Drag of Cylinders of Simple Shapes Page: 1 of 8
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REPORT No. 619
DRAG OF CYLINDERS OF SIMPLE SHAPES
By W. F. LINDSEYSUMMARY
In order to determine the efect of shape, compressi-
bility, and Reynolds Number on the drag and critical
speed for simple forms, the drag forces on models of various
simple geometric cross sections were measured in the
N. A. C. A. 11-inch high-speed wind tunnel.
The models were circular, semitubular, elliptical, square,
and triangular (isosceles) cylinders. They were tested over
a speed range from 5 percent of the speed of sound to a
value in excess of the critical speed, corresponding,.for each
model, approximately to a tenfold Reynolds Number range,
which extended from a minimum of 840 for the smallest
model to a maximum of 310,000 for the largest model.
INTRODUCTION
The aerodynamic drag of simple forms was one of the
earliest subjects of aerodynamic research. Although
numerous investigations have been conducted, drag
data for many forms, especially as affected by Reynolds
Number and compressibility, are incomplete or have
never been obtained. In accordance with a suggestion
made at one of the annual engineering conferences,
tests to investigate the variation of drag for various
simple forms with Reynolds Number were considered
for the variable-density wind tunnel. There was avail-
able, however, a large amount of data on the drag of
fundamental shapes that had been obtained under
conditions involving rather large and uncertain tur-
bulence effects. It was therefore considered preferable
to transfer the investigation to the 11-inch high-speed
tunnel, where disturbing turbulence effects were much
smaller and where new information could be obtained
concerning compressibility effects.
Previous investigations of the drag of simple forms
have included the effects of Reynolds Number on the
drag of circular cylinders (references 1 and 2), the
effect of compressibility on the drag of circular cylinders
(reference 3), the variation of drag with angle of attack
for square cylinders (reference 4), the drag of flat
plates normal to the wind (reference 4), and tests of
elliptical cylinders of various fineness ratios. Test
results, however, were not available for either triangular
or semitubular cylinders, nor were any previous in-vestigations available that included the effects of com-
pressibility on the drag characteristics of any of these
forms, except the circular cylinder (reference 3).
The present investigation, comprising measurements
of the drag of cylinders having various cross sections,
was conducted over a range extending from 5 percent
of the speed of sound to a speed above the value at
which the compressibility burble occurred. This speed
range corresponded, for each model, approximately to a
tenfold Reynolds Number range, which extended
from 840 to 8,400 for the smallest model and from
31,000 to 310,000 for the largest model.
The experiments were conducted from 1933 to 1936
in the N. A. C. A. 11-inch high-speed wind tunnel.
APPARATUS AND METHODS
The N. A. C. A. 11-inch high-speed wind tunnel,
in which the tests were made, is an induction-type
closed-throat tunnel having a circular air passage.
The tunnel is equipped with a balance, which is of the
three-componeht, photorecording, spring type. The
balance was designed for testing airfoils at speeds
from approximately 35 percent of the velocity of sound
to a speed approaching the velocity of sound. A
detailed description of the tunnel and of the photo-
recording balance is given in reference 5.
For some of the tests reported herein, the photo-
recording balance was not sufficiently sensitive to
measure the drag, and an auxiliary drag balance was
therefore used. This balance was of the pendulum
type and was designed to measure very small drag
forces on small models at low speeds. The forces
were measured by visual observation of the movement
of a beam. Three balance sensitivities were used;
a 1-inch deflection equaled 0.01 pound, 0.10 pound,
or 1.0 pound. By the variation of the sensitivity
and by the addition of counterweights, forces were
measured from a minimum of 0.001 pound to a maxi-
mum of 10 pounds. One of the features incorporated
in the construction of the balance was a means for
applying tension to the model in order to overcome
vibration difficulties encountered with some of the
models in portions of the speed range.
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Lindsey, W. F. Drag of Cylinders of Simple Shapes, report, October 27, 1937; (https://digital.library.unt.edu/ark:/67531/metadc66277/m1/1/?rotate=90: accessed July 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.