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Creeping flow of a conducting fluid past axisymmetric bodies in the presence of an aligned magnetic field
The use of strong magnetic fields for the control of particle settling in metallic systems is investigated by altering the fluid mechanics in the melt. The fluid mechanism of particle settling is analyzed for the motion around single, axisymmetric particles in the limit of creeping flow for a fluid with a large electrical conductivity. The drag is found to increase proportionately to the intensity of the magnetic field or the Hartmann number Ha. The flowfield forms boundary layers, which thin out with increasing Ha, along the surfaces parallel to the flow. For axisymmetric bodies, the boundary layer separates as the poles of the surface are approached and encloses regions of almost stagnant fluid. These regions spread upstream and downstream along the body with increasing Ha, thereby trapping the particle in a column of stagnant fluid.
Switchable positioning of plate-like inclusions in lipid membranes: Elastically mediated interactions of planar colloids in 2D fluids
Mechanical stimuli direct reversible intramembrane positioning of flat rigid microdomains on scales up to tens of micrometers.
Performance of the Mechanically Pumped Fluid Loop Rover Heat Rejection System Used for Thermal Control of the Mars Science Laboratory Curiosity Rover on the Surface of Mars
The challenging range of landing sites for which the Mars Science Laboratory Rover was designed, required a rover thermal management system that is capable of keeping temperatures controlled across a wide variety of environmental conditions. On the Martian surface where temperatures can be as cold as -123 C and as warm as 38 C, the Rover relies upon a Mechanically Pumped Fluid Loop (MPFL) Rover Heat Rejection System (RHRS) and external radiators to maintain the temperature of sensitive electronics and science instruments within a -40 C to +50 C range. The RHRS harnesses some of the waste heat generated from the Rover power source, known as the Multi Mission Radioisotope Thermoelectric Generator (MMRTG), for use as survival heat for the rover during cold conditions. The MMRTG produces 110 Watts of electrical power while generating waste heat equivalent to approximately 2000 Watts. Heat exchanger plates (hot plates) positioned close to the MMRTG pick up this survival heat from it by radiative heat transfer and supply it to the rover. This design is the first instance of use of a RHRS for thermal control of a rover or lander on the surface of a planet. After an extremely successful landing on Mars (August 5), the rover and the RHRS have performed flawlessly for close to an earth year (half the nominal mission life). This paper will share the performance of the RHRS on the Martian surface as well as compare it to its predictions.
MOOSE-Based Fast Reactor Core Bowing Capabilities: Coupled Structural Mechanics – Thermal Fluids Demonstration and Related Verification Efforts
Under the U.S. Department of Energy Office of Nuclear Energy’s Advanced Modeling and Simulation (NEAMS) Program, an integrated multiphysics approach is being developed to model the core bowing phenomena important to liquid metal-cooled fast reactors. Core bowing is an important passive safety mechanism in liquid metal-cooled fast reactors and involves multiphysics effects including radiation transport, fluid flow, heat transfer, and mechanical response to temperature and flux gradients. Verification and assessment efforts continued on the Multiphysics Object Oriented Simulation Environment (MOOSE) capabilities relevant for modeling thermo-mechanical core bowing behavior. IAEA Verification Problem 4, which was started in FY23, was further examined with MOOSE capabilities to rectify discrepancies observed in previous years when compared to IAEA benchmark participant data. Meshing and postprocessing capabilities in MOOSE were also advanced by other teams and utilized this year. A thermal fluids-structural mechanical coupling demonstration has performed on 7-assemblyand 19-assembly fast reactor assembly configurations using MOOSE. Subchannel capabilities are used to calculate coolant temperature, and heat conduction capabilities calculate duct wall temperature as well as heat transfer through the inter-assembly gap. Structural mechanical capabilities then deform the mesh, accounting for contact between assemblies, according to the temperature gradients calculated by the thermal solvers. Power distributions are imposed rather than calculated to demonstrate different deformations.
