Fluid*DTU seminar given by
\nP. Henrik Alfredsson
\nKTH
\nStockholm
\n
\nThe von Karman disk flow (and other rotating systems) - stability, transition, and turbulence
Abstract:
\nRotation is all around us and affects many of the natural fluid systems on the rotating sphere that is our habitat. Technology we develop also relies heavily on flows in rotation, for instance almost all electricity that we consume is provided by rotating machinery, whether gas, steam, water or wind turbines, and for many other applications water and air are moved with some purpose by rotating pumps and fans.
\n
\nIn this presentation, we will follow the progress in the research of boundary-layer stability, transition and turbulence in rotating systems from the early days, more than a hundred years ago, when the Swedish scientist Ekman [1] explained how the Coriolis force affected the direction of drift of ice (observed by the Norwegian explorer Nansen) on the surface of the Arctic Ocean. He showed that the oceanic flow system has a boundary-layer structure, within which the mean velocity can be represented by a vector that changes length exponentially with depth below the surface and changes angle linearly with depth; the so-called Ekman spiral. Another landmark in the history of rotating flows is the work of von Kármán [2], who, in just in a small section of a general paper on boundary-layer flows, presented the similarity solution for the infinite disk rotating in an otherwise quiescent fluid.
\n
\nStudies of ow stability, transition and turbulence in rotating systems started later but some important work appeared in the 1940s and 50s. Here we will especially focus on the rotating disk, a case that has attracted attention from a large number of research groups over the last 30 years and has been studied through experiments, theory and simulations. A feature of the rotating disk ow is the absolute instability discovered by Lingwood [3] in the mid 90s, and suggested to lie behind the rather distinct value of the Reynolds number for the onset of transition to turbulence.
[1] Ekman, V. W. (1905) On the inuence of the Earths rotation on ocean currents, Arkiv för Matematik, Astronomi och Fysik 2, 1-52.
\n[2] von Kármán, T. (1921) Über laminare und turbulent Reibung, Z. Angew. Math. Mech. 1, 233-252.
\n[3] Lingwood, R.J. (1995) Absolute instability of the boundary layer on a rotating disk, J. Fluid Mech. 199, 17-33.
\nAcknowledgement
\nThanks to E. Appelquist, S. Imayama, R.J. Lingwood, and P. Schlatter, for various contributions to this talk.
X-ALT-DESC;FMTTYPE=text/html:Fluid*DTU seminar given by
\nP. Henrik Alfredsson
\nKTH
\nStockholm
\n
\nThe von Karman disk flow (and other rotating systems) - stability, transition, and turbulence
Abstract:
\nRotation is all around us and affects many of the natural fluid systems on the rotating sphere that is our habitat. Technology we develop also relies heavily on flows in rotation, for instance almost all electricity that we consume is provided by rotating machinery, whether gas, steam, water or wind turbines, and for many other applications water and air are moved with some purpose by rotating pumps and fans.
\n
\nIn this presentation, we will follow the progress in the research of boundary-layer stability, transition and turbulence in rotating systems from the early days, more than a hundred years ago, when the Swedish scientist Ekman [1] explained how the Coriolis force affected the direction of drift of ice (observed by the Norwegian explorer Nansen) on the surface of the Arctic Ocean. He showed that the oceanic flow system has a boundary-layer structure, within which the mean velocity can be represented by a vector that changes length exponentially with depth below the surface and changes angle linearly with depth; the so-called Ekman spiral. Another landmark in the history of rotating flows is the work of von Kármán [2], who, in just in a small section of a general paper on boundary-layer flows, presented the similarity solution for the infinite disk rotating in an otherwise quiescent fluid.
\n
\nStudies of ow stability, transition and turbulence in rotating systems started later but some important work appeared in the 1940s and 50s. Here we will especially focus on the rotating disk, a case that has attracted attention from a large number of research groups over the last 30 years and has been studied through experiments, theory and simulations. A feature of the rotating disk ow is the absolute instability discovered by Lingwood [3] in the mid 90s, and suggested to lie behind the rather distinct value of the Reynolds number for the onset of transition to turbulence.
[1] Ekman, V. W. (1905) On the inuence of the Earths rotation on ocean currents, Arkiv för Matematik, Astronomi och Fysik 2, 1-52.
\n[2] von Kármán, T. (1921) Über laminare und turbulent Reibung, Z. Angew. Math. Mech. 1, 233-252.
\n[3] Lingwood, R.J. (1995) Absolute instability of the boundary layer on a rotating disk, J. Fluid Mech. 199, 17-33.
\nAcknowledgement
\nThanks to E. Appelquist, S. Imayama, R.J. Lingwood, and P. Schlatter, for various contributions to this talk.
URL:https://fluid.dtu.dk/kalender/2014/02/p-henrik-alfredsson-seminar DTSTAMP:20260515T040800Z UID:{6AEDEFF2-E708-4DB0-AD76-811DE540187A}-20140228T110000-20140228T110000 LOCATION: Building 306 Auditorium 31 END:VEVENT END:VCALENDAR