scholarly journals Low-mass planet migration in three-dimensional wind-driven inviscid discs: a negative corotation torque

2020 ◽  
Vol 493 (3) ◽  
pp. 4382-4399 ◽  
Author(s):  
Colin P McNally ◽  
Richard P Nelson ◽  
Sijme-Jan Paardekooper ◽  
Pablo Benítez-Llambay ◽  
Oliver Gressel
Keyword(s):  
Opposite Effect ◽  
Thermal Evolution ◽  
Thermal Structure ◽  
Turbulent Viscosity ◽  
Three Dimensional ◽  
Surface Layers ◽  
Horseshoe Orbits ◽  
3D Effects ◽  
Low Mass ◽  
Flow Through

ABSTRACT We present simulations of low-mass planet–disc interactions in inviscid three-dimensional discs. We show that a wind-driven laminar accretion flow through the surface layers of the disc does not significantly modify the migration torque experienced by embedded planets. More importantly, we find that 3D effects lead to a dramatic change in the behaviour of the dynamical corotation torque compared to earlier 2D theory and simulations. Although it was previously shown that the dynamical corotation torque could act to slow and essentially stall the inward migration of a low-mass planet, our results in 3D show that the dynamical corotation torque has the complete opposite effect and speeds up inward migration. Our numerical experiments implicate buoyancy resonances as the cause. These have two effects: (i) they exert a direct torque on the planet, whose magnitude relative to the Lindblad torque is measured in our simulations to be small; (ii) they torque the gas librating on horseshoe orbits in the corotation region and drive evolution of its vortensity, leading to the negative dynamical corotation torque. This indicates that at low turbulent viscosity, the detailed vertical thermal structure of the protoplanetary disc plays an important role in determining the migration behaviour of embedded planets. If this result holds up under a more refined treatment of disc thermal evolution, then it has important implications for understanding the formation and early evolution of planetary systems.

scholarly journals Turbulence Modeling in Three-Dimensional Stenosed Arterial Bifurcations

2006 ◽  
Vol 129 (1) ◽  
pp. 40-50 ◽  
Author(s):  
J. Banks ◽  
N. W. Bressloff
Keyword(s):  
Carotid Artery ◽  
Turbulence Modeling ◽  
Turbulent Viscosity ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Shape Variation ◽  
Severe Stenosis ◽  
Carotid Artery Bifurcation ◽  
Inflow Turbulence ◽  
Flow Through

Under normal healthy conditions, blood flow in the carotid artery bifurcation is laminar. However, in the presence of a stenosis, the flow can become turbulent at the higher Reynolds numbers during systole. There is growing consensus that the transitional k−ω model is the best suited Reynolds averaged turbulence model for such flows. Further confirmation of this opinion is presented here by a comparison with the RNG k−ϵ model for the flow through a straight, nonbifurcating tube. Unlike similar validation studies elsewhere, no assumptions are made about the inlet profile since the full length of the experimental tube is simulated. Additionally, variations in the inflow turbulence quantities are shown to have no noticeable affect on downstream turbulence intensity, turbulent viscosity, or velocity in the k−ϵ model, whereas the velocity profiles in the transitional k−ω model show some differences due to large variations in the downstream turbulence quantities. Following this validation study, the transitional k−ω model is applied in a three-dimensional parametrically defined computer model of the carotid artery bifurcation in which the sinus bulb is manipulated to produce mild, moderate, and severe stenosis. The parametric geometry definition facilitates a powerful means for investigating the effect of local shape variation while keeping the global shape fixed. While turbulence levels are generally low in all cases considered, the mild stenosis model produces higher levels of turbulent viscosity and this is linked to relatively high values of turbulent kinetic energy and low values of the specific dissipation rate. The severe stenosis model displays stronger recirculation in the flow field with higher values of vorticity, helicity, and negative wall shear stress. The mild and moderate stenosis configurations produce similar lower levels of vorticity and helicity.

scholarly journals Study of Mini Channel Heat Sink with Different Internal Configuration

