One form of power conversion under investigation in NASA Glenn Research Centerís Thermal Energy Conversion Branch is the closed-Brayton-cycle engine. Producing power from tens-of-kilowatts to multimegawatts, the Brayton engine lends itself to potential space nuclear power applications such as electric propulsion or surface power. The Thermal Energy Conversion Branch recently enhanced its closed-Brayton-cycle design and analysis capabilities by transporting its legacy code, the Closed Cycle Engine Program (CCEP), from Fortran to a more suitable modeling environment known as the Numerical Propulsion System Simulation (NPSS). The updated engine program, called the Closed Cycle System Simulation (CCSS), has been used so far to create models with multiple engines, higher-fidelity components, and thermal transients to match data from test hardware.
The NPSS modeling environment was created at Glenn as a joint effort with industry and the Department of Energy and is maintained by Glenn. It offers improved features such as an unlimited number of input, output, and solver variables, a powerful differential equations solver, the option of either a text or graphical user interface, and the ability to couple with external programs to increase the fidelity of individual components.
An unlimited number of variables allow a user to build models that converge to more elaborate design specifications and operate in a more flexible fashion during off-design analysis. A CCSS model was constructed of two closed-Brayton-cycle engines that shared a common gas inventory and were plumbed together at the heat-source heat exchanger. Although the engines were designed under identical specifications, they could be operated individually at different power levels. The CCSS solver was employed to appropriately balance the gas inventory shared between the two engines.
In a combined effort with Glennís Turbomachinery and Heat Transfer Branch and Thermal Energy Conversion Branch, CCSS was coupled to the mean-line compressor and turbine codes Quick and Radial Turbine Design, increasing turbomachinery fidelity over CCSSís generic performance tables. Fidelity could be increased even further by coupling CCSS to computational fluid dynamics programs. The ability to couple CCSS to external codes could facilitate collaboration with codes developed by other Government agencies or by industry.
Recuperated closed-Brayton-cycle power-conversion system with heat rejection.
Long description of figure.
A CCSS model of Glennís 2-kWe closed-Brayton-cycle engine (MiniBRU) was constructed, and results were compared with transient test data. Attention was given particularly to the modelís recuperator and electric heater components because their large masses contribute most to the engineís thermal transients. The CCSS model was able to reproduce the thermal transient timescales exhibited by the MiniBRU for operational step changes in shaft rotational speed and electric heater power input.
CCSS combines the legacy source code of CCEP with the power and extensibility of the NPSS modeling environment. More elaborate design and off-design studies can be conducted than were possible with CCEP. Efforts over the past year have enabled CCSS to replace CCEP as the Thermal Energy Conversion Branchís closed-Brayton-cycle design and analysis tool.
Johnson, Paul K.: Closed-Cycle Engine Program Used To Study Brayton Power Conversion. Research & Technology 2004, NASA/TM-2005-213419, 2005, pp. 101-102.
Lavelle, Thomas; Khandelwal, Suresh; and Owen, Albert: Intermediate Fidelity Closed Brayton Cycle Power Conversion Model. NASA/TM-2006-213993, 2006. http://gltrs.grc.nasa.gov/cgi-bin/GLTRS/browse.pl?2006/TM-2006-213993.html
Find out more about the research of Glennís Thermo-Mechanical Systems Branch: http://www.grc.nasa.gov/WWW/TECB/
Analex Corporation contact:
Paul K. Johnson, 216-433-3814, Paul.K.Johnson@nasa.gov
Glenn contacts: Dr. Michael J. Barrett, 216-433-5424, Michael.J.Barrett@nasa.gov; and Thomas M. Lavelle, 216-977-7042, Thomas.M.Lavelle@nasa.gov
Author: Paul K. Johnson
Headquarters program office: Exploration Systems
Programs/Projects: Project Prometheus, nuclear powersystems for electric propulsion or surface power
Last updated: October 16, 2006
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