Vehicle wakes in side wind
Doktorsavhandling, 2021

There is a global push to reduce the energy consumption of passenger vehicles with increasingly stringent targets and regulations. More than one-tenth of Europe's greenhouse gasses are due to passenger vehicles. The aerodynamic drag is a major contributor to energy consumption responsible for more than a quarter of the vehicle's energy usage. Thus, improving the aerodynamic drag will help us achieve our greenhouse gas emissions targets.

Vehicle aerodynamics is typically assessed and developed in idealised conditions using low turbulence wind tunnels and numerical methods. Several aspects influencing vehicle aerodynamics are often neglected such as traffic and wind conditions. This thesis explores the effects of steady wind, or yawed flow, on the wake of vehicles. The goal is to increase the knowledge of the full wake behaviour at yaw and how it is related to the aerodynamic drag. For this, an optimisation method is used throughout this work to generate robust, low-drag, reference geometries. The optimisation is done at different yaw angles, allowing asymmetric geometries at yaw. The cycle averaged drag, which takes into account the driving cycle as well as the wind distribution, is also considered to create symmetric geometries which are insensitive to yaw. The optimisation is focused on base cavities and trailing edge modifications to these cavities.

Generally, the low-drag configurations have a more balanced wake, with and without side wind, where the recirculating flow in the wake is aligned with the vehicle. The improved balance allows the wake to move more freely which often increases the large scale coherent motions of the wake. These unsteady motions are linked to increases in drag in the literature, however, in this work, improving the wake balance was found to be the more important indicator of the overall drag. At yaw, the coherent unsteady motions are reduced as a result of the wake being locked in a more stable, but higher drag, upwash or downwash dominated state.

The wake becomes increasingly downwash or upwash dominated at yaw by a large rotating structure in the wake. The yaw insensitive designs have a wake that is slightly biased towards the top or bottom of the base at zero yaw to counteract the movement of the wake at yaw. Optimising the geometry without considering yaw can reduce the performance over the entire operating range. This highlights the importance of considering several operating conditions during vehicle development.

surrogate model

aerodynamics

tomographic PIV

wind

drag

wake

yaw

CFD

crossflow

optimization

cavity

HA2
Opponent: Prof. Jens Fransson, KTH, Sweden

Författare

Magnus Urquhart

Chalmers, Mekanik och maritima vetenskaper, Fordonsteknik och autonoma system

Numerical analysis of a vehicle wake with tapered rear extensions under yaw conditions

Journal of Wind Engineering and Industrial Aerodynamics,; Vol. 179(2018)p. 308-318

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Aerodynamic drag improvements on a square-back vehicle at yaw using a tapered cavity and asymmetric flaps

International Journal of Heat and Fluid Flow,; Vol. 86(2020)

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Surrogate-based optimisation using adaptively scaled radial basis functions

Applied Soft Computing Journal,; Vol. 88(2020)

Artikel i vetenskaplig tidskrift

Magnus Urquhart, Max Varney, Simone Sebben, Martin Passmore. Drag reduction mechanisms on a generic square-back vehicle using an optimised yaw-insensitive base cavity

Magnus Urquhart, Simone Sebben. Optimisation of trailing edge flaps on the base cavity of a vehicle for improved performance at yaw

There is a global push to reduce the energy consumption of passenger vehicles with increasingly stringent targets and regulations. More than one-tenth of Europe's greenhouse gasses are due to passenger vehicles. The aerodynamic drag is a major contributor to energy consumption responsible for more than a quarter of the vehicle's energy usage. Improving the aerodynamic drag will help us achieve our greenhouse gas emissions targets.

Vehicle aerodynamics is typically assessed and developed in perfect conditions using wind tunnels and computer simulations. There are several aspects that have an impact on the aerodynamic performance and the energy usage of a vehicle that are neglected such as traffic and wind conditions. This thesis explores the effects of steady wind on the aerodynamic drag.

The results show that the aerodynamic sensitivity to wind can be improved if the performance with wind is taken into consideration during vehicle design. This results in a trade-off where a slight reduction in performance in still conditions is balanced out against a larger gain when there is wind present. A robust design with low sensitivity to side wind can be achieved efficiently using optimisation techniques to automatically balance out the trade-off in performance.

Ökad energieffektivitet genom kontroll och reduktion av det inducerade motståndet

Energimyndigheten (2016-008677/43328-1), 2016-12-01 -- 2019-12-30.

Drivkrafter

Hållbar utveckling

Styrkeområden

Transport

Energi

Fundament

Grundläggande vetenskaper

Infrastruktur

C3SE (Chalmers Centre for Computational Science and Engineering)

Ämneskategorier

Strömningsmekanik och akustik

ISBN

978-91-7905-564-6

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5031

Utgivare

Chalmers tekniska högskola

HA2

Online

Opponent: Prof. Jens Fransson, KTH, Sweden

Mer information

Senast uppdaterat

2021-09-22