Measurement of turbulence characteristics in a large scale fan-stirred spherical vessel

Particle Image Velocimetry, PIV, is employed to characterise the near-homogeneous, isotropic, turbulence generated inside a large spherical vessel by four rotating fans. Spatial and temporal distributions of mean and root mean square, rms, velocity fluctuations are investigated, as well as integral length scales, L, Taylor microscales, λ, and Kolmogorov length scales, η, in the fan speed range, 1000–6000 rpm. Mean velocities are about 10% of the turbulence velocity, u' and turbulence is close to homogeneous and isotropic in the central volume. This volume decreases with increasing fan speed, and its radius and other characteristics are expressed in terms of the fan speed. At each speed, the mean gas velocity scarcely varies with time. Relationships are presented for the variations of u' and L with fan speed, temperature and pressure. A new relationship between the autocorrelation function and integral length scale is obtained, for when Taylor's hypothesis is invalid.