Analysis of turbulent flows by simultaneous fluorescent and Mie-scattering PIV

Many flows have a multi-constituent nature, where understanding the transfer of mass and momentum between different parts of the flow is key. While experiments in liquid media have long used flow tagging techniques such as dye injection to isolate parts of the flow, analogous methods that do not compromise full-field velocimetry in gas flows are highly impractical. The recent introduction of a solution of Pyrromethene 567 (P567) in di-ethyl-hexyl-sebacate (DEHS) to produce a seeding fluid capable of fluorescent emission in addition to Mie scattering promises to address this need. By locally seeding a secondary flow of interest with the modified DEHS, the fluorescent signal can be used for tagging; global seeding of main flow with standard DEHS, which only produces Mie scattering of incident laser light, is used to obtain full-field velocimetry with established PIV techniques. Performing morphological image processing and intensity-based thresholding on the fluorescent particle images yields a continuum representation of the secondary flow. This can then be combined with velocimetric information from PIV to conduct quantitative zonal analyses. This technique has been applied to the flow behind an active synthetic-jet turbulence grid and a turbulent boundary layer (TBL). With the new zonal decomposition capabilities offered, data relating to the intermittency of the flows, statistical structure of the phenomena, turbulent/non-turbulent interface (TNTI) and entrainment and detrainment can be extracted.