SEARCH · Engineering Papers

Results for “FLUID MECHANICS”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,621 records · Page 90

All sources NASA NTRS DOE OSTI

DOE OSTI2015

A method for data handling numerical results in parallel OpenFOAM simulations

Parallel computational fluid dynamics simulations produce vast amount of numerical result data. This paper introduces a method for reducing the size of the data by replaying the interprocessor traffic. The results are recovered only in certain regions of interest configured by the user. A known test case is used for several mesh partitioning scenarios using the OpenFOAM toolkit{sup ®}[1]. The space savings obtained with classic algorithms remain constant for more than 60 Gb of floating point data. Our method is most efficient on large simulation meshes and is much better suited for compressing large scale simulation results than the regular algorithms.

42 ENGINEERING↗

DOE OSTI2022

CFD simulations of electric motor end ring cooling for improved thermal management

Proper thermal management of an electric motor for vehicle applications extends its operating range. One cooling approach is to impinge Automatic Transmission Fluid (ATF) onto the rotor end ring. Increased ATF coverage correlates to enhanced heat transfer. Computational Fluid Dynamics (CFD) analytical tools provide a mechanism to assess motor thermal management prior to hardware fabrication. The complexity of the fluid flow (e.g., jet atomization, interface tracking, wall impingement) and heat transfer makes these simulations challenging. Computational costs are high when solving these flows on high-speed rotating meshes. Typically, a Volume-of Fluid (VOF) technique (i.e., two-fluid system) is used to resolve ATF dynamics within this rotating framework. Suitable numerical resolution of the relevant physics for thin films under strong inertial forces at high rotor speeds is computationally expensive, further increasing the run times. In this work, a numerical study of rotor-ring cooling by ATF is presented using a patent automated Cartesian cut-cell based method coupled with Automatic Mesh Refinement (AMR). This approach automatically creates the Cartesian mesh on-the-fly and can effectively handle complex rotating geometries by adaptively refining the mesh based on local gradients in the flow field which results in better resolution of the air-ATF interface. A Single non-inertial Reference Frame (SRF) approach is used to account for the rotating geometry and to further improve the overall computational efficiency. Quasi-steady state conditions are targeted in the analysis of the results. Important physics such as ATF jet structure, velocity detail near the air-jet interface, ATF coverage/accumulation on the ring surface, and cooling capacity are presented for a low-resolution Reynolds averaged Navier-Stokes (RANS), high-resolution RANS, and high-resolution Large-Eddy Simulation (LES) models. Computations are scaled over hundreds of cores on a supercomputer to maximize turnaround time. Each numerical approach is shown to capture the general trajectory of the oil jet prior to surface impingement. The high-resolution LES simulation, however, is superior in capturing small scale details and heat transfer between the free jet and surrounding air.

42 ENGINEERING↗

DOE OSTI2020

Micro- and nano-porosity of the active Alpine Fault zone, New Zealand

Porosity reduction in rocks from a fault core can cause elevated pore fluid pressures and consequently influence the recurrence time of earthquakes. We investigated the porosity distribution in the New Zealand's Alpine Fault core in samples recovered during the first phase of the Deep Fault Drilling Project (DFDP-1B) by using two-dimensional nanoscale and three-dimensional microscale imaging. Synchrotron X-ray microtomography-derived analyses of open pore spaces show total microscale porosities in the range of 0.1 %–0.24 %. These pores have mainly non-spherical, elongated, flat shapes and show subtle bipolar orientation. Scanning and transmission electron microscopy reveal the samples' microstructural organization, where nanoscale pores ornament grain boundaries of the gouge material, especially clay minerals. Our data imply that (i) the porosity of the fault core is very small and not connected; (ii) the distribution of clay minerals controls the shape and orientation of the associated pores; (iii) porosity was reduced due to pressure solution processes; and (iv) mineral precipitation in fluid-filled pores can affect the mechanical behavior of the Alpine Fault by decreasing the already critically low total porosity of the fault core, causing elevated pore fluid pressures and/or introducing weak mineral phases, and thus lowering the overall fault frictional strength. We conclude that the current state of very low porosity in the Alpine Fault core is likely to play a key role in the initiation of the next fault rupture.

