Passive Scalar Injection into Smooth Wall Turbulent Boundary Layers
Open Access DepositedUnderstanding passive scalar dispersion is important as it is heavily intertwined with the study of pollutant spreading, turbulent mixing processes, nuclear device tracking, and the optimization of optical flow measurement techniques, including PLIF, MTV, and PIV. Determining the downstream region of uniform scalar distribution is essential for linking a contaminant source to where they are effectively dispersed. This is also crucial to techniques like PIV and MTV, as it affects the quality of the data obtained using scalar tracers, especially when attempting to deploy the techniques simultaneously. To accurately model a large number of ground-level point sources in smooth-wall turbulent boundary layers, an injection system with a micro-array of injector holes was designed to limit disruption of the boundary layer by minimizing the injection rate of rhodamine 6G dye compared to the bulk flow and changes in the wall surface created by the injector plate. Through the design, analysis, and testing of multiple injectors with different hole patterns and flow delivery systems, the injection system was optimized to behave within the constraints set by the flow conditions and features of the HIPRO campaign. The final injection system maintained continuous injection speeds of $1\%U, 10\%U$, and $20\%U$ through the injector holes. PLIF images were taken at various downstream locations while the dye was injected into a turbulent channel. Observing wall-normal profiles led to the selection of the optimal hole pattern and injection speeds and shed light on possible downstream locations of uniform scalar distribution. The downstream region of uniform scalar distribution was estimated to be $x \approx 800d $ from the source.
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