Seems entirely reasonable to me. It’s basically a motive flow pump. A high
velocity stream has lower static pressure, which entrains surrounding fluid.
Compared to the stream itself, the exit of the augmentor has slightly lower
velocity, and slightly higher mass flow. The work done to accelerate this
additional fluid creates thrust.
Other uses:
Some piston aircraft use this effect for cooling. The cowl is shaped carefully
around the exhaust, causing the high velocity exhaust to entrain and accelerate
surrounding air. This sucks more air through the cooling system.
Most transport aircraft have motive flow fuel pumps as boost and transfer
pumps. High pressure excess fuel exiting the engine driven mechanical high
pressure fuel pump is directed through a venturi in the fuel tanks, where it
entrains additional fuel and sends it back up the low pressure fuel lines to
the engine. Should the primary in-tank electrical pumps fail (total loss of
electrical power), the motive flow pumps should be sufficient to supply the
engines with fuel without using any electricity or moving parts (although this
flow generally isn’t enough for high thrust or altitude)
On Feb 11, 2021, at 2:38 AM, Dr Edward Jones <RocketPioneer@xxxxxxxxx> wrote:
In the early 1950s, Wilmot and Mansour of Jetex in Totten, near
Southampton UK, expanded their line of reloadable solid rocket motors
for aeromodels, with thrust from 1/2-oz up to 6-oz, burn times around
15-20 seconds. Jetex came up with "augmenter tubes" to fit around the
exhaust and increase thrust.
Per their reports: "Makers of Jetex offered two sizes of ‘augmenter
tubes’, which were formed from thin aluminum sheet; the forward end is
bell-mouthed and considerably larger in diameter than the Jetex engine
(one tube size was for the two 50 engines, the other for the
Jetmaster, PAA-Loader 150 and Scorpion 600), and the edge of the bell
is placed about even with the rear of the engine case."
"When the jet is operating, cool air is drawn into the tube mouth and
is expelled at the tail of the model along with the hot gases. This
air not only cools the gases but contributes to thrust. Figures show
that the augmenter will increase thrust from 20 to 30 percent."
"Performance tests were made by Aeromodeller in January 1954. Results
were presented as two graphs and a table."
https://archivesite.jetex.org/motors/motors-accessories.html
I remain skeptical of this thrust augmentation. What's your opinion?