58 GEOSCIENCES↗

DOE OSTI2020

Simulating Fracture Sealing by Granular LCM Particles in Geothermal Drilling

Lost circulation occurs when the returned fluid is less than what is pumped into the well due to loss of fluid to pores or fractures. A lost-circulation event is a common occurrence in a geothermal well. Typical geothermal reservoirs are often under-pressured and have larger fracture apertures. A severe lost-circulation event is costly and may lead to stuck pipe, well instability, and well abandonment. One typical treatment is adding lost-circulation materials (LCMs) to seal fractures. Conventional LCMs fail to properly seal fractures because their mechanical limit is exceeded at elevated temperatures. In this paper, parametric studies in numerical simulations are conducted to better understand different thermal effects on the sealing mechanisms of LCMs. The computational fluid dynamics (CFDs) and the discrete element method (DEM) are coupled to accurately capture the true physics of sealing by granular materials. Due to computational limits, the traditional Eulerian–Eulerian approach treats solid particles as a group of continuum matter. With the advance of modern computational power, particle bridging is achievable with DEM to track individual particles by modeling their interactive forces between each other. Particle–fluid interactions can be modeled by coupling CFD algorithms. Fracture sealing capability is investigated by studying the effect of four individual properties including fluid viscosity, particle size, friction coefficient, and Young’s modulus. It is found that thermally degraded properties lead to inefficient fracture sealing.

15 GEOTHERMAL ENERGY↗

NASA NTRSDate not supplied

Mitigating Headward Fluid Shifts with Venoconstrictive Thigh Cuffs during Spaceflight

Venoconstrictive thigh cuffs (VTC) are a mechanical countermeasure capable of attenuating the spaceflight induced headward fluid shift, and thus may be a viable spaceflight associated neuro-ocular syndrome (SANS) countermeasure. Crewmembers can use VTC to mitigate the headward fluid shift to aid in adapting to spaceflight. However, data are needed to determine if VTC affect ocular structures. PURPOSE The purpose of this study is to determine the efficacy of long duration use of VTC application to mitigate the spaceflight-induced headward fluid shift. We hypothesize that a VTC countermeasure will temporarily reverse the headward fluid shift and attenuate spaceflight-induced changes of internal jugular vein (IJV) cross-sectional area, IJV pressure, stroke volume, cardiac output, intraocular pressure (IOP), and optic nerve head and retinal morphology. METHODS This study will evaluate the effectiveness of VTC countermeasure application on the headward fluid shift, as well as cardiovascular and ocular variables. VTC during spaceflight will be worn for an extended duration (up to 6 hours) with data collected at three time points (30 minutes, 3 hours, and 6 hours) to characterize the temporal profile of key fluid shift outcome measures of the vascular fluid shift, IOP, and ocular structure changes. Ten astronauts will be recruited to participate and will be studied before and during approximately 180-day International Space Station (ISS) spaceflight missions. Baseline data collection will occur approximately 90-days before launch (Figure). Preflight, each leg of the crewmember will be measured to determine the VTC cuff size and a cuff fit check session will occur prior to the preflight baseline ground imaging to verify the appropriate fit measured via a surface contact pressure. Prior to donning the VTC, baseline measures without VTC will be collected seated, supine, and supine followed by data collection with the VTC. The baseline data collection will include ultrasound (IJV area and pressure, stroke volume and cardiac output), brachial blood pressure and heart rate, optical coherence tomography (OCT) imaging (total retinal thickness and choroid thickness), and IOP. An inflight cuff fit check session, same as the preflight fit check, will occur prior to VTC use on ISS. The inflight VTC experiment will be conducted early (FD45) and late (R-45) to determine if mission duration affects VTC fit and the efficacy of fluid redistribution. A system usability scale comfort questionnaire will be included in each VTC session to capture feedback from crewmembers regarding the comfort and usability of the VTC. SCIENTIFIC & MISSION IMPACT Results will narrow knowledge gaps described in the Human Research Roadmap to mitigate the headward fluid shift during spaceflight and help NASA to 1) determine the efficacy of extended use VTC application to mitigate the spaceflight-induced headward fluid shift and 2) further the understanding of the use of VTC on vascular fluid shifts, IOP, and ocular structure during spaceflight. Supported by NASA Human Research Program Directed Research. Figure. Detailed Testing Schedule. Baseline data collection at L-90 will be performed in a randomized order of position.

