scholarly journals Lagrangian Vortex Computations of a Four Tidal Turbine Array: An Example Based on the NEPTHYD Layout in the Alderney Race

Energies ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3826
Author(s):  
Myriam Slama ◽  
Camille Choma Bex ◽  
Grégory Pinon ◽  
Michael Togneri ◽  
Iestyn Evans
Keyword(s):  
Numerical Simulations ◽  
Turbulence Intensity ◽  
Three Dimensional ◽  
Vortex Method ◽  
Numerical Dissipation ◽  
Computational Domain ◽  
Turbulent Structures ◽  
Tidal Turbine ◽  
Straight Flow ◽  
Ambient Turbulence

This study investigates the wake interaction of four full-scale three-bladed tidal turbines with different ambient turbulence conditions, in straight and yawed flows. A three-dimensional unsteady Lagrangian Vortex Blob software is used for the numerical simulations of the turbines’ wakes. In order to model the ambient turbulence in the Lagrangian Vortex Method formalism, a Synthetic Eddy Method is used. With this method, turbulent structures are added in the computational domain to generate a velocity field which statistically reproduces any ambient turbulence intensity and integral length scale. The influence of the size of the structures and their density (within the study volume) on the wake of a single turbine is studied. Good agreement is obtained between numerical and experimental results for a high turbulence intensity but too many structures can increase the numerical dissipation and reduce the wake extension. Numerical simulations of the four turbine array with the layout initially proposed for the NEPTHYD pilot farm are then presented. Two ambient turbulence intensities encountered in the Alderney Race and two integral length scales are tested with a straight flow. Finally, the wakes obtained for yawed flows with different angles are presented, highlighting turbine interactions.

Numerical simulations and analysis of the turbulent flow field in a practical gas turbine engine combustor

2021 ◽  
pp. 095765092110632
Author(s):  
Veeraraghava R Hasti ◽  
Prithwish Kundu ◽  
Sibendu Som ◽  
Jay P Gore
Keyword(s):  
Flow Field ◽  
Turbulent Flow ◽  
Numerical Simulations ◽  
Gas Turbine ◽  
Adaptive Mesh Refinement ◽  
Three Dimensional ◽  
Adaptive Mesh ◽  
Turbulent Structures ◽  
Cut Cell ◽  
Turbulent Flow Field

The turbulent flow field in a practical gas turbine combustor is very complex because of the interactions between various flows resulting from components like multiple types of swirlers, dilution holes, and liner effusion cooling holes. Numerical simulations of flows in such complex combustor configurations are challenging. The challenges result from (a) the complexities of the interfaces between multiple three-dimensional shear layers, (b) the need for proper treatment of a large number of tiny effusion holes with multiple angles, and (c) the requirements for fast turnaround times in support of engineering design optimization. Both the Reynolds averaged Navier–Stokes simulation (RANS) and the large eddy simulation (LES) for the practical combustor geometry are considered. An autonomous meshing using the cut-cell Cartesian method and adaptive mesh refinement (AMR) is demonstrated for the first time to simulate the flow in a practical combustor geometry. The numerical studies include a set of computations of flows under a prescribed pressure drop across the passage of interest and another set of computations with all passages open with a specified total flow rate at the plenum inlet and the pressure at the exit. For both sets, the results of the RANS and the LES flow computations agree with each other and with the corresponding measurements. The results from the high-resolution LES simulations are utilized to gain fundamental insights into the complex turbulent flow field by examining the profiles of the velocity, the vorticity, and the turbulent kinetic energy. The dynamics of the turbulent structures are well captured in the results of the LES simulations.

scholarly journals Double-Diffusive Recipes. Part I: Large-Scale Dynamics of Thermohaline Staircases

2014 ◽  
Vol 44 (5) ◽  
pp. 1269-1284 ◽  
Author(s):  
T. Radko ◽  
A. Bulters ◽  
J. D. Flanagan ◽  
J.-M. Campin
Keyword(s):  
Numerical Simulations ◽  
Large Scale ◽  
Density Ratio ◽  
Three Dimensional ◽  
Flux Ratio ◽  
Double Diffusion ◽  
Spontaneous Generation ◽  
Computational Domain ◽  
The North ◽  
Basin Scale