2020 ◽  
Vol 319 ◽  
pp. 02004
Author(s):  
Muhammad Akif Rahman ◽  
Md Badrath Tamam ◽  
Md Sadman Faruque ◽  
A.K.M. Monjur Morshed
Keyword(s):  
Nusselt Number ◽  
Thermal Performance ◽  
Heat Sink ◽  
Rectangular Channel ◽  
Three Dimensional ◽  
Heat Sinks ◽  
Maximum Temperature ◽  
Rectangular Channels ◽  
Flow Through ◽  
Internal Configuration

In this paper a numerical analysis of three-dimensional laminar flow through rectangular channel heat sinks of different geometric configuration is presented and a comparison of thermal performance among the heat sinks is discussed. Liquid water was used as coolant in the aluminum made heat sink with a glass cover above it. The aspect ratio (section height to width) of rectangular channels of the mini-channel heat sink was 0.33. A heat flux of 20 W/cm2 was continuously applied at the bottom of the channel with different inlet velocity for Reynold’s number ranging from 150 to 1044. Interconnectors and obstacles at different positions and numbers inside the channel were introduced in order to enhance the thermal performance. These modifications cause secondary flow between the parallel channels and the obstacles disrupt the boundary layer formation of the flow inside the channel which leads to the increase in heat transfer rate. Finally, Nusselt number, overall thermal resistance and maximum temperature of the heat sink were calculated to compare the performances of the modified heat sinks with the conventional mini channel heat sink and it was observed that the heat sink with both interconnectors and obstacles enhanced the thermal performance more significantly than other configurations. A maximum of 36% increase in Nusselt number was observed (for Re =1044).

Influence of a Honeycomb Facing on the Flow Through a Stepped Labyrinth Seal

2000 ◽  
Vol 124 (1) ◽  
pp. 140-146 ◽  
Author(s):  
V. Schramm ◽  
K. Willenborg ◽  
S. Kim ◽  
S. Wittig
Keyword(s):  
Flow Field ◽  
Three Dimensional ◽  
Theoretical Work ◽  
Labyrinth Seal ◽  
Honeycomb Structure ◽  
Experimental Investigations ◽  
Labyrinth Seals ◽  
Numerical Predictions ◽  
Flow Through ◽  
Aero Engines

This paper reports numerical predictions and measurements of the flow field in a stepped labyrinth seal. The theoretical work and the experimental investigations were successfully combined to gain a comprehensive understanding of the flow patterns existing in such elements. In order to identify the influence of the honeycomb structure, a smooth stator as well as a seal configuration with a honeycomb facing mounted on the stator wall were investigated. The seal geometry is representative of typical three-step labyrinth seals of modern aero engines. The flow field was predicted using a commercial finite volume code with the standard k-ε turbulence model. The computational grid includes the basic seal geometry as well as the three-dimensional honeycomb structures.

Numerical Simulation for Flow Through Conducting Metal and Metallic Oxide Nanofluids

2020 ◽  
Vol 9 (4) ◽  
pp. 354-361
Author(s):  
P. K. Pattnaik ◽  
S. R. Mishra ◽  
Ram Prakash Sharma
Keyword(s):  
Metal Oxide Nanoparticles ◽  
Three Dimensional ◽  
Adomian Decomposition Method ◽  
Metallic Oxide ◽  
Electrically Conducting ◽  
Number Comparison ◽  
Adomian Decomposition ◽  
Flow Through ◽  
Analytical Result ◽  
Exponentially Stretching

Present paper aims to analyze three-dimensional (3D) motion of an electrically conducting nanofluid past an exponentially stretching sheet. Both metal and metal oxide nanoparticles (such as Cu, Al2O3, TiO2) in the base fluid (water) are examined. Nonlinear ordinary differential systems are obtained by suitable transformations. The crux of the analysis is the development of an estimated analytical result obtained by employing the “Adomian Decomposition Method” (ADM), an approximate analytical method. Momentum and energy descriptions with prescribed boundary conditions are employed. The velocity components and temperature are analyzed. Tabulated values are organized aimed at the outcomes of skin-friction coefficients and Nusselt number. Comparison with past limiting results is shown. Finally, the outstanding outcomes of the present result are; the velocity profile with the inclusion of particle concentration and magnetic parameter decelerate significantly and Al2O3 nanoparticles are favorable for the enhancement in the rate of heat transfer.

