scholarly journals Binary Neutron Star Merger Simulations with a Calibrated Turbulence Model

Symmetry ◽  
2020 ◽  
Vol 12 (8) ◽  
pp. 1249 ◽  
Author(s):  
David Radice
Keyword(s):  
Neutron Star ◽  
Turbulence Model ◽  
Reynolds Numbers ◽  
Mhd Turbulence ◽  
Binary Neutron Star ◽  
Eddy Simulation ◽  
Moderate Resolution ◽  
Scale Turbulence ◽  
High Reynolds ◽  
The Impact

Magnetohydrodynamic (MHD) turbulence in neutron star (NS) merger remnants can impact their evolution and multi-messenger signatures, complicating the interpretation of present and future observations. Due to the high Reynolds numbers and the large computational costs of numerical relativity simulations, resolving all the relevant scales of the turbulence will be impossible for the foreseeable future. Here, we adopt a method to include subgrid-scale turbulence in moderate resolution simulations by extending the large-eddy simulation (LES) method to general relativity (GR). We calibrate our subgrid turbulence model with results from very-high-resolution GRMHD simulations, and we use it to perform NS merger simulations and study the impact of turbulence. We find that turbulence has a quantitative, but not qualitative, impact on the evolution of NS merger remnants, on their gravitational wave signatures, and on the outflows generated in binary NS mergers. Our approach provides a viable path to quantify uncertainties due to turbulence in NS mergers.

Detached-Eddy Simulations and Reynolds-Averaged Navier-Stokes Simulations of Delta Wing Vortical Flowfields

2002 ◽  
Vol 124 (4) ◽  
pp. 924-932 ◽  
Author(s):  
Scott Morton ◽  
James Forsythe ◽  
Anthony Mitchell ◽  
David Hajek
Keyword(s):  
Vortex Breakdown ◽  
Delta Wing ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Fighter Aircraft ◽  
Eddy Simulation ◽  
Reynolds Averaged Navier Stokes ◽  
High Reynolds

An understanding of vortical structures and vortex breakdown is essential for the development of highly maneuverable vehicles and high angle of attack flight. This is primarily due to the physical limits these phenomena impose on aircraft and missiles at extreme flight conditions. Demands for more maneuverable air vehicles have pushed the limits of current CFD methods in the high Reynolds number regime. Simulation methods must be able to accurately describe the unsteady, vortical flowfields associated with fighter aircraft at Reynolds numbers more representative of full-scale vehicles. It is the goal of this paper to demonstrate the ability of detached-eddy Simulation (DES), a hybrid Reynolds-averaged Navier-Stokes (RANS)/large-eddy Simulation (LES) method, to accurately predict vortex breakdown at Reynolds numbers above 1×106. Detailed experiments performed at Onera are used to compare simulations utilizing both RANS and DES turbulence models.

scholarly journals Wind turbines in atmospheric flow – FSI simulations with hybrid LES-IDDES turbulence modelling

2020 ◽  
Author(s):  
Christian Grinderslev ◽  
Niels Nørmark Sørensen ◽  
Sergio González Horcas ◽  
Niels Troldborg ◽  
Frederik Zahle
Keyword(s):  
Turbulence Model ◽  
Wind Turbines ◽  
Separated Flow ◽  
Simulation Method ◽  
Turbine Rotor ◽  
Detached Eddy Simulation ◽  
Atmospheric Flow ◽  
Eddy Simulation ◽  
Significant Difference ◽  
The Impact

Abstract. In order to design future large wind turbines, knowledge is needed about the impact of aero-elasticity on the rotor loads and performance, and about the physics of the atmospheric flow surrounding the turbines. The objective of the present work is to study both effects by means of high fidelity rotor-resolved numerical simulations. In particular, unsteady computational fluid dynamics (CFD) simulations of a 2.3 MW wind turbine rotor are conducted, this rotor being the largest design with relevant experimental data available to the authors. Turbulence is modeled with two different approaches. On one hand, the well established improved delayed detached eddy simulation (IDDES) model is employed. An additional set of simulations relies on a novel hybrid turbulence model, developed within the framework of the present work. It consists on the blending of a large eddy simulation (LES) model for atmospheric flow by Deardorff with an IDDES model for the separated flow near the rotor geometry. In the same way, the assessment of the influence of the blade flexibility is performed by comparing two different sets of computations. A first group accounts for a structural multi body dynamic (MBD) model of the blades. The MBD solver was coupled to the CFD solver during run time with a staggered fluid structure interaction (FSI) scheme. The second set of simulations uses the original rotor geometry, without accounting for any structural deflection. The results of the present work show no significant difference between the IDDES and the hybrid turbulence model. However, it is expected that future simulations of more complex stratification and longer domains will benefit from the developed hybrid model. In a similar manner, and due to the fact that the considered rotor was relatively stiff, the loading variation introduced by the blade flexibility was found to be negligible when compared to the influence of inflow turbulence. The simulation method validated here is considered highly relevant for future turbine designs, where the impact of blade elasticity will be significant and the detailed structure of the atmospheric inflow will be important.

