Measured turbulent entropy production with large eddy particle image velocimetry

Abstract

In this paper, statistical post-processing of measured velocity, dissipation rate and turbulence data is performed to establish whole-field distributions of entropy production within a channel. Thermal irreversibilities arising from temperature variations were not included in the study, as the experiments were conducted between unheated plexiglass plates in an essentially isothermal water tunnel. Unlike velocity or temperature, the measurement of entropy cannot be performed directly, so entropy production is measured indirectly through spatial differencing of measured velocities in large eddy PIV. In contrast to single-point methods of anemometry, large eddy PIV enables whole-field, time-varying measurements of the velocity field, which can be post-processed to yield entire spatial variations of the entropy production rate. An uncertainty analysis is performed to estimate measurement uncertainties with the new experimental technique. The uncertainties are decomposed into systematic and random components, including a propagated uncertainty, due to spatial differencing of the velocity field. Close comparisons between measured results of turbulence dissipation and direct numerical simulations provide useful verification of the formulation, before post-processed results of dissipation rates are used to determine entropy production within a channel.