Development Of Temperature-Insensitive Membrane Pressure Sensitive Paint And Its Application In Underexpanded Jet Impingement

The thermal quenching of pressure-sensitive paint(PSP)has been effectively suppressed by restricting the lattice relaxation of luminescent molecules based on Franck-Condon principle.This is significant for reducing the temperature sensitivity while improving the signal level of PSP.This approach used a self-assembled monolayer(SAM)technique to process PSP samples based on anodized aluminum oxide membrane.Due to the aluminum oxide's capability of forming a strong bond with fatty acid,the monomolecular coating formed by SAM on the PSP membrane was highly organized and dense which restricted the lattice relaxation of luminescent molecule.The sensing performance of PSP samples,including temperature sensitivity,pressure sensitivity,signal level,and response time,was evaluated based on static and dynamic calibrations.Significant reduction in temperature sensitivity(up to 95.7%in a temperature range of 273-323 K)was achieved after the samples were coated by SAM.The effects of geometric parameters(of the porous structure)on temperature sensitivity were investigated in detail.The luminescent intensities of the samples with or without SAM coating were also compared,which showed an improvement of up to 3 times after the samples were coated by SAM.In addition,the effect of temperature in SAM process on the reduction of PSP's temperature sensitivity was evaluated to determine the optimal treatment temperature.Then,the developed temperature-insensitive PSP was applied to experimentally investigate the pressure field of underexpanded jet impingement with a short nozzle–plate distance(L/D_n)and a large impingement angle(?).The measurement of surface pressure is difficult using traditional non-transparent PSP due to optical obstruction.Here,this novel PSP with a high degree of transparency enabled back illumination and back imaging to resolve the issue of optical obstruction.With this technique,the effects of the nozzle–plate distance(L/D_n=1,2,and 3),impingement angle(?=90°,60°,and 30°),and pressure ratio(PR=1.2and 1.5)on the pressure-field characteristics were evaluated in detail,with a focus on the fine flow structures near the impingement point.The surface pressure distribution in the wall jet region was found to be significantly influenced by the nozzle–plate distance,which could be related to variation in the flow field,based on a physical model of the sonic line.The obtained PSP results with a high-spatial resolution revealed interesting flow physics that improve our understanding of high-speed near-wall jet impingement.