Electronic International Standard Serial Number (EISSN)
1873-7005
abstract
grids is performed by means of particle image velocimetry (PIV) in an open-circuit wind tunnel. Careful corrections are performed to account for and eliminate sources of noise and error that become significant in very-low-turbulence-intensity flows such as highly decayed grid turbulence. The signal-to-noise ratio varies between 20 and 70, but despite noise and some spatial filtering, it is possible to accurately measure the turbulent viscous dissipation within ±10%. The results confirm that the proportionality relation Lu /lambda ∝ Relambda (where Lu is the integral length scale, lambda is the Taylor microscale and Relambda is the Reynolds number based on the Taylor microscale), stemming from the scaling of the turbulent dissipation epsilon = Cepsilon k3/2 /Lu (where k is the turbulent kinetic energy), does not apply to the turbulence generated by square fractal grids. More importantly, the semi-empirical constant Cepsilon is not at all constant for this flow, varying by more than a factor of 4 over the observed decay range.