J V Jasien↗

DOE OSTI2018

The Role of Capillary Hysteresis and Pore-Scale Heterogeneity in Limiting the Migration of Buoyant Immiscible Fluids in Porous Media

Understanding the main mechanisms affecting long-term migration and redistribution of injected CO 2 in geological carbon storage is needed for developing predictive models to assess environmental risks and designing monitoring schemes. Preparation of a postinjection site care plan is required for CO 2 injection wells, including monitoring of pressure changes and injected CO 2 plume. Knowledge gaps exist regarding assessment of postinjection monitoring timeframes for the CO 2 plume because the processes driving long-term CO 2 plume migration and trapping are not fully understood. In the postinjection stage of geological carbon storage, redistribution of CO 2 occurs mainly due to buoyancy and capillary forces. This work presents experimental and modeling studies to investigate processes contributing to postinjection plume distribution and stabilization. We conducted a flow cell experiments (0.5 m × 0.05 m × 0.01 m) with two immiscible fluid phases in a glass bead porous medium to study postinjection plume behavior. We employed a hysteretic macroscopic two-phase flow model to interpret the experimental results and to understand main processes leading to plume stabilization. Our findings show that capillary pressure hysteresis explains the experimentally observed plume shape and redistribution at early postinjection stages; however, the long-term plume migration and eventual plume stabilization can only be represented when in addition microscale heterogeneity is accounted for. Results also show that plume stabilization can be extremely slow and that the migration of the plume front can occur through multiple intermittent bursts over long times. Here, further studies are needed to understand implications of the results for more realistic porous media and large-scale storage reservoirs.

58 GEOSCIENCES↗

DOE OSTI2020

Fluid-driven fractures in granular media: Insights from numerical investigations

We investigate the mechanisms of opening-mode fracture initiation in granular media. The study is based on a simulation of grain-scale fluid-grain interactions through a coupled numerical approach in which the discrete element method is used to solve for the mechanics of a solid granular medium, and computational fluid dynamics is used to model fluid flow and drag forces. In this work, we present benchmark problems with analytical solutions and validate this numerical model against experiments on a viscous-drag-driven cavity in the literature. Additional simulation results show fracture initiation mechanisms in a random granular packing subjected to constant boundary stresses and to fluid injection with a localized source. The dimensionless variable $F_s/F_{sk}$ (ratio of seepage force $F_s$ and skeletal force $F_{sk}$) incorporates the impacts of physical properties and injection parameters including fluid viscosity, injection velocity, grain size, and effective stresses, and it has been used as a criterion separating regimes of fluid invasion and drag-driven fracture opening. Our simulation results show that $F_s/F_{sk}$ in combination with $τ_1$ (ratio of diffusion time from hydromechanical coupling and injection time) serves as a prediction of fracture opening within granular packing. We suggest a simple criterion ($F_s/F_{sk}$ > 1 or $τ_1$ > 0.17) that is valid for various types of granular media and injection conditions to determine if fracture opening will occur. Among other applications, this study is useful to predict the initiation and propagation of fractures in natural sediments.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

