Laser velocimetry for turbofan inlet distortion applications

Purpose The purpose of this paper is to assess state-of-the-art techniques for quantifying flow distortion in the inlets of turbofan engines, particularly with respect to the prospects for future flight applications. Design/methodology/approach To adequately characterize the flow fields of complex aircraft inlet distortions, the author has incorporated laser velocimetry techniques, namely, stereoscopic particle image velocimetry (PIV) and Doppler velocimetry based on filtered Rayleigh scattering (FRS), into inlet distortion studies. Findings Overall, the results and experience indicate that the pathway for integration of FRS technologies into flight systems is clearer and more robust than that of PIV. Practical implications While always a concern, the topic of inlet distortion has grown in importance as contemporary airframe designers seek extremely compact and highly integrated inlets. This research offers a means for gaining new understanding of the in situ aerodynamic phenomena involved with complex inlet distortion. Originality/value This paper presents unique applications of turbofan inlet velocimetry methods while providing an original assessment of technological challenges involved with progressing advanced velocimetry techniques for flight measurements.

Antlions are sensitive to subnanometer amplitude vibrations carried by sand substrates

European pit-building antlions (Myrmeleon inconspicuus / Rambur 1842) are studied in their capacity to detect vibrations generated by the locomotion of an ant (Cataglyphis cursor) outside the pit. These locomotions have been recorded by laser velocimetry and copied in detail in their time sequences. The sequences are replicated by micro-controllers digital outputs acting on piezoelectric transducers placed several centimeters outside the peripheries of the pits: their actions on the surface of a sand media create surface waves with particle accelerations that are 3 orders of magnitude less than g, alleviating any possibility of sand avalanche towards the bottom of the pit. Depending on the amplitude of the vibrations, the antlions answer back, generally by sand tossing. One remarkable feature is the time delay from the start of the cue and the aggressive behavior induced by this cue. This time delay is studied versus the cue amplitude. The result of this work is that anlions answer back within minutes to cues with amplitudes between 1 to 2 nanometers at the level of their mechanosensors, and within seconds to these same cues if they are preceded by a sequence of signals at the Ångström amplitude. This induced aggressive behaviour evidences the sensitivity to vibrations at extremely low level.