Page 237 - Fluid-Structure Interactions Slender Structure and Axial Flow (Volume 1)

218 SLENDER STRUCTURES AND AXIAL FLOW

Clamp Compressed air in *Water out
7 Rzf, Water out
air in

Glass jar

Glass view
ports
Water

Sprinkler

(b)
..... - ......
,- ..
-
MU2
............... R
R

i
PA
Figure 4.14 (a) New apparatus for forcing the fluid up the pipe in experiments by PaYdoussis at
McGill in 1980s; (b) Richard Feynman’s apparatus for resolving the sprinkler problem at Princeton
in late 1939 or 1940; (c) the sprinkler problem: which way does the sprinkler turn when aspirating
fluid (Gleick 1992)? (d) ‘negative pressurization’ and centrifugal forces on one arm of the aspirating
sprinkler.

Feynman’s and most other physicists’ tea-time conversation at Princeton and the Institute
for Advanced Study was dominated by this problem: if a simple S-shaped lawn sprinkler
were made to suck up water instead of spewing it out, Figure 4.14(c), would it rotate
backwards or in the same way as for normal operation? (This problem was tied to the
issue of reversibility of atomic processes!) Feynman could apparently argue convincingly
either way.
Eventually, Feynman decided to do an experiment which, as shown in Figure 4.14(b),
was remarkably similar to the author’s. He immersed the lawn sprinkler into a glass jar
filled with water, with an outlet connected to the sprinkler and a compressed air supply to
force the water into the sprinkler and out. With increasing pressure and flow, the sprinkler
refused to budge, up to the point where the glass jar exploded, spraying water all over.
The result was that Feynman was banished from the laboratory thenceforth.?

?The author feels to be in good company with a Nobel prize winner, in retrospect, for even the accident in
his laboratory is similar to Feynman’s. More than that, however, he is thankful for his engineering training, to
know not to do pressurized air experiments in glass jars - even if he did use a rubber hose!