Material acceleration determination for high speed flows by means of ShakeTheBox multipulse particle tracking

The recent introduction of the ShakeTheBox 3D particle tracking technique (Schanz et al 2016) opened the possibility to perform accurate Lagrangian particle tracking at seeding densities typical and exceeding those applied for tomographic PIV experiments (TomoPIV, Elsinga et al 2006). The method makes use of the particle based Iterative Particle Reconstruction technique (IPR, Wieneke 2013) to initialize particle tracks over a few recordings (typically four). Subsequently, the concept of particle prediction is introduced, where the position of tracked particles at following time instants is extrapolated from the initialized tracks; the predicted particle location is then corrected by means of the IPR image matching technique, referred to as shaking. As a consequence, the full IPR reconstruction is needed only during the initialization phase, which largely reduces the computational costs of the processing technique. The particle locations along the trajectories can be fitted in order to reduce the random particle position error introduced during reconstruction and to analytically evaluate velocity and material acceleration. The measurement of the material acceleration is of particular interest for many industrial and engineering applications as it can be used to determine the instantaneous pressure field via the momentum equation (van Oudheusden 2013, Huhn et al 2015). Due to current hardware limitations in terms of maximum acquisition frequency, timeresolved sequences suitable for STB processing can be obtained only for relatively low flow speeds (typically lower than 1