Extended Abstract (236K)9.8
Turbulent pressure statistics
Natasha L. Miles, Penn State University, University Park, PA; and J. C. Wyngaard and M. J. Otte
Although the turbulent pressure field is extremely important in turbulence dynamics, it has not been studied as extensively as other fields, in part due to the inherent difficulty of its measurement. We use large-eddy simulation (LES) to calculate resolvable-scale turbulent pressure fields and their wavenumber (k) spectra in three representative atmospheric boundary layers: a free convection case, an unstable case with mean wind, and a stable case.
Turbulence spectra in the observational community, in traditional turbulence analysis, and in the present analysis all differ--a source of possible confusion. The observational community is often limited to one-dimensional spectra. Traditional turbulence analysis often assumes full homogeneity and integrates over spherical shells in k space to obtain what are called three-dimensional spectra. Our LES flow is homogeneous only in the horizontal, so we integrate over constant-k rings in the horizontal plane to obtain what we call two-dimensional spectra. We relate these one-, two-, and three-dimensional pressure spectra theoretically.
We represent the resolvable-scale pressure as the sum of mean-shear, turbulence-turbulence, subgrid, Coriolis, and buoyancy components. We compare analytical solutions for the two-dimensional spectra of buoyancy and mean-shear components of pressure with LES results in the inertial subrange. We find that in mid-ABL the mean shear, Coriolis, and buoyancy components contribute relatively little to the total pressure field there, leaving the turbulence-turbulence term as the largest contributor. Our LES results give good evidence of k-7/3 behavior of the pressure spectrum in the inertial subrange and suggest that the constant in its three-dimensional spectrum is about 4.0.
Near the surface the horizontal scale of the vertical velocity field decreases, causing the vertical velocity to be underresolved and the LES to rely more heavily on its subgrid-scale model. The spectra of pressure differences in the vertical suggest that at small k the pressure spectra remain well-behaved near the surface.
Session 9, Fundamental Studies of Turbulence, including advances in LES and DNS, Laboratory Studies, and Observations
Wednesday, 17 July 2002, 8:30 AM-12:30 PM
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