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3 Lensjet



 
 
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Old July 19th 03, 02:46 PM
johnhare
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Default 3 Lensjet

At home I don't actually number the dozens of possible configurations
of the lensjet. I'm doing it here to keep track in case anyone gets
interested. Most of them are some variation on the theme of two
axial compression fans back to back connected at the tips by dual
purpose blades and shaped into a lens built up of tension arches.
Structural seal rings seperate the various blade types in the same
arch.

The 3 dimensional structure with all tension arches is rigid
enough that very thin chord compressor and turbine blades can
be used with acceptable vibration even with the partial admission
turbine/compressor blading. The thin chord blades automatically
suggest high aspect ratio airfoils and lower end clearance losses.
The thin chord also allows close stacking of multiple stages if so
desired. The structural rings (snubbers in normal practice) are
almost parallel to the centrifugal stresses imposed on the blades
in operation. This allows considerable expansion and contraction
on the lenses with fairly low scrubbing problems as in a normal
jet with thermal and centrifugal expansion requiring margins at the
blade tips.

The partial admission turbine, and regenerative cooling allow
much higher turbine inlet temperatures than conventional, fuel
efficient turbojets. The higher turbine inlet temperatures allow
the jet to operate at lower compression ratios than conventional.
The high turbine inlet temps also eliminate the need for an
afterburner. More of the enthalpy is available behind the turbine
for thrust as a much smaller fraction is used to drive it. The lower
pressure/temperature drop across the turbine can bring the
available thrust gasses into low end rocket country.

All of this being useless if not reduced to practice, a lot of my
focus has been finding a configuration that can be built and
demonstrated inexpensively. The simplest I have found yet
is derived from the simularity between the centrifugal compressor
stage and some inflow radial turbines. The blading for centrifugal
compression outwards, and turbine flow inwards matches
reasonably well with reasonable efficiency in both modes.

This configuration has one rotating lens instead of the contrarotating
two in previous concepts. The air is drawn in through nearly full
diameter axial fans for a compression ratio of ~1.4. Then it is
expelled through partial admission centrifugal blading for a
further compression ratio of ~2 for a total of 2.8. This is burned
in the volute before being used to drive the inflow turbine.
The drive gasses pass through the turbine blades into an interior
cavity, and then out through the blades to the thrust nozzle. This
configuration has the possibility of being more aerodynamically
efficient than many of the previous ones, and can scale down
because the burner is now external to the lens. Thrust will
require more air and fuel due to the very low pressure exhaust.

A 1 foot diameter test unit should develop 1.5-2 k thrust
with high 3 digit Isp. This is clearly in the homebuilt range.
My capabilities should reach the point of starting this project
for mock up hardware by the end of the year. Static test hardware
to follow if I can get everything to seem to fit properly.

A rocket can operate in the volute of this type turning it into
a supercharged ejector turbojet. This will be done early with
small rockets for testing purposes. Later, a 0.6 scale jet of
similar configuration can be used to further compress most of
the air from the primary jet to get a compression ratio of 7.8
for the primary burn. It is possible that a third even smaller
jet would be desired to boost the second jet. The three stage
affair would have thrust nozzle pressures in the 8-10 atmosphere
range. These would be operated in the manner researched by
GE for variable cycle turbojets. As mach increases, desired
compression ratio decreases, so the higher stages are taken
off line in sequence until the first stage is operating off of ram
pressure mostly.

In this concept, as in the others, mass of the turbomachinery
seems to be less than 1% of the projected thrust. This seems
to be so far off standard practice that there are almost certainly
a few gotchas lurking around. Anyone that cares to spread these
concepts around publicly, even for the purposes of ridicule, will
be doing me a favor. Attribution is up to the individual as my
purpose is to avoid being halted by later patents rather than
credit for the concept. If it works, I'll bank the credit in dollars,
if not, I haven't wasted effort$ patenting another Dean Drive
device.

John Hare

 




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