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Questions tagged [fluid-dynamics]

The study of the properties of fluids and gases in motion

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47 views

Different Meshes Different Maximum velocities

I am working on a model in COMSOL and I am usin different meshes from coarse to fine keeping the other parameters constant. And, I got different maximum velocities for all the meshes. What can I do ...
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1answer
107 views

In which cases an interface tracking/capturing method needed along with Navier-Stokes solver for flow?

In my view, it is needed, To save computational time. To define accurate boundary conditions at interface where properties changes drastically. To solver 2 phase problems as single phase only. To ...
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3answers
783 views

Simple Simulation Examples in Computational Fluid Dynamics

I would like to incorporate a CFD topic in a project I currently have. The deadline is a little less than a month from now. Basically, what I would like to do is solve some equations and simulate ...
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1answer
45 views

How to introduce a distance vector when decompose a force?

I read reference (1),but I am confused about how to introduce a distance vector in Lorentz force like the author does it in equation (11): $$\rm J\times B = -J\cdot \nabla \left( B\times r\right)+\...
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301 views

Periodic boundary conditions for solving Navier Stokes Equations on a Staggered Grid

I want to solve two dimensional Navier Stokes equations on a staggered grid for the case of Taylor-Green Vortex. My initial conditions are standard sine and cosine functions. As I am aware, I should ...
3
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1answer
328 views

Is the Finite Volume Method conservative when the source term depends on the variable?

I trying to do a simulation where there are two quantities, $\Delta\theta(x,t) = \theta(x,t) - \theta_{o}$ and $\Delta\nu(x,t) = \nu(x,t) - \nu_{o}$. These quantities are chemical concentrations ...
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3answers
899 views

Can compressible flow solvers be used to solve incompressible flow?

I know that incompressible and compressible flow solvers are specifically designed to solve different types of problems with different fluid properties/flow conditions. Clearly, among the advantages ...
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3answers
859 views

Time step size for transient simulations of vortex shedding

I am simulating unsteady flow around a circular cylinder (using FLUENT). I am facing the following problem. Kindly please help me. OBJECTIVE: To find out the Reynolds number at which vortex shedding ...
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1answer
432 views

Continuous vs discontinuous pressure elements in fluid flow problems

When solving fluid flow problems using finite elements you typically end up requiring that $p\in L^2$. For Darcy flow problems, a popular choice of elements is the Raviart-Thomas element and ...
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0answers
73 views

PDE discretization (via finite difference sheme) question

So after posting this question and reading all your comments I would like to make this new question (update). If you consider the three equations presented here: $$\frac{\partial \rho}{\partial t} +\...
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0answers
57 views

Calculate fluid speed in a conduit with obstacles

I need some advices to start to solve some problems about fluid motion in a conduit. The problem domain is shown below: a conduit with some obstacle of different geometric properties. The fluid is ...
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1answer
169 views

A simple PDE solution question

I need to ask a question about partial derivatives. I want to solve this equation (steady state, one dimensional continuity equation): $$\frac{\partial (\rho u)}{\partial z}=0$$ which is equivalent to:...
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1answer
225 views

1D uniform flow test case for compressible flow

Are there any one dimensional hyperbolic test cases for a 1D uniform flow? (I need the test case for the purpose of showing the satisfaction of geometric conservation law on a moving mesh).
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1answer
280 views

a few questions on understanding geometric conservation law

I was wondering if anyone could help with understanding the geometric conservation law for moving domains. I came across Link1, and have tried to understood the paper by Farhat et al Link2. So far ...
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1answer
416 views

Shooting method - Matlab ODE

I'm trying to solve these equations of hypersonic adiabatic flow over a flat plate. I did all the simplifications and got these equations for the stagnation point flow. $$\left(Cf''\right)' + f f'' = \...
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1answer
227 views

boundary conditions of linear advection problem

I am solving the 1D advection problem given by: $$\frac{\partial u}{\partial t}=-c\frac{\partial u}{\partial x}$$ where c is the wave speed, and u is the unknown field variable, and x and t are time ...
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1answer
3k views

how can i show flow is incompressible?

How can I understand the flow is incompressible or not with this information at 4 edges?
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0answers
60 views

Solving a nonlinear problem with CDF

I'm trying to solve this problem: $\begin{cases} \partial_t E=-k\left([f(\rho)-i.\left[\delta+\frac{1}{2}a\left[\dfrac{\nabla^2_{\bot}}{4}+1-\rho^2\right]\right]]E - 2CP\right)\\ \partial_t P=-\...
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4answers
387 views

Are there any general fluid dynamics frameworks?

