Questions tagged [fluid-dynamics]

The study of the properties of fluids and gases in motion

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3
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1answer
158 views

Reasons to choose LES in stead of RANS models? (turbulence)

In oceanography, is there any particular reason why choosing large eddy simulations in stead of RANS (regardless of the type of flow)? In both cases, 2d simulations would be used (shallow water model)....
2
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1answer
375 views

1-D turbulent energy spectra in homogeneous direction (non-isotropic)

I am trying to compute the one-dimensional energy spectra for my channel-flow simulation. I have already written a post-processing script to achieve this; however, I need to validate my code before ...
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0answers
49 views

Perfect filtering of high frequencies in 2D FFT (Multidimensional 2/3 Rule)

Let $u_n$ be an array containing discrete values of the function $u(x,y)$. Performing a 2D FFT to this array we obtain $\hat{u_n}$ representing the values of $\hat{u}(k_x,k_y)$. I would like to ...
3
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1answer
185 views

Resources for solving fluid-structure interaction problems

I would like to get started solving Fluid-Structure interaction problems. I already have some experience with Finite Elements, including my own MATLAB and Julia software packages for developing ...
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2answers
126 views

If a numerical solution remains constant for different grid sizes, what does it mean?

I'm testing a finite volume scheme, Godunov type solver, using a problem with analytical solution. I'm not able to reproduce the solution, which includes source terms. I tried with different mesh ...
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0answers
229 views

Physics of explosions: just vorticity?

eg 1 2. Is it just vorticity? What's actually happening? (Similar: steam engines, volcanoes, clouds). examples are grid-based, using "vorticity confinement" in Phoenix FD. EDIT Some techniques: "...
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0answers
48 views

Simulation of 2D impulse response using finite volume

Finite volume methods can be used to simulate the acustic wave equation (linearized Euler equations) in complex domains. I have developed a FV and a Discontinuous Galerkin code for 2D acoustic ...
2
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2answers
349 views

In practice, what are the most useful ways to visualize 2d fluid flow, to tell what is happening in the simulation? Esp for verification and debugging

My simulation creates a 2d grid of vectors and scalars (EDIT of velocity, depth etc), at 60 frames per second. Is it correct? It looks sort of right... but who knows? How can I tell what's happening - ...
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0answers
48 views

How is the Gastner-Newman equation implemented to create value-by-area cartograms?

There is a paper called "Density-equalizing map projections: Diffusion-based algorithm and applications" by Michael T. Gastner and M. E. J. Newman, which explains their algorithm (which is based in ...
2
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2answers
303 views

Can we simulate compressible flows by simple direct explicit calculation, without solving systems of linear equations (such as Poisson eq)?

Is this is plausible at all? It seems the most obvious/naive approach, so there's probably good reasons why it's not used - what are they? Viscosity is not important. Starting with inviscid Navier ...
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0answers
46 views

How do we implement Parameter free generalised Moment limiter in 1D Case in Discontinuous Galerkin methods?

I am referring to this paper:- "A Parameter-Free Generalized Moment Limiter for High- Order Methods on Unstructured Grids " by Michael Yang and Z.J. Wang. http://dept.ku.edu/~cfdku/papers/AIAA-2009-...
3
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1answer
322 views

Can we simulate incompressible flows using the (slight) density changes to give pressure?

A common approach says an incompressible flow has velocity divergence of 0; use this to solve for pressure in the Navier Stokes momentum equation. Or, using the Helmholtz Decomposition "project" the ...
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2answers
226 views

Preconditioner for the GMRES method in the Uzawa algorithm

I'm trying to solve \begin{equation}\left\{ \begin{split} \frac{\partial u}{\partial t}+(u\cdot\nabla)u-\nu\Delta u+\frac1\rho\nabla p&=f\;\;\;\text{in }\Lambda\\ u&=0\;\;\;\text{on }\partial\...
2
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1answer
89 views

Deposition model in laminar flow

I have a chamber full with a fluid flowing horizontally in laminar regime from one side to the other. It carries a suspension with concentration $c$. This suspension also falls to the bottom of the ...
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0answers
198 views

Outflow boundary condition - second derivative of velocity

Consider a fluid flow simulation in a pipe. At the outflow, instead of explicitly imposing a boundary condition, I linearly extrapolate information from the interior (for velocity components). This ...
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0answers
276 views

How to perform Taylor series expansion consisting of cell averaged derivatives in a computational element?

