Open and closed-loop experiments to identify the separated flow dynamics of a thick turbulent boundary layer

Open and closed-loop experiments to identify the separated flow dynamics of a thick turbulent... Open and closed-loop flow control experiments were performed on the transient attachment and separation mechanisms of a thick turbulent boundary layer (TBL). Without actuation, the TBL is subjected to an adverse pressure gradient and separates downstream of a sharp variation in the wall geometry. Departing from a given geometry and steady operations of vortex generator actuators, the control objective was to attach the flow in the separated region with a minimum of injected fluid using adaptation of the closed-loop control. The large scale of the facility (i.e., δ = 20 cm upstream of separation) induces large time scales and large Reynolds numbers of the flow to be controlled. It is found to consequently induce large time scales of the separation/attachment mechanisms, making the dynamic closed-loop implementation easier. Open-loop tests were first performed to extract the adequate input/output variables for closed-loop implementations. The chosen input variable was the Duty Cycle, DC, which enables sending of a control action at least 10 times faster than the time scales of the attachment/separation process. The chosen output variable was the voltage signal from a hot-film probe located on the flap which characterizes the degree of separation. In open loop, both the large scale (i.e., large time scales) of the present facility (Carlier and Stanislas in J Fluid Mech 535(36):143–188, 2005) and the well-defined excitation (Braud and Dyment in Phys Fluids 24:047102, 2012) help to extract the different time scales involved and to identify the whole system (actuators, baseline flow and sensor). Three Reynolds numbers based on the momentum thickness of the boundary layer near the actuators and upstream of separation were investigated (Re θ  = 7,500, 10,500 and 12,600) through variation of the free-stream velocity (U ∞ = 5, 8, 10 m/s). These three systems were found to behave like first-order linear systems, with coefficients that need to be adapted depending on the Reynolds number. From Re θ  = 7,500 to Re θ  = 12, 600, the time scale and static gain of the linear system needed to be almost doubled. A simple controller (Proportional-Integral) was implemented in closed-loop configuration, improving the reactivity of the system. Robustness was tested by varying the free-stream velocity. Closed-loop control based on a fixed reference was unsuccessful as it failed to account for the effect of the Reynolds number. This was successfully overcome by tracking a given state of the flow using a simple P controller to adapt the reference according to variations of Re. The P controller, acting on the DC variable, compensates the corresponding variations of VR (ratio between the free-stream and the jet exit velocity). Experiments in Fluids Springer Journals

Open and closed-loop experiments to identify the separated flow dynamics of a thick turbulent boundary layer

Loading next page...
Copyright © 2013 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