Conservation of Energy Method for On-Road Aerodynamic Drag Investigation

Bratschitsch, Emilia; Bischof, Günter; Haas, A; Kaltenhauser, Albert

doi:10.4271/2004-01-1148

Cited by 2 publications

(1 citation statement)

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“…This technique is also occasionally used for larger vehicles that cannot fit in a wind tunnel, from Walter et al (2001), and was also a common method used prior to ground simulation becoming more widespread in wind tunnels, from Howell et al (2002). In addition to simply being used to assess the drag of a vehicle, investigations have been carried out using coastdown techniques, such as those by Bratschitsch et al (2004) Whilst it is these spectra that currently form the most complete set of targets for turbulence generation systems, since they are based on averaged on-road data, they dilute the potentially important impact of less common but more extreme conditions.…”

Section: By Taking a Reference Speed Ref And Corresponding Spl The Imentioning

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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Section: By Taking a Reference Speed Ref And Corresponding Spl The Imentioning

confidence: 99%