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DOE OSTI2015

Plethora of transitions during breakup of liquid filaments

Significance Fluid flows, governed by nonlinear equations, permit formation of singularities. Often, singularities are artifacts of neglecting physical effects. However, free-surface flows exhibit observable singularities including filament pinch-off. As filaments thin, slightly (highly) viscous filaments are expected from theory to transition from an inertial (viscous) regime where viscosity (density) is negligible to an inertial–viscous regime where viscous and inertial effects are important. Previous works show this transition either does not occur or occurs for filament radii well below theoretical predictions. We demonstrate that thinning filaments unexpectedly pass through a number of intermediate transient regimes, thereby delaying onset of the final regime. The findings raise the question if similar dynamical transitions arise in problems that are not necessarily hydrodynamic in nature.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

NASA NTRS1979

Vortex pattern development on the upper surface of a swept wing at high angle of attack

An experimental study, based on a swept wing, was undertaken in the water tunnel and the wind tunnel at low speeds, with a view to improving the understanding of the intervening phenomena and to make easier their modelling. The vortex flow effects on the wing are first illustrated from global effort measurements and static pressure distributions. The domain of existence of this type of flow is deduced as a function of both sweep angle and angle of attack. By a phenomenological study in the water tunnel, an attempt is made to describe the physical pattern of the vortex flow, from its formation near the apex to its breakdown at the trailing edge. Lastly, by means of a clinometric probe, the flow field over the wing is determined.

Mirande, J.↗

DOE OSTI2025

The Alamo multiphysics solver for phase field simulations with strong-form mechanics and block structured adaptive mesh refinement

Alamo is a high-performance scientific code that uses block-structured adaptive mesh refinement to solve such problems as: the ignition and burn of solid rocket propellant, plasticity, damage and fracture in materials undergoing loading, and the interaction of compressible flow with eroding solid materials. Alamo is powered by AMReX, and provides a set of unique methods, models, and algorithms that enable it to solve solid-mechanics problems (coupled to other physical behavior such as fluid flow or thermal diffusion) using the power of block-structured adaptive mesh refinement.

36 MATERIALS SCIENCE↗

DOE OSTI2017

Coupling of damped and growing modes in unstable shear flow

Analysis of the saturation of the Kelvin-Helmholtz instability is undertaken to determine the extent to which the conjugate linearly stable mode plays a role. For a piecewise-continuous mean flow profile with constant shear in a fixed layer, it is shown that the stable mode is nonlinearly excited, providing an injection-scale sink of the fluctuation energy similar to what has been found for gyroradius-scale drift-wave turbulence. Quantitative evaluation of the contribution of the stable mode to the energy balance at the onset of saturation shows that nonlinear energy transfer to the stable mode is as significant as energy transfer to small scales in balancing energy injected into the spectrum by the instability. The effect of the stable mode on momentum transport is quantified by expressing the Reynolds stress in terms of stable and unstable mode amplitudes at saturation, from which it is found that the stable mode can produce a sizable reduction in the momentum flux.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2020

Inertial dynamics of an interface with interfacial mass flux: Stability and flow fields’ structure, inertial stabilization mechanism, degeneracy of Landau’s solution, effect of energy fluctuations, and chemistry-induced instabilities

This work focuses on the long-standing problem of inertial dynamics of an interface with interfacial mass flux and reports new mechanisms for the interface stabilization and destabilization. The interface is a phase boundary separating fluids of different densities and having interfacial mass flux. To analyze the interface dynamics from a far field, we develop and apply the general matrix method to rigorously solve the boundary value problem involving the governing equations in the fluid bulk and the boundary conditions at the interface and at the outside boundaries of the domain. We find the fundamental solutions for the linearized system of equations and analyze the interplay of interface stability with flow fields’ structure by directly linking rigorous mathematical attributes to physical observables. We find that the interface is stable when the dynamics conserves the fluxes of mass, momentum, and energy; the stabilization is due to an inertial mechanism causing small oscillations of the interface velocity. In the classic Landau’s dynamics, the postulate of perfect constancy of the interface velocity leads to the development of Landau–Darrieus instability. This destabilization is also linked to the imbalance of the perturbed energy at the interface. The classic Landau’s solution is found to have degeneracy; lifting of the degeneracy may lead to singularity and self-similar dynamics. Our results compare well with traditional theories of combustion and propose new experiments to study the dynamics of the interface and the flow fields in combustible systems. We further conduct reactive molecular dynamics simulations to elucidate the complexity of chemical processes, to study the destabilizing effect of energy fluctuations on the interface stability, and to illustrate the chemistry-induced instabilities. In summary, we identify the extreme sensitivity of the interface dynamics to the interfacial boundary conditions, including the formal properties of fundamental solutions and the qualitative and quantitative properties of the flow fields. This provides new opportunities for studies, diagnostics, and control of multiphase flows in a broad range of processes in nature and technology.

