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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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Thread | Thread Starter | Forum | Replies | Last Post |
1 Lensjet | johnhare | Technology | 0 | July 13th 03 07:47 PM |