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Questions tagged [fluid-dynamics]

The study of the properties of fluids and gases in motion

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403 views

Simple turbulence model appropriate for buoyancy-driven cavity like problem

Which turbulence model is suitable for resolving incompressible buoyancy-driven flow of a fluid within an cylindrical ampoule? I prefer turbulence model which is sufficiently simple so that fully ...
6
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0answers
1k views

What is the best OpenFOAM RAS turbulence model for a motorbike/vespa problem?

I am learning OpenFOAM as a hobby and using my Vespa racing as the topic to apply it to. The objective is to produce modifications that improve the top speed (as well as getting some values such as ...
5
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0answers
149 views

Is it generally unstable to use in multidimensional simulations finite difference schemes with higher orders than 2?

I'm part of a team trying to generalize a 1D Advection-Diffussion-Reaction code we inherited by extending it to 2D by using dimensional splitting, i.e. solving advection and diffusion for x and y ...
5
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0answers
350 views

How does GAMG in OpenFOAM really work?

I use OpenFOAM for CFD simulations. A very popular preconditioner is GAMG which needs a low number of iterations per a time step in SIMPLE or PISO solvers that are used to simulate the fluid flow. I ...
4
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0answers
162 views

A good 2D finite difference for the continuity equation

How could I go about solving the continuity equation below in 2D? $$\frac{\partial \rho}{\partial t} + \nabla \cdot \left(\rho u\right)=0$$ I saw that a similar question was posted here: A good ...
4
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0answers
169 views

Rhie--Chow interpolation on PDE level

The Rhie--Chow [1] interpolation seems to be a standard tool in the Finite-Volume discretization of incompressible flows. It is commonly defined on the discrete level [2]. In the lecture notes [3] --...
4
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0answers
599 views

How to implement boundary conditions on Finite Difference WENO5 scheme for the Euler equations

I'm implementing a Finite Difference WENO5 with Lax-Friedrich flux splitting on a uniform, structured grid to solve the 2D Euler equations of fluid dynamics on a rectangular domain in cartesian ...
4
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0answers
221 views

Negative viscosity stabilized by fourth order terms

I am trying to solve a "Navier-Stokes"-type problem where the viscosity is negative. Of course this renders the equation unstable and thus I add a fourth order term, so the entire equation becomes: $$...
4
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0answers
112 views

What are the governing equations solved in coupled atmosphere-ocean models?

In (hydrostatic) atmospheric general circulation models, for example the so-calle Primitive Equations, consisting of the horizontal momentum equation, the hydrostatic balance, the continuity equation, ...
3
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0answers
53 views

Should I expect computational gains using a second-order splitting method here?

I am trying to solve a three-dimensional baroclinic transport problem. The hydrodynamic (three-dimensional shallow water) equations are: \begin{align} \nabla \cdot \vec{v} = 0, \tag{1} \\ \frac{\...
3
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0answers
127 views

Finite Element Stabilization for Drift-Diffusion/Advection-Diffusion Equations

I've tried my best to look through the relevant suggested similar questions when posting this, and hopefully this contains enough new material to not be considered a duplicate. I'm currently trying ...
3
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0answers
96 views

Non-reflecting boundary conditions for compressible Navier-Stokes equations

I have some questions about the implementation of non-reflecting OUTFLOW boundary condition for Navier Stokes equations. Following Poinsot, Lele "Boundary Conditions for Direct Simulations of ...
3
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0answers
114 views

How one could choose the value of viscous coefficient for obtaining stable solution of Burgers' equation?

Burgers' equation is a fundamental PDE used in various fields such as number theory, gas dynamics, heat conduction, elasticity, etc. It is crucial especially for developing numerical models for ...
3
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0answers
66 views

Cavity Flow CFD Boundary conditions and strange waves

So I have a PDE that I use to describe how material flows through a volume(2D or 3D). $$\frac{\partial C}{\partial t} + \vec{u} \cdot \nabla C = (D' + D )\nabla^2C$$ Now using finite differences I get ...
3
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0answers
292 views

Euler Equation Eigensystem with Gravity in the Energy Flux

I am modifying a conservative form of the Euler equations with gravity in the energy flux (see previous question: Energy Conservation in Conservation Laws with Source Terms) for use in a Riemann ...
3
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0answers
352 views

Transport Equation in a Tube: Source Term on Boundary

I'm modeling mass transport in a flow reactor. The flow reactor is a tube, which allows me to use cylindrical symmetry in solving the Convection-Diffusion-Reaction (CDR) Equation, which governs the ...
3
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0answers
613 views

Immersed boundary method

I'm trying to use immersed boundary method for the 3D flow problem (Navier-Stokes equations), but I'm maybe misunderstood something in this method. Main principles I took from this book. I use the ...
3
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0answers
222 views

N-body simulation for particles

I would like use N-body simulation for measure a torque on an object in a liquid (helium). It's a 2D study. On the site : http://www.browndeertechnology.com/docs/BDT_OpenCL_Tutorial_NBody-rev3.html I ...
3
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0answers
190 views

How to estimate if a velocity field is statistically homogeneous?