Mechanical design and stress analysis challenges overcome to ensure the structural integrity of Europa Clipper's mechanical pumped fluid loop Heat Redistribution System (HRS)
Launching in 2023, NASA’s Europa Clipper mission will place a spacecraft into a long, looping orbit around Jupiter to perform a series of close flyby investigations of its moon Europa. Strong evidence suggests that Europa hosts an ocean of liquid water beneath its icy crust that could harbor conditions favorable for life. The spacecraft is currently under development by the Jet Propulsion Laboratory (JPL) and the Applied Physics Laboratory (APL) and nearing completion of its Detailed Design Phase. A Mechanical Pumped Fluid Loop (MPFL) architecture known as the Heat Redistribution System (HRS) has been baselined to provide power efficient thermal control of the sensitive components within the Avionics, Radio Frequency (RF), and Propulsion Modules. Principally, the HRS harvests waste heat from the onboard dissipating equipment and distributes it to a 1.4 m diameter by 3 m tall cylindrical structure that cocoons and keeps the propulsion subsystem warm. Numerous technical issues had to be resolved in order to securely attach nearly 100 m of HRS tubing to the spacecraft, which is predicted to experience high launch loads. This paper will review the relevant environments and mission constraints as well as outline the stress and fatigue analysis approach taken to verify the detailed mechanical design of the HRS.
3D probabilistic fracture mechanics / computational fluid dynamics simulation of a reactor pressure vessel under transient conditions
Reactor pressure vessels (RPVs) are safety-critical light-water-reactor components that, under irradiation, experience long-term material degradation in the form of embrittlement. This can increase their susceptibility to fracture under thermal-shock conditions, which could occur during off-normal transients such as loss-of-coolant accidents (LOCAs). During a LOCA, the most severe conditions for the RPV occur when emergency core cooling water is injected through the cold legs into the water-and-steam-filled RPV. The rapid cooling of the downcomer and internal RPV surface causes decreased temperature and elevated thermally driven tensile stresses in the RPV wall. This, combined with long-term material embrittlement, may cause fracture initiation at pre-existing flaws, challenging the integrity of the RPV. Assessing RPV integrity during transients with a large spatial variation in the coolant temperature requires a modeling approach that considers the effects of spatially varying coolant temperature on the fracture probability of a population of flaws distributed throughout the RPV, accounting for spatially varying embrittlement. Here, the present study addresses this need by demonstrating first-of-its-kind coupling of a high-fidelity 3D computational fluid dynamics code with 3D probabilistic fracture mechanics This was accomplished using representative models of a pressurized-water reactor subjected to small- and medium-break LOCA conditions, both of which can result in large spatial temperature variations. While the observed impact of accounting for 3D effects was minimal under the small-break LOCA this study indicates a significant increase in the probability of fracture initiation under the medium-break LOCA when 3D effects are considered, relative to a spatially uniform cooling scenario.
Notes on Earth Atmospheric Entry for Mars Sample Return Missions
The entry of sample return vehicles (SRVs) into the Earth's atmosphere is the subject of this document. The Earth entry environment for vehicles, or capsules, returning from the planet Mars is discussed along with the subjects of dynamics, aerodynamics, and heat transfer. The material presented is intended for engineers and scientists who do not have strong backgrounds in aerodynamics, aerothermodynamics and flight mechanics. The document is not intended to be comprehensive and some important topics are omitted. The topics considered in this document include basic principles of physics (fluid mechanics, dynamics and heat transfer), chemistry and engineering mechanics. These subjects include: a) fluid mechanics (aerodynamics, aerothermodynamics, compressible fluids, shock waves, boundary layers, and flow regimes from subsonic to hypervelocity; b) the Earth s atmosphere and gravity; c) thermal protection system design considerations; d) heat and mass transfer (convection, radiation, and ablation); e) flight mechanics (basic rigid body dynamics and stability); and f) flight- and ground-test requirements; and g) trajectory and flow simulation methods.
Thermophysical property data: Who needs them?
