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<DOCNO>
252
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<TITLE>
an investigation of interference effects on similar models of
different size in various transonic tunnels in the u.k. .
</TITLE>
<AUTHOR>
f. o/hara and l. c. squire, r.a.e.
</AUTHOR>
<BIBLIO>
and a. b. haines, a.r.a.
</BIBLIO>
<TEXT>
details are given of a programme of tests being made on similar sweptwing
models in transonic tunnels of different types .  force measurement
results at subsonic speeds in the r.a.e. 3 ft. by 3 ft. slotted tunnel
show only small interference effects for models of moderate blockage
at low incidence., at higher incidences, the interference effect on
lift becomes appreciably greater than estimated by theory, and
significant pitching moment differences occur, apparently due to wall
interference on the wing flow field .  comparable but smaller effects
are evident in the results from the a.r.a. 9 ft. by 8 ft. perforated
tunnel .  at speeds just above m = 1, the force fluctuates as speed
is increased, because of wave reflection interference .  the magnitude
of the fluctuations diminishes as speed is further increased and this
reduction is more marked in the perforated tunnel .  pressure
measurements along the top of the body at zero incidence show delay in
shock movements at high subsonic speeds indicating a blockage effect
on speed., the effect is larger in the perforated tunnel though
smaller than predicted by theory .  above m = 1, both expansion and
shock waves are strongly reflected in the slotted tunnel but
considerable alleviation, particularly of shock waves, is achieved
in the perforated tunnel, for which an analysis of the effects is
given, showing for example, the effect of the open-area distribution of
the walls .
</TEXT>
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