scholarly journals VIScous Vorticity Equation (VISVE) for Turbulent 2-D Flows with Variable Density and Viscosity

2020 ◽  
Vol 8 (3) ◽  
pp. 191 ◽  
Author(s):  
Spyros A. Kinnas
Keyword(s):  
Variable Viscosity ◽  
Variable Density ◽  
Vorticity Equation ◽  
Navier Stokes ◽  
Cavitating Flows ◽  
Rans Equations ◽  
Reynolds Averaged Navier Stokes

The general vorticity equation for turbulent compressible 2-D flows with variable viscosity is derived, based on the Reynolds-Averaged Navier-Stokes (RANS) equations, and simplified versions of it are presented in the case of turbulent or cavitating flows around 2-D hydrofoils.

scholarly journals RANS MODELLING OF CROSS-SHORE SEDIMENT TRANSPORT AND MORPHODYNAMICS IN THE SWASH-ZONE

2020 ◽  
pp. 14
Author(s):  
Joost Kranenborg ◽  
Geert Campmans ◽  
Niels Jacobsen ◽  
Jebbe van der Werf ◽  
Robert McCall ◽  
...  
Keyword(s):  
Sediment Transport ◽  
Numerical Model ◽  
Navier Stokes ◽  
Swash Zone ◽  
Rans Equations ◽  
Model Based ◽  
Numerical Studies ◽  
Reynolds Averaged Navier Stokes ◽  
Averaged Models

Most numerical studies of sediment transport in the swash zone use depth-averaged models. However, such models still have difficulty predicting transport rates and morphodynamics. Depth-resolving models could give detailed insight in swash processes but have mostly been limited to hydrodynamic predictions. We present a depth-resolving numerical model, based on the Reynolds Averaged Navier-Stokes (RANS) equations, capable of modelling sediment transport and morphodynamics in the swash zone.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/PB8Vs0LJq88

scholarly journals Reynolds-averaged Navier–Stokes equations with explicit data-driven Reynolds stress closure can be ill-conditioned

2019 ◽  
Vol 869 ◽  
pp. 553-586 ◽  
Author(s):  
Jinlong Wu ◽  
Heng Xiao ◽  
Rui Sun ◽  
Qiqi Wang
Keyword(s):  
Reynolds Stress ◽  
Condition Number ◽  
Stokes Equations ◽  
Plane Channel ◽  
Channel Flows ◽  
Data Driven ◽  
Navier Stokes ◽  
Rans Equations ◽  
Reynolds Averaged Navier Stokes ◽  
Stress Models

Reynolds-averaged Navier–Stokes (RANS) simulations with turbulence closure models continue to play important roles in industrial flow simulations. However, the commonly used linear eddy-viscosity models are intrinsically unable to handle flows with non-equilibrium turbulence (e.g. flows with massive separation). Reynolds stress models, on the other hand, are plagued by their lack of robustness. Recent studies in plane channel flows found that even substituting Reynolds stresses with errors below 0.5 % from direct numerical simulation databases into RANS equations leads to velocities with large errors (up to 35 %). While such an observation may have only marginal relevance to traditional Reynolds stress models, it is disturbing for the recently emerging data-driven models that treat the Reynolds stress as an explicit source term in the RANS equations, as it suggests that the RANS equations with such models can be ill-conditioned. So far, a rigorous analysis of the condition of such models is still lacking. As such, in this work we propose a metric based on local condition number function for a priori evaluation of the conditioning of the RANS equations. We further show that the ill-conditioning cannot be explained by the global matrix condition number of the discretized RANS equations. Comprehensive numerical tests are performed on turbulent channel flows at various Reynolds numbers and additionally on two complex flows, i.e. flow over periodic hills, and flow in a square duct. Results suggest that the proposed metric can adequately explain observations in previous studies, i.e. deteriorated model conditioning with increasing Reynolds number and better conditioning of the implicit treatment of the Reynolds stress compared to the explicit treatment. This metric can play critical roles in the future development of data-driven turbulence models by enforcing the conditioning as a requirement on these models.

A Numerical Method for 3D Turbomachinery Aeroelasticity

2004 ◽  
Author(s):  
Paola Cinnella ◽  
Emanuele Cappiello ◽  
Pietro De Palma ◽  
Michele Napolitano ◽  
Giuseppe Pascazio
Keyword(s):  
Rigid Body ◽  
Numerical Method ◽  
Integral Form ◽  
Navier Stokes ◽  
Moving Grid ◽  
Time Step ◽  
Rans Equations ◽  
Standard Configuration ◽  
Reynolds Averaged Navier Stokes

This work provides an extension to 3D aeroelastic problems of a recently developed numerical method for turbomachinery aeroelasticity. The unsteady Euler or Reynolds-averaged Navier-Stokes (RANS) equations are solved in integral form, the blade passages being discretised using a deforming grid. The grid is regenerated at each time step using a novel methodology, that automatically avoids grid lines overlapping and guarantees the smoothness of the regenerated mesh. Firstly, the method has been validated versus the 2D 4th Aeroelastic Turbine Standard Configuration. Both inviscid and viscous turbulent computations have been performed, and the results previously obtained usind a different moving grid strategy have been recovered. In order to prove the robustness of the proposed deforming grid methodology, the same case has also been computed with the blade under-going large torsion displacements, the regenerated grid always preserving a good smoothness. Then, the methodology has been validated versus the 3D 4th Standard Aeroelastic Configuration, that involves a rigid body blade motion. Finally, a more severe 3D configuration, involving a clamped-beam-like blade deformation, has been considered.

