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

摘要

We present direct multipoint velocity measurements of the two-dimensional velocity field in the central region of turbulent Rayleigh-Benard 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 Gamma(r) are 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 Gamma(r) is found to depend on the scale r, 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 less than or similar to 5), whereas, for high-order moments (p greater than or similar to 5), the anomalous scaling exponents for circulation are found to be systematically smaller than the scaling exponents of the longitudinal and transverse structure functions.