Specific examples are cited to illustrate the universal needs and demands for thermophysical property data. Applications of the principle of similarity in fluid mechanics and heat transfer and extensions of the principle to fluid mixtures are discussed. It becomes quite clear that no matter how eloquent theories (or experiments) in fluid mechanics or heat transfer are, results of their application can be no more accurate than the thermophysical properties required to transform these theories into practice - or in the case of an experiment, to reduce the data. Present day projects take place on such a scale that the need for international standards groups and mutual cooperation is evident.
Thermophysical property data - Who needs them
Specific examples are cited herein to illustrate the universal needs and demands for thermophysical property data. Applications of the principle of similarity in fluid mechanics and heat transfer and extensions of the principle to fluid mixtures are discussed. It becomes quite clear that no matter how eloquent theories or experiments in fluid mechanics or heat transfer are, the results of their application can be no more accurate than the thermophysical properties required to transform these theories into practice, or in the case of an experiment, to reduce the data. Present-day projects take place on such a scale that the need for international standards and mutual cooperation is evident.
NASA's Microgravity Fluid Physics Strategic Research Roadmap
The Microgravity Fluid Physics Program at NASA has developed a substantial investigator base engaging a broad crosssection of the U.S. scientific community. As a result, it enjoys a rich history of many significant scientific achievements. The research supported by the program has produced many important findings that have been published in prestigious journals such as Science, Nature, Journal of Fluid Mechanics, Physics of Fluids, and many others. The focus of the program so far has primarily been on fundamental scientific studies. However, a recent shift in emphasis at NASA to develop advanced technologies to enable future exploration of space has provided motivation to add a strategic research component to the program. This has set into motion a year of intense planning within NASA including three workshops to solicit inputs from the external scientific community. The planning activities and the workshops have resulted in a prioritized list of strategic research issues along with a corresponding detailed roadmap specific to fluid physics. The results of these activities were provided to NASA s Office of Biological and Physical Research (OBPR) to support the development of the Enterprise Strategy document. This paper summarizes these results while showing how the planned research supports NASA s overall vision through OBPR s organizing questions.
Bioreactors Drive Advances in Tissue Engineering
It was an unlikely moment for inspiration. Engineers David Wolf and Ray Schwarz stopped by their lab around midday. Wolf, of Johnson Space Center, and Schwarz, with NASA contractor Krug Life Sciences (now Wyle Laboratories Inc.), were part of a team tasked with developing a unique technology with the potential to enhance medical research. But that wasn t the focus at the moment: The pair was rounding up colleagues interested in grabbing some lunch. One of the lab s other Krug engineers, Tinh Trinh, was doing something that made Wolf forget about food. Trinh was toying with an electric drill. He had stuck the barrel of a syringe on the bit; it spun with a high-pitched whirr when he squeezed the drill s trigger. At the time, a multidisciplinary team of engineers and biologists including Wolf, Schwarz, Trinh, and project manager Charles D. Anderson, who formerly led the recovery of the Apollo capsules after splashdown and now worked for Krug was pursuing the development of a technology called a bioreactor, a cylindrical device used to culture human cells. The team s immediate goal was to grow human kidney cells to produce erythropoietin, a hormone that regulates red blood cell production and can be used to treat anemia. But there was a major barrier to the technology s success: Moving the liquid growth media to keep it from stagnating resulted in turbulent conditions that damaged the delicate cells, causing them to quickly die. The team was looking forward to testing the bioreactor in space, hoping the device would perform more effectively in microgravity. But on January 28, 1986, the Space Shuttle Challenger broke apart shortly after launch, killing its seven crewmembers. The subsequent grounding of the shuttle fleet had left researchers with no access to space, and thus no way to study the effects of microgravity on human cells. As Wolf looked from Trinh s syringe-capped drill to where the bioreactor sat on a workbench, he suddenly saw a possible solution to both problems. It dawned on me that rotating the wall of the reactor would solve one of our fundamental fluid mechanical problems, specifically by removing the velocity gradient of the tissue culture fluid media near the reactor s walls, says Wolf. It looked as though it would allow us to suspend the growing cells within the reactor without introducing turbulent fluid mechanical conditions.