I have encountered the term cell "Cell averaged derivatives" and "Taylor series expansion using cell averaged derivatives about centroid" in the context of polynomial representation in any cell (...
4
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5answers
3k views

What is the difference between MATLAB and FORTRAN?

In our university some Ph.D students for computational methods prefer FORTRAN over MATLAB. I can't understand why? What is the difference between them when are used in computational methods like ...
3
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0answers
189 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] --...
5
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2answers
508 views

Reference request for computational fluid dynamics

I have good background of finite element methods and continuum mechanics and I am familiar with fluid mechanics. My aim is to understand the required theory and to write my own simple codes using ...
1
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4answers
289 views

Mass transport in porous media

My goal is to numerically solve the convection-diffusion equation of the form: $$\frac{\partial C}{\partial t} = \nabla (D \nabla C) - \nabla (v C)$$ $C$ is concentration and $D$ is the diffusivity ...
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0answers
116 views

How do we derive the elemental equation for Discontinuous Galerkin method using Centered Numerical Flux?

If we take a 1st order polynomial approximation in each cell, we can find the (2x2) -mass matrix, differentiation matrix, and flux matrix through the integration of Lagrange polynomials. However, I ...
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0answers
80 views

Modelling fracture flow in stress field in COMSOL [closed]

I am new to COMSOL and I want to model fluid flow in stress field. As starting point I want a simple 2D box having a fracture from right to left while pressure gradient vertically. I want to know the ...
3
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1answer
199 views

Is it possible to solve Euler equation numerically without using any flux limiter (in DG scheme)?

I have recently learned about Discontinuous Galerkin method to solve differential equations and I was trying to implement it to solve Euler equation. For now, consider the standard Sod Shock Tube Case....
2
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1answer
54 views

Can 3rd order TVD admit perfect shift for Upwind 1D Advection equation?

I recently coded a 1 stage and 3 stage optimal TVD-RK explicit scheme using eqn 3.3 here http://www.ams.org/journals/mcom/1998-67-221/S0025-5718-98-00913-2/ on the equation Ux+Uy=0, where x and y ...
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4answers
2k views

Practical coding resources for new CFD practicioners

There seem to be many books and papers that explain various CFD methods in great detail, but unfortunately I have not been able to find many good resources of such methods implemented in codes such as ...
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2answers
76 views

Avoid component mixing in eulerian simulation of plastic deformation of solid

Just for my interest I'm thinking how to make some cheap-and-dirty simulation of processes such as: penetration of metal plate by projectile explosion of shaped charge (for example https://www....
3
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1answer
160 views

Numerical computation of the velocity in the steady Navier-Stokes equation

I've asked this question on Math.SE too. Let $d\in\left\{1,\ldots,4\right\}$ $\Lambda\subseteq\mathbb R^d$ be bounded, nonempty and open and $\partial\Lambda$ be Lipschitz $V:=\left\{u\in H_0^1(\...
9
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2answers
599 views

Time discretization of the variational formulation of the Navier-Stokes equation

I've asked this question on mathoverflow too. Let $T>0$ $I:=(0,T]$ $d\in\mathbb N$ $\Lambda\subseteq\mathbb R^d$ be nonempty and open, $$\mathcal V:=\left\{\phi\in C_c^\infty(\Lambda,\mathbb R^d):...
3
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1answer
225 views

Software/code to extract a solenoidal (a.k.a. divergence-free) field from a 2D vector field numerically

Can somebody point me to software/code to extract a solenoidal (a.k.a. divergence-free) field from a 2D vector field numerically? There are a plethora of papers and documents describing how to do ...
0
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1answer
139 views

Initial Condition in a Numerical Problem

In a initial value problem does the initial condition has to satisfy the boundary condition and the governing equation? For example: If a non-homogeneous Neumann boundary condition for the pressure ...
4
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2answers
541 views

