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The wakes of Ahmed bodies with varying aspect ratio

Citation

Venning, J and Burton, D and Lo Jacono, D and Thompson, M and Sheridan, J, The wakes of Ahmed bodies with varying aspect ratio, Book of Abstracts of the 9th European Fluid Mechanics Conference, 9-13 September 2012, Rome, Italy, pp. 98. (2012) [Conference Extract]


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Abstract

An Ahmed body is a generalized three-dimensional model that generates a similar flow structure to that of road vehicles. One of the key features of this flow is the generation of C-Pillar vortices off the rear slant edges. These vortices form a pair of large, counter-rotating, unsteady structures of a conical shape which are generated as the flow moves across the rear slant. It has been demonstrated that these vortices play a significant role on the drag force acting on the body. The effect on the drag by separating these vortices from each other (by increasing the width of the body) is therefore of interest. The findings are presented of an investigation into the wakes of 25.7% scale Ahmed bodies with slant angles of 25◦ and with varying widths: 0.6, 1, and 1.25 times the standard Ahmed dimensions (denoted Narrow, Standard and Wide respectively). The models were tested in a water channel with flow speeds up to 0.5 m/s. Particle image velocity (PIV) was used in the spanwise direction (ie. yz-plane) which allowed the capture of the C-Pillar vortices. Figure 1 shows the velocity field and vorticity in this plane. With increased body width, there is a decrease in the strength of the C-Pillar vortex; additionally, a large vortex of opposite sign is evident below the vortex. The effect of the aspect ratio on the drag force will also be discussed. In addition to the mean velocity field, time-resolved PIV was gathered, allowing the dynamics of the vortices to be analysed. The analysis of the frequency spectra throughout the wake will be presented and discussed.

Item Details

Item Type:Conference Extract
Keywords:Ahmed body, vehicle aerodynamics, vortex flow, PIV, dynamics
Research Division:Engineering
Research Group:Interdisciplinary Engineering
Research Field:Fluidisation and Fluid Mechanics
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in the Physical Sciences
Author:Venning, J (Mr James Venning)
ID Code:115605
Year Published:2012
Deposited By:NC Maritime Engineering and Hydrodynamics
Deposited On:2017-03-31
Last Modified:2017-04-07
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