When there is a wall near the jet, it deflects and flows while being
attached to the wall owing to the Coanda effect. The flow characteristics of
the incompressible and two-imensional (2D) Coanda-reattached jets have been
considerably explained. However, 2D supersonic under-expanded jets, reattached
to side walls, have not been sufficiently investigated. These jets are used in
gas-atomization to produce fine metal powder particles of several micrometers
to several tens micrometers. In this case, the supersonic under-expanded jets
are issued from an annular nozzle, which is set around a vertically installed circular nozzle for molten metal. The jet
flow at the center cross-section
of the annular jet resembles a 2D Coanda-reattached jet that deflects and attaches
on the central axis. In this study, the flow characteristics of a supersonic under-expanded
Coanda air jet from a 2D nozzle that reattaches to an offset side wall are
elucidated through experiment and numerical analysis. For numerical analysis,
we show how much it can express experimental results. The effects of supply
pressure P0 on the flow characteristics
such as the flow pattern, size of shock cell, reattachment distance, and
velocity and pressure distributions, etc. are examined. The flow pattern was
visualized by Schlieren method and the velocity distribution was measured using
a Pitot tube. These results will be also useful in understanding the flow
characteristics of a gas-atomization annular nozzle approximately.
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