Determining the Effectiveness of Vortex Generators with regards to Automotive Applications

Greenbank, Luke (2019) Determining the Effectiveness of Vortex Generators with regards to Automotive Applications. [USQ Project]

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Engineers are continuously looking at ways of redesigning vehicles to reduce aerodynamic drag as this is the major contributor to the total resistive force at highway speeds. Any reduction in the drag coefficient of a vehicle will improve the fuel economy for a standard commuter car and increase the top speed of a performance car. In the past, vortex generators have been investigated for use on aircraft with once classified studies dating back to the 1950’s, however since this time there has been infrequent testing on vehicles.

In 2004, Mitsubishi released the Lancer Evolution 8 MR, amongst numerous performance upgrades it included vortex generators into the design (in the form of a row attached to the trailing edge of the roofline). Not only was this a bold statement fifteen years ago, but there has only been one other vehicle since this time (released in 2017) to include these devices from the factory. The press release stated that the inclusion of vortex generators was an innovation in aerodynamics technology. However, there was no quantifiable data included to go along with these claims. This study investigates the question of whether vortex generators can reduce aerodynamic drag of a vehicle and whether lift forces are impacted as well.

This research project included experimental and computational data collection. The experiments were separated into full-scale and small-scale testing. For the full-scale tests a row of vortex generators was positioned on the trailing edge of roofline of a test vehicle that also had a multitude of twine pieces attached all over the rear windscreen. Three speeds were tested, up to and including 100 km/h in an attempt to gain a variety of data. It was discovered that due to the high aerodynamic efficiency of the test vehicle the boundary layer did not noticeably separate from the surface, even in the control test where no vortex generators were installed. Therefore, this made identifying benefits of the vortex generators difficult. An additional test was undertaken where the devices were setup at a 25° incident angle to the oncoming airflow, based on a previous study that stated this angle was the most effective. However, for this situation there was no discernible difference from the original tests and it did not reveal any supplementary information that could be discussed.

The small-scale tests used 1:24 models in the wind tunnel to calculate the impact 3D printed vortex generators had on the drag and lift forces. It was discovered that drag slightly increased along with a decrease in lift. The reasoning behind this was due to the fact the scaled vortex generators were 1:12, which essentially made them twice the size of the original design for the vehicle. Due to 3D printing and handling limitations a matching scale was not practicable in this instance. From research compiled in the literature review it was discovered that there is an optimum height of the device, relating to the boundary layer thickness and if this is exceeded the form drag created outweighs the drag reduction ii of the devices. This creates a situation where they become redundant and lead to greater drag forces and inefficiencies. Smoke visualisation was attempted via a machine but due to the relatively small size of the model any flow characteristics around the shape were not explicit in detail.

Computational fluid dynamics (CFD) software was used to collect the quantifiable data. The scale vehicle with and without vortex generators was tested over a range of scenarios involving airspeeds up to 50 m/s. From the initial low airspeeds it was found that there was a reduction in drag force for the model that had vortex generators and this trend continued throughout all data points up until the maximum airspeed, where this reduction reached 15%. Vector, contour and streamline plots were used in the study to visualise the air flow around the vehicle. These images added additional depth to the study along with the raw data that the wind tunnel smoke visualisation failed to provide. However, upon analysis the findings were not conclusive by way of displaying the benefits compared to the control tests.

This study relied on complex and highly detailed 3D models. It would not be recommended for future investigations to include 3D scanning into the process, as to help reduce the quantity of geometry errors encountered. Another consideration would be the scaling of the vehicle in the tests. As this differs from a full-sized vehicle the results can only be an indication and not conclusive in the findings.

In theory, vortex generators can reduce aerodynamic drag of a vehicle but ascertaining conclusive results via experimentation can be challenging. From the research completed it is likely that vortex generators need to be specifically designed for each application to determine the parameters leading to the greatest reduction in drag, thereby the optimal design. Aspects such as vortex generator height relative to boundary layer thickness, the positioning relative to each other, the quantity used and the shape of the device are to be studied. Mainstream adoption may not be viable due to the additional research and development (R&D) costs. Also, factors such as the effect on aesthetic appeal for a standard commuter car will need to be considered.

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Item Type: USQ Project
Item Status: Live Archive
Faculty/School / Institute/Centre: Historic - Faculty of Health, Engineering and Sciences - School of Mechanical and Electrical Engineering (1 Jul 2013 - 31 Dec 2021)
Supervisors: Sharifian-Barforoush, Ahmad
Qualification: Bachelor of Engineering (Honours) (Mechanical)
Date Deposited: 18 Aug 2021 04:23
Last Modified: 26 Jun 2023 22:34

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