“Gray Zone” Simulations using a Three-Dimensional Planetary Boundary Layer Parameterization in the Weather Research and Forecasting Model

2021 ◽  
Author(s):  
Timothy W. Juliano ◽  
Branko Kosović ◽  
Pedro A. Jiménez ◽  
Masih Eghdami ◽  
Sue Ellen Haupt ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Three Dimensional ◽  
Grid Cell ◽  
Weather Research And Forecasting ◽  
Forecasting Model ◽  
Gray Zone ◽  
Pbl Scheme ◽  
3D Effects ◽  
Mesoscale Simulations

AbstractGenerating accurate weather forecasts of planetary boundary layer (PBL) properties is challenging in many geographical regions, oftentimes due to complex topography or horizontal variability in, for example, land characteristics. While recent advances in high-performance computing platforms have led to an increase in the spatial resolution of numerical weather prediction (NWP) models, the horizontal grid cell spacing (Δ x) of many regional-scale NWP models currently fall within or are beginning to approach the gray zone (i.e., Δ x ≈ 100 – 1000 m). At these grid cell spacings, three-dimensional (3D) effects are important, as the most energetic turbulent eddies are neither fully parameterized (as in traditional mesoscale simulations) nor fully resolved [as in traditional large eddy simulations (LES)]. In light of this modeling challenge, we have implemented a 3D PBL parameterization for high-resolution mesoscale simulations using the Weather Research and Forecasting model. The PBL scheme, which is based on the algebraic model developed by Mellor and Yamada, accounts for the 3D effects of turbulence by calculating explicitly the momentum, heat, and moisture flux divergences in addition to the turbulent kinetic energy. In this study, we present results from idealized simulations in the gray zone that illustrate the benefit of using a fully consistent turbulence closure framework under convective conditions. While the 3D PBL scheme reproduces the evolution of convective features more appropriately than the traditional 1D PBL scheme, we highlight the need to improve the turbulent length scale formulation.

scholarly journals Numerical Calculation of Flow for Cascade With Tip Clearance

1994 ◽  
Author(s):  
Shimpei Mizuki ◽  
Hoshio Tsujita
Keyword(s):  
Three Dimensional ◽  
Tip Clearance ◽  
Turbine Cascade ◽  
Governing Equations ◽  
Tensor Form ◽  
Pressure Surface ◽  
Rear Part ◽  
Blade Tip ◽  
Flow Through ◽  
Blade Tip Geometry

Three-dimensional incompressible turbulent flow within a linear turbine cascade with tip clearance is analyzed numerically. The governing equations involving the standard k-ε model are solved in the physical component tensor form with a boundary-fitted coordinate system. In the analysis, the blade tip geometry is treated accurately in order to predict the flow through the tip clearance in detail when the blades have large thicknesses. Although the number of grids employed in the present study is not enough because of the limitation of computer storage memory, the computed results show good agreements with the experimental results. Moreover, the results clearly exhibit the locus of minimum pressure on the rear part of the pressure surface at the blade tip.

Computation of Flow Through a Three-Dimensional Periodic Array of Porous Structures by a Parallel Immersed-Boundary Method

2014 ◽  
Vol 136 (4) ◽  
Author(s):  
Zhenglun Alan Wei ◽  
Zhongquan Charlie Zheng ◽  
Xiaofan Yang
Keyword(s):  
Porous Media ◽  
Parallel Implementation ◽  
Flow Behavior ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Periodic Array ◽  
Immersed Boundary ◽  
Navier Stokes Equation ◽  
Flow Through ◽  
Ib Method

