Estimation of Time-Resolved 3D Pressure Fields in an Impinging Jet Flow from Dense Lagrangian Particle Tracking

Abstract

Lagrangian particle tracking (LPT) using the Shake-The-Box (STB) method enables a dense and accurate 3D measurement of position, velocity and acceleration vectors of a large amount of single seeding tracers imaged by a multiple camera system. A subsequent application of the data assimilation technique “FlowFit” to the reconstructed particle tracks provides access to the full time resolved velocity gradient tensor together with the 3D pressure (gradient) fields. A perpendicular impinging jet flow with exit velocities at U = 1, 4 and 16 m/s and nozzle to plate spacing of H/D = 5 has been investigated using largevolume STB. Helium-filled soap bubbles are used as tracer particles which are illuminated with pulsed LED arrays. A large measurement volume has been covered (cloud of tracked particles in a volume of 54 liters, ∼ 190,000 particles). The reconstructed time-resolved 3D pressure fields have been validated against microphone recordings at the wall with high correlation coefficients up to R = 0.88. In this paper the experimental conditions are described together with the main processing parameters adopted for the STB strategy and the applied FlowFit data assimilation method. Results are shown in terms of instantaneous flow and pressure fields together with comparisons to time-traces of synchronously measured microphone signals.