Jet Diffusion in Proximity of a Wall Page: 3 of 24
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NACA TM No. 1214
to future experiments.a As variable parameters there remain'
the velocity of the jet, for which as criterion the mean velocity vA
in the exit of the engine model is chosen, and the outer
flow velocity vo; and indeed it suggests itself to once consider
the difference VA - vo and then the quotient VA/ o as significant.
Another parameter is the distance a of the exit cone from the
wall (that is, the distance of the point of exit closest to the
wall from the wall), and lastly the design of the fairing betweon
engine and wall will also play a part. In every case, the three-
dimensional variation of the jet downstream from the exit must be
II. CONVERSION TO OTHER OPERATING CONDITIONS
In view of the multiplicity of potential variations, it is
desirable to establish simplifying connections. For practical
purposes it would be more advantageous to be able to use easily
made static tests (without stream flow) and to compute all phases
with stream flow from it. Such a process is described in the
It is assted that the general state of flow (v) results,
in first approximation, from the superposition of the stream
flow (vo) with the jet flow (v'):
v = vt + vo (1)
This implies that the jot diffusion is to depend only on the
difference of the velocity in the Jet (vA) and outside of the
jet (vo), so that the velocity v in the form (w - vo)/(VA - vo)
for fixed particles is independent of the operating condition.
A .certain difficulty is involved in the finding of the location
of these particles, that is, to pass from the velocity transfonna-
tion (1) to the related transformation of the coordinates. A
rectangular system of body axes (x, y, z) is used with x in
the flow direction and the time coordinate t, with x = 0 (plane
of exit) for t = 0. The space coordinates of the particles
are functions of the time. Thus for equal time intervals t we
get a relation between the coordinates x,y,z of the particle
in the general flow (vo 1 0) andI the coordinates x',y',z' of
the flow without stream flow (vo = 0).
iThe problems of model similarity and reproduction of the hot-jet
in wind-tunnel tests are discussed in reference 1.
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Küchemann, D. Jet Diffusion in Proximity of a Wall, report, May 1949; (digital.library.unt.edu/ark:/67531/metadc64828/m1/3/: accessed January 19, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.