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

 

Energy efficiency and performance limitations of linear adaptive control for transition delay

Fabbiane, Bagheri & Henningson
J. Fluid Mech Vol 810, 2017

[Abstract] [Open Access]

 

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.

 

Passive control of a falling sphere by elliptic-shaped appendages

Lacis, Olivieri, Mazzino & Bagheri
ArXiv 1610.03601, 2016

[Abstract] [ArXiv]

 

Abstract. The majority of investigations characterizing the motion of single or multiple particles in fluid flows consider canonical body shapes, such as spheres, cylinders, discs, etc. However, protrusions on bodies -- being either as surface imperfections or appendages that serve a function -- are ubiquitous in both nature and applications. In this work, we characterize how the dynamics of a sphere with an axis-symmetric wake is modified in the presence of thin three-dimensional elliptic-shaped protrusions. By investigating a wide range of three-dimensional appendages with different aspect ratios and lengths, we clearly show that the sphere with an appendage may robustly undergo an inverted-pendulum-like (IPL) instability. This means that the position of the appendage placed behind the sphere and aligned with the free-stream direction is unstable, in a similar way that an inverted pendulum is unstable under gravity. Due to this instability, non-trivial forces are generated on the body, leading to turn and drift, if the body is free to fall under gravity. Moreover, we identify the aspect ratio and length of the appendage that induces the largest side force on the sphere, and therefore also the largest drift for a freely falling body. Finally, we explain the physical mechanisms behind these observations in the context of the IPL instability, i.e., the balance between surface area of the appendage exposed to reversed flow in the wake and the surface area of the appendage exposed to fast free-stream flow.

 

In‑flight active wave cancelation with delayed‑x‑LMS control algorithm in a laminar boundary layer

Simon, Fabbiane, Nemitz, Bagheri, Henningson & Grundmann
Exp. Fluids Vol 57:160, 2016

[Abstract] [Online PDF]

 

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.

 

Full list of papers

 

news

Selected as Wallenberg Academy Fellow

Wallenberg Academy Fellows is a carreer programme that provides long-term funding for the most promising young researchers of all disciplines to develop their projects.

[Link to Wallenberg Foundation]

 

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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