4 s was used, corresponding to a temporal resolution of 406 time steps of the freestream to travel the length of the vehicle. A study by kman et al [35] found this temporal resolution adequate when using the SBES model. Four inner iterations were performed at each time step, allowing the residuals to converge well below 10 −3 .…”

Section: Cfd Mesh and Numerical Approachmentioning

confidence: 96%

High speed driving stability of road vehicles under crosswinds: an aerodynamic and vehicle dynamic parametric sensitivity analysis

Brandt

Jacobson

Sebben

2021

Vehicle System Dynamics

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Crosswinds affect vehicle driving stability and their influence increase with driving speed. To improve high speed driving stability, interdisciplinary research using unsteady aerodynamics and vehicle dynamics is necessary. The current demands of faster development times require robust virtual methods for assessing stability performance in early design phases. This paper employs a numerical one-way coupling between the two disciplines and uses a variety of realistic crosswind gust profiles for the aerodynamic simulations to output representative forces and moments on three vehicle dynamic models of different fidelity levels, ranging from a one-track model to a full multi-body dynamic model of a sports utility vehicle. An investigation on required model fidelity was conducted along with a sensitivity study to find key aerodynamic and vehicle dynamic characteristics to minimise the yaw velocity and lateral acceleration response during crosswinds. Transient aerodynamic simulations were used to model crosswind gusts at high speeds. Analysis of the forces and moments showed that rapid changing gusts generate overshoots in the yaw moment, due to the phase delay of the flow between the front and rear of the vehicle. A methodology for modelling this phase delay is proposed. The response of the vehicle was captured equally well by the enhanced model (mid-level fidelity) and the full multibody dynamic model, while the simplest one-track model failed to emulate the correct vehicle response. The sensitivity study showed the importance of the positioning of the centre of gravity, the aerodynamic coefficient of yaw moment, wheel base, vehicle mass and yaw inertia. In addition, the axles' side force steer gradients and other suspension parameters revealed potential in improving crosswind stability.

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Section: Cfd Mesh and Numerical Approachmentioning

confidence: 96%

High speed driving stability of road vehicles under crosswinds: an aerodynamic and vehicle dynamic parametric sensitivity analysis

Brandt

Jacobson

Sebben

2021

Vehicle System Dynamics

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“…A verification simulation with a timestep of 1.875 × 10 −4 s was performed to confirm if the larger timestep was appropriate. The results showed a ∆C D and a ∆C L of only 2 counts and 4 counts, respectively, which verified that the larger timestep was sufficiently small and practical for efficient use of the computational resources [22]. Ideally, the mesh resolution for these types of transient simulations should be higher, and the number of flow passes used before and during averaging should be much higher, but due to limitations on computational resources, this could not be achieved.…”

Section: Mesh and Solver Settingsmentioning

confidence: 86%

Reducing Aerodynamic Drag on Roof-Mounted Lightbars for Emergency Vehicles

Connolly,

O’Rourke,

Ivankovic

2024

Fluids

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This paper investigates the impact of contemporary lightbars on vehicle fuel efficiency with a focus on quantifying their effects on fuel consumption and exploring strategies to improve drag performance through modifications. Simulations showed an 8–11% increase in drag for square-back vehicles, with greater penalties outlined for vehicles with rear-slanting roofs. Given the moderate drag increase, the impact on the driving range, especially for electric vehicles, remains minimal, supporting the continued use of external lightbars. Positioning experiments suggest marginal drag reductions when lowering the lightbar to its lowest position due to additional drag effects that can be caused by the mounting mechanism in its condensed form. Angling the lightbar showed negligible drag increases up to an angle of 2.5 degrees, but beyond that, a 4% increase in drag was observed for every additional 2.5 degrees. Additionally, fitting drag-reducing ramps ahead of the lightbar yielded no significant drag savings. Noise analysis identified that the lightbar’s wake and rear surfaces were responsible for the largest production of noise. The optimal lightbar design was found to incorporate overflow rather than underflow and rear tapering in sync with roof curvature. Appendable clip-on devices for the lightbar, particularly rear clip-ons, demonstrated appreciable drag reductions of up to 2.5%. A final optimised lightbar design produced a minimal 2.8% drag increase when fitted onto an unmarked vehicle, representing a threefold improvement compared with the current generation of lightbars. This study advances the field of lightbar aerodynamics by precisely quantifying drag effects by using highly detailed geometry and examines the significance of optimal positioning, angle adjustment, and appendable clip-on devices in greater depth than any existing published work.

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“…A larger time step requires less computational resources to simulate a specified physical time but may not sufficiently resolve time scales. Ekman et al [41] conducted studies on the accuracy of scale-resolving simulations with various time-step sizes on the DrivAer reference model. The authors found that significant savings in computational time were achieved with sufficiently accurate results up to a CFL of 20; however, as the time-step size increased, larger discrepancies were seen at the Apillar, side window, C-pillar, and the wheels.…”

Section: Spatial and Temporal Discretizationmentioning

confidence: 99%

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

Nabutola

Boetcher

2021

Adv. Aerodyn.

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Aerodynamic 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.

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Accuracy and Speed for Scale-Resolving Simulations of the DrivAer Reference Model

Cited by 13 publications

References 17 publications

High speed driving stability of road vehicles under crosswinds: an aerodynamic and vehicle dynamic parametric sensitivity analysis

High speed driving stability of road vehicles under crosswinds: an aerodynamic and vehicle dynamic parametric sensitivity analysis

Reducing Aerodynamic Drag on Roof-Mounted Lightbars for Emergency Vehicles

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

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