Shervin Bagheri

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contact
KTH Mechanics
100 44 Stockholm
Sweden
shervin (at) mech.kth.se
+46(0)8-790 6770

visiting adress
Room: 2718
Osquars Backe 18
Stockholm

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.

 

recent papers

 

Stabilizing effect of porosity on a flapping filament

Natali, Pralits, Mazzino & Bagheri
J. Fluids and Structures. Vol 61, 2016

[Abstract] [doi] [PDF]

 

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

 

A stable fluid-structure-interaction solver for low-density rigid bodies using the immersed boundary projection method

Lacis, Taira & Bagheri
J. Comp. Phys. vol. 305, 2015

[Abstract] [arXiv] [doi]

 

Abstract. Dispersion of low-density rigid particles with complex geometries is ubiquitous in both natural and industrial environments. We show that while explicit methods for coupling the incompressible Navier-Stokes equations and Newton's equations of motion are often sufficient to solve for the motion of cylindrical particles with low density ratios, for more complex particles - such as a body with a protrusion - they become unstable. We present an implicit formulation of the coupling between rigid body dynamics and fluid dynamics within the framework of the immersed boundary projection method. Similar to previous work on this method, the resulting matrix equation in the present approach is solved using a block-LU decomposition. Each step of the block-LU decomposition is modified to incorporate the rigid body dynamics. We show that our method achieves second-order accuracy in space and first-order in time (third-order for practical settings), only with a small additional computational cost to the original method. Our implicit coupling yields stable solution for density ratios as low as $10^{-4}$. We also consider the influence of fictitious fluid located inside the rigid bodies on the accuracy and stability of our method.

 

Experimental study of a three dimensional cylinder-filament system

Brosse, Finmo, Lundell & Bagheri
Exp. Fluids 56:130 2015

[Abstract] [PDF (Pre-print)] [doi]

 

Abstract. This experimental study reports on the behavior of a filament attached to the rear of a three-dimensional cylinder. The axis of the cylinder is placed normal to a uniform incoming flow and the filament is free to move in the cylinder wake. The mean position of the filament is studied as a function of the filament length L. It is found that for long (L/D > 6.5, where D is the cylinder diameter) and short (L/D < 2) filaments the mean position of the filament tends to align with the incoming flow, whereas for intermediate filament lengths (2 < L/D < 6.5) the filament lies down on the cylinder and tends to align with the cylinder axis. The underlying mechanism of the bifurcations are discussed and related to buckling and inverted-pendulum-like instabilities.

 

Full list of papers

 

news

Appearence in an article in SVT vetenskap

Read my comments in news article about how the bat uses hairs on its wing as sensors.

[Link to article]

 

Ercoftac Montestigliano Spring School 2015

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.

[Workshop home page]

 

Paper published in Nature Communications

 

Nicolo Nicolo Nicolo

 

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.

 

Montestigliano workshop 2014

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

[Workshop home page]

 

Appearence in Swedish Television (SVT, Hjärnkontoret)

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.

[Hjärnkontoret].

 

Interview in Swedish national radio (SR P3)

Here is a link to an interview (in Swedish) of me by Jesper Rönndahl in the popular science programme Institutet.

[Pod file]

 

Postdoctoral fellowship 2013

Please contact me, if you are interested in postdoctral position related to biological or mathematical fluid mechanics.

 

Winner of Göran Gustafsson prize 2013

I was awared a prize of 500000 SEK from Göran Gustafsson stiftelse for young researchers.

 

Nordita workshop in Stability and Transition 2013

I will co-organize a one month workshop on Stability and Transition May 6-31, 2013, in Stockholm

[Workshop home page]

 

Media coverage 2013

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)

 

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