An experimental study of weak turbulence

Abstract

Photon homodyne correlation spectroscopy (HCS) and laser Doppier velocimetry (LDV) have been used to study turbulent velocity fluctuations V(R) associated with eddies of size R. The turbulence was produced by a grid in a water tunnel. For small R, both types of measurement were consistent with a model in which the active regions of turbulence lie on a fractal of dimension D, with D increasing from ≈ 2 to ≈ 3 as the Reynolds number (Re) increases above some threshold value. At larger eddy sizes, the LDV measurements show a different scaling of the velocity fluctuations. We associate these larger eddies with the energy reservoir that feeds the inertial cascade. The scaling exponent for this "energetic" subrange is also a function of Re.