Zero gradient points in turbulent mixing

Abstract

According to the theory proposed by Gibson [ 1, 2 ] , the essential mechanism of small scale turbulent mixing is the interaction of local strain rate with points of maximum and minimum scalar value (zero gradient points). This is contrary to the theory of Batchelor, Howells and Townsend [ 3 ] that local strain rate should be irrelevant for strongly diffusive scalars like temperature in mercury. Temperature fluctuations measured in turbulent mercury by Clay [ 4 ] compared to predictions of the two theories shows a strong strain rate temperature dissipation-rate correlation as expected from the zero gradient point theory, as well as inertial -diffusive spectral subranges consistent with both the k⁻³ andk^−17/3 predictions of the Gibson [ 2 ] and Batchelor et al [ 3 ] theories, respectively.