Computational Analysis and Design to Minimize Vehicle Roof Rack Wind Noise

Karbon, Kenneth; Dietschi, U. D.

doi:10.4271/2005-01-0602

Cited by 11 publications

(4 citation statements)

References 7 publications

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“…The Thomas et al (2014) study did not consider the FC penalty of an unloaded roof rack and the authors didnot extrapolate the vehicle-level FC impacts to the national fleet. Other studies explored roof racks' impacts on design, noise, and forces (Jawad, et al, 2000;Lee, et al, 2002;Karbon and Dietschi, 2005;Senthooran, et al, 2007;Mandadapu et al, 2011).…”

Section: )mentioning

confidence: 99%

“…To be sure, built-in roof rails alter the vehicle frontal area and therefore can potentially increase aerodynamic drag force. However, the change in vehicle frontal shape is usually small, in part because car manufacturers have been continuously improving the aerodynamics of built-in rails (Carr, 1976;Howard, 1986;Karbon and Dietschi, 2005;Kelly and Holcombe, 1964). In any event, the aerodynamic impacts of these racks are often already captured in fuel economy tests because they are part of many packages for new vehicles.…”

Section: Roof Rackcategorizationmentioning

confidence: 99%

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Fuel consumption impacts of auto roof racks

Chen

Meier

2016

Energy Policy

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The after-market roof rack is one of the most common components attached to a vehicle for carrying over-sized items, such as bicycles and skis. It is important to understand these racks'fuel consumption impacts on both individual vehicles and the national fleet because they are widely used.We estimate the national fuel consumption impacts of roof racks using a bottom-up approach. Our model incorporates real-world data and vehicle stock informationto enable assessing fuel consumption impacts for several categories of vehicles, rack configurations, and usage conditions.In addition, the model draws on two new data-gathering techniques, on-line forums and crowd-sourcing. The results show that nationwide, roof racks are responsible for 0.8‰ oflight duty vehicle fuel consumption in 2015, corresponding to100million gallonsof gasoline per year. Sensitivity analyses show that results are most sensitive to the fraction of vehicles with installed roof racks but carrying no equipment. The aerodynamic efficiency of typical roof racks can be greatly improved and reduce individual vehicle fuel consumption; however, government policies to minimize extensive driving with empty racks-if successful-could save more fuel nationally.

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Section: )mentioning

confidence: 99%

Section: Roof Rackcategorizationmentioning

confidence: 99%

Fuel consumption impacts of auto roof racks

Chen

Meier

2016

Energy Policy

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“…One example of this is noise transmission thourgh the Roof bars are commonly known as a noise source on a vehicle, as well as creating additional levels of parasitic drag. Karbon and Dietschi (2005) investigated roof bar noise using CFD. A RANS-based CFD code was used, coupled with an acoustic analogy, which found that relative levels of noise generation were predicted with sufficient accuracy.…”

Section: Other Noise Sourcesmentioning

confidence: 99%

The Effects of Unsteady On-Road Flow Conditions on Cabin Noise

Oettle¹,

Sims-Williams²,

Dominy³

et al. 2010

SAE Technical Paper Series

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On-road, a vehicle experiences unsteady flow conditions due to turbulence in the natural wind, moving through the unsteady wakes of other road vehicles and travelling through the stationary wakes generated by roadside obstacles. There is increasing concern about potential differences between steady flow conditions that are typically used for development and the transient conditions that occur on-road. This work considers whether steady techniques are able to predict the unsteady results measured on-road, the impact of this unsteadiness on the noise perceived in the cabin and whether minor changes made to the geometry of the vehicle could affect this. Both external aerodynamic and acoustic measurements were taken using a full-size vehicle combined with measurements of the noise inside the cabin. Data collection took place on-road under a range of wind conditions to accurately measure the response of the vehicle to oncoming flow unsteadiness, with steady-state measurements taking place in full-scale aeroacoustic wind tunnels.Overall it was demonstrated that, using a variety of temporal and spectral approaches, steady techniques were able to predict unsteady on-road results well enough to assess cabin noise by correctly taking into account the varying on-road flow conditions. Aerodynamic admittance values remained less than unity in the sideglass region of the vehicle, with the exception of the the region nearest the A-pillar. The reducing unsteady energy at frequencies greater than 10 Hz, combined with the corresponding roll-off in admittance, implies that unsteady frequencies below 10 Hz affect the vehicle most, where the response remains quasi-steady.Quasi-steady cabin noise simulations allowed a subjective assessment of the predicted unsteady cabin noise, where the impact of cabin noise modulations were quantified and found to be important to perception. Minor geometry changes affected the sensitivity of cabin noise to changes in yaw angle, altering modulation and therefore having an important impact on the unsteady wind noise perceived on-road.iii DeclarationThe work in this thesis is based on research carried out at the School of Engineering and Computing Sciences, Durham University, UK. No part of this thesis has been submitted elsewhere for any other degree or qualification and it all my own work unless referenced to the contrary in the text.

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“…Designing profiles such that they are irregular and incorporating crenelated strips can reduce coherent vortex shedding and the resultant dipole noise sources 73 .…”

Section: Vehicle Formmentioning

confidence: 99%

Automotive aeroacoustics: An overview

Oettle

Sims-Williams

2017

Proceedings of the Institution of Mechanical Engineers, Part D:

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The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. AbstractVehicle aeroacoustic performance has a strong influence on customer perception and also has importance for safety and comfort. Wind noise performance was once differentiated by the quality of sealing. Today, achieving competitive wind noise performance also depends on minimising aeroacoustic noise sources generated by the vehicle form, and on attenuation in the noise pathway from sources on the exterior to the vehicle interior. Attenuation in the noise pathway from sources on the exterior to the vehicle interior, especially through glazed surfaces, will continue to play an important role in controlling cabin noise, with a particular emphasis on achieving attenuation efficiently in terms of component mass. The human brain is not only sensitive towards the level of steady broadband noise, but distinctive features such as tonality or modulation draw the attention of the vehicle occupant and impact negatively on perception. Complex indices are often required to define good wind noise performance. This includes the consideration of multiple frequency bands and effects of the range of yaw angles experienced on-road. A key to achieving future vehicle refinement is bringing together an understanding of unsteady onset flow conditions, their impact on cabin sound pressure level and modulation and in turn the impact of noise level and modulation on psychoacoustic perception.

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Computational Analysis and Design to Minimize Vehicle Roof Rack Wind Noise

Cited by 11 publications

References 7 publications

Fuel consumption impacts of auto roof racks

Fuel consumption impacts of auto roof racks

The Effects of Unsteady On-Road Flow Conditions on Cabin Noise

Automotive aeroacoustics: An overview

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