Bluff body drag manipulation using pulsed jets and Coanda effect

The impact of fluidic actuation on the wake and drag of a three-dimensional blunt body is investigated experimentally. Jets blowing tangentially to the main flow force the wake with variable frequency and amplitude. Depending on the forcing conditions, two flow regimes can be distinguished. First, i...

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Bibliographic Details
Published in:Journal of fluid mechanics 2016-10, Vol.805, p.422-459
Main Authors: Barros, Diogo, Borée, Jacques, Noack, Bernd R., Spohn, Andreas, Ruiz, Tony
Format: Article
Language:English
Subjects:
Actuation
Aerodynamics
Base pressure
Blowing pressure
Boats
Broadband
Coanda effect
Computational fluid dynamics
Convection
Deviation
Drag
Dynamics
Entrainment
Fluid flow
Jets
Kinetic energy
Momentum
Pressure
Pressure recovery
Sleep and wakefulness
Three dimensional bodies
Turbulence
Vehicles
Velocity
Vortices
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Summary:The impact of fluidic actuation on the wake and drag of a three-dimensional blunt body is investigated experimentally. Jets blowing tangentially to the main flow force the wake with variable frequency and amplitude. Depending on the forcing conditions, two flow regimes can be distinguished. First, in the case of broadband actuation with frequencies comprising the natural wake time scale, the convection of the jet structures enhances wake entrainment, shortens the length of the recirculating flow and increases drag. Secondly, at higher actuation frequencies, shear-layer deviation leads to fluidic boat tailing of the wake. It additionally lowers its turbulent kinetic energy thus reducing the entrainment of momentum towards the recirculating flow. The combination of both mechanisms produces a rise in the base pressure and reduces the drag of the model. Both actuation regimes are characterized by complementary velocity, pressure and drag measurements at several upstream conditions and control parameters. By adding curved surfaces to deviate the jets by the Coanda effect, periodic actuation is reinforced and drag reductions of approximately 20 % are achieved. The unsteady Coanda blowing not only intensifies the flow deviation and the base pressure recovery but also preserves the unsteady high-frequency forcing effect on the turbulent field. The present results encourage further development of fluidic control to improve the aerodynamics of road vehicles and provide a complementary insight into the relation between wake dynamics and drag.
ISSN:0022-1120
1469-7645
DOI:10.1017/jfm.2016.508