NASA and the Department of Energy are developing a high-efficiency Stirling radioisotope power system for future NASA space science missions, including such potential uses as powering rovers on planetary surfaces, lunar communication stations, and spacecraft power for deep-space missions. Stirling analysis tools are key elements in the ability to design, analyze, diagnose, test, and subsequently, improve these Stirling power systems. The NASA Glenn Research Center has created a suite of industry-leading tools for dynamic system analysis and multidimensional thermodynamic and electromagnetic analyses. These provide a complete picture of both overall system and detailed component behavior. In addition, Glenn research on understanding losses in Stirling systems has led to improved one-dimensional Stirling design codes.
Lockheed Martin (Valley Forge, PA) is the system integrator for the 110-W, first-generation Stirling radioisotope power system, known as the Stirling Radioisotope Generator (SRG110). Infinia Corporation (Kennewick, WA) is providing the Stirling convertor (integrated Stirling engine and linear alternator). The SRG110 is being developed under contract to the Department of Energy, with Glenn providing key supporting technology developments and advanced technology efforts. The projected SRG110 system efficiency of 23 percent will reduce the required amount of radioisotope by a factor of 4 or more in comparison to currently used radioisotope thermoelectric generators. A next-generation Stirling system is expected to exceed 30-percent efficiency and to double the power output per unit mass for a radioisotope power system.
The Stirling System Dynamic Model (SDM), based on Ansoft Simplorer, is a nonlinear, time-domain model that simulates Stirling cycle thermodynamics; heat flow; gas, mechanical, and mounting dynamics; the linear alternator; and the controller. It allows complex interactions among the various Stirling subsystems to be studied and can model transient and dynamic phenomena from startup to full-power conditions. In 2005, SDM’s thermodynamic modeling was improved by coupling the SDM to Sage, an industry-standard Stirling design code. In addition, linear modeling techniques were developed that can produce models to be used with classical controls and stability analysis techniques.
Radial velocity distribution inside a Stirling engine. Time, 5.1547 sec.
The first U.S. multidimensional computational fluid dynamics (CFD) model for a complete Stirling engine was developed in 2005. The preceding figure shows the radial velocity distribution for an axisymmetric simulation of the Stirling engine being developed for the SRG110, and the following photograph shows the Microway 32-processor parallel computer cluster that was set up to run the multidimensional models. More recently, a complete three-dimensional simulation was achieved for this same engine. The commercial CFD code FLUENT is used for the simulation platform.
Parallel computer cluster for high-speed processing of complex geometry Stirling simulations.
These analysis tools have affected the SRG110 design as well as advanced technology efforts. The SDM has been used to provide key input for the SRG110 controller development and to study system integration issues and off-nominal behavior. The SDM is also being used in the design of advanced controllers and linear alternators. The three-dimensional electromagnetic model, based on Ansoft Maxwell, was used to estimate the linear alternator’s margin to demagnetization, which impacted SRG110 magnet selection. This demagnetization margin was verified with test data in 2005.
The multidimensional CFD models will soon be used to evaluate effects that could not previously be studied with simpler models and cannot be determined from testing. These include the effects of uneven circumferential heating and the effect of possible regenerator bypass flow that may be caused by small dimensional changes due to heater head creep over very long operating times. The CFD models have also already been used to provide estimations of operating temperatures that cannot otherwise be determined for parts undergoing reliability studies. Perhaps most importantly, this set of tools can enable detailed investigation of a design and its modifications before expensive hardware is fabricated.
Dyson, R.W., et al.: Fast Whole-Engine Stirling Analysis. AIAA-2005-5558, 2005.
Regan, Timothy F.; and Lewandowski, Edward J.: Development of a Stirling System Dynamic Model With Enhanced Thermodynamics. AIP Conference Proceedings, vol. 746, no. 1, 2005, pp. 658-665.
Geng, Steven M.; Niedra, Janis M.; and Schwarze, Gene E.: Overview of NASA Magnet and Linear Alternator Research Efforts. AIP Conference Proceedings, vol. 746, no. 1, 2005, pp. 666-673.
Find out more about the research of Glenn’s Thermo-Mechanical Systems Branch: http://www.grc.nasa.gov/WWW/TECB/
Glenn contacts:
Dr. Rodger W. Dyson, 216-433-9083, Rodger.W.Dyson@nasa.gov; Dr. Roy C. Tew, 216-433-8471, Roy.C.Tew@nasa.gov; and Steve M. Geng, 216-433-6145, Steven.M.Geng@nasa.gov
SEST contacts:
Tim F. Regan, 216-433-2086, Timothy.F.Regan@nasa.gov; and Ed J. Lewandowski, 216-433-5525, Edward.J.Lewandowski@nasa.gov
Authors:
Dr. Rodger W. Dyson and Lanny G. Thieme
Headquarters program office:
Science Mission
Programs/Projects:
Nuclear Radioisotope Power System Development
Last updated: October 16, 2006
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