On curve and surface stretching in isotropic turbulent flow

Cocke (1969) showed that, on average, infinitesimal material lines and surfaces are stretched in incompressible isotropic turbulence. We have extended those results to obtain upper and lower bounds for the stretching of such infinitesimal elements in terms of the eigenvalues of the Green deformation tensor. These bounds are in turn used to find bounds for the stretching of finite material lines and surfaces.