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Questions tagged [fluid-dynamics]

The study of the properties of fluids and gases in motion

4
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1answer
462 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
43 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
250 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 ...
10
votes
1answer
375 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 ...
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0answers
88 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?
6
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1answer
442 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
573 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
45 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
votes
4answers
578 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 ...
3
votes
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 ...
1
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1answer
215 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
44 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 ...
0
votes
1answer
575 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 ...
1
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0answers
118 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
169 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
votes
1answer
223 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 ...
4
votes
2answers
170 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
227 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
1k 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 ...
0
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1answer
253 views

Outlet boundary condisions in lattice Boltzmann Method

Here is the flow past a square cylinder configuration. The problem is a viscous and incompressible with parabolic velocity profile using freestream velocity U across single cylinder. I use the single ...
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0answers
81 views

What is a good algorithm to solve a discrete continuity equation in Cylindrical coordinates?

The equation is: $\partial f/\partial t + \nabla \cdot (v f) = 0$ $, \;\; f \in [0,1] $ and $v$ is a velocity known at every grid cell. A more precise constraint is that $f$ is either 0 or 1 but ...
3
votes
2answers
7k views

The real myth of GPU (specifically CUDA) really speed up FEM/CFD

Now I have been believing that FEM/CFD is supposed to be faster on a GPU unit - here I am using CUDA as solid example. However, I have not been able to find a convincing paper where the benchmark ...
3
votes
2answers
464 views

Discrete conservation and Finite Element methods

What would be the rigorous mathematical expression of the fact that a conservation law discretized with a Finite Element method with Galerkin discretization does not result in a conservative scheme ?
1
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1answer
101 views

How to discretize the surface of a prolate spheroid?

I need to discretize the surface of prolate spheroid given by the equation $$\frac{x^2}{L^2} + \frac{y^2}{D^2} + \frac{z^2}{D^2} = \frac{1}{4}$$ The surface has to be divided to 500 equal panels to ...
3
votes
1answer
257 views

Pressure-Pressure BC

My FDM code simulates Backward Facing Step flow when I use conventional BCs such as defining velocity profile at inlet and fully developed condition at outlet. I have validated the results and it ...
3
votes
0answers
64 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 ...
0
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1answer
269 views

Difficult bug in my 2D Compressible Euler solver

For the past few days I have been writing a numerical solver for the 2D compressible Euler equations for an ideal gas. My numerical method has been the Local Lax Friedrichs or "Rusanov's method." ...
1
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2answers
102 views

Definition of inflow boundary in CFD

If $w$ is the vector of conservative variables, $f=f(w)$ the flux function, I think have read somewhere (I can not find it anymore) that the inflow boundary $\Sigma$_ is characterized by: $\Sigma_{-}...
0
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1answer
64 views

Conservatives in shock tube

We know shock tube problem will give discontinuous solution of primitive variables ($\rho$, $v$, $p$). Will it give discontinuous result in flux terms? $F =[\rho u, \rho u^2 +p, \rho e_v]^T$. I tried ...
1
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0answers
45 views

Square error estimate for adaptive mesh refinement

In a particular implementation(Finite volume advection using upwind) of adaptive mesh refinement the error square estimate for a cell C is given as $$ \sum_{i = x,y,z} vol * \frac{1}{12} * h^{2} * (\...
3
votes
1answer
143 views

Relaxation Parameters for Steady Navier-Stokes

I am working on a project involving steady solutions for the Navier-Stokes Equations. In the past I've only worked with the unsteady Navier-Stokes, so some of this is new to me. In particular, at ...
1
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1answer
244 views

Can I model laminar incompressible fluid flow and heat transfer in MATLAB's PDE toolbox?

