Questions tagged [fluid-dynamics]

The study of the properties of fluids and gases in motion

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0answers
144 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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2answers
170 views

Why have specialised upwind schemes been developed to solve hyperbolic equations?

Are upwind schemes such as Godunov type methods superior to central differencing schemes? Do the reasons include superiority in modelling hyperbolic problems with Dirichlet BC's?
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2answers
326 views

upwind schemes for solving inviscid euler equations

I'm new to the modelling of inviscid euler equations. I have come across few different upwind schemes that are used instead of central differencing schemes to model such flows, such as flux vector ...
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0answers
522 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 ...
9
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2answers
7k views

Use of machine learning in computational fluid dynamics

Background: I have only built one working numeric solution to 2d Navier-Stokes, for a course. It was a solution for lid-driven cavity flow. The course, however, discussed a number of schemas for ...
4
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1answer
302 views

OpenFOAM precipitation/crystallisation reaction solver

This question is probably related to chemical engineers that are around this forum. I am looking into writing a solver for a precipitation reaction (struvite to be precise): A+B+C+D <=> E+F A, B, ...
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2answers
482 views

Estimation of time taken to reach steady state in an MD simulation of Poiseuille flow

I am trying to do a Molecular Dynamics Simulation of a complex fluid, confined between solid surfaces. I would like to find the flow rate as a function of fluid film thickness, $h$, for a plane ...
2
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0answers
270 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 ...
3
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2answers
61 views

Adding artificial fluctuations to trigger hydrodynamic instabilities.

I'm doing a 2D combustion hydrodynamic simulation and there's a hydrodynamic instability that should be triggered because of the particular physical properties of my system. The key to the instability ...
4
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2answers
956 views

How to discretize Burger's equation?

I am trying to solve the very simple one dimensional burgers equation which is: $$\frac{\delta U}{\delta t} + \frac{\delta F}{\delta x} = 0$$ where the flux F of some variable U is defined as$$ F= \...
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2answers
248 views

3D Divergence-free Stokes equations

I would like to have a divergence-free formulation of the Navier-Stokes equations for creeping flow (a.k.a. Stokes equation, N.-S. without the inertial terms) in 3D, for purposes of tracking particle ...
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157 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 ...
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2answers
2k views

9-point stencil finite difference Laplacian with variable diffusion coefficients

So I'm trying to implement a 9-point stencil discretization to the 2D difussion equation. The stencil is here. However, most of the literature deals with a Laplacian that has a constant diffusion ...
4
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1answer
130 views

transverse component for multidimensional advection in method of lines

So I inherited from some people a code that solves the advection-diffusion-reaction equation for a particular system. The original code was first implemented in 1D which worked fine in cartesian ...
3
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1answer
413 views

Darcy flow finite elements

The Darcy equations for porous media flow are given by: $\frac{\mu}{\kappa}\mathbf{u} - \nabla p = \mathbf{0}$ $\nabla\cdot\mathbf{u} = 0$ where $\kappa$ is the permeability and can in general be ...
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384 views

ANSYS Fluent: Defining External Force on a Cell Zone [closed]

I am using ANSYS Fluent 15 to simulate a case of fluid flow. In my case, I have three cell zones in my simulation, let's call them top, middle and bottom. My requirement is to put a vertical constant ...
2
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1answer
112 views

CFD turbulence modelling mean pressures vs peak pressures

I have been experimenting with using Autodesk CFD to investigate facade/ cladding pressures on a (rectangular) building, comparing results with cladding/ facades pressures pressures from design codes ...
2
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1answer
487 views

What are acceptable boundary conditions for porous media flow?

I am attempting to simulate fluid flow through a porous foam. I would like to have no-slip boundary conditions on part of the boundary and free flow conditions on the inlet and outlet. Right now I am ...
6
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3answers
607 views

Fluid-structure interaction solver for cardiovascular applications

I would like to start running FSI simulations for cardiovascular applications. More precisely, I'm interested in the behaviour of aortic valve under physiological flow conditions in which the ...
3
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3answers
731 views

Where do I begin learning CFD?