NASA NTRS1944

The "limiting line" in mixed subsonic and supersonic flow of compressible fluids

It is well known that the vorticity for any fluid element is constant if the fluid is non-viscous and the change of state of the fluid is isentropic. When a solid body is placed in a uniform stream, the flow far ahead of the body is irrotational. Then if the flow is further assumed to be isentropic, the vorticity will be zero over the whole filed of flow. In other words, the flow is irrotational. For such flow over a solid body, it is shown by Theodorsen that the solid body experiences no resistance. If the fluid has a small viscosity, its effect will be limited in the boundary layer over the solid body and the body will have a drag due to the skin friction. This type of essentially isentropic irrotational flow is generally observed for a streamlined body placed in a uniform stream, if the velocity of the stream is kept below the so-called "critical speed." At the critical speed or rather at a certain value of the ratio of the velocity of the undisturbed flow and the corresponding velocity of sound, shock waves appear. This phenomenon is called the "compressibility bubble." Along a shock wave, the change of state of the fluid is no longer isentropic, although still adiabatic. This results in an increase in entropy of the fluid and generally introduces vorticity in an originally irrotational flow. The increase in entropy of the fluid is, of course, the consequence of changing part of the mechanical energy into heat energy. In other words, the part of fluid affected by the shock wave has a reduced mechanical energy. Therefore, with the appearance of shock waves, the wake of the streamline body is very much widened, and the drag increases drastically. Furthermore, the accompanying change in the pressure distribution over the body changes the aerodynamic moment acting on it and in the case of an airfoil decreases the lift force. All these consequences of the breakdown of isentropic irrotational flow are generally undesirable in applied aerodynamics. Its occurrence should be delayed as much as possible by modifying the shape or contour of the body. However, such endeavor will be very much facilitated if the cause or the criterion for the breakdown can be found first.

MACH NUMBER↗

NASA NTRS1974

U.S. National Congress of Applied Mechanics, 7th, University of Colorado, Boulder, Colo., June 3-7, 1974, Proceedings

A series of experimental, theoretical, and review papers dealing with various aspects of applied mechanics, including structural analysis, mathematical methods, and fluid dynamics. Some of the topics covered are: the direct formulation of two-dimensional mechanics problems, the mechanical aspects of athletics, Laplace's tidal equations, cochlear mechanics, dynamic constitutive equations, optical techniques for the determination of displacement and strain fields, chemical and biochemical problems involving nonlinear diffusion processes, thermal stresses, the rotating rod viscometer, finite-element methods in plasticity, ships of minimum resistance, and wide-band random vibration of structures. Individual items are announced in this issue.

Source record↗

NASA NTRS1993

Time-dependent thermocapillary convection in a Cartesian cavity - Numerical results for a moderate Prandtl number fluid

The present numerical simulation explores a thermal-convective mechanism for oscillatory thermocapillary convection in a shallow Cartesian cavity for a Prandtl number 6.78 fluid. The computer program developed for this simulation integrates the two-dimensional, time-dependent Navier-Stokes equations and the energy equation by a time-accurate method on a stretched, staggered mesh. Flat free surfaces are assumed. The instability is shown to depend upon temporal coupling between large scale thermal structures within the flow field and the temperature sensitive free surface. A primary result of this study is the development of a stability diagram presenting the critical Marangoni number separating steady from the time-dependent flow states as a function of aspect ratio for the range of values between 2.3 and 3.8. Within this range, a minimum critical aspect ratio near 2.3 and a minimum critical Marangoni number near 20,000 are predicted below which steady convection is found.

