Experimental investigation of homogeneity, isotropy, and circulation of the velocity field in buoyancy-driven turbulence

Abstract

We present direct multipoint velocity measurements of the two-dimensional velocity field in the central region of turbulent Rayleigh–Bénard convection. The local homogeneity and isotropy of the velocity field are tested using a number of criteria and are found to hold to an excellent degree. The properties of velocity circulation Γrare also studied. The results show that the circulation appears to be more effective in capturing the effect of local anisotropy than the velocity field itself. The distribution of Γris found to depend on the scaler, reflecting strong intermittency. It is further found that the velocity circulation has the same anomalous scaling exponents as the longitudinal and transverse structure functions for low-order moments (p≲5), whereas, for high-order moments (p≳5), the anomalous scaling exponents for circulation are found to be systematically smaller than the scaling exponents of the longitudinal and transverse structure functions.