CFD Investigation of the Effect of Current Turbulence on the Hydrodynamic Forces on a Cylinder

2005 ◽  
Author(s):  
Hyung Taek Ahn ◽  
Yannis Kallinderis
Keyword(s):  
Turbulence Model ◽  
Reynolds Numbers ◽  
Offshore Structures ◽  
Hydrodynamic Forces ◽  
Current Profile ◽  
Time Step ◽  
Lack Of Information ◽  
Turbulent Inflow ◽  
Inflow Condition ◽  
High Reynolds

Practical cases of flow-structure interactions involve ocean currents with turbulence. Ocean turbulence effects on offshore structures are of high interest due to the lack of information about its role regarding the hydrodynamic forces and fatigue load on structures. Current turbulence profiles are employed for various Reynolds numbers that are based on an isotropic geophysical turbulence model. These turbulence profiles are specified as the inflow condition for the numerical simulations over a circular cylinder. The present work consists of three parts: (i) determination of appropriate mesh and time step resolution to accommodate the turbulence, (ii) investigation of the effect of current profile turbulence on the amplitude and frequencies of the hydrodynamic forces acting on a cylinder, and (iii) study of the sensitivity of the hydrodynamic load exerted on the cylinder for a range of Reynolds numbers with a turbulent inflow profile. Spalart-Allmaras one-equation turbulence model is used for high Reynolds number simulations.

New thermal-hydraulic correlations for printed circuit heat exchangers (PCHEs) with zigzag channels under high Reynolds numbers

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Carolina P. Naveira-Cotta ◽  
Jian Su ◽  
Paulo Lucena Kreppel Paes ◽  
Philippe R. Egmont ◽  
Rodrigo P. M. Moreira ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Design Parameters ◽  
Channel Diameter ◽  
Content Type ◽  
Printed Circuit ◽  
High Reynolds Numbers ◽  
High Reynolds ◽  
The Impact

Purpose The purpose of this paper is to investigate the impact of semi-circular zigzag-channel printed circuit heat exchanger (PCHE) design parameters on heat transfer and pressure drop of flows under high Reynolds numbers and provide new thermal-hydraulic correlations relevant to conditions encountered in natural gas processing plants. Design/methodology/approach The correlations were developed using three-dimensional steady-state computational fluid dynamics simulations with varying semicircular channel diameter (from 1 to 5 mm), zigzag angle (from 15° to 45°) and Reynolds number (from 40,000 to 100,000). The simulation results were validated by comparison with experimental results and existing correlations. Findings The results revealed that the thermal-hydraulic performance was mostly affected by the zigzag angle, followed by the ratio of the zigzag channel length to the hydraulic diameter. Overall, smaller zigzag angles favored heat transfer intensification while keeping reasonably low pressure drops. Originality/value This study is, to date, the only one providing thermal-hydraulic correlations for PCHEs with zigzag channels under high Reynolds numbers. Besides, the broad range of parameters considered makes the proposed correlations valuable PCHE design tools.

Efficient Computation and Modeling of Viscous Flow Effects in ComFLOW

2013 ◽  
Author(s):  
Henri J. L. van der Heiden ◽  
Peter van der Plas ◽  
Arthur E. P. Veldman ◽  
Roel W. C. P. Verstappen ◽  
Roel Luppes
Keyword(s):  
Reynolds Number ◽  
Viscous Flow ◽  
Turbulence Model ◽  
Cfd Simulation ◽  
Stokes Equations ◽  
Reynolds Numbers ◽  
Second Order ◽  
Efficient Computation ◽  
Flow Effects ◽  
High Reynolds

In offshore applications, details of viscous flow effects can become relevant when predicting e.g. drag forces on the columns of oil drilling rigs, or the flow around a semisubmersible in figure 1. This motivates a novel approach for efficiently simulating viscous flow effects at high Reynolds numbers with the CFD simulation tool ComFLOW. In ComFLOW, the Navier–Stokes equations can be solved for one-phase and for two-phase flow. The equations are discretized second-order in space, and second-order in time. An Improved Volume-of-Fluid (IVOF) algorithm is used for free-surface advection and reconstruction [1, 2]. Modeling viscous flow effects in high Reynolds number flows requires a turbulence model that provides accurate results on coarse grids. We pursue to achieve a high local grid resolution in a computationally efficient manner. Both approaches are tested for flows around a square cylinder: grid refinement at Reynolds numbers 10 and 100, and the turbulence model at Reynolds number 22,000.

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