Second Law Characterization of Confined Turbulent Flows

Abstract

In this paper, a new measurement technique for turbulent entropy production is developed and applied to confined channel flows. Past methods of dimensional analysis, Clark gradient, and Smagorinsky models for subgrid turbulent stresses are examined to determine the flow irreversibilities throughout the flow field. The new experimental method obtains the turbulent irreversibilities up to a certain particle image velocimetry (PIV) cut-off wavelength, very close to the wall of the channel. Measured results of turbulence dissipation and entropy production at varying Reynolds numbers are presented and compared successfully against results from direct numerical simulations. The subgrid scale models of turbulent flow irreversibilities are shown to provide an effective alternative to direct PIV averaging of turbulent stresses, particularly close to the wall, where PIV resolution makes it difficult to precisely determine the averaged turbulence fluctuations. This paper develops a new PIV based method that enables the whole-field measurements of turbulent entropy production, and it presents new experimental data for entropy production in channel flows.