Bojan Vukasinovic							home page

High-Frequency Flow Control

Traditional approach to the control of shear layer, and separated flows in general, has been focused on the manipulation of global motions that are induced by the fundamental instability modes. However, high-frequency control, where the control frequency is substantially higher than the fundamental (natural) flow frequencies, has recently emerged as a successful control tool for numerous applications related to the mixing enhancement, separation delay, mitigation of optical aberrations, noise suppression, etc. The high-frequency control directly excites the small-scale motions that subsequently alter energy distribution across a wide range of scales.

Bluff Body - Turret

model schematics

Flow separation off an airborne bluff-body turret (hemispherical cap elevated on a matching cylinder) can adversely affect optical transmission, and induce excess dynamic loads and structural vibrations. The present work demonstrates the effectiveness of active flow control in mitigation of undesirable effects via flow-separation delay and direct broadband suppression of turbulent motions, particularly those of the energy-bearing, large-scale structures. An alternate approach that leads to “regularization” of the shedding structures is also explored.

REFERENCE

Vukasinovic, B. and Glezer, A., Control of a Separating Flow over a Turret, AIAA Paper 2007-4506.


Axisymmetric Body of Revolution

model schematics

This investigation focuses on fluidic actuation of the wake behind a wind tunnel model of an axisymmetric bluff body. The aerodynamic forces and moments on the model are altered by induced local attachment and vectoring of the separated base flow. Such segmented alteration of the base flow induces asymmetric aerodynamic forces and moments, which can be used for maneuvering during flight. Both quasi-steady and transitory aerodynamic effects are studied.

REFERENCE

Abramson, P, Rinehart, C., Vukasinovic, B., and Glezer, A., Fluidic Control of Aerodynamic Forces on a Body of Revolution, AIAA Paper 2007-4505.


Surface-Mounted Hemisphere

model schematics

The flow over a hemisphere presents challenges to separation control beyond those associated with the separation behind two-dimensional aerodynamic surfaces. Locally, the development of a shear layer at the origin of a separated region is subject to the same instability considerations as that in a two-dimensional flow. The three-dimensional geometry of the surface, which curves not only in the streamwise but also in the lateral direction, subjects the developing spanwise vorticity lines to distortion that makes the overall separation region fairly complex. The present work draws on previous experience with the application of high-frequency control to explore the response of the separated region behind a hemisphere to various control strategies, including both pure high-frequency and concomitant low- and high-frequency control.

REFERENCES

Vukasinovic, B., Glezer, A., Gordeyev, S., Jumper, E., and Kibens, V., Active Control and Optical Diagnostics of the Flow over a Hemispherical Turret, AIAA Paper 2008-598.

Vukasinovic, B., Brzozowski, D., Glezer, A., Bower, W. W., and Kibens, V., Separation Control over a Surface-Mounted Hemispherical Shell, AIAA Paper 2005-4878.

Planar Shear Layer

schematics The effects of high-frequency fluidic actuation on the evolution of small- and large-scale motions in a turbulent shear layer downstream of a backward-facing step are investigated experimentally. The flow behind the step is characterized in the spatial and spectral domain by high-resolution diagnostic tools. The actuation is applied either as a pure harmonic or amplitude-modulated high-frequency signal, which enhances either direct small-scale motions or both large- and small-scale motions, respectively.

REFERENCES

Vukasinovic, B., Glezer, A., and Rusak, Z., Experimental and Numerical Investigation of Controlled, Small-Scale Motions in a Turbulent Shear Layer, Proc. 3rdInternational Symposium on Integrating CFD and Experiments, USAFA, June 20-21, 2007.

Vukasinovic, B. and Glezer, A., Transitory Fluidic Control of Turbulent Shear Flows, AIAA Paper 2006-3227.

Vukasinovic, B., Lucas, D. G., and Glezer, A., Controlled Manipulation of Small- and Large-Scales in a Turbulent Shear Layer, Part I: Experimental Studies, AIAA Paper 2005-4753.

Vukasinovic, B., Lucas, D. G., and Glezer, A., Direct Manipulation of Small-Scale Motions in a Plane Shear Layer, AIAA Paper 2004-2617.