42 ENGINEERING↗

DOE OSTI2016

Dependency of the Reynolds number on the water flow through the perforated tube

Safe and effective loading of nuclear reactor fuel assemblies demands qualitative and quantitative analysis of the relationship between the coolant temperature in the fuel assembly outlet, measured by the thermocouple, and the mean coolant temperature profile in the thermocouple plane position. It is not possible to perform the analysis directly in the reactor, so it is carried out using measurements on the physical model, and the CFD fuel assembly coolant flow models. The CFD models have to be verified and validated in line with the temperature and velocity profile obtained from the measurements of the cooling water flowing in the physical model of the fuel assembly. Simplified physical model with perforated central tube and its validated CFD model serve to design of the second physical model of the fuel assembly of the nuclear reactor VVER 440. Physical model will be manufactured and installed in the laboratory of the Institute of Energy Machines, Faculty of Mechanical Engineering of the Slovak University of Technology in Bratislava.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗

DOE OSTI2020

Simulator for Hydrologic Unstructured Domains (SHUD v1.0): numerical modeling of watershed hydrology with the finite volume method

Abstract. Hydrologic modeling is an essential strategy for understanding and predicting natural flows, particularly where observations are lacking in either space or time or where complex terrain leads to a disconnect in the characteristic time and space scales of overland and groundwater flow. However, significant difficulties remain for the development of efficient and extensible modeling systems that operate robustly across complex regions. This paper introduces the Simulator for Hydrologic Unstructured Domains (SHUD), an integrated, multiprocess, multiscale, flexible-time-step model, in which hydrologic processes are fully coupled using the finite volume method. SHUD integrates overland flow, snow accumulation/melt, evapotranspiration, subsurface flow, groundwater flow, and river routing, thus allowing physical processes in general watersheds to be realistically captured. SHUD incorporates one-dimensional unsaturated flow, two-dimensional groundwater flow, and a fully connected river channel network with hillslopes supporting overland flow and baseflow. The paper introduces the design of SHUD, from the conceptual and mathematical description of hydrologic processes in a watershed to the model's computational structures. To demonstrate and validate the model performance, we employ three hydrologic experiments: the V-catchment experiment, Vauclin's experiment, and a model study of the Cache Creek Watershed in northern California. Ongoing applications of the SHUD model include hydrologic analyses of hillslope to regional scales (1 m2 to 106 km2), water resource and stormwater management, and interdisciplinary research for questions in limnology, agriculture, geochemistry, geomorphology, water quality, ecology, climate and land-use change. The strength of SHUD is its flexibility as a scientific and resource evaluation tool where modeling and simulation are required.

58 GEOSCIENCES↗

NASA NTRS1991

An inverse inviscid method for the design of quasi-three dimensional rotating turbomachinery cascades

A new inverse inviscid method suitable for the design of rotating blade sections lying on an arbitrary axisymmetric stream-surface with varying streamtube width is presented. The geometry of the axisymmetric stream-surface and the streamtube width variation with meridional distance, the number of blades, the inlet flow conditions, the rotational speed and the suction and pressure side velocity distributions as functions of the normalized arc-length are given. The flow is considered irrotational in the absolute frame of reference and compressible. The output of the computation is the blade section that satisfies the above data. The method solves the flow equations on a (phi 1, psi) potential function-streamfunction plane for the velocity modulus, W and the flow angle beta; the blade section shape can then be obtained as part of the physical plane geometry by integrating the flow angle distribution along streamlines. The (phi 1, psi) plane is defined so that the monotonic behavior of the potential function is guaranteed, even in cases with high peripheral velocities. The method is validated on a rotating turbine case and used to design new blades. To obtain a closed blade, a set of closure conditions were developed and referred.

