Application of Tomo-PIV in a large-scale supersonic jet flow facility

Abstract

Particle imaging velocimetry (PIV) has been used extensively at NASA GRC over the last 15 years to build a benchmark data set of hot and cold jet flow measurements in an effort to understand acoustic noise sources in high-speed jets. Identifying the noise sources in high-speed jets is critical for ultimately modifying the nozzle hardware design/operation and therefore reducing the jet noise. Tomographic PIV (Tomo-PIV) is an innovative approach for acquiring and extracting velocity information across extended volumes of a flow field, enabling the computation of additional fluid mechanical properties not typically available using traditional PIV techniques. The objective of this work was to develop and implement the Tomo-PIV measurement capability and apply it in a large-scale outdoor test facility, where seeding multiple flow streams and operating in the presence of daylight presents formidable challenges. The newly developed Tomo-PIV measurement capability was applied in both a subsonic M 0.9 flow and an under-expanded M 1.4 heated jet flow field. Measurements were also obtained using traditional two-component (2C) PIV and stereo PIV in the M 0.9 flow field for comparison and validation of the Tomo-PIV results. In the case of the M 1.4 flow, only the 2C PIV was applied to allow a comparison with the Tomo-PIV measurement. The Tomo-PIV fields-of-view covered 180 × 180 × 10 mm, and the reconstruction domains were 3500 × 3500 × 200 voxels. These Tomo-PIV measurements yielded all three components of vorticity across entire planes for the first time in heated supersonic jet flows and provided the first full 3D reconstruction of the Mach disk and oblique shock intersections inside of the barrel shocks. Measuring all three components of vorticity across multiple planes in the flow, potentially reduces the number of measurement configurations (streamwise and cross-stream PIV) required to fully characterize the mixing-enhanced nozzle flows routinely studied in aeroacoustics research.