Are there any frameworks that could be classified as "general computational fluid dynamics framework"? What I'm thinking of is a framework that's modular and extensible in order to allow the ...
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1answer
121 views

maltab ode solver- user defined criteria to stop calculations

is there a way to add a user defined convergence criteria to an ode solver so that the solution is stopped? I know that Matlab uses absolute and relative tolerances but would that suffice in solving ...
4
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1answer
260 views

Fast Multipole Method in 3D

I am writing a FMM (Fast Multipole Method) algorithm in 3D. I generated the mesh and, currently, I am developing the expansion and the three (M2M, M2L, L2L) translation operators using spherical ...
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0answers
119 views

Do collocated grid arrangements definitely result in the checkerboard effect?

I understand the checkerboard effect due to the use of collocated grid arrangements in FVM. However, I wanted to know whether this problem is definitely bound to effect the results? For instance, I ...
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0answers
81 views

problem with understanding the fluid boundary conditions of a 1D probelm

I am having problems understanding the boundary conditions of the problem described in this paper on researchgate Essentially the problem consists of a one dimensional fluid chamber in contact with a ...
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0answers
39 views

Coriolis test problem

I have a eulerian hydrodynamic code, which I have recently implemented the Coriolis force in the integrator. Is there a standard test problem for the Coriolis force? Since this isn't a Lagrangian ...
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1answer
2k views

computing turbulent energy spectrum from isotropic turbulence flow field in a box

I have my 3 dimensional velocity flow-field u, v and w at a given instant of time from DNS using pseudo-spectral method. I need to calculate the energy spectrum ( in Fourier space ) as a function of ...
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0answers
101 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 ...
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2answers
301 views

significance of energy equation and its conservation

I am interested to know the significance of the energy conservation laws when modelling fluids (or other materials). Am I correct in saying that if energy is conserved then stability is achieved. In ...
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2answers
283 views

Stagnation or Total conditions in a pipe with moving fluid?

In Flow Science, they provide an example of boundary conditions and how to specify them for CFD simulations. The following is stated: Pressure Boundary Example For example, consider the ...
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0answers
111 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 ...
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2answers
301 views

2d Euler manufactured solutions

Where can I find manufactured solutions for the 2d Euler equations, with the complete analytical terms, including the Jacobian of the source term ?
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1answer
107 views

A tweakable software for simulating VOF problem

I have to solve a simulation of fluid flow on Ansys, but my prof wants me to run a parallel simulation using the Volume of Fluid method in something with more visible guts than Ansys? Any ...
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0answers
78 views

Application of vector extrapolation methods to convergence to a steady state solution

I'm working on a fluid solver using dual-time stepping and everything works really well, except the convergence in pseudo-time is slow. I'd like to accelerate the convergence. I know multigrid methods ...
3
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1answer
151 views

LU-SGS and boundary conditions

I am trying to understand how boundary conditions are implemented when one uses the nonlinear LU-SGS algorithm for Euler equations. Most papers describe the Gauss-Seidel sweep over mesh cells, but do ...
3
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1answer
312 views

How to model the mixing of two fluids in a container?

In the context of a research project of mine, I am faced with the difficult task of modeling the mixing of two fluids in a container. I would like to achieve the following: Given a container (...
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0answers
33 views

Transient manufacturated solution

I'm using the method of manufacturated solution (MMS) to verify a cfd code (Transient energy equations). The equations are discretised with an implicit scheme and allow large time step without any ...
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1answer
318 views

Finite difference scheme for 2D sound propagation

I am simulating the sound wave propagation in non-rectangular and asymetric spaces using finite-difference method. I presume linear acoustics equations to be enough (i.e. $\Box p = 0$, $\Box \vec{v} = ...
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2answers
364 views

How are Spectral Methods applied to CFD? In particular, how is the pressure-velocity coupling implemented?

I know that spectral-methods which are weighted-residual methods can be applied to solve for the incompressible N-S equations. In particular, they are applied to Direct Numerical Simulations (DNS) for ...
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1answer
83 views

solving a hyperbolic set of equations - upwind type method

I want to solve a set of hyperbolic equations (not the Euler equations) using an upwind type method. I am interested in using a first order upwind scheme and one that is not based on the method of ...
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2answers
146 views

what do zero real parts of eigenvalues mean? Any good references?

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

MAC Projection in Projection method?

My question concerns the following paper: A Conservative Adaptive Projection Method for the Variable Density Incompressible Navier–Stokes Equations (http://www.sciencedirect.com/science/article/pii/...
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0answers
44 views

comparison of stability of two non-linear methods

I have solved a numerical problem using two different sets of non-linear governing equations. I want to get an understanding of the stability of the methods relative to each other. To do so, I solving ...
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0answers
125 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
163 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
279 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
418 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 ...
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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 ...
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1answer
278 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
400 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 ...
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0answers
240 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 ...
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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 ...