Feedback control for drag reduction on a bluff body with a blunt trailing edge

2011 ◽  
Author(s):  
Jeremy Dahan ◽  
Aimee Morgans ◽  
Sylvain Lardeau
Keyword(s):  
Feedback Control ◽  
Drag Reduction ◽  
Bluff Body ◽  
Trailing Edge ◽  
Blunt Trailing Edge

Drag reduction in flow over a two-dimensional bluff body with a blunt trailing edge using a new passive device

2006 ◽  
Vol 563 ◽  
pp. 389 ◽  
Author(s):  
HYUNGMIN PARK ◽  
DONGKON LEE ◽  
WOO-PYUNG JEON ◽  
SEONGHYEON HAHN ◽  
JEONGLAE KIM ◽  
...  
Keyword(s):  
Drag Reduction ◽  
Bluff Body ◽  
Two Dimensional ◽  
Trailing Edge ◽  
Passive Device ◽  
Blunt Trailing Edge

A study of three-dimensional aspects of vortex shedding from a bluff body with a mild geometric disturbance

1997 ◽  
Vol 330 ◽  
pp. 85-112 ◽  
Author(s):  
N. TOMBAZIS ◽  
P. W. BEARMAN
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Bluff Body ◽  
Vortex Formation ◽  
Three Dimensional ◽  
Base Pressure ◽  
Trailing Edge ◽  
Blunt Trailing Edge ◽  
Trailing Edges ◽  
Mode Transitions

Experiments have been carried out to study the three-dimensional characteristics of vortex shedding from a half-ellipse shape with a blunt trailing edge. In order to control the occurrence of vortex dislocations, the trailing edges of the models used were constructed with a series of periodic waves across their spans. Flow visualization was carried out in a water tunnel at a Reynolds number of 2500, based on trailing-edge thickness. A number of shedding modes were observed and the sequence of mode transitions recorded. Quantitative data were obtained from wind tunnel measurements performed at a Reynolds number of 40000. Two shedding frequencies were recorded with the higher frequency occurring at spanwise positions coinciding with minima in the chord. At these same positions the base pressure was lowest and the vortex formation length longest. Arguments are put forward to explain these observations. It is shown that the concept of a universal Strouhal number holds, even when the flow is three-dimensional. The spanwise variation in time-average base pressure is predicted using the estimated amount of time the flow spends at the two shedding frequencies.

Feedback Control Using Extremum Seeking Method for Drag Reduction of a 3D Bluff Body

2008 ◽  
pp. 365-372 ◽  
Author(s):  
Jean-François Beaudoin ◽  
Olivier Cadot ◽  
José Eduardo Wesfreid ◽  
Jean-Luc Aider
Keyword(s):  
Feedback Control ◽  
Drag Reduction ◽  
Bluff Body ◽  
Extremum Seeking

scholarly journals Gross separation approaching a blunt trailing edge as the turbulence intensity increases

2014 ◽  
Vol 372 (2020) ◽  
pp. 20140001 ◽  
Author(s):  
B Scheichl
Keyword(s):  
Turbulence Intensity ◽  
Bluff Body ◽  
Core Layer ◽  
Intensity Level ◽  
Trailing Edge ◽  
Developed Turbulence ◽  
Blunt Trailing Edge ◽  
Attached Flow ◽  
The One ◽  
Massive Separation

A novel rational description of incompressible two-dimensional time-mean turbulent boundary layer (BL) flow separating from a bluff body at an arbitrarily large globally formed Reynolds number, Re , is devised. Partly in contrast to and partly complementing previous approaches, it predicts a pronounced delay of massive separation as the turbulence intensity level increases. This is bounded from above by a weakly decaying Re -dependent gauge function (hence, the BL approximation stays intact locally), and thus the finite intensity level characterizing fully developed turbulence. However, it by far exceeds the moderate level found in a preceding study which copes with the associated moderate delay of separation. Thus, the present analysis bridges this self-consistent and another forerunner theory, proposing extremely retarded separation by anticipating a fully attached external potential flow. Specifically, it is shown upon formulation of a respective distinguished limit at which rate the separation point and the attached-flow trailing edge collapse as and how on a short streamwise scale the typical small velocity deficit in the core region of the incident BL evolves to a large one. Hence, at its base, the separating velocity profile varies generically with the one-third power of the wall distance, and the classical triple-deck problem describing local viscous–inviscid interaction crucial for moderately retarded separation is superseded by a Rayleigh problem, governing separation of that core layer. Its targeted solution proves vital for understanding the separation process more close to the wall. Most importantly, the analysis does not resort to any specific turbulence closure. A first comparison with the available experimentally found positions of separation for the canonical flow past a circular cylinder is encouraging.

scholarly journals Feedback control for form-drag reduction on a bluff body with a blunt trailing edge

2012 ◽  
Vol 704 ◽  
pp. 360-387 ◽  
Author(s):  
Jeremy A. Dahan ◽  
A. S. Morgans ◽  
S. Lardeau
Keyword(s):  
Feedback Control ◽  
Drag Reduction ◽  
Bluff Body ◽  
Numerical Study ◽  
Pressure Fluctuations ◽  
Open Loop ◽  
Base Pressure ◽  
Disturbance Attenuation ◽  
Linear Feedback ◽  
Backward Facing Step

AbstractThe objective of this numerical study is to increase the base pressure on a backward-facing step via linear feedback control, to be ultimately translated to a drag reduction on a blunt-based bluff body. Two backward-facing step cases are simulated: a laminar two-dimensional (2D) flow at a Reynolds number of ${\mathit{Re}}_{\theta } = 280$, and a turbulent three-dimensional (3D) flow at ${\mathit{Re}}_{\theta } = 1500$ using large-eddy simulation. The control is effected by a full-span slot jet with zero-net-mass-flux, and two jet locations are examined. Linear system identification is performed to characterize the flow response to actuation, used to synthesize a control law. The control strategy is based on the premise that an attenuation of the instantaneous pressure fluctuations on the base of the step should lead to an increase in the time-averaged base pressure. Open-loop harmonic forcing is examined within a broad frequency range for both the 2D and 3D flows, which are found to respond differently to actuation. The controllers based on disturbance attenuation lead to sensible increases in base pressure (up to 70 % in 2D and 20 % in 3D) with higher efficiency than the best results achieved in open-loop. The results support the conjecture about the link between the base pressure fluctuations and mean, although it is shown that such a black-box model approach is not suitable for optimization without further physical insight.

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