Intermittency and multi-fractal velocimetry (IMFV) in Rayleigh-Taylor and convective flows

Abstract

New descriptors to investigate mixing in multi-scale turbulence analysis and couple PIV Laser induced applications with Fractal analysis in Shock induced flows as well as in convective driven flows are discussed. The comparison of different measures applied to complex non-homogeneous flows aid the understanding of mixing processes. We concentrate on the use of PIV and advanced multi-fractal methods in order to evaluate the “scale to scale” transfer of energy and other descriptors of great importance in mixing processes. In particular we discuss the evolution of fluxes as molecular mixing takes place, here the use of fast reactive indicators such as Phenoftalein or Rhodamine, provides visual indication of the complexity of Rayleigh-Taylor and buoyancy driven flows. Surface Flow image velocimetry (SFIV) as discussed in this volume by (Jackson et al. 2016) also allows to measure complex surface velocity fields in engineering. These involve 3D flow-boundary conditions in divergence and wave prone nonuniform flows and boundary layer interactions, this is particularly important when a single camera for PIV provides a 2D image of the real complex 3D flows. The use of multi-fractal analysis and improvements on Structure function calculations on standard PIV, and on other methods used in experimental fluids mechanics have to be calibrated, both in Eulerian and Lagrangian frameworks towards the understanding of molecular mixing and the role of vorticity and helicity in the analysis of velocity vectors. Energy, Enstrophy, Divergence and Vorticity- Helicity scaling and stream function parameter spaces in stirring and mixing, seem very important. The link between Fractal spectra and energy Fourier and wavelet spectral behavior at different levels of intermittency still waits to be fully explained.