cancellation exponents in helical and non-helical flows

PAOLA RODRIGUEZ IMAZIO; PABLO DANIEL MININNI

Buenos Aires, Argentina.

Congreso; Principles and applications of fluid dinamics; 2008

Facultad de Ciencias Exactas y Naturales, UBA

Energy and Helicity are two a quadratic invariant of the Euler equation. Both quantities cascades to smaller scales where they dissipate. However, it is know that they play different roles in this cascade, and the role played by helicity remains unclear. In both helical and non-helical flows, helicity changes sign rapidly in space. To meassure this fast changes in sign, we use a concept introduced by Ott et al., the cancellation exponent. The exponent is a measure of sign-singularity and can be related to the fractal dimension and to the first order scaling exponent. Flows with different forcing functions and at different Reynolds numbers are studied. We show that the cancellation exponent is useful to study scaling laws in quantities that present fast fluctuations around zero.