Interactions of oblique waves have recently been investigated theoretically
and numerically and found to give rise to rapid transition in flows subcritical
to linear wave
disturbances. The transition scenario consists of the formation and transient
growth
of streamwise streaks of high and low velocity and later a rapid growth
of high-frequency
disturbances leading to breakdown. The present study is the first extensive
experimental investigation of oblique transition. The experiments were
carried out in
a plane Poiseuille flow air channel in which the oblique waves were generated,
one at
each wall, by vibrating ribbons and the development of the flow was mapped
with
hot-wire anemometry. The experiments consist both of low- and high-amplitude
wave
disturbances; in both cases streaky structures are created. For the low-amplitude
case
these structures decay, whereas for the high amplitude the flow goes towards
breakdown. This study has confirmed and extended previous theoretical and numerical
results showing that oblique transition may be an important transition
scenario.