Effects of low Reynolds number on decay exponent in grid turbulence

This present work is to investigate on the decay exponent (n) of decay power law (q'²~(t-t_o)ⁿ, q'²0 is the virtual origin) at low Reynolds numbers based on Taylor microscale R_λ(≡ u'λ/v) ≤ 64. 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 43.75 mm and solidity 43%); small square holes (mesh size 14.15 mm and solidity 43%) and woven mesh grid (mesh size 5 mm and solidity 36%). The decay exponent (n) is determined using three different methods: (i) decay of q'², (ii) transport equation for ɛ, the mean dissipation of the turbulent kinetic energy and (iii) λ method (Taylor microscale λ ≡ √5〈q'²〉/〈ɛ_d〉 angular bracket denotes the ensemble). Preliminary results indicate that the magnitude n increases while R_λ(≡ u'λ/v) decreases, in accordance with the turbulence theory.