Abstract Three-dimensional dynamics of thermohaline staircases are investigated using a series of basin-scale staircase-resolving numerical simulations. The computational domain and forcing fields are chosen to reflect the size and structure of the North Atlantic subtropical thermocline. Salt-finger transport is parameterized using the flux-gradient formulation based on a suite of recent direct numerical simulations. Analysis of the spontaneous generation of thermohaline staircases suggests that thermohaline layering is a product of the gamma instability, associated with the variation of the flux ratio with the density ratio . After their formation, numerical staircases undergo a series of merging events, which systematically increase the size of layers. Ultimately, the system evolves into a steady equilibrium state with pronounced layers 20–50 m thick. The size of the region occupied by thermohaline staircases is controlled by the competition between turbulent mixing and double diffusion. Assuming, in accordance with observations, that staircases form when the density ratio is less than the critical value of , the authors arrive at an indirect estimate of the characteristic turbulent diffusivity in the subtropical thermocline.

Numerical simulations of nonlinear axisymmetric flows with a free surface

1987 ◽  
Vol 178 ◽  
pp. 195-219 ◽  
Author(s):  
Douglas G. Dommermuth ◽  
Dick K. P. Yue
Keyword(s):  
Free Surface ◽  
Numerical Simulations ◽  
Three Dimensional ◽  
Vertical Cylinder ◽  
Free Surface Flows ◽  
Boundary Integral ◽  
The Body ◽  
Special Treatment ◽  
Computational Domain ◽  
Vortex Sheets

A numerical method is developed for nonlinear three-dimensional but axisymmetric free-surface problems using a mixed Eulerian-Lagrangian scheme under the assumption of potential flow. Taking advantage of axisymmetry, Rankine ring sources are used in a Green's theorem boundary-integral formulation to solve the field equation; and the free surface is then updated in time following Lagrangian points. A special treatment of the free surface and body intersection points is generalized to this case which avoids the difficulties associated with the singularity there. To allow for long-time simulations, the nonlinear computational domain is matched to a transient linear wavefield outside. When the matching boundary is placed at a suitable distance (depending on wave amplitude), numerical simulations can, in principle, be continued indefinitely in time. Based on a simple stability argument, a regriding algorithm similar to that of Fink & Soh (1974) for vortex sheets is generalized to free-surface flows, which removes the instabilities experienced by earlier investigators and eliminates the need for artificial smoothing. The resulting scheme is very robust and stable.For illustration, three computational examples are presented: (i) the growth and collapse of a vapour cavity near the free surface; (ii) the heaving of a floating vertical cylinder starting from rest; and (iii) the heaving of an inverted vertical cone. For the cavity problem, there is excellent agreement with available experiments. For the wave-body interaction calculations, we are able to obtain and analyse steady-state (limit-cycle) results for the force and flow field in the vicinity of the body.

The Effects of Inlet Turbulence Intensity and Computational Domain on a Nonpremixed Bluff-Body Flame

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
Lu Chen ◽  
Francine Battaglia
Keyword(s):  
Boundary Condition ◽  
Turbulence Intensity ◽  
Bluff Body ◽  
Mixture Fraction ◽  
Three Dimensional ◽  
Plane Channel ◽  
Cfd Modeling ◽  
Computational Domain ◽  
Substantial Impact ◽  
Turbulent Nonpremixed