Peltier, L. J.↗

NASA NTRS1998

The bearable lightness of being: bones, muscles, and spaceflight

Bones and muscles support and move the body. Tendons link the two tissues and serve as a mechanism for transfer of forces from muscle to bone. These three tissues interact and respond to periods of activity or inactivity with appropriate alterations in structure and strength. There is substantial evidence that an environment devoid of mechanical stress on the skeleton (such as reduced gravitational forces during spaceflight, a "microgravity environment") produces direct effects on bone structure and function. There is little agreement concerning the biologic mechanisms for these atrophic changes. Changes in fluid balance and distribution coincident to spaceflight also affect muscles and bones by an unknown mechanism. Tendon-bone junctions are presumed to be spared from the effects of spaceflight. However, recent evidence from rodents suggests that spaceflight profoundly effects both the skeleton and the tendon-bone junctions. These effects include cortical bone resorption, which undermines the Sharpey's fibers that anchor the tendon to the bone matrix. The challenge to biomedical scientists is to devise methods for protecting spaceflight crews from these atrophic changes; such protection would allow for longer and more extensive spaceflights.

manned↗

NASA NTRS1991

Experimental investigations of He II flows at high Reynolds number

Fluid dynamics studies of He II at high Reynolds number (Re(d) greater than 10 exp 6) reveal characteristics which are best interpreted in terms of classical scaling relationships. In particular, the smooth tube friction factor is seen to correlate with the Von Karman-Nikuradse formulation. Also, the performance of a centrifugal pump is unchanged whether being used with He I or He II. These effects are expected to result provided the He II possesses a viscous sublayer and that the drag is determined by laminar flow within this layer. On the other hand, heat transfer in He II is substantially different from that of He I because of the unique internal convection mechanism present in this quantum fluid. These experiments are performed in the University of Wisconsin liquid helium flow facility which has unique capabilities of He II temperature, pressure and flow.

Van Sciver, Steve W.↗

DOE OSTI2016

Quadratic formula for determining the drop size in pressure-atomized sprays with and without swirl

We use a theoretical framework based on the integral form of the conservation equations, along with a heuristic model of the viscous dissipation, to find a closed-form solution to the liquid atomization problem. The energy balance for the spray renders to a quadratic formula for the drop size as a function, primarily of the liquid velocity. The Sauter mean diameter found using the quadratic formula shows good agreements and physical trends, when compared with experimental observations. This approach is shown to be applicable toward specifying initial drop size in computational fluid dynamics of spray flows.

42 ENGINEERING↗

NASA NTRS1982

Fluid and electrolyte homeostasis in space - A primate model to look at mechanisms

To elucidate the physiological mechanisms involved in the cardiovascular and renal responses to spaceflight, a ground-based primate model has been developed which uses lower body positive pressure (LBPP) to simulate the chronic central vascular expansion associated with weightlessnes. Four male squirrel monkeys with chronically implanted arterial and venous catheters and the capacity for continuous urine collection were subjected to LBPP for 4 days. Onset of LBPP resulted in an immediate diuresis, natriuresis and kaliuresis and a significant fall in plasma aldosterone and potassium levels. By day 2 the level of natriuresis had decreased by half, while potassium excretion and plasma aldosterone values had returned to control levels despite the persistence of a significantly reduced plasma potassium concentration. It is concluded that the low plasma potassium level appears not to stimulate a compensatory fall in plasma aldosterone because of the simultaneous presence of body volume contraction acting to raise aldosterone levels.

Moore-Ede, M. C.↗

NASA NTRS2007

Robustness of Modeling of Out-of-Service Gas Mechanical Face Seal

Gas lubricated mechanical face seal are ubiquitous in many high performance applications such as compressors and gas turbines. The literature contains various analyses of seals having orderly face patterns (radial taper, waves, spiral grooves, etc.). These are useful for design purposes and for performance predictions. However, seals returning from service (or from testing) inevitably contain wear tracks and warped faces that depart from the aforementioned orderly patterns. Questions then arise as to the heat generated at the interface, leakage rates, axial displacement and tilts, minimum film thickness, contact forces, etc. This work describes an analysis of seals that may inherit any (i.e., random) face pattern. A comprehensive computer code is developed, based upon the Newton- Raphson method, which solves for the equilibrium of the axial force and tilting moments that are generated by asperity contact and fluid film effects. A contact mechanics model is incorporated along with a finite volume method that solves the compressible Reynolds equation. Results are presented for a production seal that has sustained a testing cycle.

