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Onset of instabilities in rotating flows by direct numerical simulation
A rotating disk is the canonical experiment for measuring surface reaction rates in geochemical and electrochemical systems. Using the similarity solution for laminar flow around an infinite disk, the mass transfer coefficient can be simply related to the intrinsic reaction rate at the surface. However, measurements of mass transfer rates use a finite-size disk within a larger container of solution; here the flow is no longer strictly laminar, but there must always be some recirculation. Our interest was initially in the assumption of a uniform radial concentration field, how this breaks down near the perimeter of the disk, and what effect that might have on the measured mass transfer rates. However, our numerical simulations suggest that the flow around a finite-size disk becomes time dependent at Reynolds number ($\textit{Re}$) below 1000, which is much smaller than the typical values in mass-transfer measurements ($\textit{Re}$~10 4 ). In this work, we observe the formation of coherent structures in the flow, which suggest a non-uniform mass transfer at the disk surface. The rotating-disk flow follows a similar sequence of instabilities to the Taylor–Couette flow: a centrifugal instability leading an axisymmetric, time-invariant flow, followed by a Hopf bifurcation to a time-periodic flow. To minimise the possibility that our results are a numerical artefact, we have also simulated the instability in the stationary boundary layer of a rotor–stator flow, comparing with self-similar solutions at low $\textit{Re}$ and with spectral methods near the critical Reynolds number.
Direct Numerical Simulation of Low and Unitary Prandtl Number Fluids in Reactor Downcomer Geometry
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Direct Numerical Simulation of Single- and Two-Phase Flows for Nuclear Engineering Geometries
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Direct Numerical Simulation of High Prandtl Number Fluid Flow in the Downcomer of an Advanced Reactor
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Study of Stable Stratification in HiRJET Facility With Direct Numerical Simulation
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Multiscale Modeling of Flow in Rod Bundles: From Direct Numerical Simulation and Subchannel to Coarse-Mesh CFD
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Challenge Problem 1: Benchmark Specifications for the Direct Numerical Simulation of Canonical Flows
In this report detailed specifications for the canonical problems to study the heat transfer in different coolants, geometries and conditions are presented. The scope has been chosen with industry input and will address the outstanding challenges in predictive capabilities of coolant flows in advanced reactor-relevant conditions.
Direct Numerical Simulations of the Conventional Prompt Strike Vehicle?s Ogive at Hypersonic Flight Conditions.
Abstract not provided.
Robust, segregated time integration for direct numerical simulation of low-Mach, variable-density flows.
Abstract not provided.
A direct numerical simulation study of NO and N2O formation in turbulent premixed ammonia/hydrogen/nitrogen-air flames.
Abstract not provided.
Constrained Tucker Decompositions and Conservation Principles for Direct Numerical Simulation Data Compression
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Direct Numerical Simulation of turbulent nonpremixed “cool” flames: Applicability of flamelet models
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Direct numerical simulation of curved turbulent channel flow
Low Reynolds number, mildly curved, turbulent channel flow has been simulated numerically without subgrid scale models. A new spectral numerical method developed for this problem was used, and the computations were performed with 2 million degrees of freedom. A variety of statistical and structural information has been extracted from the computed flow fields. These include mean velocity, turbulence stresses, velocity skewness, and flatness factors, space time correlations and spectra, all the terms in the Reynolds stress balance equations, and contour and vector plots of instantaneous velocity fields. The effects of curvature on this flow were determined by comparing the concave and convex sides of the channel. The observed effects are consistent with experimental observations for mild curvature. The most significant difference in the turbulence statistics between the concave and convex sides was in the Reynolds shear stress. This was accompanied by significant differences in the terms of the Reynolds shear stress balance equations. In addition, it was found that stationary Taylor-Gortler vortices were present and that they had a significant effect on the flow by contributing to the mean Reynolds shear stress, and by affecting the underlying turbulence.
Direct numerical simulations of a reacting mixing layer with chemical heat release
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Direct numerical simulations of a temporally evolving mixing layer subject to forcing
The vortical evolution of mixing layers subject to various types of forcing is numerically simulated using pseudospectral methods. The effect of harmonic forcing and random noise in the initial conditions is examined with some results compared to experimental data. Spanwise forcing is found to enhance streamwise vorticity in a nonlinear process leading to a slow, secondary growth of the shear layer. The effect of forcing on a chemical reaction is favorably compared with experimental data at low Reynolds numbers. Combining harmonic and subharmonic forcing is shown to both augment and later destroy streamwise vorticity.