Experimental and numerical investigations of underhood flow for vehicle thermal management
Doktorsavhandling, 2021

Electrified vehicles are an essential part in reducing emissions from the transportation sector. Their development comes with a variety of new challenges. Most of them revolve around the energy efficiency of the vehicles as it directly relates to the range that can be covered with one charge. In the area of vehicle thermal management, this means that the focus shifts from a pure cooling perspective towards providing a thermal environment in which the electric power components can operate most efficiently. As the required amount of cooling air through the front is lower than in conventional combustion vehicles, an additional benefit can be gained from smaller front openings that reduce the aerodynamic drag. However, this requires a deeper knowledge of the flow physics in the underhood environment in order to utilise the available cooling air efficiently.

Computational Fluid Dynamics (CFD) is an important tool for the investigation of the underhood flow, since it gives the possibility to look at the flow field even in areas where measurement equipment cannot reach. In the first part of this work, the focus is on the simulation of the axial cooling fan. Different methods to simulate an axial cooling fan were compared to each other and to experimental data that was acquired using Laser-Doppler-Anemometry. The commonly used Multiple Reference Frame approach was shown not to be suitable for investigating underhood flow, as the stationary blades leave an imprint on the wake flow. In addition, inhomogeneous temperature distributions experienced an unphysical rotation due to the switch in reference frame. These issues do not occur with the Rigid Body Motion approach, and the simulation results compared well to the measurements.

In the second part of this project, it was investigated how the flow downstream of a fan is affected by different components placed up- and downstream. A simplified underhood rig was designed and constructed to provide a controlled, vehicle-like environment for the measurements and simulations. Two front designs, representative of a hybrid and a battery electric vehicle, were utilised and it could be shown that the upper grille opening that is missing in the battery electric vehicle configuration has a visible impact on the flow field downstream of the fan. Simulating the same configurations in CFD showed some differences to the experimental data. For a second cooling fan, the results were well matched.

CFD

Axial fan

Laser-Doppler anemometry

MRF

Vehicle thermal management

Cooling flow

Underhood flow

RBM

Simplified underhood environment

Vasa A, Vera Sandberg allé 8, Chalmers
Opponent: Dr. Burkhard Hupertz, Ford Motor Company, Germany

Författare

Randi Franzke

Chalmers, Mekanik och maritima vetenskaper, Fordonsteknik och autonoma system

Validation of Different Fan Modelling Techniques in Computational Fluid Dynamics

Proceedings of the 21st Australasian Fluid Mechanics Conference ,; (2018)

Paper i proceeding

Franzke, R., Sebben, S., Willeson, E., "Experimental investigation of the air flow in a simplified underhood environment"

Franzke, R., Sebben, S., Willeson, E., "Numerical investigation of the air flow in a simplified underhood environment"

Electrified vehicles are an essential part in reducing emissions from the transportation sector. Their development comes with a variety of new challenges. Most of them revolve around the energy efficiency of the vehicles as it directly relates to the range that can be covered with one charge. In the area of vehicle thermal management, this means that the focus shifts from a pure cooling perspective towards providing a thermal environment in which the electric power components can operate most efficiently. As the required amount of cooling air through the front is lower than in conventional combustion vehicles, an additional benefit can be gained from smaller front openings that reduce the aerodynamic drag. However, this requires a deeper knowledge of the flow physics in the underhood environment to utilise the available cooling air efficiently.

Numerical simulations are an important tool for the investigation of the underhood flow since they provide insight into the flow field even in areas where measurement equipment cannot reach. In the first part of this work, the focus is on the simulation of an axial cooling fan. Different methods to simulate the axial cooling fan were compared to each other and to experimental data. It was shown that advanced models are necessary to accurately capture the flow field and the transport of flow properties through the fan region.

For the second part of the thesis, a simplified underhood rig was designed and built to provide a controlled, vehicle-like environment for physical measurements and numerical simulations. Significant changes to the flow field could be triggered by restricting the front openings or placing different blockages into the test section. It could, for example, be seen that the reduced grille opening in a battery electric car has a notable effect on the flow field behind the fan. The simulations on the same configurations showed good agreement to the measurements for one fan design, while for a second fan some deviations were noticeable.

Industriell applicerbar simuleringsmodell för hybrid- och elbilar för analys av termodynamisk status i komplett bil

Energimyndigheten (2015-011207), 2016-10-25 -- 2019-12-31.

Ämneskategorier

Farkostteknik

ISBN

978-91-7905-585-1

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5052

Utgivare

Chalmers tekniska högskola

Vasa A, Vera Sandberg allé 8, Chalmers

Online

Opponent: Dr. Burkhard Hupertz, Ford Motor Company, Germany

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Senast uppdaterat

2021-11-09