Modeling and computation of the cavitating flow in injection nozzle holes

2015 ◽  
Vol 06 (01) ◽  
pp. 1550003 ◽  
Author(s):  
Hatem Kanfoudi ◽  
Ridha Zgolli
Keyword(s):  
Transport Equation ◽  
Source Term ◽  
Stokes Equations ◽  
Volume Fraction ◽  
Variable Density ◽  
Navier Stokes ◽  
Physical Parameters ◽  
Cavitating Flows ◽  
Navier Stokes Equations ◽  
Injection Nozzle

Cavitating flows inside a diesel injection nozzle hole were simulated using a mixture model. A two-dimensional (2D) numerical model is proposed in this paper to simulate steady cavitating flows. The Reynolds-averaged Navier–Stokes equations are solved for the liquid and vapor mixture, which is considered as a single fluid with variable density and expressed as a function of the vapor volume fraction. The closure of this variable is provided by the transport equation with a source term Transport-equation based methods (TEM). The processes of evaporation and condensation are governed by changes in pressure within the flow. The source term is implanted in the CFD code ANSYS CFX. The influence of numerical and physical parameters is presented in detail. The numerical simulations are in good agreement with the experimental data for steady flow.

scholarly journals Advances in Numerical Reynolds-Averaged Navier–Stokes Modelling of Wave-Structure-Seabed Interactions and Scour

2021 ◽  
Vol 9 (6) ◽  
pp. 611
Author(s):  
Pilar Díaz-Carrasco ◽  
Sergio Croquer ◽  
Vahid Tamimi ◽  
Jay Lacey ◽  
Sébastien Poncet
Keyword(s):  
Sediment Transport ◽  
Numerical Modelling ◽  
Review Paper ◽  
Fluid Phase ◽  
Wave Structure ◽  
Numerical Approach ◽  
Navier Stokes ◽  
Future Prospects ◽  
Rans Equations ◽  
Reynolds Averaged Navier Stokes

This review paper presents the recent advances in the numerical modelling of wave–structure–seabed interactions. The processes that are involved in wave–structure interactions, which leads to sediment transport and scour effects, are summarized. Subsequently, the three most common approaches for modelling sediment transport that is induced by wave–structure interactions are described. The applicability of each numerical approach is also included with a summary of the most recent studies. These approaches are based on the Reynolds-Averaged Navier–Stokes (RANS) equations for the fluid phase, and mostly differ in how they tackle the seabed response. Finally, future prospects of research are discussed.

A NUMERICAL MODEL TO SIMULATE THE CAVITATING FLOWS

2011 ◽  
Vol 02 (03) ◽  
pp. 277-297 ◽  
Author(s):  
HATEM KANFOUDI ◽  
RIDHA ZGOLLI
Keyword(s):  
Single Phase ◽  
Stokes Equations ◽  
Volume Fraction ◽  
Computer Time ◽  
Variable Density ◽  
Navier Stokes ◽  
Engineering Practice ◽  
Physical Parameters ◽  
Cavitating Flows ◽  
Flow Models

The object of this paper is to propose a model to simulate steady and unsteady cavitating flows. In the engineering practice, cavitation flow is often modeled as a single-phase flow (mixture), where the cavitation area is handled as an area with the pressure lower than the vapor pressure. This approach always leads to the result, and the requirement of computer time is many times lower in comparison with multiphase flow models. The Reynolds-averaged Navier–Stokes equations are solved for the mixture of liquid and vapor, which is considered as a single-phase with variable density. The vaporization and condensation processes are controlled by barocline low. A transport equation with source terms is implanted in the code Computational Fluid Dynamics (CFD) to compute the volume fraction of the vapor. The CFD code used is ANSYS CFX. The influence of numerical and the physical parameters are presented. The numerical results are compared to previous experimental measures. For steady flow, a SST turbulence model is adopted and LES for the unsteady flow.

Reynolds-averaged Navier–Stokes simulation of hydrofoil effects on hydrodynamic coefficients of a catamaran in forced oscillation

2016 ◽  
Vol 231 (2) ◽  
pp. 364-383
Author(s):  
Amin Najafi ◽  
Mohammad Saeed Seif
Keyword(s):  
High Speed ◽  
Experimental Approach ◽  
Navier Stokes ◽  
Hydrodynamic Coefficients ◽  
Laboratory Equipment ◽  
Factors Affecting ◽  
High Frequencies ◽  
Frequency Independent ◽  
Reynolds Averaged Navier Stokes

Determination of high-speed crafts’ hydrodynamic coefficients will help to analyze the dynamics of these kinds of vessels and the factors affecting their dynamic stabilities. Also, it can be useful and effective in controlling the vessel instabilities. The main purpose of this study is to determine the coefficients of longitudinal motions of a planing catamaran with and without a hydrofoil using Reynolds-averaged Navier–Stokes method to evaluate the foil effects on them. Determination of hydrodynamic coefficients by experimental approach is costly and requires meticulous laboratory equipment; therefore, utilizing the numerical methods and developing a virtual laboratory seem highly efficient. In this study, the numerical results for hydrodynamic coefficients of a high-speed craft are verified against Troesch’s experimental results. In the following, after determination of hydrodynamic coefficients of a planing catamaran with and without foil, the foil effects on its hydrodynamic coefficients are evaluated. The results indicate that most of the coefficients are frequency-independent especially at high frequencies.

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