For a 3D velocity field $\mathbf{u}$ obtained by direct numerical simulation. Assuming that the field is defined on a periodic domain $\mathcal{P}$ of periodicity $L_x$ in the $x$ direction, $L_y$ ...
3
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0answers
2k views

Create 2D plot from two data sets in ParaView

I'm currently running a CFD simulation for an internal flow and need to compare my computed results to experimental data. The experimental data is saved as a comma separated file with columns for x,y,...
2
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0answers
51 views

Why do stabilized formulations for the Navier-Stokes equation maintain the convergence rate for high order polynomial interpolation?

I have a quick questions which has been troubling me lately. When reading the FENICS Finite Element Book they assess various approaches to solver the Stokes equation. Obviously, they discuss the ...
2
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0answers
48 views

WENO methods: why the characteristic wise method resulting big errors?

I was doing my research/project using WENO as the limiter in finite volume methods to solve hyperbolic conservation law. I have no idea why the result in the characteristic wise method has a big error ...
2
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0answers
106 views

Simulation of surface tension-dominated interfaces

I want to simulate the shape of the free surface in a small fuel tank in microgravity, which is very slowly being emptied. The tank is not symmetric, the geometry is given by CAD (e.g. step file). ...
2
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0answers
244 views

Algorithm for face based data-structure - CFD

Good morning I'm trying to develop an unstructured CFD code to solve Euler equations in a finite-volume (cell-centered) context (learning purposes). I was able to build from a cgns file some basic ...
2
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0answers
271 views

Collocated Grid Navier Stokes Solver

I want to solve Navier Stokes equations on a collocated grid. Earlier, I was using a MacCormick scheme based solver where I discretized predictor step in forward differences and corrector step in ...
2
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0answers
105 views

an ideal fluid in a reservoir

Let us imagine that we have an ideal fluid in a reservoir, not full, which means there is a free surface of an ideal fluid on top, this reservoir makes no movements. This problem mathematical ...
2
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0answers
112 views

Finite difference aproximation - Darcy law

I am solving following problem: Filtration of water can be described in bi-dimensional case by $$- \partial_x(K(x,y) \partial_x u ) - \partial_y (K(x,y) \partial_y u ) = 0, $$ where $u$ - water ...
2
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0answers
128 views

what do positive real parts of eigenvalues mean?

I am solving a 1D advection problem of the the form $$d{Q}/dt = [A]{Q}$$ where {Q} is the vector of unknowns and [A] is the matrix of coefficients of spatial discretisation. I have worked out the ...
2
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0answers
450 views

Molecular dynamics: Lennard-Jones forces in 2D system

As I am new to all these stuff I would like to verify whether my procedure is correct. I need to calculate the Lennard-Jones potential, potential energy of the system and the forces. The procedure ...
2
votes
0answers
243 views

Implementation of no-slip boundary conditions in lattice Boltzmann method fluid simulation

My faculty advisor recommended that I take a look at the lattice Boltzmann method as an introduction to scientific computing and potentially an undergraduate honors thesis topic. I cooked up a some ...
2
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0answers
128 views

Arbitrary Choosing of the Solution Domain - Navier Stokes and Manufactured Solutions

I want to verify a finite-volume solver (SIMPLE-Algorithm) for the incompressible Navier-Stokes equations by using a manufactured solution. I use Dirichlet boundary conditions for the velocity at all ...
2
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0answers
55 views

When a flow changes its character from time-periodic to chaotic?

In this simple benchmark describing the flow around a disc in the plane with stationary bc, for low Reynolds numbers the solution is stationary and for higher RN it is periodic in time. Is there a ...
2
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0answers
52 views

Solving nonlinear wave equation in a dispersive infinite waveguide

I would like to solve a three-dimensional nonlinear wave equation in an infinite cylindrical waveguide numerically. Since the waveguide is dispersive, shocks are less likely to form. Both the ...
2
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0answers
371 views

Which turbulence model: k-epsilon or k-omega?

