Shake-The-Box for multi-pulse tomographic systems: towards high seeding density particle tracking in high speed flows

Abstract

A turbulent boundary layer flow with adverse pressure gradient in air at 36 m/s is investigated by means of a multi-pulse tomographic system. The acquisition strategy allows for the recording of short time-resolved sequences using four pulses with a time separation of a few microseconds. The experimental setup consists of a dual-imaging system and a dual-double cavity laser emitting orthogonal polarization directions to separate the four pulses. The Shake-The-Box 3D particle tracking technique, recently introduced for time-resolved investigations, is applied to the multi-pulse data. The iterative particle tracking strategy is investigated in the present study; the processing approach takes advantage of the ghost-free tracking possibility offered by the use of the dual-imaging system. Furthermore, a correction scheme to compensate for the vibrations between the two independent imaging systems is discussed, together with a method to accurately identify the position of the wall within the measurement domain. Results show that approximately 70,000÷80,00 tracks can be reconstructed in the measurement volume, enabling the evaluation of highly spatially resolved boundary layer profiles and dense velocity fields suitable for spatial gradients evaluation.