I am working on some CFD codes - generating adjoint of a CFD model, for example. My background however is in computer science. I have absolutely no clue what the model represents or what it is doing. ...
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1answer
85 views

Visualise data under Tecplot

I have a set of data that I need to visualise under Tecplot, the file format is for example: ...
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0answers
104 views

Conservation at grid interface in adaptive mesh refinement

I am using adaptive mesh refinement to solve one dimensional inviscid Burgers equation. However I am facing some difficulty to handle grid interfaces which are not uniform (coarse-fine grid interface)....
2
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1answer
557 views

openfoam - Programming customized PDEs

I am looking for a method to automatically solve custom PDEs on a custom control volume. Specifically I would like to solve equations similar (but not exactly alike) to: $$\frac{\partial y}{\partial ...
3
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2answers
1k views

GPU-enabled Lattice Boltzmann solvers?

Is anybody aware of any GPU-enabled Lattice Boltzmann solvers (preferably on C++/OpenCL and open-source) that would be recommended? I have found Advanced Simulation Library, but it seems to be very ...
4
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3answers
2k views

How to deal with nonlinear term in Navier Stokes equations (finite element code)

I am trying to solve the Navier Stokes equations using the finite element method. I plan on using the pressure correction method to deal with the pressure and an implicit time stepping scheme for ...
0
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1answer
250 views

Adaptive mesh refinement basic conceptual problem

I am a beginner in adaptive mesh refinement (AMR). After I am done with the first two papers by Dr. Marsha Berger, I was trying to write my own code for a problem which has a parabolic partial ...
0
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1answer
86 views

Representation of polynomial order in CFD codes

I am currently working on a CFD code over a cubic grid. Now, the number of elements used in the simulation is decomposed among the number of processors. Each of those processors (a section of the cube)...
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4answers
2k views

Why are upwind schemes stable in convection flow calculation?

It is well known that upwind schemes are stable when calculating convection flows with $|\text{Pe}|>2$, $\text{Pe}$ is the Peclet number. Why is that, and why is central difference unstable? Is ...
5
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2answers
748 views

A Question About the Rhie-Chow Interpolation Used for Solving the Incompressible Navier-Stokes Equations on Unstructured Grids

When using the SIMPLE method on a mesh with a collocated variable arrangement, the following interpolation is used for the advecting velocities: \begin{equation} u_f = \overline{u}_f - \overline{D}_f\...
3
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2answers
293 views

Direct Numerical Simulation of reacting flows

I need to write a DNS code for simulating reacting flows in turbulent conditions. The code has to be highly scalable, because the computational cost of simulations is expected very large. My idea is ...
3
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1answer
642 views

2D Poisson Solver for Taylor Green Vortex Problem

I am trying to write a 2D Navier Stokes solver using an RK3 for time advancement in python. For debugging, I have converted the RK3 to an Euler step for simplicity. Checking my divergence for my ...
7
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2answers
437 views

applications of computational geometry in fields such as CFD?

Out of curiosity, I was recently trying to search what skills are required to be successful as developer in scientific computing field (e.g. CFD or similar). And to do so, I was going to through ...
1
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1answer
101 views

alternatives to moving mesh technique

If one has to simulate oscillating plate/solid wall ( sinusoidal function of time) in a domain (a simple piston movement in 'y' direction), the obvious way would be scenario 1. For brevity, assume ...
2
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3answers
1k views

2D Stokes equation Code

Does anyone know where could I find a code (in Matlab or Mathematica, for example) for he Stokes equation in 2D? It has been solved numerically by so many people and referenced in so many paper that I ...
3
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1answer
688 views

Add User-defined/custom differential equations in OpenFoam (CFD)

