Engineering topics

Stewart, Mark E.

Publications and source records attributed to Stewart, Mark E..

7 records

NASA NTRS2017

Pressurization of a Flightweight, Liquid Hydrogen Tank: Evaporation and Condensation at a Liquid Vapor Interface

Evaporation and condensation at a liquidvapor interface is important for long-term, in-space cryogenic propellant storage. Yet the current understanding of interfacial physics does not predict behavior or evaporation condensation rates. The proposed paper will present a physical model, based on the 1-D Heat equation and Schrages equation which demonstrates thin thermal layers at the fluidvapor interface.

Cryogenic hydrogen↗

NASA NTRS2015

Multidisciplinary Simulation of Graphite-Composite and Cermet Fuel Elements for NTP Point of Departure Designs

This paper compares the expected performance of two Nuclear Thermal Propulsion fuel types. High fidelity, fluid/thermal/structural + neutronic simulations help predict the performance of graphite-composite and cermet fuel types from point of departure engine designs from the Nuclear Thermal Propulsion project. Materials and nuclear reactivity issues are reviewed for each fuel type. Thermal/structural simulations predict thermal stresses in the fuel and thermal expansion mis-match stresses in the coatings. Fluid/thermal/structural/neutronic simulations provide predictions for full fuel elements. Although NTP engines will utilize many existing chemical engine components and technologies, nuclear fuel elements are a less developed engine component and introduce design uncertainty. Consequently, these fuel element simulations provide important insights into NTP engine performance.

Cermets↗

NASA NTRS2015

Comparison of Computational Results with a Low-g, Nitrogen Slosh and Boiling Experiment

This paper compares a fluid/thermal simulation, in Fluent, with a low-g, nitrogen slosh and boiling experiment. In 2010, the French Space Agency, CNES, performed cryogenic nitrogen experiments in a low-g aircraft campaign. From one parabolic flight, a low-g interval was simulated that focuses on low-g motion of nitrogen liquid and vapor with significant condensation, evaporation, and boiling. The computational results are compared with high-speed video, pressure data, heat transfer, and temperature data from sensors on the axis of the cylindrically shaped tank. These experimental and computational results compare favorably. The initial temperature stratification is in good agreement, and the two-phase fluid motion is qualitatively captured. Temperature data is matched except that the temperature sensors are unable to capture fast temperature transients when the sensors move from wet to dry (liquid to vapor) operation. Pressure evolution is approximately captured, but condensation and evaporation rate modeling and prediction need further theoretical analysis.

Cryogenic Fluid Storage↗

NASA NTRS2015

A Historical Review of Cermet Fuel Development and the Engine Performance Implications

To better understand Cermet engine performance, examined historical material development reports two issues: High vaporization rate of UO2, High temperature chemical stability of UO2. Cladding and chemical stabilizers each result in large, order of magnitude improvements in high temperature performance. Few samples were tested above 2770 K. Results above 2770 K are ambiguous. Contemporary testing may clarify performance. Cermet sample testing during the NERVA Rover era. Important properties, melting temperature, vaporization rate, strength, Brittle-to-Ductile Transition, cermet sample test results, engine performance, location, peak temperature.

Nuclear Propulsion↗

NASA NTRS2013

A Comparison of Materials Issues for Cermet and Graphite-Based NTP Fuels

This paper compares material issues for cermet and graphite fuel elements. In particular, two issues in NTP fuel element performance are considered here: ductile to brittle transition in relation to crack propagation, and orificing individual coolant channels in fuel elements. Their relevance to fuel element performance is supported by considering material properties, experimental data, and results from multidisciplinary fluid/thermal/structural simulations. Ductile to brittle transition results in a fuel element region prone to brittle fracture under stress, while outside this region, stresses lead to deformation and resilience under stress. Poor coolant distribution between fuel element channels can increase stresses in certain channels. NERVA fuel element experimental results are consistent with this interpretation. An understanding of these mechanisms will help interpret fuel element testing results.

Nuclear Propulsion↗

NASA NTRS2006

Fabrication Materials for a Closed Cycle Brayton Turbine Wheel

A multidisciplinary analysis of a radial inflow turbine rotor is presented. This work couples high-fidelity fluid, structural, and thermal simulations in a seamless multidisciplinary analysis to investigate the consequences of material selection. This analysis extends multidisciplinary techniques previously demonstrated on rocket turbopumps and hypersonic engines. Since no design information is available for the anticipated Brayton rotating machinery, an existing rotor design (the Brayton Rotating Unit (BRU)) was used in the analysis. Steady state analysis results of a notional turbine rotor indicate that stress levels are easily manageable at the turbine inlet temperature, and stress levels anticipated using either superalloys or ceramics.

Khandelwal, Suresh↗

NASA NTRS2001

Space Transportation Propulsion Systems

This report outlines the Space Transportation Propulsion Systems for the NPSS (Numerical Propulsion System Simulation) program. Topics include: 1) a review of Engine/Inlet Coupling Work; 2) Background/Organization of Space Transportation Initiative; 3) Synergy between High Performance Computing and Communications Program (HPCCP) and Advanced Space Transportation Program (ASTP); 4) Status of Space Transportation Effort, including planned deliverables for FY01-FY06, FY00 accomplishments (HPCCP Funded) and FY01 Major Milestones (HPCCP and ASTP); and 5) a review current technical efforts, including a review of the Rocket-Based Combined-Cycle (RBCC), Scope of Work, RBCC Concept Aerodynamic Analysis and RBCC Concept Multidisciplinary Analysis.

Liou, Meng-Sing↗