Time discretization: Runge-Kutta methods vs. standard backward difference

I've recently written a code that solves the incompressible/low-Mach number formulation of the Navier-Stokes equation with high-order methods for both time and space. My advisor insisted that I use ...
3
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1answer
816 views

1-D incompressible unsteady Couette Flow Explicit finite differece CFD

I am currently following J.Anderson Jr.'s CFD with basic application and I came into some troubles while coding for my very first CFD problem. As the title suggests I am solving an incompressible ...
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0answers
46 views

Shallow water equations with moving body

I was wondering if there are any shallow water equation solvers out there that can include rigid body motion for the surface the water flows on?
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0answers
388 views

Rhie and Chow Pressure Velocity Coupling

In a collocated grid, which velocity is used in the convective term in the momentum equation? Is the Rhie and Chow constructed face velocity or an average of the adjacent cell center values(in a ...
9
votes
1answer
560 views

CFL condition in Discontinuous Galerkin schemes

I have implemented an ADER-Discontinuous Galerkin scheme for the resolution of linear systems of conservation laws of the type of $\partial_t U + A \partial_x U + B \partial_y U=0 $ and observed that ...
2
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0answers
102 views

Order of local and global truncation error in a finite volume scheme

Can the order of the local truncation error be higher than the order of global truncation error in a finite volume method?
5
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1answer
510 views

Finite volume a posteriori error estimation

I'm wondering what alternatives there are to a grid convergence study to judge solution accuracy for a given grid resolution when doing steady-state RANS simulations on an automatically generated ...
4
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0answers
818 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 ...
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0answers
49 views

A stable method for solving monontoe HJB equation

I am considering solving HJB equation of the form $$ v_t=g(a(x)v_x),\quad x\in \mathbb{R}, t>0, $$ with initial condition $v(0)=v_0$. Here $g:\mathbb{R}\to \mathbb{R}$ is Lipschitz and monotone ...
2
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4answers
844 views

Simple methods for solving 2D steady incompressible flow?

I'm trying to make a CFD model where I can place a source and a sink anywhere in a grid and get the fluid flow rate across each cell boundary between those locations. I'm starting simple with a 3x3 ...
2
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0answers
124 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 ...
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1answer
221 views

Implicit integration for FLIP?

I have problem with volume loss in FLIP simulation. Unfortunately it's necessary to obey the CFL condition when using explicit integration methods (RK2 in my case) to advance particle positions using ...
1
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0answers
45 views

Number of particles that could be used in a simulation

For a computer with 8 GB of memory, which is the order of magnitude for the number of particles that could be used in a simulation. Is the answer $N=8/6\times 10^9$? or do the particles take up more ...
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1answer
1k views

How to choose the relaxation time in the Lattice Boltzmann Method?

We know that the relaxation time is very important in LBM. I have searched lost of papers, but can't find some systematic introductions about the choice of relaxation time in SRT LBM. Could you give ...
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0answers
150 views

Stability of the explicit MacCormack Scheme to solve the Navier Stokes equations with Wilcox's K-Omega Turbulence Model

I am solving turbulent pipe flow with an explicit MacCormack scheme and Wilcox k-omega model. The laminar version of the code had three distinct stability criteria which worked fine after ...
1
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2answers
213 views

Flow past square cylinder benchmark in 2D. Famous papers to compare

I'm looking for a benchmark for the flow past square cylinder problem in 2D to compare my results. I have found some papers, but it seems that there are different results in different papers. I want ...
0
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1answer
241 views

How can an engineering student become a computational scinece expert in a short time [closed]

How can a student with zero computing or programming language knowledge, few engineering mathematics knowledge, understand computational science especially Finite Element Modelling (FEM) from ...
3
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2answers
210 views

Benchmark setup for incompressible Rayleigh-Taylor flow

I'm trying to benchmark a new numerical method for the incompressible Navier-Stokes equations. I'd like to use the most widely-accepted test cases possible. In particular, I'm looking for a ...
2
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0answers
293 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 ...
1
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1answer
2k views

Is there an advantage of using a staggered grid over a regular one when combined with high order methods?

The title says is all. This question is in the contest of an incompressible Navier-Stokes solver. Specifically, I am currently working on a new solver while referring myself to an older code for ...

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