• Version
• 100 Downloads
• 311.76 KB File Size
• 1 File Count
• November 25, 2016 Create Date
• November 25, 2016 Last Updated

National Advisory Committee for Aeronautics, Technical Notes - The Wave Suppressors used in the NACA Tank

So long a time was required for the disturbed water
to become quiet after a model had been towed down the
N.A.G.A. tank. that only 12 to 18 runs a day could be
made. In order to shorten the time lost in waiting be—
tween runs, several different methods of suppressing the
waves were tried.

The most effective form of wave suppressor developed
consists of wooden frames covered with fine copper screen—
ing and secured horizontally just beneath the surface of
the water at the sides of the tank. with these suppressors"—
placed every 50 feet along the length of the tank, 40 to
60 test runs a day can be made.

The effect of the waves produced by the models on the
frequency with which test runs could be made was given
very careful consideration in the preparation of the de—
sign for the N.A.C.A. tank (reference 1). Side overflow
troughs such as are used in the Washington Experimental
Model Basin, or in a somewhat different form in the Ottawa
tank (reference 2), are most effective wave suppressors
because the crests of the waves fall over the overflow
edge and are removed. It was not possible to provide such
troughs in the N.A.C.A. tank because of the additional
cost.

The University of Michigan tank has the side walls
coved in from the water line. The cove turns the wave
crests back on the waves and is quite successful in damp»
ing the waves and reducing the time between runs. It also
has an important advantage in that it makes possible a
considerable reduction in the weight of the towing car-
riage because the running rails are placed on the contin-
ous bracket formed by the cove, thus making the carriage
narrower. The lighter carriage structure can be acceler—
ated more easily and the weight of the prOpelling equip—
ment is reduced accordingly.

The saving in weight of towing carriage was thought
to be of special value and the coved~in sides were adOpted
for the N.A.C.A. tank in the hepe that they would also
prove effective as wave suppressors.

The effect of the coved~in sides on the waves was ob-
served very carefully when making test runs. Although the
larger waves were reduced in height quite rapidly, the
smaller ones were apparently not affected and it was nec—
essary to wait from 10 to 30 minutes after each run, ac—
cording to the amount of disturbance that had been pro—
duced, before beginning the next run.