I am new to OpenFoam. And I am trying to add a set (user defined) of differential equations to OpenFoam. I want to solve this user defined set of equations at each time point in addition to standard ...
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0answers
62 views

Help about Fluid-Fluid coupling techniques

I need a little help and advice with a project I want to do: the idea is to "couple" (I don't know whether I can call it like this) a conservative Navier-Stokes Solver (Fractional-step, 2nd order FDM) ...
0
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2answers
172 views

The “standard map” and Jupiter's red spot [closed]

Has there been an attempt to "explain" Jupiter's Red Spot via what is known as the standard map in chaos theory? I cannot be the first to notice the visual similarities...       &...
2
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2answers
568 views

How to interpret/convert density in 2D simulations?

Density has units of $kg/m^3$. In simulations often scaling is done to deal with non-dimensional values, so the physical density is converted to the non-dimensional density so that it can be used in ...
2
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2answers
164 views

Value of density when there are no or very few neighbours in SPH simulation

Sorry for the noob question. I am trying to implement SPH using the directions shown in this paper. The density needs to be updated using the formula The smoothing kernel is If there are no ...
4
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2answers
544 views

Manufactured solution for pressure based 3d incompressible Navier-Stokes solver with wall boundaries

I already successfully verified my solver (SIMPLE-type FVM-method) with the following manufactured solution (3d Taylor-Green vortex) on the solution domain $[-1,1]^3$ with Dirichlet boundary ...
0
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1answer
668 views

How to solve Energy Balance equation by numerical method

Good Day I am new to heat transfer technique please give me some suggestion on solving energy balance equation $$a \frac{\partial T_p}{\partial t}=\frac{\partial}{\partial x}\left(b\frac{\partial ...
2
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2answers
397 views

How to prove the strong formulation for Discontinuous Galerkin is conservative?

I've been trying to figure out how to prove that the following equation is conservative $$\int_{D^k} \partial_t(u^k) v_j^k + \partial_x(f) v_j^k dx = [(f -f^*) v^k_j]_{x^k}^{x^{k+1}}$$ where $v_j^k$ ...
2
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0answers
129 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 ...
5
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3answers
421 views

Variable viscosity Stokes equation

One very efficient way to solve Stokes equation with periodic boundary conditions \begin{equation} -\eta \nabla^{2} \bf{v} + \nabla p = f \\ \nabla \cdot \bf{v} = 0 \end{equation} is using the ...
6
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2answers
1k views

Solution blows up when using Runge-Kutta to solve simultaneous ODEs for liquid film equations

This is a continuation of a problem I asked over at physics exchange and math exchange. Basically I have two ODEs that I am solving in order to calculate the radial and tangential velocity of liquid ...
2
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1answer
4k views

What's the difference between grid-based and mesh-based methods for PDEs?

I am into computational fluid dynamics and so far I've found that the most common approaches to solve for the governing equations are Eulerian and Lagrangian. The former samples the domain at fixed ...
4
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1answer
98 views

Zero-k mode in Pseudo-spectral solution of Stokes Flow

I'm trying to solve a Stokes flow problem with a pseudo-spectral method in periodic boundary conditions. The equations of interest are $-\nabla^2 \bf{v} + \nabla p = \bf{f} \\ \nabla \cdot \bf{v} = ...
6
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1answer
688 views

ENO/WENO component-wise vs characteristic-wise

Can someone give some references to understand what's the differences between a component-wise and a characteristic-wise ENO scheme? If I'm right, the characteristic variables come from the ...
2
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2answers
123 views

Expected computational time for DNS computation of fluid flow

Using an established criterion involving capturing eddies down to the Kolmogorov length scale it can be reasoned that the order of grid points in the computational mesh needs to be $N^3 \ge Re^{9/4}$ ...
3
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1answer
360 views

Finite Element integration with tensor notation

While I was studying discontinuous finite element methods I found an integration of a Navier Stokes equation using tensorial notation. The equation is the following: $\mathbf{\bar {u}}_{t} + (\...

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