Active Flow Control

Active Flow Control

With the term "Active Flow Control" (AFC), which could also be described as a "flow manipulation", we summarize methods that can influence a flow field or an aerodynamic body in a desired way. Although many methods of  passive flow manipulation are known -- in particular to give the aerodynamic body a suitable shape -- these methods are sometimes limited and active flow control -- where additional energy is utilized to actively modify the flow field -- is eventually more versatile.

In our working group we research different methods of active flow control, which may serve to lower the drag, increase the lift and/or the maximum lift and thus increase the overall efficiency of aerodynamic bodies, such as aircraft, spacecraft or road vehicles.

 

Winglet
A scaled model of a wing tip extension ("Winglet") in the wind tunnel MUB. The region, where the slat has ended, but the wing is still not bending upwards, is particularly prone to separations. Therefore, in this model, different rows of vortex generating jets (VGJs) are implemented in this region to delay the separations, incrase lift and reduce drag
beispiel3
A "Swept-Constant-Chord" model with active flow control in the wind tunnel DNW-NWB. In this test entry several different methods of active flow control with fluidic actuation were tested. All methods serve to delay turbulent separation and contribute to an additional lift, such that the final maximum lift is larger compared to a "clean" wing.

In most cases we utilize fluidic energy for active flow control. Typically by generating wall jets ("tangential blowing"), by generating longitudinal vortices with small fluidic jets ("vortex generating jets") or by directy blowing or sucking air through porous sheets into/out-of laminar or turbulent boundary layers.

 

DES-Simulation von VGJs
Visualization of results of a DES-Simulation of "Vortex generating Jets" (VGJs) embedded in a turbulent boundary layer flow.

Selected References

RADESPIEL, R., BURNAZZI, M., CASPER, M., SCHOLZ, P., Active flow control for high lift with steady blowing, The Aeronautical Journal, Vol. 120, Special Issue 1223, S. 171-200, 2016, doi:10.1017/aer.2015.7

SUN, S., EILTS, P., HAUBOLD, S., SCHOLZ, P. Active Control of Cylinder Charge Motion Using Vortex Generating Jets on Generic Intake Port Geometries, SAE Journal of Engines, Vol. 11, Nr. 4, 2018, doi: 10.4271/03-11-04-0032

SCHOLZ, P., SINGH, V.M., GEBHARDT, A., LÖFFLER, S., WEISS, J., The Efficiency of Different Flow Control Methods on a Vertical Tail, AIAA 2020-1537, AIAA Scitech 2020, 6.-10, Jan. 2020, Orlando, USA, doi: 10.2514/6.2020-1537