Experimental characterization of the unsteady natural wake of the full-scale square back Ahmed body: flow bi-stability and spectral analysis

Experimental characterization of the unsteady natural wake of the full-scale square back Ahmed... In recent years, the increasing interest in reducing the aerodynamic drag of vehicles, such as station wagons, minivans or buses, has led research to focus on the characterization of square back bluff geometries. In this paper, the results of an extensive experimental campaign on the full-scale well-known body of Ahmed et al. (1984) are presented, for two height-based Reynolds numbers, $$Re_{\rm H} = 5.1 \times 10^5$$ R e H = 5.1 × 10 5 and $$7.7 \times 10^5$$ 7.7 × 10 5 . Eighty-one measurement points were used to map the base pressure field, while the wake topology was investigated by means of a series of ten 2D Particle Image Velocimetry planes. These measurements clearly show that the wake presents a bi-stable behavior, characterized by a random succession of switches between two well-defined mutually symmetric configurations, confirming the results from Grandemange et al. (J Fluid Mech 722:51–84, 2013b. doi: 10.1017/jfm.2013.83 ) for the same model. For the presented results, the timescale of this phenomenon is of the order of $$800 \, V_{\infty} / H$$ 800 V ∞ / H . The sensitivity of the bi-stability to the yaw angle was also investigated, and considerations on how to take such a behavior into account in post-processing this kind of field are given. High-frequency measurements were also carried out with four piezoelectric transducers and a synchronized two-component hot-wire. The results show a low-frequency spectral activity: peaks at $$St_{\rm H} = 0.13$$ S t H = 0.13 and 0.19, corresponding to vortex shedding modes, were found on the lateral base pressures and in the far wake, whereas a signature at $$St_{\rm H} = 0.08$$ S t H = 0.08 was visible on the vertical base centerline and in the recirculation bubble shear layer. Correlation analysis and proper orthogonal decomposition confirm the interpretation of the latter mode as the pumping of the recirculation bubble. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Experiments in Fluids Springer Journals

Experimental characterization of the unsteady natural wake of the full-scale square back Ahmed body: flow bi-stability and spectral analysis

Loading next page...
Springer Berlin Heidelberg
Copyright © 2015 by Springer-Verlag Berlin Heidelberg
Engineering; Engineering Fluid Dynamics; Fluid- and Aerodynamics; Engineering Thermodynamics, Heat and Mass Transfer
Publisher site
See Article on Publisher Site


You’re reading a free preview. Subscribe to read the entire article.

DeepDyve is your
personal research library

It’s your single place to instantly
discover and read the research
that matters to you.

Enjoy affordable access to
over 12 million articles from more than
10,000 peer-reviewed journals.

All for just $49/month

Explore the DeepDyve Library

Unlimited reading

Read as many articles as you need. Full articles with original layout, charts and figures. Read online, from anywhere.

Stay up to date

Keep up with your field with Personalized Recommendations and Follow Journals to get automatic updates.

Organize your research

It’s easy to organize your research with our built-in tools.

Your journals are on DeepDyve

Read from thousands of the leading scholarly journals from SpringerNature, Elsevier, Wiley-Blackwell, Oxford University Press and more.

All the latest content is available, no embargo periods.

See the journals in your area

Monthly Plan

  • Read unlimited articles
  • Personalized recommendations
  • No expiration
  • Print 20 pages per month
  • 20% off on PDF purchases
  • Organize your research
  • Get updates on your journals and topic searches


Start Free Trial

14-day Free Trial

Best Deal — 39% off

Annual Plan

  • All the features of the Professional Plan, but for 39% off!
  • Billed annually
  • No expiration
  • For the normal price of 10 articles elsewhere, you get one full year of unlimited access to articles.



billed annually
Start Free Trial

14-day Free Trial