Aspiration has been experimentally proven to roughly double the allowable stage loading of a fan or compressor in a gas turbine engine. The potential exists to cut the number of stages required for a given pressure ratio in half, essentially halving the weight and length of the component. This will directly affect the power to weight ratio the engine and reduce the overall engine volume. This technology is applicable to air vehicles requiring high thrust to weight or compact engines. In particular, the combination of high thrust to weight and compact form factor makes the technology attractive for military fighter aircraft engines. Additionally, this technology may be applied in vertical takeoff and landing (VTOL) aircraft, where thrust to weight is of paramount concern. Finally, the low Reynolds number aspect of the proposed research could have implications for small engines. Whereas high altitude engines experience low Reynolds numbers due to low density, the short length scale in small engines increases the importance of viscosity and reduces performance. This technology could be utilized to increase the performance of smaller gas turbines that power many unmanned vehicles. NASA has operated many high altitude science platforms that could benefit from the application of compressor aspiration. Vehicles such as the General Atomics Altair, Lockheed Martin ER-2, the Northrop Grumman Global Hawk, and WB-57 are powered by turboprop or turbofan engines, and all provide NASA with time on station at high altitude to perform scientific missions. Several of the aircraft built for NASA's ERAST program used internal combustion engines with multiple stages of turbocharging. The proposed work specifically aims to improve the utility of these kinds of aircraft by increasing the altitude and endurance that can be achieved despite the low density, low Reynolds number conditions. Compressor aspiration has the potential to control the effects of increased viscosity with increasing altitude through the removal of low energy flow from the compressor before it can cause separation and ultimately reduce compressor efficiency. It can also increase stage loading, reducing the number of axial compressor or turbocharger stages required. These performance and weight enhancements could allow for a leap in the ability of high altitude science vehicles to stay on station, as well as allow for increases in the maximum service ceiling.
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