Dual particle image velocimetry for transient flow field measurements

Abstract.

This paper describes an experimental approach to obtain transient flow structure and flow turbulence characteristics with the mean of a dual particle image velocimetry (PIV) system. Temporal evolution of the tumble motion is visualised on two sequences of consecutive velocity fields with a short delay time in the range of 70 µs. Original experimental set-up and synchronisation are proposed for this purpose and a detailed description of the set-up along with the solutions adopted for the implementation and synchronisation of a dual PIV are given. As traditional PIV analysis consists of instantaneous measurement of a 2D velocity field, the new approach allows a comparison to be made over time between results obtained with two instant consecutive velocity fields with dual PIV and over space because of the technique itself. Consequently, the analysis of the reciprocating engine turbulence, particularly the characterisation of the time and space autocorrelation coefficients, and the time and length macro scales on the analogy of the integral time scale turbulence for stationary flows are proposed. Results give spatio-temporal evolution of the autocorrelation coefficients. The calculation of the integral scales for different crank angles shows a changing pattern during the admission and compression processes. Characteristic mean velocities are proposed according to the integral length and time scales.