On three-dimensional bluff body wake symmetry breaking with free-stream turbulence and residual asymmetry

The influence of background turbulence on Ahmed-body wake bistability

“…In comparison with other studies, these rates are close to those of Grandemange et al (2013a), who found a rate of St N = 6.7 × 10 −4 , whereas they are lower than in Cadot et al (2020) who found a rate of St N = 7.2 × 10 −3 and St N = 5.7 × 10 −3 , for low and high (6 %) turbulence, respectively. The differences in the sensitivity to turbulence in our results to those of Cadot et al (2020) may be caused by a number of factors, which require future attention, including the baseline (low-turbulence) switching rate in each study, the turbulence range (we note that the change in switching rate is least obvious over low-turbulence ranges), Reynolds number (as turbulence may interfere with upstream flow structures, e.g. separated flow at the nose), the approach to identification of a switching event, and other set-up differences.…”

“…Finally, a comparison with the recent experimental study of Cadot et al (2020) is warranted, where they conclude that turbulence does not enhance the switching rate. Despite their different conclusion, our switching rate data are only weakly contradictory with theirs.…”

“…Re H I x (%) Yaw (deg.) Geometry Grandemange et al (2013a) 3 .3 × 10 4 0.5 0 a Grandemange et al (2013b) 9 .2 × 10 4 < 0.3 0 a Cadot et al (2015) 1 .7 × 10 4 -1.6 × 10 5 < 0.3 [ −1, 1] a Volpe et al (2015) 5 .1 × 10 5 , 7.7 × 10 5 < 0.4 0, −0.4, −1, −2 a Brackston et al (2016) 1 .1 × 10 6 -2.0 × 10 6 < 0.1 0 a Cadot et al (2020) 3 .14 × 10 6 1.8 to 5.6 [−2, 2] a Herry et al (2011) 5 .0 × 10 3 -8.0 × 10 4 0.6 0 b Yan et al (2019) 2 .4 × 10 5 < 0.5 0 c Pavia, Passmore & Sardu (2018) 7 .7 × 10 5 0.2 0, 0.6 d Bonnavion et al (2017) 2 .5 × 10 6 0.4 [−10, 10] e Bonnavion et al (2017) 3 .14 × 10 6 0.4 [−8, 8] f bistability may also exist, depending upon aspect ratio, ground clearance and underbody conditions (Grandemange, Gohlke & Cadot 2013a). This bistability, including the reflectional axis (either horizontal or vertical) has subsequently been observed to be sensitive to external flow conditions, including geometric configuration (Herry et al 2011;Grandemange et al 2013a), yaw angle (Volpe, Devinant & Kourta 2015) and free-stream Reynolds number (Grandemange, Gohlke & Cadot 2013b).…”

“…The test conditions of some previous studies are listed in table 1. An exception is a study by Cadot et al (2020), which compared the switching rate for two turbulence levels (∼2 % and 6 %) and found the bistability present in both cases with a slight decrease in the switching rate for higher turbulence; this was related to a postulated increase in boundary-layer thickness on the body.…”

Low-order modelling of the wake dynamics of an Ahmed body

“…2015; Cadot et al. 2020) and can be successfully modelled using a Langevin equation as first introduced by Rigas et al. (2014, 2015).…”