Imaging Technology of Surface Pressure Distribution using Luminescent Coatings

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We studied the imaging technology of surface pressure distribution on the aerodynamic models using luminescent coatings. We improved the anodized aluminum pressure sensitive paint (AA-PSP), which is a state-of-the-art paint for measuring unsteady pressure fluctuations. Furthermore, we developed a measuring technique of surface stress field using soft gel.(1) The pressure-sensitive paint is luminescent dyes with their binder. The intensity of the luminescence depends on the oxygen concentration in the binder. The AA-PSP has a quite fast-responding characteristic due to large gas diffusivity of the porous structure of the anodized aluminum, in which the dyes are adsorbed on the surface of pores. The anodized aluminum, however, exhibits a hydrophilic property, which causes a severe humid sensitivity in the response of the AA-PSP. We reduced the humid sensitivity by coating amphipathic molecules on the anodized aluminum as well as the luminescent dyes. We used the alkanoic acid as amphipat … More hic molecules. We successfully reduced the humid sensitivity to a quarter of the sensitivity of original AA-PSP. Then we measured unsteady pressure fluctuation on the delta wing in transonic flow using the hydrophobic AA-PSP. We captured the pressure fluctuation having a frequency of 1 kHz within the uncertainty of 1 kPa.(2) We developed a coating method of porous alumina on arbitrary surface. We successfully made the porous alumina via a sol-gel route (Yoldas method) using an aluminum alcoxide as the material. The porous structure was achieved adding polyethylene glycol in the alumina sol. The pressure-sensitivity is equal to that of the anodized aluminum PSP.(3) We developed a smart film to measure the surface stress field. The stress filed can be estimated from the deformation of the film based on the theory of elasticity. The elasticity of the film must be chosen carefully to detect the small amount of the stress. We used gelatin with luminescent fine powders. The thickness and shear deformation were successfully estimated from the images of the luminescent fine powders, although there still remain considerable errors in the calculated stress value. Further improvement was needed to calculate full-field measurement of the stress on the surface. Less