Bonataki, E.↗

DOE OSTI2021

Baseline predictions of elliptic flow and fluctuations for the RHIC Beam Energy Scan using response coefficients

Currently the RHIC Beam Energy Scan is exploring a new region of the Quantum Chromodynamic phase diagram at large baryon densities that approaches nuclear astrophysics regimes. This provides an opportunity to study relativistic hydrodynamics in a regime where the net conserved charges of baryon number, strangeness, and electric charge play a role, which will significantly change the theoretical approach to simulating the baryon-dense Quark-Gluon Plasma. In this work, we detail many of the important changes needed to adapt both initial conditions and the medium to baryon-rich matter. Then, we make baseline predictions for the elliptical flow and fluctuations based on extrapolating the physics at LHC and top RHIC energies to support future analyses of where and how the new baryon-dense physics causes these extrapolations to break down. First we compare eccentricities across beam energies, exploring their underlying assumptions; we find the the extrapolated initial state is predicted to be nearly identical to that at AuAu $\sqrt{s_{NN}}$ = 200 GeV. Then the final flow harmonic predictions are based on linear+cubic response. We discuss preliminary STAR results in order to determine the implications that they have for linear+cubic response coefficients at the lowest beam energy of AuAu $\sqrt{s_{NN}}$ = 7 GeV.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2019

Development of Critical Experiments to Provide Validation Data for Multiphysics Coupling Methods (Final Report)

Computational simulation has become one of the most important tools in the modern toolbox for nuclear reactor design. Reactor simulations, like the reactors themselves, involve multiple physical processes including neutronics, fluid flow and heat transfer (thermal-hydraulics), thermo-mechanics, fuel behavior, chemistry, and balance of plant. Each process can affect the behavior of the others, and advanced computational tools have been developed that couple separate physics models together to simulate the feedback effects. The objective of this work is to generate experimental data to support the validation of multi-physics reactor codes. It specifically targets the SHARP toolset from the NEAMS Reactor Product Line, but it is intended to be useful in any set of coded that couples thermal-hydraulics with neutronics simulations. The project takes advantage of the inherent flexibility of the RPI Reactor Critical Facility (RCF), a low power open-pool research reactor. The standard configuration of the RCF is used to explore the effects of moderator temperature on neutronic behavior and reactivity. Because the low power of the reactor generates no appreciable temperature change in the moderator, the moderator temperature is artificially changed with two 18 kW electric immersion heaters. The temperature feedback effects can be observed by recording the change in the reactor power as the reactor goes from a supercritical state, to critical, to a subcritical state. To expand the temperature range and temperature rate of change that can be investigated, an experimental apparatus consisting of a heated water loop was designed and installed in the RCF. In this setup, water from a heated reservoir tank is pumped through a pipe placed through the center of the reactor core. The water in the reservoir can be heated to around 70 °C and pumped through the system. The pump has a variable flow rate and electronic control, so a number of scenarios can be developed. A slug of water can be pushed through the system to generate a reasonably fast change in reactivity. The pump speed can be increased or decreased over the course of a measurement, or even oscillated at different periods, to observe the response of the reactor. To complement the experimental data generated by the RCF, a set of computational models have been developed. They are intended to illustrate the usefulness of the experimental data generated in validating coupled multi-physics simulations. A model previously constructed in MCNP has been used in conjunction with safety analysis at the RCF for many years and was modified to support the design of the heated water loop experiment. This model was translated into Serpent 2, a similar Monte Carlo code, which provided the added advantage of being able to produce collapsed cross-section data files for use in the deterministic neutron transport codes that are part of the SHARP toolset. A complete reconstruction of the RCF model, both with and without the heated fluid loop experiment, were necessary for use with the SHARP codes, PROTEUS (neutronics) and Nek5000 (thermal hydraulics), as these require an unstructured mesh format to operate. The computational requirements for fully coupled three dimensional simulations are significant, and challenges to full implementation and comparison with RCF experiments remain. A wide variety of experiments have been conducted for eventual benchmarking and validation of multi-physics reactor codes. A complete database of detailed time- and temperature-dependent measurements have been generated and stored. Several examples of the experimental results are presented here, with refinement and analysis of experiments ongoing. While these experiments still only address a finite range of operating conditions, in particular being limited to water in the sub-boiling regime, they represent a unique (to date) look at the feedback between temperature and neutronic behavior suited for validation of the coupling routines in multi-physics codes. It is hoped that these will be the foundation of future benchmarks that will provide confidence in the tools that will be used to develop the next generation of nuclear reactor systems.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2017

Discrete and Continuum Plane-Hopper Flow Simulations with Experimental Validation Using X-Ray Imaging, Arch Profilometry and Wall Pressure Measurements

