A novel pressure-sensitive luminescent coating on porous anodized aluminium is developed. A method of making the coating is described in detail. The coating is a thin anodized aluminium layer, which is formed onto the surface of aluminium by an electro-chemical process. The luminophore is adsorbed directly onto the surface of the layer via chemical or physical adsorption. This coating is suitable for measuring unsteady pressure fields due to its fast-responding characteristics. The time response of the present coating is evaluated theoretically and experimentally. Four kinds of luminophore, tris(4,7-diphenylphenanthroline)ruthenium(II) ([Ru(dpp) 3 ] 2+ ), tetrakis(4-carboxyphenyl)porphyrin (TCPP), platinum tetrakis(4-carboxyphenyl)porphyrin (PtTCPP), and pyrene butylic acid (PBA), have been tested on their response to a step change in pressure. A pressure jump apparatus and a shock tube were utilized to generate a pressure discontinuity. Some static characteristics were also tested. The theoretical analysis shows that the present coating should have a time response in the order of microseconds due to its porous structure. The time response depends not only on luminescence lifetime, which imposes an ultimate limit on the time response, but also on the thickness of the anodized aluminium layer, because oxygen permeation to the pores existing on the anodized aluminium layer can be described as a diffusive phenomenon. The effective diffusion coefficient is estimated to be approximately 5 × 10 −6 m 2 s −1 . Experimental results show that all the tested coatings except the PtTCPP coating have a response time of less than 1 ms. Only the PBA coating shows a substantial photodegradation. The response time of the [Ru(dpp) 3 ] 2+ coating is longer than 20 µs, and depends on the thickness of the anodized aluminium layer. The response time of the TCPP coating, on the other hand, is less than 10 µs, and is independent of the thickness of the layer. This independence suggests that the arrangement of the luminophore on the surface of the anodized aluminium layer affects the time response.
Experimental investigation of transonic buffet was conducted in JAXA 2m×2m transonic wind tunnel in order to obtain the validation data for unsteady computational fluid dynamics and to clarify the buffet phenomena of an 80% scaled NASA common research model. Unsteady pressure distributions on the two lines of the main wing were successfully measured on the transonic buffet condition. Mach number of the uniform flow was 0.85. Reynolds numbers based on the reference chord length were 1.515×10 6 and 0.947×10 6 . The shockwave oscillation on the wing can be classified into three regions, a small oscillation region without separation, an oscillation region with bump in the power spectrum, and a large oscillation region with broadband power spectrum. The Strouhal number based on the bump peak frequency was about 0.3. The cross-correlation and the phase analysis revealed that the pressure fluctuation of the bump frequency propagated from the wing root side to the wing tip side. Nomenclature b = span of the model f = frequnecy C p = pressure coefficient on the main wing C prms = root mean square of pressure coefficient fluctuation C p95% = pressure coefficient at 95% of local chord of the main wing c = local chord length Mach number P 0 = total pressure of uniform flow PSD = power spectrum density Re = Reynolds number RMS = root mean square St = Strouhal number, Stfc/U U = velocity of uniform flow U c = propagation velocity of the pressure fluctuation x = coordinate in chord direction at each span location y = coordinate in span direction angle of attack phase of cross-spectrum analysis dimensionless coordinate in span direction, y/(b/2)
Pressure-sensitive luminescent coating on porous anodized aluminium (AA-PSP) was applied to measure non-periodic unsteady pressure distribution on a wind-tunnel model. A high-speed digital video camera was used to capture the PSP signal. The pressure-sensitive dye was tris(4,7-diphenylphenanthroline) ruthenium(II) ([Ru(dpp)3]2+). The coating has a short response time of O(10 µs), although it exhibits temperature and humidity sensitivities. A hydrophobic coating was applied on the anodized aluminium surface to suppress the humidity sensitivity. A temperature sensitive paint was used to obtain the temperature distribution instantaneously with the pressure. The temperature data were used to correct the PSP response. An appropriate data acquisition procedure as well as digital image processing algorithm was established to compensate for the error from the temperature and humidity sensitivities. The present system was applied to measure the pressure distribution on a delta wing at a high angle of attack in transonic flow, whose flow is unsteady due to the interaction between shock waves and leading edge vortices. The non-periodic unsteady pressure distribution on the delta wing was successfully measured with the sampling rate of 1 kHz and within a few per cent error in absolute pressure level.
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