Undulatory swimming in viscoelastic fluids
Paulo E. Arratia, University of Pennsylvania

In this talk, the effects of fluid elasticity on undulatory swimming are investigated in experiments using particle image velocimetry, and by tracking the motion of the nematode Caenorhabditis elegans. Results show that the organism moves in highly periodic fashion and generate traveling waves that decay from head to tail. We find that fluid elasticity hampers the nematode’s swimming speed compared to a Newtonian fluid of same shear viscosity. Also, the nematode’s propulsion speed and efficiency decrease as elasticity increases or the Deborah number (De) increases, where De=fl. Here, f is the nematode beating frequency and l is the fluid relaxation time. Velocimetry data shows that fluid elasticity alters the flow patterns around the nematode. The velocity decay, normal to the swimming direction, decays faster for the viscoelastic case than for the corresponding Newtonian case. Finally, we compare our experimental results to recent theoretical and numerical predictions.