Spatially resolved heat transfer measurements of impinging jets on statistically rough surfaces using an infrared-based gradient sensor

This study presents an infrared‑thermography‑based gradient sensor that enables spatially resolved wall‑heat‑flux measurements on thermally thick plates with embedded, statistically homogeneous roughness. The method is validated against direct numerical simulation and established smooth‑wall datasets for Reynolds numbers in the range $5000 \leq Re \leq 30000$ and nozzle-to-plate distances in the range $2 \leq H/D \leq 5$, showing good accuracy and repeatability.

Using two roughness scales ($k_{99}/D = 0.04$ and 0.12), we provide the first systematic dataset of local Nusselt‑number distributions for turbulent impinging jets on rough surfaces at Reynolds numbers relevant for practical applications. Roughness is shown to have little effect at low $Re$, but a pronounced heat‑transfer enhancement appears once a combined threshold in roughness height and Reynolds number is exceeded.