results: analysis of a
thin-airfoil stall phenomena
Existence of the laminar small bubble near the leading edge is known to be
the flow feature of a NACA64A006 airfoil at 5.5 degrees angle of attack. The
appearance of the bubble on the suction surface is the main mechanism of thin-airfoil
stall phenomena.
| Figure shown right is instantaneous pressure
distributions and total pressure iso-surfaces.
Present hybrid method properly resolves
small vortices shedding after the laminar separation
and uneven pressure distribution patterns resulting from the
existence of three dimensional vortices structures.
|
Instantaneous pressure distributions over the surface
and total pressure iso-surfaces. |
Figures shown below are instantaneous and time-averaged Mach number distributions
and velocity vectors near the leading edge.
From the plots of the instantaneous flow-field, the existence of the typical laminar small bubble is not clearly observed.
On the other hand,
the time-averaged flow-field clearly shows the laminar separation
with turbulent reattachment in the short distance behind the leading
edge where the typical laminar small bubble is formed.
Such flow-field is also observed in the experiments.
From the computational results shown in below,
the typical laminar small bubble near leading edge
is considered to be the phenomenon
observed as a time-averaged flow-field of the unsteady small vortices
shedding for a certain time length.
The computational results suggest that the stationary bubble dose not
exist practically but the unsteady small vortices shedding do exist.
Recent improvement of the time resolution in an experiment may help to
resolve such mechanism of the formation of the bubble.
Instantaneous flowfield |
Time-averaged flowfield |
Instantaneous and time-averaged local Mach number distributions
and velocity vector near leading edge at 5.5 degs. angle of attack.
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