Imaging of an underexpanded nozzle flow by UV laser Rayleigh scattering |
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Authors: | N J Dam M Rodenburg R A L Tolboom G G M Stoffels P M Huisman-Kleinherenbrink J J ter Meulen |
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Institution: | (1) University of Nijmegen, Department of Molecular and Laser Physics Toernooiveld, NL-6525 ED Nijmegen, The Netherlands, NL |
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Abstract: | Rayleigh scattering of ultra-violet laser light is applied as a diagnostic tool to record gas density distributions in a
supersonic nozzle flow. The output beam of a pulsed ArF excimer laser (λ=193.4 nm) is focussed into a thin light sheet radially
intersecting a dry air flow emanating from a circular nozzle. An intensified CCD camera is used to record the Rayleigh scattered
light in a direction perpendicular to the light sheet. Since the Rayleigh scattering intensity is directly proportional to
the local gas density, this results in two-dimensional gas density distribution maps of radial slices through the flow. Images
of the flow density are presented for stagnation pressures between 0.2 and 0.7 MPa (0.1 MPa ≡1 bar), showing the transition
from subsonic to supersonic flow and, at higher pressures, the formation of a Mach disk. Density maps can be recorded with
single laser pulses, effectively freezing the flow structure on a 20 ns time scale. The diamond pattern, characteristic for
underexpanded supersonic nozzle flows, is quantitatively monitored, with the experimental results being in reasonable agreement
with predictions from a simplified theoretical model.
Received: 25 September 1996/Accepted: 19 May 1997 |
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