The spatial evolution of the disturbances that lead to boundary-layer
transition on a
swept wedge is computed by large-eddy simulations (LES). Stationary and
travelling
crossflow-vortex disturbances are generated using steady and random-amplitude
suction
and blowing on the wedge. For a fixed initial amplitude of the stationary
vortex
and low-amplitude unsteady disturbances, the LES show the evolution of
stationary-dominated crossflow disturbances similar to previous simulations and experiments:
linear amplification is followed by vortex roll-over and doubly inflectional
velocity
profiles just prior to transition. A high-frequency secondary instability
is associated
with the double inflection points in the velocity profiles. The harmonic
modes of the
primary disturbance were found to be amplified, while no energy was found
in any
subharmonic mode. The physical phenomena were significantly different when
the
stationary and travelling vortices have comparable initial amplitudes:
in this case, the
vortex roll-over does not occur and transition is dominated by the travelling-wave
component.
HIFiRE-1 Boundary-Layer Transition: Ground Test Results and Stability Analysis
