Propulsion System for Very High Altitude Subsonic Unmanned Aircraft

Bents, David J.; Mockler, Ted; Maldonado, Jaime J.; Harp, James L.; King, Joseph F.; Schmitz, Paul

doi:10.4271/981261

Cited by 15 publications

(10 citation statements)

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“…The future application of altitude ignition in HALE flight is necessary to take care of the temperature condition. The power plant for near-future HALE flights will be chosen from among turbocharged reciprocating engines and turbojet engines 13 . An investigation has suggested that turbocharged reciprocating engines are more favorable because of cost and some other restrictions.…”

Section: Discussion Of Altitude Ignition Conditionsmentioning

confidence: 99%

Investigation of Combustion and Altitude-Ignition Performance of a Small Hydrogen-Fueled Reversed-Flow Turbine Combustor

Okai

Himeno

Watanabe

et al. 2014

52nd Aerospace Sciences Meeting

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This paper describes altitude ignition experiment results for a scaled hydrogen-fueled turbojet engine model applied for Balloon-Based Operational Vehicle in-flight testing.Although hydrogen has remarkable combustion characteristics among the combustion fuels, at low pressures, the hydrogen-fueled combustor showed difficulty in the originally planned altitude ignition conditions. The follow-up step-by-step refinement of the ignition sequence is explained using experimental data. A similar situation might occur for future hydrogenfueled High Altitude Long Endurance (HALE) flights. These limited but still wide combustion capabilities of the hydrogen fuel might facilitate the introduction of gas-turbine power plants in the HALE flights. NomenclatureBOV = Balloon-based operation vehicle HALE = High Altitude Long Endurance HATS = High-altitude test stand d = Diameter PC = Pre-cooler T = Temperature U = Velocity UAS = Unmanned Aircraft System ∆ = Difference τ = Delay time Subscripts H = Horizontal scale V = Vertical scale

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Section: Discussion Of Altitude Ignition Conditionsmentioning

confidence: 99%

Investigation of Combustion and Altitude-Ignition Performance of a Small Hydrogen-Fueled Reversed-Flow Turbine Combustor

Okai

Himeno

Watanabe

et al. 2014

52nd Aerospace Sciences Meeting

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“…The impeller efficiency calculated by using the gas-state parameters of the inlet, the rotor-stator interface and the outlet of the compressor and Equation (2).…”

Section: Discussion On Efficiency Performancementioning

confidence: 99%

“…Besides gas turbines and turboshaft engines, unmanned air vehicles (UAVs) are also one of the important applications of centrifugal compressors. Compression ignition engines are suggested as a suitable choice for the propulsion system of high altitude unmanned air vehicles [2][3][4]. Because of the lower air consumption compared to turbojets, turbocharged compression ignition engines can deliver constant power at different levels of altitude.…”

Section: Introductionmentioning

confidence: 99%

Effects of Variable Diffuser Vanes on Performance of a Centrifugal Compressor with Pressure Ratio of 8.0

Ebrahimi¹,

Huang²,

He³

et al. 2017

Energies

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Abstract:In numerous applications, centrifugal compressors are required to provide a high pressure ratio with good efficiency while also working in a wide operating range. This is a challenge because as pressure ratio increases, efficiency and operating range inevitably decline. This paper studies the effects of a variable geometry diffuser on the performance and operating range of a centrifugal compressor with high pressure ratios of up to 8.0. The numerical method employed three-dimensional Reynolds-averaged Navier-Stokes simulations. An analysis of the matching of the vaned diffuser with the impeller for different working conditions and diffuser vane angles is presented. The results show that improved matching of the adjusted diffuser increased efficiency by 4.5%. The range extension mechanism of the variable diffuser is explained, and it is shown that adjusting the vane angle by +6 • to −6 • extended the operating range of the compressor by up to 30.0% for pressure ratios between 5.0 and 6.0. The interaction between diffuser and impeller was examined, and the independent characteristic of the impeller is illustrated. The connection between the incidence angle at the leading edge of the impeller and flow separation near the tip of the impeller is discussed.

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“…In addition, the turbocharged spark-ignited gasoline engine has been considered as the only option for the subsonic propulsion system of high-altitude unmanned air vehicles (UAVs). 14) Studies that analyze the Reynolds number effects on the performance of centrifugal compressors have been ongoing for a long time. When an existing compressor that is originally designed for air is applied for use with different gases in the chemical and petroleum industries, or a scaled-down version of it is required for small applications, the Reynolds number can change.…”

Section: Introductionmentioning

confidence: 99%

Effects of Low Reynolds Number on Performance in a Centrifugal Compressor

Kim¹,

Jeon²,

Jung

et al. 2018

Trans. Japan Soc. Aero. S Sci.

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The centrifugal compressor is an essential part of the auxiliary power unit (APU) for airplanes and helicopters. As aircrafts are sometimes required to operate at high altitudes, the aerodynamic condition of the gas turbine and APU lies at low Reynolds numbers. This study presents numerical simulations to investigate the effects of low Reynolds numbers on the flow and performance of a centrifugal compressor, including the impeller, diffuser and volute. For the reference Reynolds number (8.4©10 5), the numerical results agreed well with the experimental measurement in total pressure ratio. It was found that the performance of the overall compressor decreases slowly as the Reynolds number decreases, but drops significantly below the threshold of 200,000. The flow inside the impeller didn't separate in spite of thick boundary layers, even at the lowest Reynolds number (8.4©10 4). In this study, it was found that the diffuser is the most susceptible part for separation caused by low Reynolds numbers. The large separation in the diffuser vanes degrades the flow, and decreases the efficiency of the diffuser and volute successively.

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Propulsion System for Very High Altitude Subsonic Unmanned Aircraft

Cited by 15 publications

References 0 publications

Investigation of Combustion and Altitude-Ignition Performance of a Small Hydrogen-Fueled Reversed-Flow Turbine Combustor

Investigation of Combustion and Altitude-Ignition Performance of a Small Hydrogen-Fueled Reversed-Flow Turbine Combustor

Effects of Variable Diffuser Vanes on Performance of a Centrifugal Compressor with Pressure Ratio of 8.0

Effects of Low Reynolds Number on Performance in a Centrifugal Compressor

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