Affiliations: Graduate Research Assistant, School of Mechanical and
Aerospace Engineering, Seoul National University, Shilim-dong, Kwanak-gu,
Seoul, 151-742, Korea | Associate Professor, School of Mechanical and
Aerospace Engineering, Seoul National University, Shilim-dong, Kwanak-gu,
Seoul, 151-742, Korea. E-mail: ybyoon@snu.ac.kr
Abstract: Two-dimensional velocity distributions outside a Mach 2.0 supersonic
nozzle have been investigated using a digital particle image velocimetry (PIV).
Mean velocities, vorticity field and volume dilatation field were obtained from
PIV images using 0.33 μm titanium dioxide (TiO_2)
particle. The seeding particle of larger size, 1.4 μm
TiO_2, was also used for the experimental comparison of
velocity lag downstream of shock waves. The results have been compared and
analyzed with schlieren photographs for the locations of shock waves and
over-expanded shock structure to inspect possibilities and limits of a PIV
technique to over-expanded supersonic flows. It is found that although the
quantitative velocity measurement using PIV on over-expanded supersonic flows
with large velocity and pressure gradients is limited, the locations of normal
shock and oblique shock waves can be resolved by the axial/radial velocity
fields, and over-expanded shock structure can be predicted by vorticity field
and volume dilatation field which are acquired from the spatial differential of
the velocity field.
Keywords: PIV, Over-expanded supersonic flows, Mean velocity, Vorticity, Volume dilatation
