*ENIAC* *U. S. Army*

# A Logical Coding System Applied to the ENIAC

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SECTION VI:
FLOW DIAGRAM OF TYPICAL PROBLEM

Suppose that we wish to have the ENIAC compute the supersonic airflow past
a body of revolution ABC, without yaw. If the Mach number M(velocity in units
of sound velocity) is sufficiently large, the nose angle sufficiently small on
the curve ABC concave toward the axis, it is believed that there will exist an
attacked shock-wave front (surface of discontinuous pressure, density, and
velocity) and the velocity will be everywhere supersonic. It is then
reasonable to assume that replacing a small Section AE of the nose contour AB
by a straight line will have little influence on the flow at a distance from
AE. This assumption does, however, have the following effects:

1. If the characteristic (curve making angle (omega) = csc**-1 M with
streamlines at each point, or curve of propagation of weak disturbances) from
E, making an acute angle with the velocity vector, hits the shock wave at a
point F, then the shock front is straight from A to F.

2. In the region AEF, the partial differential equations defining velocity
distribution can be satisfied by assuming that the velocity is constant on
straight lines through A (G. I. Taylor and J. W. Maccoll, The Air Pressure on
a Cone Moving at High Speeds," Proc. Roy. Soc. A139, 278-311 (1938).). Thus u
and v are functions of a single parameter in AEF and the partial differential
equations become ordinary. It is the solution of these equations for x, y, u,
v, and z along EF which we shall choose as an illustrative problem.

Figure 6.1

Figure 6.2

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