100 44 Stockholm
shervin (at) mech.kth.se
Osquars Backe 18
I'm an Associate Professor in fluid mechanics at the Royal Institute of Technology (KTH) and the Linné Flow Centre.
In my research, I try to understand and use physical principles that enable manipulation of fluid flows. I investigate both passive and active means to decrease drag, increase mixing or enhance lift on bodies. Much of my research involves finding appropriate models that enable systematic and efficient fluid flow control.
Simon, Fabbiane, Nemitz, Bagheri, Henningson & Grundmann
Exp. Fluids Vol 57:160, 2016
Abstract. This manuscript demonstrates the first successful application of the delayed-x-LMS (dxLMS) control algorithm for TS-wave cancelation. Active wave cancelation of two-dimensional broadband Tollmien–Schlichting (TS) disturbances is performed with a single DBD plasma actuator. The experiments are conducted in flight on the pressure side of a laminar flow wing glove, mounted on a manned glider. The stability properties of the controller are investigated in detail with experimental flight data, DNS and stability anal-ysis of the boundary layer. Finally, a model-free approach for dxLMS operation is introduced to operate the control-ler as a ‘black-box’ system, which automatically adjusts the controller settings based on a group speed measurement of the disturbance wave packets. The modified dxLMS control-ler is operated without a model and is able to adapt to vary-ing conditions that may occur during flight in atmosphere.
Lacis & Bagheri
ArXiv 1604.02880v1, 2016
Abstract. Interfacial boundary conditions determined from empirical or ad-hoc models remain the standard approach to model fluid flows over porous media, even in situations where the topology of the porous medium is known. We propose a non-empirical and accurate method to compute the effective boundary conditions at the interface between a porous surface and an overlying flow. Using multiscale expansion (homogenization) approach, we derive a tensorial generalized version of the empirical condition suggested by Beavers & Joseph (1967). The components of the tensors determining the effective slip velocity at the interface are obtained by solving a set of Stokes equations in a small computational domain near the interface containing both free flow and porous medium. Using the lid-driven cavity flow with a porous bed, we demonstrate that the derived boundary condition is accurate and robust by comparing an effective model to direct numerical simulations. Finally, we provide an open source code that solves the microscale problems and computes the velocity boundary condition without free parameters over any porous bed.
Natali, Pralits, Mazzino & Bagheri
J. Fluids and Structures. Vol 61, 2016
Abstract. A new way of handling, simultaneously, porosity and bending resistance of a massive filament is proposed. Our strategy extends the previous methods where porosity was taken into account in the absence of bending resistance of the structure and overcomes related numerical issues. The new strategy has been exploited to investigate how porosity affects the stability of slender elastic objects exposed to a uniform stream. To understand under which conditions porosity becomes important, we propose a simple resonance mechanism between a properly defined characteristic porous time-scale and the standard characteristic hydrodynamic time-scale. The resonance condition results in a critical value for the porosity above which porosity is important for the resulting filament flapping regime, otherwise its role can be considered of little importance. Our estimation for the critical value of the porosity is in fairly good agreement with our DNS results. The computations also allow us to quantitatively establish the stabilizing role of porosity in the flapping regimes
Read my comments in news article about how the bat uses hairs on its wing as sensors.
One week workshop on Modelling and control of combustion instabilities is organized by myself and Prof. Peter Schmid during 12-18 April 2015 , in Montestigliano, Italy Invited Keynote speaker this year is Prof. Aimee Morgans, Imperial College, London, UK. Deadline for application is 12 March.
How do appendages such as hair, feathers and plumes of an organism contribute to locomotion? In contrast to active mechanisms such flapping or undulating, passive mechanisms for locomotion are much harder to identify, since they have to extract energy from the surrounding fluid by exploiting instabilities. In a paper published in Nature Comm, we present a new fundamental mechanism for how passive appendages can aid locomotion.
Our experiments, computations and theoretical model establish that a body with a protrusion drifts to the right or left of the incoming stream of water or air. This phenomenon arises due to the nonlinear and many-degree-freedom interaction of the fluid and body, yet – as we uncover with a simple model – its physical mechanism is simple and intuitive. We all have an intuition for the inverted-pendulum instability from balancing a pen on our finger; the same instability occurs when a body moves in a fluid, but instead of a gravitational force, a pressure force behind a body provides the destabilizing conditions.
One week workshop on Radial Basis Function Methods for Scientific Computing is organized by myself and Prof. Peter Schmid during 12-19 April 2014 , in Montestigliano, Italy
About half-way in this popular science programme for children you can listen to my collegue Fredrik Lundell (in Swedish) explain vortices using my groups Soap Film Facility.
Here is a link to an interview (in Swedish) of me by Jesper Rönndahl in the popular science programme Institutet.
Please contact me, if you are interested in postdoctral position related to biological or mathematical fluid mechanics.
I was awared a prize of 500000 SEK from Göran Gustafsson stiftelse for young researchers.
I will co-organize a one month workshop on Stability and Transition May 6-31, 2013, in Stockholm
Here are links some of the media attention we got so far during 2013:
PhysOrg by Lisa Zyga (English)
Science Nordic by Ingrid Spilde (English)
Videnskab dk by Jeppe Wojcik (Danish)
NRK by Ingrid Spilde (Norwegian)
KTH by Peter Larsson (Swedish)