Unsteady convective heat transfer of an impinging sweeping jet: A discussion on the effect of spatiotemporal filtering

Accurately assessing unsteady convective heat transfer is crucial for optimising thermal management strategies. This study investigates the heat transfer characteristics of an impinging sweeping jet, highlighting the role of spatiotemporal filtering in infrared thermography-based measurements. A heated thin foil sensor combined with high-speed infrared thermography captures time-resolved temperature distributions on a target surface exposed to a sweeping jet at $Re\approx 6600$. Unlike conventional phase-averaged approaches, this work enables the assessment of instantaneous convective heat transfer, offering deeper insights into unsteady thermal phenomena. The inherent noise and artefacts in infrared thermography are systematically addressed through an optimised filtering strategy, ensuring minimal data distortion while preserving critical flow structures. The effects of various filtering techniques, both individually and in combination, are evaluated to achieve a robust estimation of the Nusselt number distribution. The findings underline the importance of advanced post-processing in extracting meaningful heat transfer data, particularly in non-stationary flows like sweeping jets. This study advances infrared thermography methodologies, providing a framework for more accurate and reproducible convective heat transfer measurements in dynamically evolving thermal environments.