The Pressure-Sensitive-Paint (PSP) measurement technique is based on the dependence of the intensity or decay time of its luminescence on the pressure, brought about by oxygen quenching. PSP is usually exited by light of an appropriate wavelength (e.g. UV-light) and its pressure dependent luminescence decay time or lifetime is detected by a camera system (CCD or CMOS). Two basic types of lifetime measurement exist: the first type is a time-domain lifetime method. For this method a pulsed light is used to excite the paint and the pressure dependent time constant is determined from the decay curve of luminescence intensity. The second type is a frequency-domain fluorescence lifetime imaging (FLIM) where sinusoidal modulated light is used to excite the paint and the PSP luminescence is simultaneously detected to calculate its pressure dependent phase shift and amplitude ratio. Based on UV-LEDs a light source has been designed which provides high intensity stable and low distorted sine-modulated light of constant amplitude which is essential for the accuracy of the presented method. The new light source is used to investigate the influence of frequency on pressure sensitivity of a PSP sample to optimize the system for application in transonic wind tunnel tests.
The rapid progress of light emitting diode (LED) technology has recently resulted in the availability of high power
devices with unprecedented light emission intensities comparable to those of visible laser light sources. On this basis two
versatile devices have been developed, constructed and tested.
The first one is a high-power, single-LED illuminator equipped with exchangeable projection lenses providing
a homogenous light spot of defined diameter. The second device is a multi-LED illuminator array consisting of a number
of high-power LEDs, each integrated with a separate collimating lens. These devices can emit R, G, CG, B, UV or white
light and can be operated in pulsed or continuous wave (CW) mode. Using an external trigger signal they can be easily
synchronized with cameras or other devices. The mode of operation and all parameters can be controlled by software.
Various experiments have shown that these devices have become a versatile and competitive alternative to laser and
xenon lamp based light sources.
The principle, design, achieved performances and application examples are given in this paper.
The non-intrusive in-flight deformation measurement and the resulting local pitch of an aircraft propeller or helicopter rotor blade is a demanding task. The idea of an imaging system integrated and rotating with the air-craft propeller has already been presented at the 30th International Congress on High-Speed Imaging and Photonics (ICHSIP30) in 2012. Since then this system has been designed, constructed and tested in the laboratory as well as in-flight on the Cobra VUT100 of Evektor Aerotechnik, Kunovice (CZ). The major aim of the EU FP7 project AIM2 ("Advanced In-flight Measurement techniques 2" – contract No. 266107) was to ascertain the feasibility of this technique under extreme conditions - vibration and large centrifugal forces – to real flight testing. Based on the gained experience a new rotating system for the application on helicopter rotors has recently been constructed and tested on the whirl tower of Airbus Helicopters, Donauwoerth (D). In this paper the principle of the applied Image Pattern Correlation Technique (IPCT), a specialized type of Digital Image Correlation (DIC), is outlined and the construction of both rotating 3D image acquisition systems dedicated to the in-flight deformation measurement of the aircraft propeller and helicopter rotor are described. Furthermore, the results of the ground and in-flight tests of these systems will be shown and discussed. The obtained results will be helpful for manufacturers in the design of their future aircrafts.
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