Turbulent Diffusion Pattern of Turbojet Exhaust Page: 4 of 8
This report is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to UNT Digital Library by the UNT Libraries Government Documents Department.
Extracted Text
The following text was automatically extracted from the image on this page using optical character recognition software:
UNCLASSIFIED
Lexington Project Report #14-9
Title: Turbulent Diffusion Pattern of Turbojet Exhaust
Author: W. C. Cooley
Date: September 9, 1948
Place: Lexington
The purpose of this study is to estimate the extent of the region
in the wake of an open-cycle nuclear turbojet aircraft, which would contain
an appreciable concentration of air which has been made radioactive or
has been contaminated by fission products in pasting through the nuclear
reactor. This region of turbulent spreading of the jet would be the
region of greatest danger to the occupants of a towed aircraft.
The case investigated was a turbojet tug airplane delivering
20,000 lb, thrust at a lMach number of 0.9 and 30,000 ft. altitude. A
previous design study resulted in the following data which were assumed
to apply in this case.
Specific impulse, I 4.3 lb.-sec./lb.
Reactor air-flow rate, W x465-b./sec.
Nozzle exit area, A 16.9 sq. ft.
- * Noz21e exit diameter (one Unit), D 14.63 ft.
Jet velocity, Vj 2290 ft./sec.
Plane velocity, VP 893 ft./sec.
Conversation with Mr. W. Forstall, Jr. of the M. I. T. Gas Turbine
Laboratory indicated that no good experimental results for the spreading
of a supersonic jet were available. However, for subsonic flow, the
radius of the mixing region (that is, the radius at which the concentration
of primary jet gas has dropped to a negligible value) is found to be
mainly a function of the ratio of the velocity of the primary jet to the
velocity of the secondary air. Experiments by Mr. Forstall have resulted
in values of ro/a (see figures 1 and 2) as a function of X/D for various
ratios of primary-to-secondary air velocities. In the case under con-
sideration, the ratio Vj/VS 2290/893 = 2.57. It was desired to de-
termine the radius of the mixing region at a distance of 3000 ft. (X/D
3000/4.63 = 650 diameters) back from the turbojet exhaust. These values
fall within the range of values of velocity ratio and X/D investigated
by Forstall, except that the actual velocities and distances are greater
in this case. It was assumed that the jet as it first issues from the
nozzle will be rapidly decelerated and the data for subsonic flow should
apply at least approximately.
In Figure 2, a curve was estimated for Vj/Vp u 2.57 and a value of
ro/a = 15 was read at X/D = 650 diameters. The nozzle radius, a, is
2.31 ft. and therefore the radius of the jet mixing region would be
15(2.31) = 35 ft. at a distance of 3000 ft. downstream.
The concentration of exhaust air at the center of the mixing region
decreases very rapidly with distance downstream. At any value of X, the
radial distribution of contaminated air would be approximately as shown
Upcoming Pages
Here’s what’s next.
Search Inside
This report can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Report.
Cooley, W. C. Turbulent Diffusion Pattern of Turbojet Exhaust, report, September 9, 1948; United States. (https://digital.library.unt.edu/ark:/67531/metadc931802/m1/4/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.