Evaluation of the structure function method to compute turbulent dissipation within boundary layers using numerical simulations

Abstract

Well-resolved numerical simulations of turbulent open channel flows are analyzed to evaluate the accuracy of the 2nd order structure function method (SFM) in estimating the rate of dissipation of turbulent kinetic energy within boundary layers. The objective is to assess the variation in the 2/3 Kolmogorov constants due to flow anisotropy with distance from the wall. Comparison of the dissipation calculated directly from the numerical data, with that from the SFM shows that usage of the canonical constants, based on the assumption of local isotropy, can result in considerable error (>50%) in the prediction of dissipation when using the vertical or spanwise velocity components. From the numerically calculated dissipation, optimal Kolmogorov 2/3 constants were obtained and empirical relations, which account for near-wall effects, were proposed. Usage of the optimal constants will improve estimation of the dissipation rate when the SFM is applied to compute dissipation in geophysical boundary-layer flows.