Mixing, Noise and Thrust Benefits Using Corrugated Designs
This project was conducted as a support for effective research, training and teaching of Hampton University students in Fluid Mechanics and Acoustics. Basically, this work is organized and implemented by the new Fluid Mechanics and Acoustics Laboratory (FM & AL) which was established at Hampton University in the School of Engineering and Technology (E & T) in 1996. In addition, FM & AL in cooperation with NASA LaRC jointly conducts research with the Central AeroHydrodynamics Institute (TSAGI, Moscow) in Russia under a 2 year Civilian Research and Development Foundation (CRDF). This project is also conducted under control of NASA HQ. For fulfillment of the current project, several researchers were involved as was shown in the proposal to NASA in 1996. This work is the development and support for projects solve problems with the goal of reducing jet noise and increasing nozzle thrust.
Fluid control mechanisms in weightlessness
Experiments performed on Space Shuttle flights have emphasized study of the earliest effects of the cephalad fluid shift resulting from microgravity. Analysis of one subject's urine collected during flight showed that a sharp increase in antidiuretic hormone occurred within 2 h of launch, followed by an increase in cortisol excretion. Although this subject had symptoms of the space adaptation syndrome (SAS), inflight data from Spacelab missions suggested that these transient changes were not caused by SAS. Unpaired t-tests and Mann-Whitney tests showed that before and after flight, plasma thyroxine and urine osmolality were significantly higher in Shuttle crewmembers who exhibited more severe symptoms of SAS than in asymptomatic crewmembers.
Finite element procedures for coupled linear analysis of heat transfer, fluid and solid mechanics
Coupled finite element formulations for fluid mechanics, heat transfer, and solid mechanics are derived from the conservation laws for energy, mass, and momentum. To model the physics of interactions among the participating disciplines, the linearized equations are coupled by combining domain and boundary coupling procedures. Iterative numerical solution strategy is presented to solve the equations, with the partitioning of temporal discretization implemented.
Multiscale Porous High-temperature Heat Exchanger Using Ceramic Co-extrusion
In this project, our MIT, Purdue, and GE team aims to design, model, fabricate, and test a novel high temperature, compact, and durable ceramic heat exchanger to be operated under high temperature and pressure conditions for aerospace applications. Our approach is grounded in introducing multiscale porosity, i.e., centimeter-scale channels embedded with micrometer-scale channels, into the ceramic heat exchanger to significantly improve its heat transfer performance and mechanical strength while maintaining minimal pressure losses. We first developed high-fidelity thermal-fluid-mechanical model capable of precisely capturing the heat transfer rate, temperature profile, pressure drop, and mechanical stress throughout the entire heat exchanger design. Guided by our model, we identified the optimal design parameters for the SiC heat exchanger body and manifolds. Then, we established a completed fabrication procedure to create multiscale features in the ceramic heat exchanger, including co-extrusion, lamination, burnout, and sintering. We fabricated multiple heat exchanger bodies consisting of 6 × 6 and 3 × 3 centimeter-scale channels where each individual centimeter-scale channel comprises 625 crack-free microchannels with 90 μm × 90 μm opening. Owing to the multiscale features, our fabricated heat exchanger bodies exhibited desirable mechanical strength with 156 MPa flexural strength under 1300 Celsius degree. Despite the demonstrated highly tailorable microscopic features and superior mechanical strength, we identified delamination due to the complex interaction among ceramic, polymer, and gas species can be a critical challenge to create fully defect-free heat exchanger, which requires further fundamental investigations in future works. To test the heat exchanger performance, we constructed a high-temperature and high-pressure experimental apparatus that can be safely operated under 400 Celsius degree and 4 bar. With insights gained from mechanistic modeling, material development, and detailed characterization, a cost model was finally developed to understand the market potential of the developed technology, where a cost of $43,000 Celsius degree/kW was envisioned. This project developed a transformative approach to high-performance heat exchanger design. The thermal-fluid-mechanical design approach developed in this project can serve as a generic tool to guide the design of various heat-exchangers operated under high-temperature and high-pressure conditions. The material fabrication approach established in this project can be a useful guide for ceramic processing at extreme length scales.
