Estimate of turbulent dissipation in a decaying grid turbulent flow

Abstract

The dissipation rate of kinetic energy is a key quantity in turbulent flows. The number of measured components and the resolution of the measurement techniques limit dissipation rate estimates; thus, they are derived by surrogates of dissipation. We examine the validity and accuracy of these estimates by investigating decaying grid turbulence using particle image velocimetry and laser Doppler velocimetry. Dissipation rates are computed and compared via three different methods (i) using the decay rate of turbulent kinetic energy, (ii) direct calculation using measured velocity gradients, and (iii) using second and third order structure functions. Discrepancies have been found between the surrogate methods; specifically, the structure function method requires correction terms. The known factors leading to bias are viscous correction which is significant at low Reynolds numbers and inhomogeneity of the decaying flow. Furthermore, we demonstrate inaccuracy in calculations of the third order structure function which are related to inter-scale dependencies. Test procedures are suggested for decaying and inhomogeneous flows to determine susceptibility to these sources of error.