Other Error Sources and Limitations

Other error sources include the self-illumination and induction effect; there are limitations in the time response and spatial resolution of PSP. The self­illumination is a phenomenon that the luminescent emission from one part of a model surface reflects to another surface, thus distorting the observed luminescent intensity at a point by superposing all the rays reflected from other points. It often occurs on surfaces of neighbor components of a complex model (Ruyten 1997a, 1997b, 2001a; Le Sant 2001b). The self-illumination effect on calculation of pressure and temperature are discussed in Section 5.3. Another problem is the ‘induction effect’ observed as an increase in the luminescent emission during the first few minutes of illumination for certain paints; the photochemical process behind it was explained by Uibel et al. (1993) and Gouterman (1997). In PSP measurements in unsteady flows, the limiting time response of PSP, which is
mainly determined by oxygen diffusion process across a PSP layer (see Chapter 8), imposes an additional restriction on the accuracy of PSP measurements. The spatial resolution of PSP is limited by oxygen diffusion in the lateral direction along a paint surface. Considering a pressure jump across a point on a surface (a normal shock wave), Mosharov et al (1997) gave a solution of the diffusion equation describing a distribution of the oxygen concentration in a PSP layer near the pressure jump point. According to this solution, the limiting spatial resolution is about five times of the paint layer thickness.

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