Effects of Low Reynolds Number on Decay Exponent in Grid Turbulence

Abstract

This present work is to investigate on the decay exponent (n) of decay power law ▪ is the total turbulent kinetic energy, t is the decay time, t0 is the virtual origin) at low Reynolds numbers based on Taylor microscale ▪. Hot wire measurements are carried out in a grid turbulence subjected to a 1.36:1 contraction. The grid consists in large square holes (mesh size 43.75mm and solidity 43%); small square holes (mesh size 14.15mm and solidity 43%) and woven mesh grid (mesh size 5mm and solidity 36%). The decay exponent (n) is determined using three different methods: (i) decay of ▪, (ii) transport equation for ɛ, the mean dissipation of the turbulent kinetic energy and (iii) λ method (Taylor microscale ▪, angular bracket denotes the ensemble). Preliminary results indicate that the magnitude n increases while ▪ decreases, in accordance with the turbulence theory.