The flow of spherical glass beads, approximately cubic wood crumbles®, and wood microchips are investigated using a combination of discrete element modeling (DEM), finite element analysis (FEA), and physical experiments using a custom plane-flow hopper in which the flow is characterized using x-ray imaging, profilometry to measure arching geometry and pressure measurements at the wall. The purpose of this study is to investigate fundamental flow behavior, and for this purpose the simulations and physical tests are specially designed. During the physical tests and simulations, the hopper geometry begins as a V shape with the two opposing side walls touching at the bottom of the V. Basic tests are performed by first filling the hopper with material, and then rotating the opposing side walls inward about their common intersection axis to cause an approximately uniform stress condition throughout most of the hopper. The side walls then slide upward to effectively increase the size of the opening at the bottom of the hopper until the arch of material in the hopper breaks, and all of the material falls out of the hopper. More advanced tests are also performed in which the initial rotation of the walls is slightly reversed to decrease the pressure in the hopper, corresponding to “preshear” and “shear” conditions in standard shear tests. Shear tests of the materials are also performed using a Schulze automated ring shear tester with a standard size M shear cell, and the shear tests of the glass beads and wood crumbles® are also simulated using DEM to calibrate the DEM with the FEA. Reasonable agreement between predicted and measured flow behavior is obtained indicating that this type of physical tests and modeling shows promise for characterizing and predicting the flow behavior of compressible and anisotropic materials.

09 BIOMASS FUELS↗

DOE OSTI2016

Counting RG flows

Here, interpreting renormalization group flows as solitons interpolating between different fixed points, we ask various questions that are normally asked in soliton physics but not in renormalization theory. Can one count RG flows? Are there different "topological sectors" for RG flows? What is the moduli space of an RG flow, and how does it compare to familiar moduli spaces of (supersymmetric) dowain walls? Analyzing these questions in a wide variety of contexts -- from counting RG walls to AdS/CFT correspondence -- will not only provide favorable answers, but will also lead us to a unified general framework that is powerful enough to account for peculiar RG flows and predict new physical phenomena. Namely, using Bott's version of Morse theory we relate the topology of conformal manifolds to certain properties of RG flows that can be used as precise diagnostics and "topological obstructions" for the strong form of the C-theorem in any dimension. Moreover, this framework suggests a precise mechanism for how the violation of the strong C-theorem happens and predicts "phase transitions" along the RG flow when the topological obstruction is non-trivial. Along the way, we also find new conformal manifolds in well-known 4d CFT's and point out connections with the superconformal index and classifying spaces of global symmetry groups.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2020

Analytical model for quasi-linear flow response to resonant magnetic perturbation in resistive-inertial and viscous-resistive regimes

In this work, a quasi-linear model for plasma flow response to the resonant magnetic perturbation (RMP) in a tokamak has been rigorously developed in the resistive-inertial (RI) and viscousresistive (VR) regimes purely from the two-field reduced MHD model. Models for plasma response to RMP are commonly composed of equations for the resonant magnetic field response (i.e. the magnetic island) and the torque balance of plasma flow. However, in previous plasma response models, the magnetic island and the torque balance equations are often derived separately from reduced MHD and full MHD equations, respectively. By contrast, in this work we derive both the magnetic island response and the torque balance equations in a quasi-linear model for plasma flow response entirely from a set of two-field reduced MHD equations. Such a quasi-linear model can recover previous plasma flow response models within certain limits and approximations. Furthermore, the physical origins of quasi-linear forces and moments in the flow response equation are also accurately calculated and clarified self-consistently.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS1977

Combustion of hydrogen injected into a supersonic airstream (the SHIP computer program)

The mathematical and physical basis of the SHIP computer program which embodies a finite-difference, implicit numerical procedure for the computation of hydrogen injected into a supersonic airstream at an angle ranging from normal to parallel to the airstream main flow direction is described. The physical hypotheses built into the program include: a two-equation turbulence model, and a chemical equilibrium model for the hydrogen-oxygen reaction. Typical results for equilibrium combustion are presented and exhibit qualitatively plausible behavior. The computer time required for a given case is approximately 1 minute on a CDC 7600 machine. A discussion of the assumption of parabolic flow in the injection region is given which suggests that improvement in calculation in this region could be obtained by use of the partially parabolic procedure of Pratap and Spalding. It is concluded that the technique described herein provides the basis for an efficient and reliable means for predicting the effects of hydrogen injection into supersonic airstreams and of its subsequent combustion.