A parallel implementation of an immersed-boundary (IB) method is presented for low Reynolds number flow simulations in a representative elementary volume (REV) of porous media that are composed of a periodic array of regularly arranged structures. The material of the structure in the REV can be solid (impermeable) or microporous (permeable). Flows both outside and inside the microporous media are computed simultaneously by using an IB method to solve a combination of the Navier–Stokes equation (outside the microporous medium) and the Zwikker–Kosten equation (inside the microporous medium). The numerical simulation is firstly validated using flow through the REVs of impermeable structures, including square rods, circular rods, cubes, and spheres. The resultant pressure gradient over the REVs is compared with analytical solutions of the Ergun equation or Darcy–Forchheimer law. The good agreements demonstrate the validity of the numerical method to simulate the macroscopic flow behavior in porous media. In addition, with the assistance of a scientific parallel computational library, PETSc, good parallel performances are achieved. Finally, the IB method is extended to simulate species transport by coupling with the REV flow simulation. The species sorption behaviors in an REV with impermeable/solid and permeable/microporous materials are then studied.

Numerical Investigation of Heat Transfer of Twelve Plastic Leaded Chip Carrier (PLCC) by Using Computational Fluid Dynamic, FLUENTTM Software

2013 ◽  
Vol 795 ◽  
pp. 603-610 ◽  
Author(s):  
Mohamed Mazlan ◽  
A. Rahim ◽  
M.A. Iqbal ◽  
Mohd Mustafa Al Bakri Abdullah ◽  
W. Razak ◽  
...  
Keyword(s):  
Printed Circuit Board ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Circuit Board ◽  
Junction Temperature ◽  
Inlet Velocity ◽  
Chip Carrier ◽  
Flow Through ◽  
Package Density ◽  
Heat And Fluid Flow

Plastic Leaded Chip Carrier (PLCC) package has been emerged a promising option to tackle the thermal management issue of micro-electronic devices. In the present study, three dimensional numerical analysis of heat and fluid flow through PLCC packages oriented in-line and mounted horizontally on a printed circuit board, is carried out using a commercial CFD code, FLUENTTM. The simulation is performed for 12 PLCC under different inlet velocities and chip powers. The contours of average junction temperatures are obtained for each package under different conditions. It is observed that the junction temperature of the packages decreases with increase in inlet velocity and increases with chip power. Moreover, the increase in package density significantly contributed to rise in temperature of chips. Thus the present simulation demonstrates that the chip density (the number of packages mounted on a given area), chip power and the coolant inlet velocity are strongly interconnected; hence their appropriate choice would be crucial.

Computer simulation of target link explosion in laser programmable redundancy for silicon memory

1986 ◽  
Vol 1 (2) ◽  
pp. 368-381 ◽  
Author(s):  
L.M. Scarfone ◽  
J.D. Chlipala
Keyword(s):  
Thermal Evolution ◽  
Three Dimensional ◽  
Heat Diffusion ◽  
Dielectric Films ◽  
Threshold Temperature ◽  
Heat Diffusion Equation ◽  
Heating Effects ◽  
Transparent Dielectric ◽  
Difference Form ◽  
Pulse Energies

Pulses of Q-switched Nd-YAG radiation have been used to remove polysilicon target links during the implementation of laser programmable redundancy in the fabrication of silicon memory. The link is encapsulated by transparent dielectric films that give rise to important optical interference effects modifying the laser flux absorbed by the link and the silicon substrate. Estimates of these effects are made on the basis of classical plane-wave procedures. Thermal evolution of the composite structure is described in terms of a finite-difference form of the three-dimensional heat diffusion equation with a heat generation rate having a Gaussian spatial distribution of intensity and temporal shapes characteristic of commercial lasers. Temperature-dependent thermal diffusivity and melting of the polysilicon link are included in the computer modeling. The calculations account for the discontinuous change in the link absorption coefficient at the transition temperature. A threshold temperature and corresponding pressure, sufficiently high to rupture the dielectric above the link and initiate the removal process, are estimated by treating the molten link as a hard-sphere fluid. Numerical results are presented in the form of three-dimensional temperature distributions for 1.06 and 0.53 μm radiation with pulse energies 3.5 and 0.15μJ, respectively. Similarities and differences between heating effects produced by long (190 ns FWHM/740 ns duration) and short (35 ns FWHM/220 ns duration) pulses are pointed out.

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