In my research, I use numerical simulations, theoretical analysis and experiments to investigate the physics of fluids.
Theoretical tools contribute to identify the relevance of the different parameters, yielding hence clear suggestions about the configurations to be analysed in the numerical simulations. The importance of wind-tunnel tests to verify the results of the theoretical analysis is also recognized. Therefore I also run experiments in collaborations with colleagues at KTH and abroad.

My current research interests are:

Master thesis project on stability and transition of Non-Newtonian fluids: send me an e-mail.
Master thesis project on Modeling of Bacteria Propagation in Water Distribution Lines: PDF


Deformable capsules in micro-devices

Numerical simulations of cell sorting device based on capsule deformability.

Bypass transition

Numerical simulations of bypass transition in boundary layers exposed to free-stream turbulence....

Transition delay with optimal streaks

Reducing skin friction is important in nature and in many technological applications. This reduction may be achieved by reducing stresses in turbulent boundary layers, for instance tailoring biomimetic rough skins. We take a second approach consisting of keeping the boundary layer laminar as long as possible by forcing small optimal vortices. Because of the highly non-normal nature of the underlying linearized operator, these vortices are highly amplified into large amplitude streaks that are able to modify the mean velocity profiles at leading order and act as a sort of `vaccination' of the boundary layer against viscous instabilities. Theoretical predictions and wind-tunnel experiments where this concept is implemented using small roughness elements show that by using this passive control technique it is possible to sensibly delay transition to turbulence.These findings prove that well designed roughness can stabilize the boundary layer. The theory has been developed in collaboration with LadHyX, Ecole Polytechnique while the experiments have been performed in the MTL wind-tunnel at KTH. Further studies are currently onging to demonstrate the range of applicability of this method to real world settings as airplanes, ships etc. and its relevance to the motion of aquatic animals.
To read about the media coverage of these findings take a look here!

Smoke flow visualizations from above with flow from left to right. (a) and (b) show the two-dimensional boundary layer, without streaks, with no excitation and with excitation of 201 mV, respectively. The flow in (b) is turbulent, (c) shows the streaky base flow with no excitation. In the presence of streaks with excitation of 450 mV (d), the flow remains laminar; (e) shows a half-streaky boundary layer obtained removing half the roughness elements and without forcing. With a forcing at 157 mV (f), the streaky part of the boundary layer remains laminar while the uncontrolled part undergoes transition. From Fransson, Talamelli, Brandt & Cossu (PRL, 2006).

Numerical simulations of transition delay when adding streamwise streaks of linearly incresing amplitude. See also Schlatter, Deusebio, DeLange & Brandt (Int. J. FLow Control, 2011).

More to come!