Index of content:
Volume 10, Issue 9, September 1998
10(1998); http://dx.doi.org/10.1063/1.869731View Description Hide Description
We study the scaling behavior of the pressure structure function for isotropic turbulence. This function is given exactly by Hill and Wilczak [J. Fluid Mech. 296, 247 (1995)] in terms of the three independent fourth order velocity structure functions, and We show from direct numerical simulation (DNS) that the cancellation between the positive terms proportional to L(r) and T(r) and the negative terms proportional to M(r) is almost complete. This suggests that the pressure structure function is extremely sensitive to recently observed small differences in scaling among the three quantities L(r), T(r), and M(r). We illustrate this sensitivity by calculating the pressure structure function in the atmospheric boundary layer using the recent data of B. Dhruva, Y. Tsuji, and K. R. Sreenivasan [Phys. Rev. E 56, R4928 (1997)]. The cancellation among the three terms persists, and gives an effective scaling exponent for the pressure structure function, which is smaller than the scaling exponent for any of the three velocity structure functions.
10(1998); http://dx.doi.org/10.1063/1.869732View Description Hide Description
Given (and confirmed numerically) that the exponents and in the passive scalar and velocity structure functions and are anomalous, the scaling of in is investigated. Analytical estimates show that cannot be as anomalous as or Numerical computations show that is closer to than to In addition, the statistical dependence of the velocity and passive scalar differences leads to an enhanced anomaly in
10(1998); http://dx.doi.org/10.1063/1.869733View Description Hide Description
Massively parallel computers are now large enough to support accurate direct numerical simulations (DNSs) of laboratory experiments on isotropic turbulence, providing researchers with a full description of the flow field as a function of space and time. The high accuracy of the simulations is demonstrated by their agreement with the underlying laboratory experiment and on checks of numerical accuracy. In order to simulate the experiments, requirements for the largest and smallest length scales computed must be met. Furthermore, an iterative technique is developed in order to initialize the larger length scales in the flow. Using these methods, DNS is shown to accurately simulate isotropic turbulence decay experiments such as those of Comte-Bellot and Corrsin [J. Fluid Mech. 48, 273 (1971)].