Lagrangian and Eulerian Measurements in High-Speed Jets Using Multi-Pulse Shake-The-Box and Fine Scale Reconstruction (VIC#)

Accurate measurement of high-speed flows in the presence of elevated levels of shear and turbulence is a challenging yet necessary endeavor in order to understand ubiquitous flows that are of great engineering importance. While Eulerian methods, such as Particle Image Velocimetry, represent the traditional approach, Lagrangian alternatives, such as Particle Tracking Velocimetry, has witnessed a resurgence recently due to improved technology and interest in Lagrangian analysis methods. In this research, a recently developed implementation of a volumetric Lagrangian technique for tracking particles in densely seeded flows, namely, Multi–Pulse Shake-The-Box (MP–STB) with the specific implementation referred to as Four–Pulse Shake-The-Box, is described and its performance in high-speed jet flows is evaluated. The MP–STB technique is based on recent developments in the Shake-The-Box method (Novara et al. 2019) and uses low-speed cameras combined with a double exposed image acquisition strategy and multi-pulse tracking. Its use of four laser pulses in quick succession with an uneven pulse timing scheme allows for high-accuracy estimates of velocity and acceleration, and repeated ensembles of short-duration, time-resolved measurements in realistic high-speed flows. Experiments with circular jets operating at exit Mach numbers of 0.31 and 0.59 in two different configurations, namely, free jets and jets impinging on a ground plate located 4.75 jet diameters away from the nozzle, were performed to evaluate MP–STB. Scattered four particle tracks from MP–STB were mapped onto a regular Eulerian grid through the Fine Scale Reconstruction implementation of the VIC# data assimilation method (Jeon et al. 2018). Unique information, including acceleration fields, are presented for these well-known canonical flows. Comparisons with traditional Eulerian measurements from Tomographic PIV, Stereoscopic PIV, and planar PIV are provided to validate the accuracy and comparative cost of volumetric MP–STB measurements combined with the VIC# data assimilation technique.