Quantitative NO2 molecular tagging velocimetry at 500 kHz frame rate

NO 2 molecular tagging velocimetry (MTV) is demonstrated at repetition rates as high as 500 kHz in a laboratory scale Mach 5 wind tunnel. A pulse burst laser and a home built optical parametric oscillator system were used to simultaneously generate the required 355 and 226 nm wavelengths for NO2 photodissociation (tagging) and NO planar laser induced fluorescence imaging (interrogation), respectively. NO2 MTV images were obtained both in front and behind the characteristic bow shock from a 5 mm diameter cylinder. From Gaussian curve fitting, an average free stream flow velocity of 719 m/s was obtained. Absolute statistical precision in velocity of ∼11.5 m/s was determined, corresponding to relative precision of 1.6%–5%, depending upon the region of the flow probed.