<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body style="overflow-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;"><div style="font-family: HelveticaNeue;"><font face="HelveticaNeue">Dear Soft Matter & Complex Systems Colleagues and Friends,</font></div><div style="font-family: HelveticaNeue;"><font face="HelveticaNeue"><br></font></div><div><div style="font-family: HelveticaNeue;"><font face="HelveticaNeue">In a fortunate turn of events, we have secured a new speaker for the seminar. </font></div><div style="font-family: HelveticaNeue;"><font face="HelveticaNeue">On Friday 13 December 2024 at 9:30 AM at the UW Faculty of Physics (Pasteura 5, Warsaw; room 1.40) we are hosting a seminar during which </font></div><div style="font-family: HelveticaNeue;"><font face="HelveticaNeue"><br></font></div><div style="font-family: HelveticaNeue; margin: 0px; font-stretch: normal; line-height: normal; min-height: 14px;"><font face="HelveticaNeue"><b>Reinier van Buel</b></font><font face="HelveticaNeue"><b> </b></font><font face="HelveticaNeue">(FUW</font><font face="HelveticaNeue">)</font></div><div style="font-family: HelveticaNeue; margin: 0px; font-stretch: normal; line-height: normal; min-height: 14px;"><font face="HelveticaNeue"><br></font></div><div style="font-family: HelveticaNeue; margin: 0px; font-stretch: normal; line-height: normal;"><font face="HelveticaNeue">will give a talk</font></div><div style="margin: 0px; font-stretch: normal; line-height: normal; min-height: 14px;"><div><h2 style="margin: 6px 0px 12px; padding: 0px;"><font face="HelveticaNeue"><span style="font-size: 12px;">Active and passive control of elastic turbulence at low Reynolds numbers</span></font></h2></div><h2 style="font-family: HelveticaNeue; margin: 6px 0px 12px; padding: 0px; caret-color: rgb(68, 68, 68);"><b><font face="HelveticaNeue" style="font-size: 12px;">Abstract</font></b></h2><div><font face="HelveticaNeue">Elastic turbulence, a chaotic flow state occurring in viscoelastic fluids at negligible Reynolds numbers, enhances fluid mixing on small scales, making it valuable for applications like lab-on-a-chip devices. Here, we show the influence of active and passive control on elastic turbulence using numerical simulations of the Oldroyd-B model in OpenFOAM®. In a two-dimensional Taylor-Couette geometry, the onset of elastic turbulence is characterised by a critical Weissenberg number, marking a transition from laminar to turbulent flow. Flow resistance and secondary-flow strength, serving as order parameters, increase with turbulence, correlating strongly with enhanced fluid mixing. Power-law scaling of velocity fluctuations aligns with experimental results, confirming the turbulent nature of the flow. Active control, implemented through imposed shear-rate modulations, shows promise for managing turbulence. Slow modulations induce complex behaviours, while fast modulations suppress turbulence. The state diagram of Weissenberg and Deborah numbers highlights the transition to turbulence and suggests an effective critical Weissenberg number to approximate the transition line. In three-dimensional von Kármán flow, elastic turbulence exhibits a subcritical transition, marked by bistable behaviour and hysteresis. Flow resistance and order parameters increase significantly, confirming turbulence. Active control applied here reduces turbulence and relaminarises the flow, mirroring results from the Taylor-Couette system. These findings underscore the potential of controlling elastic turbulence to optimise fluid mixing and stability in viscoelastic systems.</font></div><div style="font-family: HelveticaNeue;"><br></div></div><div style="font-family: HelveticaNeue; margin: 0px; font-stretch: normal; line-height: normal;"><font face="HelveticaNeue">We warmly welcome everyone to attend the talk and the Soft Matter Coffee Break after the seminar, held in room 2.63 (2nd floor).</font></div></div><div style="font-family: HelveticaNeue;"><font face="HelveticaNeue"><br></font></div><div style="font-family: HelveticaNeue;"><div dir="auto" style="overflow-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;"><div style="margin: 0px; font-stretch: normal; line-height: normal;"><font face="HelveticaNeue">Maria Ekiel-Jeżewska</font></div><div style="margin: 0px; font-stretch: normal; line-height: normal;"><font face="HelveticaNeue">Maciej Lisicki</font></div><div style="margin: 0px; font-stretch: normal; line-height: normal;"><font face="HelveticaNeue">Piotr Szymczak</font></div><div style="margin: 0px; font-stretch: normal; line-height: normal;"><font face="HelveticaNeue">Panagiotis Theodorakis</font></div><div style="margin: 0px; font-stretch: normal; line-height: normal;"><font face="HelveticaNeue">Marek Trippenbach</font></div></div></div></body></html>