A local measure of the helicity in turbulent flows

Helical structures are a hallmark of hydrodynamic turbulence, and they play a key role in determining the transport and diffusion properties of the flow. Helicity, defined by the linking of velocity and vorticity, is, thus, of primary significance, particularly in systems such as propelled jet wakes. In this paper, we present a novel approach for determining helicity in turbulence, based on one-dimensional filtering methods. First, we test our new technique using analytical solutions and numerical simulations and find that the model can identify high-helicity patterns qualitatively well. Then, we employ the technique in experiments with propelled, helical turbulent flows. The model reliance on singlepoint velocity measurement may be especially advantageous for measurements with limited acquisition dimensionality.