Comparison of Lifetime-based Pressure-Sensitive Paint Measurements in a Wind Tunnel using Model Pitch-traverse and Pitch-pause Modes

Abstract

In order to improve the data productivity of a wind tunnel test, the model under investigation in the wind tunnel is moved continuously with a predetermined constant angular speed in the so-called pitch-traverse mode. Alternatively, the wind tunnel model can be moved in the so-called pitch-pause mode, in which it keeps its position for a certain (measurement) time at a fixed pitch position, after which it is moved to the next pitch position. The latter procedure is more time-consuming, so that, for the same time interval, the number of measured data points taken in pitch-pause mode is less than that for the pitch-traverse mode. Since wind tunnel test time can be quite expensive, in most wind tunnel tests where only conventional forces and pressures are recorded with conventional measuring systems, the wind tunnel model is moved in pitch-traverse mode in order to obtain as much aerodynamic data as possible during the tun-nel runtime. The application of the Pressure-Sensitive Paint (PSP) technique has been widely used in wind tunnel testing for the purpose of providing pressure data on wind tunnel models with high spatial resolution. The lifetime-based PSP method has several advantages over the in-tensity-based method, since it often has higher accuracy. Up until now, the lifetime-based PSP technique has mainly been used for wind tunnel testing where the test model has been moved in the pitch-pause mode. The traditional lifetime method using on-chip accumulation requires multiple (~1,000) excitation light pulses to accumulate enough luminescence (fluorescence or phosphorescence) photons on the camera sensor to provide acceptable signal-to-noise ratios, and therefore it may seem per se to be not compatible with a continuously moving wind tunnel model. Nevertheless, the present study verifies the application of lifetime-based PSP utilizing on-chip accumulation with a continuously moving wind tunnel model which would make the entire PSP data acquisition compatible with that of the conventional measurements (forces and pressures), as mentioned above. In this paper, the applicability of the lifetime-based PSP tech-nique to a continuously moving wind tunnel model (in pitch-traverse mode) is investigated with the help of measurements in the transonic wind tunnel in Göttingen (TWG). For this inves-tigation, PSP was applied on the delta-wing model DLR-F22, which is to be tested in TWG. The pressure distribution on the wind tunnel model was measured using the PSP lifetime method for both model movement modes (pitch-pause and pitch-traverse mode), so that the corresponding PSP results could be directly compared with each other. In addition, an error analysis of the PSP results was carried out and compared with the conventional pressure measurement results, hence providing an assessment of the accuracy of the PSP results; finally, a recommendation for future PSP measurements could be given.