Study on the characteristics of the pressure fluctuations and their contribution to turbulence kinetic energy

Abstract

In this study, the integral and microscopic turbulent statistical characteristics of pressure fluctuations, applicability of the pressure gradient and pressure flux divergence to the Monin-Obukhov similarity theory (MOST), and contribution of the pressure transport term to turbulence kinetic energy (TKE) were analyzed using the turbulence observational data obtained from a field observational station over the Horqin Sandy Land in Inner Mongolia, China. The normalized standard deviations of the pressure fluctuations have no obvious relationship with the dimensionless stability parameter (z/L). The turbulent variance spectra of pressure fluctuations Sp(n) follow the n−2 scaling law with a peak frequency of approximately one to two orders of magnitude lower than that of the wind speed and temperature. The spectral gap also shifts to lower frequencies, and the transition from turbulent scale to the larger scale is sharper. The normalized vertical pressure gradient (κzp∗∂p¯∂z) has no significant relationship with z/L. The non-dimensional pressure transport term (φp=κzρ¯u∗3∂w'p'¯∂z) represents the pressure flux divergence and is well related to the z/L with expressions of φp = ± (1 − 14.5z/L) for unstable stratifications and φp = ± (1 + 15.0z/L) for stable stratifications. The relative importance of pressure transport term in the TKE budget equation with respect to the shear production and buoyancy terms is larger at larger scales. The pressure transport term is averagely one order of magnitude larger than the sum of these two terms at scales above 5 min. The contribution of the pressure transport term to the TKE is non-negligible.