Application of the direct PSP-lifetime method on pyren-based paint as a completion of the existing DLR PSP system

Pressure Sensitive Paint (PSP) provides a pressure map on the whole surface of a wind tunnel model without transducers and tubing. In principle there are two different ways to gather experimental data-by using the fluorescent decay time of excited luminophore molecules (lifetime method) or by detecting its integrated fluorescent emission (intensity method). During the last five years PSP measurements utilizing the intensity of the luminescence are performed at DLR with pyren-based paints. This paint is characterized by its low temperature sensitivity and high quantum efficiency-due to these qualities the lifetime technique is also developed for this paint type. PSP measurements utilizing the lifetime of the luminescence are independent of particles in the flow (dust, oil, condensed water, etc.), change in density, light source instabilities and light reflection and less sensitive to the model movements because there is no need for a reference image. The short luminescence decay time of pyren, of the order of 50 ns, gives the possibility to investigate fast flow processes (pressure measurements on helicopter blades, propellers, turbines, etc.)