Acceleration statistics as measures of statistical persistence of streamlines in isotropic turbulence

We introduce the velocity V-s of stagnation points as a means to characterize and measure statistical persistence of streamlines. Using theoretical arguments, direct numerical simulations (DNS), and kinematic simulations (KS) of three-dimensional isotropic turbulence for different ratios of inner to outer length scales L/eta of the self-similar range, we show that a frame exists where the average <V-s>=0, that the rms values of acceleration, turbulent fluid velocity, and V-s are related by La'/u'(2)similar to(V'(s)/u')(L/eta)(2/3+q), and that V'(s)/u'similar to(L/eta)(q) with q=-1/3 in Kolmogorov turbulence, q=-1/6 in current DNS, and q=0 in our KS. The statistical persistence hypothesis is closely related to the Tennekes sweeping hypothesis.