Ensemble Diffraction Measurements of Spray Combustion in a Novel Vitiated Coflow Turbulent Jet Flame Burner
An experimental investigation is presented of a novel vitiated coflow spray flame burner. The vitiated coflow emulates the recirculation region of most combustors, such as gas turbines or furnaces; additionally, since the vitiated gases are coflowing, the burner allows exploration of the chemistry of recirculation without the corresponding fluid mechanics of recirculation. As such, this burner allows for chemical kinetic model development without obscurations caused by fluid mechanics. The burner consists of a central fuel jet (droplet or gaseous) surrounded by the oxygen rich combustion products of a lean premixed flame that is stabilized on a perforated, brass plate. The design presented allows for the reacting coflow to span a large range of temperatures and oxygen concentrations. Several experiments measuring the relationships between mixture stoichiometry and flame temperature are used to map out the operating ranges of the coflow burner. These include temperatures as low 300 C to stoichiometric and oxygen concentrations from 18 percent to zero. This is achieved by stabilizing hydrogen-air premixed flames on a perforated plate. Furthermore, all of the CO2 generated is from the jet combustion. Thus, a probe sample of NO(sub X) and CO2 yields uniquely an emission index, as is commonly done in gas turbine engine exhaust research. The ability to adjust the oxygen content of the coflow allows us to steadily increase the coflow temperature surrounding the jet. At some temperature, the jet ignites far downstream from the injector tube. Further increases in the coflow temperature results in autoignition occurring closer to the nozzle. Examples are given of methane jetting into a coflow that is lean, stoichiometric, and even rich. Furthermore, an air jet with a rich coflow produced a normal looking flame that is actually 'inverted' (air on the inside, surrounded by fuel). In the special case of spray injection, we demonstrate the efficacy of this novel burner with a methanol spray in a vitiated coflow. As a proof of concept, an ensemble light diffraction (ELD) optical instrument was used to conduct preliminary measurements of droplet size distribution and liquid volume fraction.
Numerical Modeling of a Vortex Stabilized Arcjet
Arcjet thrusters are being actively considered for use in Earth orbit maneuvering applications. Experimental studies are currently the chief means of determining an optimal thruster configuration. Earlier numerical studies have failed to include all of the effects found in typical arcjets including complex geometries, viscosity, and swirling flow. Arcjet geometries are large area ratio converging nozzles with centerbodies in the subsonic portion of the nozzle. The nozzle walls serve as the anode while the centerbody functions as the cathode. Viscous effects are important because the Reynolds number, based on the throat radius, is typically less than 1,000. Experimental studies have shown that a swirl or circumferential velocity component stabilizes a constricted arc. This dissertation describes the equations governing flow through a constricted arcjet thruster. An assumption that the flowfield is in local thermodynamic equilibrium leads to a single fluid plasma temperature model. An order of magnitude analysis reveals the governing fluid mechanics equations are uncoupled from the electromagnetic field equations. A numerical method is developed to solve the governing fluid mechanics equations, the Thin Layer Navier-Stokes equations. A coordinate transformation is employed in deriving the governing equations to simplify the application of boundary conditions in complex geometries. An axisymmetric formulation is employed to include the swirl velocity component as well as the axial and radial velocity components. The numerical method is an implicit finite-volume technique and allows for large time steps to reach a converged steady-state solution. The inviscid fluxes are flux-split, and Gauss-Seidel line relaxation is used to accelerate convergence. Converging-diverging nozzles with exit-to-throat area ratios up to 100:1 and annular nozzles were examined. Quantities examined included Mach number and static wall pressure distributions, and oblique shock structures. As the level of swirl and viscosity in the flowfield increased the mass flow rate and thrust decreased. The technique was used to predict the flow through a typical arcjet thruster geometry. Results indicate swirl and viscosity play an important role in the complex geometry of an arcjet.