Markatos, N. C.↗

NASA NTRS1991

Thermal and solutal convection with conduction effects inside a rectangular enclosure

We numerically investigate the effects of various boundary conditions on the flow field characteristics of the physical vapor transport process. We use a prescribed temperature profile as boundary condition on the enclosure walls, and we consider parametric variations applicable to ground-based and space microgravity conditions. For ground-based applications, density gradients in the fluid phase generate buoyancy-driven convection which in turn disrupts the uniformity of the mass flux at the interface depending on the orientation. Heat conduction in the crystal can affect the fluid flow near the interface of the crystal. When considering isothermal source and sink at the interfaces, we observe a diffusive mode and three modes (i.e., thermal, solutal, and thermo-solutal). The convective modes show opposing flow field trends between thermal and solutal convection; theoretically, these trends can be used to achieve a uniform mass flux near the crystal. However, under the physical conditions chosen, the mathematical condition necessary for uniform mass flux cannot be satisfied because of thermodynamic restrictions. When a longitudinal thermal gradient is prescribed on the boundary of the crystal, a non-uniform interface temperature results, which induces a symmetrical fluid flow near the interface for the vertical case. For space microgravity applications, we show that the flow field is dominated by the Stefan wind and a uniform mass flux results at the interface.

Mennetrier, Christophe↗

NASA NTRS1991

Theoretical and computational dynamics of a compressible flow

An introduction to the theoretical and computational fluid dynamics of a compressible fluid is presented. The general topics addressed include: thermodynamics and physical properties of compressible fluids; 1D flow of an inviscid compressible fluid; shock waves; fundamental equations of the dynamics of a compressible inviscid non-heat-conducting and radiating fluid, method of small perturbations, linearized theory; 2D subsonic steady potential flow; hodograph and rheograph methods, exact solutions of 2D insentropic steady flow equations, 2D steady transonic and hypersonic flows, method of characteristics, linearized theory of 3D potential flow, nonlinear theory of 3D compressibe flow, anisentropic (rotational) flow of inviscid compressible fluid, electromagnetogasdynamics, multiphase flows, flows of a compressible fluid with transport phenomena.

Pai, Shih-I↗

DOE OSTI2023

Particle transport-driven flow dynamics and heat transfer modulation in solar photovoltaic modules: Implications on soiling

Wind-swept debris and excessive heating reduce solar photovoltaic efficiency and accelerate panel degradation. For many solar plants in open environments, particle deposition is well-understood to exacerbate efficiency losses by blocking useable light and insulating panel surfaces. However, little is known about particle behavior in multi-panel systems, where complex wakes dominate and alter trajectories. This study examines debris-laden flow within a scaled array of two model solar panels, observing convective cooling and focusing on turbulent inter-panel flow dynamics. Convection is compared between the first and second panels (P 1 and P 2 ) and for a single inflow velocity at four particle concentrations (Φ v ), including a neutrally buoyant particle (i.e. tracer) case and three water droplet cases. Tracers and Φ v > 0 concentrations show increased convective heat transfer for P 2 compared to P 1 , while inertial particle presence and increased concentration reduces this improvement from +170% to +90%. Particle image velocimetry surrounding P 2 reveals dampened inter-panel wake features for particle-laden flow compared to the tracer case, where diminished mean flow and mean kinetic energy breakdown are observed for the particles due to their inertia. Together, the reduction in comparative convection and dampened wake effects accompanying inertial particle concentration motivates further studies on coupled array physics in debris-filled flow.

14 SOLAR ENERGY↗

DOE OSTI2015

Isolation of flow and nonflow correlations by two- and four-particle cumulant measurements of azimuthal harmonics in s NN = 200 GeV Au+Au collisions

A data-driven method was applied to Au+Au collisions at root S-NN = 200 GeV made with the STAR detector at RHIC to isolate pseudorapidity distance Delta eta-dependent and Delta eta-independent correlations by using two- and four-particle azimuthal cumulant measurements. We identified a Delta eta-independent component of the correlation, which is dominated by anisotropic flow and flow fluctuations. It was also found to be independent of. within the measured range of pseudorapidity vertical bar eta vertical bar < 1. In 20-30% central Au+Au collisions, the relative flow fluctuation was found to be 34% +/- 2%(stat.) +/- 3%(sys.) for particles with transverse momentum p(T) less than 2 GeV/c. The Delta eta-dependent part, attributed to nonflow correlations, is found to be 5% +/- 2%(sys.) relative to the flow of the measured second harmonic cumulant at vertical bar Delta eta vertical bar > 0.7. (C) 2015 The Authors. Published by Elsevier B.V.

74 ATOMIC AND MOLECULAR PHYSICS↗