I'm modelling a tidal harbour in Ansys Fluent and want to include a turbulence model in my simulation. I want to predict the water movements around a pontoon which is situated in the harbour. Which ...
2
votes
0answers
75 views

Can similarity criterion help reducing calculations in Finite Element Analysis (FEA) problems?

Can similarity criterion help reducing calculations in Finite Element Analysis (FEA) problems? I'm using NX (a thermal and CFD simulation software) to simulate the temperature and fluid field of a ...
2
votes
0answers
133 views

Would anyone give some review on adjoint methods in shape optimization method <in fluid dynamics>?

Modification Is a continuous adjoint approach a reliable/promising method for optimizing the shape of an airfoil under conditions of unsteady turbulence flow? Original Question I saw lots of people ...
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0answers
13 views

Instability in Lattice Boltzmann Solver

I wrote a Lattice Boltzmann Solver in Rust a little while back using both the BGK approximation and the TRT (two relaxation time) method on the D2Q9 lattice. In both cases I run into major stability ...
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0answers
64 views

How to solve potential flow with FEM, stream function, and the Kutta condition?

I'm trying to solve two-dimensional potential flow over airfoils with the finite element method, using the stream function formulation ($\Delta\psi = 0$, $u = -\partial\psi/\partial y$, $v = \partial\...
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0answers
88 views

How to simulate water, falling under gravity, and impinging on a curved surface, which is kept/present in a domain, containing air?

TL;DR: How do I simulate a hole, at the bottom of a (full) water tank? I am attempting to simulate water, flowing out of a hole/slit, at the bottom of a tank (Water Domain) (under the influence of ...
1
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0answers
44 views

Has there been a comparison bewteen SIMPLE/SIMPLER and JFNK for steady CFD?

I'm looking for a comparison between the Jacobian-Free Newton-Krylov (JFNK) method performance compared to the conventional CFD nonlinear solution methodologies like SIMPLE. Does anyone know if such ...
1
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0answers
34 views

How to remove sigularities from 3D Vortex Lattice Method

I'm trying to solve aerodynamics of whole aircraft by vortex lattice method (or deeper here). The problem is that sometimes trailing vortex filaments from Horse Shoe Vortexes of main wing hits panels ...
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0answers
73 views

Comparison between FEM and FDM methods for flow simulations

What are the main differences between finite element and finite difference approach for incompressible flow simulations? I have a vague idea about how FE methods rely on minimizing the residual over ...
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0answers
51 views

fourth order Poisson iterative solver --in Matlab

I want to calculate the stream function $\psi$ starting from a velocity field $(u,v)$ (such that $u=-\frac{\partial\psi}{\partial y}$ and $v=\frac{\partial\psi}{\partial x}$). I thus calculate the ...
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0answers
51 views

Stokes flow around rigid body

I'm trying to simulate Stokes flow in 2D around an arbitrary polygon (representing a rigid body). I'd like to get both the effect of the body on the flow velocity and the forces on the body by the ...
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0answers
79 views

(Approximate) Incremental Projection Method for Navier-Stokes equations

I am trying to implement an incremental projection method for the 2D incompressible Navier-Stokes. The type of projection method I am trying is $$ \frac{u^{*} - u^{n}}{dt} = - \nabla p^{n} - u \cdot ...
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0answers
56 views

Vortex Lattice Method: better basis than horse-shoe vortex?

I read several introductory texts about potential flow and vortex lattice method. Basically, it is fitting of some velocity field described by conditions on velocity at some control points using basis ...
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0answers
79 views

Computational approaches to analyse numerical solutions

I apologise beforehand if the question isn't well defined or is too broad, I'm just having some difficulty finding the information I need. I also apologise if this should have been asked on stack ...
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0answers
51 views

Detecting stability in solutions to coupled nonlinear equations in aerodynamics,

I'm studying a quasi-steady force model (published in a fluid dynamics journal) that consists of coupled, nonlinear ODEs that describe unsteady aerodynamics -- recently, my advisor and I have found ...
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0answers
40 views

CFD Mass exchange across a reactive front

I have a CFD solver at hand which can deal with 2 phases and so far is able to exchange momentum and energy across the interface, where both phases meet. How this is done is well documented in the ...
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0answers
95 views

Definition of CFL number in Arbitrary Lagrangian-Eulerian framework

In an Eulerian frame of reference, the CFL number is defined as $$\sigma=\frac{u \Delta t}{\Delta x}$$ with $u$ the magnitude of the fluid velocity. A restriction such as $\sigma<1$ for time ...