3D Lagrangian particle tracking of a transonic jet using four-pulse Shake-The-Box

Abstract

Three-dimensional Lagrangian Particle Tracking (LPT) was performed on a transonic jet flow in air at Mach 0.84 generated by a round and chevron nozzle with an inner diameter (DDjj) of 15 mmmm. The Shake­The-Box (STB) technique for multi-pulse data was employed to reconstruct particle tracks along the 4-pulse sequences and provided highly resolved accurate flow velocity and material acceleration data. The study of transonic jets has a long history both in the fields of fluid mechanics and aeroacoustics. To date there have only been a limited number of studies investigating these flow phenomena with volumetric measurement techniques. STB for time resolved applications (typically for flow speeds in air less than 30 m/s) is described in [S] and allows for accurate particle tracking of densely seeded (>O.OSppp) flows. Novara et al [3] showed that a short time sequence (or multi-pulse) implementation of STB was able to retrieve most particle tracks with dynamic velocity and acceleration ranges comparable to those obtained with STB in the time-resolved domain, and they stipulated the possibilities of measuring the material acceleration (and pressure) for high speed flows by means of multi-pulse acquisition systems. This experimental investigation shall serve to provide further validation and assessment in real experimental conditions. A multi-pulse setup with a combination of two dual-frarneacquisition systems was used to record tracer particle images of DEHS droplets (-1 µmm diameter) within a volume of 90x70x10 mmmm3 along the jet axial (xx) and two radial directions (yy) and (zz), respectively. The multi-pulse strategy described by (4] is applied here, where the use of two different states of polarization for the illumination sources is used to separate the pulses on the camera images [2]. The two imaging systems consisted each of four sCMOS PCO-Edge cameras and the digital resolution was -33.6 ppp /mmmm. An uneven pulse separation is employed to increase the velocity and acceleration dynamic ranges of the measurement. This allowed a maximum total particle shift of up to 100 px tobe measured. The seeding concentration for the experiment ranged from 0.02 to 0.05 pppppp. For each measurement configuration, a total of 40,000 4-pulse sequences were recorded at a sampling frequency of 10 H H H . The multi-pulse STB technique relies on the Iterative Particle Reconstruction technique (IPR, [6]) to reconstruct particle positions in a volume over a few recordings (typically four) and employs an iterative STB processing strategy to compensate for the lack of a long observation time [4].