Statistics and structures of pressure in isotropic turbulence

Statistics and structures of pressure in three-dimensional incompressible i sotropic turbulence are studied using high-resolution direct numerical simu lation for Taylor microscale Reynolds numbers up to 220. It is found that t he probability distribution function (PDF) of pressure has negative skewnes s due to both kinematic and dynamic effects, in contrast to the statistics of the pressure head, whose PDF is almost symmetric. The statistical relati ons among pressure, vorticity, dissipation and kinetic energy are investiga ted using conditional averaging. The averaged pressure, conditional on the local enstrophy, shows a linear dependence on enstrophy in the high-enstrop hy region. Structure relations between pressure and other physical quantiti es are qualitatively examined using three-dimensional visualization of iso- surfaces. It is found that the high-vorticity regions are strongly correlat ed with the low-pressure regions. However, it appears that experimental vis ualization techniques for detecting high-intensity vortices using microbubb les in low-pressure regions might only be valid for those very-high-vortici ty regions where the local enstrophy is at least five times higher than the root mean square enstrophy. The scaling law of the pressure structure func tion is also presented for both conventional and extended self-similarity. It is found that the pressure increment, delta(r)p, scales with the velocit y increment, delta(r)u, for the Reynolds numbers studied: delta(r)p similar to delta(r)u. For flows at moderate Reynolds numbers, it is demonstrated t hat the extended self-similarity gives better pressure scalings than result s from traditional similarity solutions. (C) 1999 American Institute of Phy sics. [S1070-6631(99)00108-7].