Journal of Fluid Mechanics

Papers

Nonlinear dynamics and synthetic-jet-based control of a canonical separated flow

RUPESH B. KOTAPATIa1 p1, RAJAT MITTALa1 c1, OLAF MARXENa2, FRANK HAMa2, DONGHYUN YOUa3 and LOUIS N. CATTAFESTA IIIa4

a1 Department of Mechanical and Aerospace Engineering, The George Washington University, Washington, DC 20052, USA

a2 Centre for Turbulence Research, Stanford University, Stanford, CA 94305, USA

a3 Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA

a4 Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611, USA

Abstract

A novel flow configuration devised for investigation of active control of separated airfoil flows using synthetic jets is presented. The configuration consists of a flat plate, with an elliptic leading edge and a blunt trailing edge, at zero incidence in a free stream. Flow separation is induced on the upper surface of the airfoil at the aft-chord location by applying suction and blowing on the top boundary of the computational domain. Typical separated airfoil flows are generally characterized by at least three distinct frequency scales corresponding to the shear layer instability, the unsteadiness of the separated region and the vortex shedding in the wake, and all these features are present in the current flow. Two-dimensional Navier–Stokes simulations of this flow at a chord Reynolds number of 6 × 104 have been carried out to examine the nonlinear dynamics in this flow and its implications for synthetic-jet-based separation control. The results show that there is a strong nonlinear coupling between the various features of the flow, and that the uncontrolled as well as the forced flow is characterized by a variety of ‘lock-on’ states that result from this nonlinear coupling. The most effective separation control is found to occur at the highest forcing frequency for which both the shear layer and the separated region lock on to the forcing frequency. The effects of the Reynolds number on the scaling of the characteristic frequencies of the separated flow and its subsequent control are studied by repeating some of the simulations at a higher Reynolds number of 1 × 105.

(Received January 13 2009)

(Revised January 22 2010)

(Accepted January 23 2010)

(Online publication May 11 2010)

Correspondence:

c1 Present address: Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD 21218, USA. Email address for correspondence: mittal@jhu.edu

p1 Present address: Exa Corporation, 55 Network Drive, Burlington, MA 01803, USA.

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