Application of Pressure-Sensitive Paint to Low-Speed Flow around a U-Bend of Strong Curvature

Two in-house Pressure-Sensitive Paint (PSP) formulations have been developed and tested in the low-speed regime on the flow around a U-bend of strong curvature. The two PSP formulations use tris-Bathophenanthroline Ruthenium Perchlorate (Ru (II)) and Platinum tretakis (pentafluorophenyl) Porphyrin (PtTFPP) as their photoactive molecules, incorporated in identical sol-gel matrices. Ru (II) emits a broad peak centered at 610nm while PtTFPP emits a much narrower peak at 650nm. The paints were illuminated using two in-house constructed blue LED lights with peak emission of 468nm. These luminophores have been tested with gauge inlet pressures of 3000 and 1250 Pa respectively. A further sample was tested with a gauge pressure of 500 Pa. In-situ calibration was utilized to minimize the temperature dependency change between wind-on and wind-off images. Both paints captured the flow characteristics and gave predictable surface pressure maps despite the challenges inherent with using such low pressures.