A bluff body burner was investigated using computational fluid dynamics (CFD) to assess the effects of inlet turbulence intensity and compare the combustion characteristics with and without the bluff-body modeled in the computational domain. The effects of the CFD modeling techniques were assessed for inlet turbulence intensity, using a two-dimensional (2D) versus three-dimensional (3D) computational domain, and whether to include the bluff body in the domain. The simulations were compared with experimental data from the Turbulent Nonpremixed Flames workshop. The results showed that the turbulence intensity specified as a boundary condition at the fuel-jet inlet had a substantial impact on the axial decay of mixture fraction and temperature, which was overlooked by previous researchers when the bluff body was not modeled. The numerical results of the 2D axisymmetric and 3D domains without the bluff body showed that the 3D domain provided the best predictions when the turbulence intensity was defined using a published correlation versus experimental estimates since the k–ε turbulence model underestimated dissipation. It was shown that a 2D axisymmetric domain can be used to obtain predictions with acceptable numerical errors without the inclusion of the bluff body, and that a uniform inlet velocity can be specified, provided that the inlet turbulence intensity is defined using the correlation by Durst et al. (“Methods to Set Up and Investigate Low Reynolds Number, Fully Developed Turbulent Plane Channel Flows,” ASME J. Fluids Eng., 120(3), pp. 496–503.). Finally, further analysis of flow and flame characteristics demonstrated that when the bluff-body was included for the 2D axisymmetric domain, predictions improved and the flow was insensitive to inlet turbulence intensities because the bluff-body provided an entrance region for the flow to develop before mixing, thus reducing inlet effects. Thus, if experimental inlet data are not available, the addition of the bluff-body in the computational domain provides a more accurate jet velocity profile entering the reacting domain and eliminates errors caused by the inlet boundary condition.

Numerical Simulations of Confined, Turbulent, Lean, Premixed Flames Using a Detailed Chemistry Combustion Model

2011 ◽  
Author(s):  
Massimiliano Di Domenico ◽  
Peter Gerlinger ◽  
Berthold Noll
Keyword(s):  
Numerical Simulations ◽  
Three Dimensional ◽  
Combustion Products ◽  
Reaction Scheme ◽  
Flame Stabilization ◽  
Combustion Model ◽  
Turbulent Structures ◽  
Detailed Chemistry ◽  
Jet Flame ◽  
Radial Profiles

In this paper numerical simulations of a confined, high strained jet flame employing a detailed chemistry combustion model are presented. Unlike other configurations available in literature, the geometry under investigation presents the jet axis shifted one side of the confining chamber in order to get non-symmetric recirculation zones and a flame stabilization mechanism based on the recirculation of a high percentage of hot combustion products. Fully three-dimensional unsteady simulations are carried out with finite-rate chemistry effects included by means of a detailed reaction scheme. Turbulence-chemistry interaction is taken into account by employing a presumed PDF approach, which is able to close species source terms by solving two additional transport equations. The use of the hybrid RANS/LES SST-SAS turbulence model is able to include large unsteady turbulent structures according to the local grid size and flow conditions. The approach presented here allows an in-depth investigation of flame stabilization mechanisms, ignition phenomena and influence of recirculation regions on flame stability. Additional simulations adopting simpler combustion models (i.e. Eddy-dissipation Concept) are also presented in order to assess the prediction capabilities of methods widely used in design environments. The paper also includes experimental data while comparison in terms of radial profiles at different heights above the burner are provided.

scholarly journals Influence of Mechanical Stirring on the Crucible Dissolution Rate and Impurities Distribution in Directional Solidification of Multicrystalline Silicon

2015 ◽  
Vol 58 (1) ◽  
pp. 27-37
Author(s):  
Alexandra Popescu ◽  
Daniel Vizman
Keyword(s):  
Numerical Simulations ◽  
Dissolution Rate ◽  
Total Mass ◽  
Three Dimensional ◽  
Pilot Scale ◽  
Time Dependent ◽  
Multicrystalline Silicon ◽  
Computational Domain ◽  
Mechanical Stirring ◽  
Silicon Melt