Green, Itzhak↗

DOE OSTI2016

The magnetic shear-current effect: Generation of large-scale magnetic fields by the small-scale dynamo

A novel large-scale dynamo mechanism, the magnetic shear-current effect, is discussed and explored. Here, the effect relies on the interaction of magnetic fluctuations with a mean shear flow, meaning the saturated state of the small-scale dynamo can drive a large-scale dynamo – in some sense the inverse of dynamo quenching. The dynamo is non-helical, with the mean field ${\it\alpha}$ coefficient zero, and is caused by the interaction between an off-diagonal component of the turbulent resistivity and the stretching of the large-scale field by shear flow. Following up on previous numerical and analytic work, this paper presents further details of the numerical evidence for the effect, as well as an heuristic description of how magnetic fluctuations can interact with shear flow to produce the required electromotive force. The pressure response of the fluid is fundamental to this mechanism, which helps explain why the magnetic effect is stronger than its kinematic cousin, and the basic idea is related to the well-known lack of turbulent resistivity quenching by magnetic fluctuations. As well as being interesting for its applications to general high Reynolds number astrophysical turbulence, where strong small-scale magnetic fluctuations are expected to be prevalent, the magnetic shear-current effect is a likely candidate for large-scale dynamo in the unstratified regions of ionized accretion disks. Evidence for this is discussed, as well as future research directions and the challenges involved with understanding details of the effect in astrophysically relevant regimes.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2024

Acceleration mechanisms of energetic ion debris in laser-driven tin plasma EUV sources

Laser-driven tin plasmas are driving new-generation nanolithography as sources of extreme ultraviolet (EUV) radiation centered at 13.5 nm. A major challenge facing industrial EUV source development is predicting energetic ion debris produced during the plasma expansion that may damage the sensitive EUV channeling multilayer optics. Gaining a detailed understanding of the plasma dynamics and ion acceleration mechanisms in these sources could provide critical insights for designing debris mitigation strategies in future high-power EUV sources. Here, we develop a fully kinetic model of tin-EUV sources using one-dimensional particle-in-cell simulations to study ion debris acceleration, which will be valuable for cross-validation of radiation-hydrodynamic simulations. An inverse-bremsstrahlung heating operator is used to model the interaction of a tin target with an Nd:YAG laser, and thermal conduction is included through a Monte Carlo Coulomb collision operator. While the large-scale evolution is in reasonable agreement with analogous hydrodynamic simulations, the significant timescale for collisional equilibration between electrons and ions allows for the development of prominent two-temperature features. A collimated flow of energetic ions is produced with a spectrum that is significantly enhanced at high energies compared to fluid simulations. The dominant acceleration mechanism is found to be a large-scale electric field supported mainly by the electron pressure gradient, which is enhanced in the kinetic simulations due to the increased electron temperature. We discuss the implications of these results for future modeling of tin-EUV sources and the development of debris mitigation schemes.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2016

A field theory approach to the evolution of canonical helicity and energy

A redefinition of the Lagrangian of a multi-particle system in fields reformulates the single-particle, kinetic, and fluid equations governing fluid and plasma dynamics as a single set of generalized Maxwell's equations and Ohm's law for canonical force-fields. The Lagrangian includes new terms representing the coupling between the motion of particle distributions, between distributions and electromagnetic fields, with relativistic contributions. The formulation shows that the concepts of self-organization and canonical helicity transport are applicable across single-particle, kinetic, and fluid regimes, at classical and relativistic scales. The theory gives the basis for comparing canonical helicity change to energy change in general systems. For example, in a fixed, isolated system subject to non-conservative forces, a species' canonical helicity changes less than total energy only if gradients in density or distribution function are shallow.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