Abstract
In this study the structured laser illumination planar imaging (SLIPI) technique is combined with gas phase phosphor thermometry to measure quasi-instantaneously two-dimensional temperature fields with reduced bias from multiple scattering. Different reconstruction strategies are implemented, evaluated and compared, including a two-pulse and one-pulse SLIPI approach. A gradient-based threshold algorithm for particle detection is applied to conventional planar light sheet imaging as an alternative to reduce the bias caused by multiple scattering in seeding-free regions. As a demonstration, measurements are performed in a canonical flow configuration, consisting of a heated, turbulent, air jet surrounded by an ambient co-flow. Both air flows are seeded with the thermographic phosphor BaMgAl10O17:Eu2+.Conventional light sheet imaging in the context of gas phase phosphor thermometry suffers from multiple scattering causing a significant temperature bias and low temperature sensitivity. Applying the gradient threshold algorithm removes areas without any seeding particles which improves accuracy, precision and temperature sensitivity. However, multiple scattering influences are still present and may cause an increasing bias particularly for higher seeding density. One pulse (1p) SLIPI exhibits high accuracy at intermediate precision. Multiply scattered luminescence is not fully removed and spatial resolution is lowered. Two pulse (2p) SLIPI is recommended for high temperature sensitivity and accuracy, removing impact of multiple scattering furthermost. However, 2p-SLIPI exhibits reduced temperature precision.
Highlights
In this study the structured laser illumination planar imaging (SLIPI) technique is combined with gas phase phosphor thermometry to measure quasi-instantaneously two-dimensional temperature fields with reduced bias from multiple scattering
Scattered light and the resulting effects can be suppressed applying a structured illumination approach designed for macroscopic flow systems called structured laser illumination planar imaging (SLIPI), introduced to fluid mechanics by Berrocal et al [19] and Kristensson et al [20]
This study extends the previous SLIPI-laser-induced luminescence (LIL) approach to quasi-instantaneous temperature field measurements in gaseous flows
Summary
Chemical and process engineering, fluid flow temperature is a vital parameter. Previous investigations indicated that multiply scattered luminescence emission originating from seeding particles can strongly bias temperature measurements [12, 13, 17, 18]. Scattered light and the resulting effects can be suppressed applying a structured illumination approach designed for macroscopic flow systems called structured laser illumination planar imaging (SLIPI), introduced to fluid mechanics by Berrocal et al [19] and Kristensson et al [20]. By SLIPI post-processing, multiple scattering contributions can be mitigated This technique has demonstrated its capabilities in numerous applications in the past and has advanced over the years. The capability of 1p- and 2p-SLIPI-LIL gas phase thermometry is benchmarked against the conventional approach, considering temperature sensitivity, accuracy and precision of each reconstruction technique
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