Abstract In this study, time dependent three-dimensional numerical simulations were carried out using the STHAMAS3D software in order to understand the effects of forced convection induced by mechanical stirring of the melt, on the crucible dissolution rate and on the impurities distribution in multicrystalline silicon (mc-Si) melt for different values of the diffusion coefficient.Numerical simulations were performed on a pilot scale furnace with crucible dimensions of 38x38x40cm3. The computational domain used for the local 3D-simulations consists of melt and crystal.The dissolution rate was estimated from the total mass of impurities that was found in the silicon melt after a certain period of time. The obtained results show that enhanced convection produced by a mechanical stirrer leads to a significant increase of the dissolution rate and also to a uniform distribution of impurities in the melt.

scholarly journals The intermediate Rossby number range and two-dimensional–three-dimensional transfers in rotating decaying homogeneous turbulence

2007 ◽  
Vol 587 ◽  
pp. 139-161 ◽  
Author(s):  
LYDIA BOUROUIBA ◽  
PETER BARTELLO
Keyword(s):  
Numerical Simulations ◽  
Three Dimensional ◽  
Domain Size ◽  
Homogeneous Turbulence ◽  
Finite Domain ◽  
Rossby Number ◽  
Computational Domain ◽  
Two Dimensional ◽  
Number Range ◽  
Wide Range

Rotating homogeneous turbulence in a finite domain is studied using numerical simulations, with a particular emphasis on the interactions between the wave and zero-frequency modes. Numerical simulations of decaying homogeneous turbulence subject to a wide range ofbackground rotation rates are presented. The effect of rotation is examined in two finiteperiodic domains in order to test the effect of the size of the computational domain on the results obtained, thereby testing the accurate sampling of near-resonant interactions.We observe a non-monotonic tendency when Rossby number Ro is varied from large values to the small-Ro limit, which is robust to the change of domain size. Three rotation regimes are identified and discussed: the large-, the intermediate-, and the small-Ro regimes. The intermediate-Ro regime is characterized by a positive transfer of energy from wave modes to vortices. The three-dimensional to two-dimensional transfer reaches an initial maximum for Ro ≈ 0.2 and it is associated with a maximum skewness of vertical vorticity in favour of positive vortices. This maximum is also reached at Ro ≈ 0.2. In the intermediate range an overall reduction of vertical energy transfer is observed. Additional characteristic horizontal and vertical scales of this particular rotation regime are presented and discussed.

Experimental and numerical investigation of an axisymmetric divergent dual throat nozzle

2019 ◽  
Vol 234 (3) ◽  
pp. 563-572 ◽  
Author(s):  
Yang-Sheng Wang ◽  
Jing-Lei Xu ◽  
Shuai Huang ◽  
Yong-Chen Lin ◽  
Jing-Jing Jiang
Keyword(s):  
Numerical Simulations ◽  
Skin Friction ◽  
Flow Structure ◽  
Static Pressure ◽  
Three Dimensional ◽  
Computational Domain ◽  
Thrust Vectoring ◽  
Separation Line ◽  
Pressure Distributions ◽  
Actual Flow

The dual throat nozzle achieves higher thrust vectoring efficiencies and lesser thrust loss than other fluidic thrust-vectoring nozzles. Separation always occurs at the bottom of the cavity with complex three-dimensional characteristics for the dual throat nozzle. In this paper, by comparing the flow structure, nozzle surface static pressure distributions and skin friction lines, which are obtained by numerical simulations and wind tunnel experiments, an axisymmetric divergent dual throat nozzle is investigated in detail. The main results show the following findings. (1) The experimental schlieren photographs confirm again that the divergent nozzle configuration has the starting problem from an intuitive perspective. Meanwhile, the flow structure and nozzle surface static pressure distributions obtained by numerical simulations are consistent with the experimental results, except for the low nozzle pressure ratios. (2) The circumferential pressure difference is negligible upstream of the separation line but obvious downstream of the separation line. The skin friction lines and nozzle surface static pressure distributions of different circumferential angles obtained by experiments both prove that the actual flow in the axisymmetric divergent dual throat nozzle indeed possesses three-dimensional characteristics. Therefore, it is necessary to utilize the full three-dimensional computational domain to study the complex three-dimensional characteristics of the flow for the axisymmetric divergent dual throat nozzle thoroughly.

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