ONGOING ACTIVITIES

There is a wealth of ongoing activities, both of experimental and numerical nature. In terms of turbulent drag reduction, we are consolidating and further developing the technique known as the streamwise-traveling waves. We are steadily increasing its TRL by investigating real-world effects (for example a physical actuator would produce a non-ideal forcing whose effects need to be assessed) and collaborating with research groups abroad towards developing better and more efficient actuators. Our experimental test rig with the rotating pipe is being upgraded with a specially built probe to measure within the bulk of the moving section and to help us improve our understanding of the physics of drag reduction. On the same setup we are also preparing the experimental realization of another interesting flow control technique for drag reduction (traveling waves of peristaltic motion) thanks to a recent FARB grant. We have also very recently put in production a new and unique solver especially suited for the DNS of turbulent pipe flow to compare with experiments.
At the same time, we are widening the scope of our research. In this respect we are exploring both new fields (e.g. microfluidics, porous materials) where our expertise could be leveraged, and new techniques (e.g. adjoint calculations as used in industrial problems) to deploy in such fields. This recent activity started some time ago and we are still narrowing down the list of possible options.
Mostly on the experimental side, we are also developing corona and DBD plasma actuators.
One research theme is particularly hot: we have recently introduced,within an international collaboration with Germany and Japan, an interesting new concept that helps setting up the flow control problem in general, and that we name the Money-vs-Time concept. Significant further work is awaiting us, and a few days ago we have just made public our new concept of running a fluidic system under constant power input (CPI), with extremely positive feedback and encouragement from the community.
Stability-related ongoing studies concern attempts to control global instabilities on bluff-body geometries of industrial interest; to enhance natural instabilities in the flow to the purpose of energy harvesting; to verify where some turbulent drag reduction concepts are also valid for transition delay. We expect stability and flow control studies to integrate even more tightly in the coming years.

FUTURE PLANS

In the next 3 years, we will obviously continue on examining real-world effects for traveling waves (and similar open-loop techniques), with regard to their spatial discretization. Most importantly, we will try to understand how the performance at low Re are modified at higher Re. It is well possible that such results will be universal and thus of benefit to a much larger scientific community.
We are also initiating a serious work on porosity. We are developing tools for studying the flow over a porous wall (either stability or DNS) and we are also planning some experiments with a bluff body. One of the aims is to trial the way blowing and suction (a very common way of controlling the flow, particularly in numerical simulations) is typically represented. The expected impact of the results is large.
The Money-vs-Time approach, and the CPI concept for running simulations of fluid flows, are very general concepts that probably apply to a wide range of problems (first example we are considering now is stenotic flow in arteries). In the context of flow control, we will systematically try to use the CPI concept to make clear-cut comparisons of the various flow control techniques in order to unequivocally establish the promising ones and discard the others, something that only CPI can provide.
While the usability of adjoint techniques as an optimization tool in applications will be further investigated, a new research line is opening about the impact of heat transfer and fluid-structure interaction on the stability of low-Reynolds-number flows. Another research field deals with flow-plasma interactions: non-conventional corona actuators, DBD and sliding discharge devices will be tested in order to assess their capabilities and limits in flow control applications. Among the feasible applications, it is worth mentioning the dynamic stall control implementable on a helicopter rotor model.

ERC KEYWORDS

• PE1-19 Control theory and optimization
• PE3-14 Fluid Dynamics (physics)
• PE8-4 Computational Engineering
• PE8-1 Aerospace Engineering

FREE KEYWORDS

• Turbulent flows
• Flow instability and transition