Two time and two point shifted velocity measurements in decaying homogeneous turbulence

Abstract

Obtention of some characteristics as Eulerian 2 times 2 points shifted velocity correlations for isotropic homogeneous turbulence is still difficult to obtain. Nevertheless, it is necessary, particularly for 2 points and 2 times or Lagrangian turbulence modelling, to improve our knowledge of the deduced characteristic turbulent time scales. In the present work the flow is a water decaying turbulence. We use particle image velocimetry (PIV) to obtain velocity field measurements in a first fixed point x and in a second moving point x + Δ x . The velocity field at x is obtained at time t and at x + Δ x at time t + T (where Δ t = Δ x / U ¯ ( U ¯ being the mean velocity at x)). Our turbulence is the same as Comte-Bellot and Corrsin (1971) [1] (GCBC) but in water. They used two hot-wire anemometers to obtain velocity field x and x + Δ x along their tunnel axis, whereas we used two PIV systems. This allows us to have measurement points closer each together, compare to GCBC. We present our PIV measurements that will be compared with the ones of GCBC (Comte-Bellot and Corrsin, 1971) [1] and Schlien and Corrsin (1974) [2] (SC). We first demonstrate the validity of our water experiment then the use of the synchronised two PIV systems. We further present the velocity correlation results and the deduced turbulent time scale.