Forebody and leading edge vortex measurement using planar Doppler velocimetry

The planar Doppler velocimetry (PDV) technique has been demonstrated by emp loying it in a large-scale wind tunnel to record velocity fields surroundin g a model of a generic fighter plane. The PDV instrument employed here incl uded the following: (i) a frequency monitoring system for measuring the las er frequency corresponding to each set of scattering images, (ii) two detec tor systems (each composed of two 16-bit CCD cameras), one viewing the mode l from the top of the wind tunnel and the second from the side; (iii) iodin e vapour cells based on the starved-cell design, which eliminated the need for separate temperature control of the iodine reservoir; iv) a vibration-i solated, injection-seeded, Q-switched Nd:YAG laser and (v) custom data acqu isition software for linking the four cameras, the laser and the frequency monitor The PDV instrument was validated by comparing the PDV-derived veloc ity to the known value in the empty wind tunnel. An error of about 1 m s(-1 ) out of an 18.9 m s(-1) velocity component was found; the image noise comp onent (resulting primarily from the speckle effect) was found to be about 1 m s(-1). In addition, as a result of laser-sheet impingement on the model surface, velocities near the model surfaces are biased by background scatte ring effects. Nonetheless, it has been shown that PDV can be used effective ly to map velocity fields with high spatial resolution over complex model g eometries. Frame-averaged velocity images recorded at four axial stations a long the model have shown the formation of forebody and leading-edge vortic es and their complex interaction in the presence of the wing flow field.