I have a system of PDEs in cylindrical coordinates that needs to be solved: 1. Continuity equation 2. Incompressible Navier stokes ( in r & z coordinates) 3. Heat transfer equation with both ...
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0answers
74 views

Oscillations in Chorin's method due to the BC

I am pretty new to the CFD and I wanted to start with Chorin's projection. The starting problem is just a free jet flowing in the investigated area. I got terrible oscillations almost immediately and ...
0
votes
1answer
189 views

Heat Equation in 3D mass Matrix set-up

I am solving a 3D heat transfer equation with variable boundaries (insulated, convective, radiative or free) using a F.D.M. technique. My geometry of choice is a cube. The purpose of my work is to get ...
3
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2answers
152 views

Implicit projection method with inflow boundary conditions

I am trying to use a projection method that deals with the viscous effects implicitly to model flow around a cylinder. I'm having trouble figuring out what the boundary conditions should be, ...
3
votes
2answers
566 views

How should I set the velocity conditions when you have a pressure inlet and pressure outlet?

I know that when modeling incompressible flow in a pipe, it is common practice that when you have a velocity inlet, there should be a zero pressure gradient at the inlet as well. Also, when you have ...
1
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0answers
188 views

Implementing pressure inlet boundary condition

I am interested in implementing pressure inlet boundary conditions for the 2D compressible Euler equations. My equation of state is an ideal gas ($p=\rho R T$) which is thermally prefect but not ...
0
votes
1answer
66 views

Implementing temperature depending viscosity in a finite-difference scheme

I have a little question that might be basic for some experts, but right now, its not clear for me. I want to implement temperature depending viscosity in a finite difference scheme (incompressible ...
1
vote
2answers
681 views

New to CFD, Lattice Boltzmann or Navier-Stokes?

I apologize if some of my questions are naive; I am very new to computer simulations and fluid-dynamics. I am going to start a PhD in early 2017, and I would like to bone-up on some Computational ...
1
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0answers
260 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 ...
5
votes
2answers
1k views

Recovering pressure from velocity or streamfunction fields

I am interested in 2D channel flow of an incompressible Stokes fluid (Re << 1), with periodic boundary conditions in the x-direction and no-slip at the walls in the y-direction. I have existing ...
6
votes
3answers
997 views

Constructing random divergence-free velocity fields

I am trying to simulate decaying homogeneous isotropic turbulence. As initial condition I want a divergence-free vector-field, i.e, $\mathrm{div} U = 0$. How do I initialize random velocity field in ...
3
votes
1answer
174 views

Generalized Eigenvalue Problem from linear stability analysis

I also posted this in the physics forum, but maybe here it fits better. I am trying to solve a generalized eigenvalue problem raised by linear stability analysis $$AV=\lambda BV.$$ $A$ and $B$ are ...
1
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1answer
77 views

Convergence Criteria for Two Fluid Flow Solver

Which one of the following is suitable for judging convergence in Two-Fluid Flow Solver? 1) Absolute Residual (L^2-Norm). 2) Relative Residual. 3) Fraction Change in Velocity, Pressure and Volume ...
2
votes
1answer
363 views

How to define residual in multigrid approach?

I wish to solve the two-dimensional Navier Stokes equations using multigrid method on a collocated grid using the Predictor-Corrector method mentioned below. But first, let me elaborate on what I had ...
4
votes
1answer
129 views

Decaying turbulence and simulation

I am a beginner in CFD having written few codes for laminar flow cases using SIMPLE and some other explicit solvers. Now, I want to use my solvers and some other models to solve for the turbulent flow ...
3
votes
1answer
191 views

Stability Criterion for this Explicit Scheme

I am solving an unsteady flow using the dual-time Navier-Stokes equation in which I write my momentum equation as: $$\frac{\partial u}{\partial \tau} + \frac{\partial u}{\partial t} + \frac{\partial u^...
1
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1answer
268 views

Outflow boundary condition

I know that in outflow boundary we assume a zero normal gradient condition and use upwind scheme for approximation. However, I saw this sentence in a book which I do not understand; "Convective fluxes ...
1
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0answers
106 views

CFD implementation in software [closed]

I've been learning CFD theory for 4 months (which includes FEA, FDM AND FVM) and now I want to start running simulations. As a novice to CFD software, I would appreciate some advice on where to start, ...
2
votes
3answers
134 views

combination of field and particle methods for fluid dynamics

In numerical fluid dynamics there are field methods like finite-volume, finite-element, etc. and particle methods like Smoothed-Particle-Hydrodynamics – SPH and others. Both approaches have advantages ...