Department of Aerospace Engineering

Midwest Mechanics Seminar Series: Professor Michael Brenner, Harvard University, "Ejected Fungal Spores, and Solutions to the Moderate Reynolds number navier Stokes Equation"

Midwest Mechanics Seminar

Professor Michael P. Brenner
Glover Professor of Applied Mathematics and Applied Physics
School of Engineering & Applied Sciences
Harvard University

Wednesday, December 3, 2008
1:10 PM
Room 1235 Howe Hall

Ejected Fungal Spores, and Solutions to the Moderate Reynolds number navier Stokes EquationTo disperse effectively the explosively launched spores of ascomycete fungi must eject through a thin layer of still air surrounding the fruiting body and reach air flows that can take the spores away from the parent fungus. Spores are very small and therefore experience enormous fluid drag. We use a phylogeny of over 110 ascomycete species to compare optimal and real spore shapes and find that spores are shaped to remain within 1\% of the drag minimum. A predicted  launch speed is confirmed by high-speed imaging of ejection in \emph{Neurospora tetrasperma}.  The optimal drag shapes themselves exhibit a surprising feature: they are very nearly fore-aft symmetric, despite the fact that the flow field around them is very asymmetric. We use this observation as a basis for constructing a surprisingly accurate linear approximation to steady flows of the Navier Stokes equations that works at least up to Reynolds number of order 100.