TY - JOUR
T1 - Aspect ratio and the dynamic wake of the Ahmed body
AU - Venning, James
AU - McQueen, Thomas
AU - Jacono, David Lo
AU - Burton, David
AU - Thompson, Mark
AU - Sheridan, John
N1 - Funding Information:
The authors would like to acknowledge the financial support of the Australian Research Council (ARC) through Linkage Project LP0991170 and the Centre National de la Recherche Scientifique (CNRS) through Grant No. PICS161793 under the Projet International de Coopération Scientifique. TM acknowledges the support of an Australian Government Research Training Program Scholarship.
Publisher Copyright:
© 2021
Copyright:
Copyright 2021 Elsevier B.V., All rights reserved.
PY - 2022/1/1
Y1 - 2022/1/1
N2 - The dynamic structures in the wake of the Ahmed body with a 25° slant angle were investigated. It is well established that the wake is dominated by two, counter rotating, streamwise vortex structures (C-pillar vortices). The influence these vortices have on the flow over the slant back was altered by modifying the width of the body between 60% to 120% of the standard width. The wake was measured using time-resolved particle-image velocimetry in several streamwise and spanwise planes for a height-based Reynolds number of 2.6×104. The wake measurements were decomposed with a spectral proper orthogonal decomposition technique, revealing two oscillatory modes. Firstly, the C-pillar vortical structures alternately contract and expand with a Strouhal number of 0.24, mildly dependent on the width. Secondly, the boundary layers on the sides of the body separate at the end of the body, forming shear layers with a dominant frequency of St = 2.30. Reducing the width of the body to 60% rotates the symmetry axis of the shedding mode. Furthermore, changing the spacing between the C-pillar vortices, by changing the width of the body, alters the nature of the spanwise vortical structures that form behind the base of the model. Intermediate width bodies produce two stable spanwise vortices. For wide bodies, the flow remains separated over the entire slant, and the top spanwise vortex does not form. Rather, the flow over the slant resembles a free shear layer with a Kelvin–Helmholtz-like instability leading to periodic shedding of small-scale vortex structures. Conversely, for narrow bodies, this phenomenon is observed at the bottom of the body and the lower spanwise vortex no longer forms while the flow over the slant remains attached.
AB - The dynamic structures in the wake of the Ahmed body with a 25° slant angle were investigated. It is well established that the wake is dominated by two, counter rotating, streamwise vortex structures (C-pillar vortices). The influence these vortices have on the flow over the slant back was altered by modifying the width of the body between 60% to 120% of the standard width. The wake was measured using time-resolved particle-image velocimetry in several streamwise and spanwise planes for a height-based Reynolds number of 2.6×104. The wake measurements were decomposed with a spectral proper orthogonal decomposition technique, revealing two oscillatory modes. Firstly, the C-pillar vortical structures alternately contract and expand with a Strouhal number of 0.24, mildly dependent on the width. Secondly, the boundary layers on the sides of the body separate at the end of the body, forming shear layers with a dominant frequency of St = 2.30. Reducing the width of the body to 60% rotates the symmetry axis of the shedding mode. Furthermore, changing the spacing between the C-pillar vortices, by changing the width of the body, alters the nature of the spanwise vortical structures that form behind the base of the model. Intermediate width bodies produce two stable spanwise vortices. For wide bodies, the flow remains separated over the entire slant, and the top spanwise vortex does not form. Rather, the flow over the slant resembles a free shear layer with a Kelvin–Helmholtz-like instability leading to periodic shedding of small-scale vortex structures. Conversely, for narrow bodies, this phenomenon is observed at the bottom of the body and the lower spanwise vortex no longer forms while the flow over the slant remains attached.
KW - Ahmed body
KW - Aspect ratio
KW - Spectral POD
KW - Time-resolved PIV
KW - Trailing vortices
UR - http://www.scopus.com/inward/record.url?scp=85112822947&partnerID=8YFLogxK
U2 - 10.1016/j.expthermflusci.2021.110457
DO - 10.1016/j.expthermflusci.2021.110457
M3 - Article
AN - SCOPUS:85112822947
SN - 0894-1777
VL - 130
JO - Experimental Thermal and Fluid Science
JF - Experimental Thermal and Fluid Science
M1 - 110457
ER -