The study of the properties of fluids and gases in motion

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14 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, ...
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14 views

Are Tecplot's streamtraces different from streamlines? [on hold]

In Tecplot, there is option to plot streamtraces. Are these same as streamlines. If yes, why is it names streamtraces and not streamlines. Is there any difference between the two.
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2answers
77 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 ...
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0answers
40 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 ...
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1answer
52 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 ...
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0answers
23 views

Rogallo Procedure

can anybody please give an explanation on how Rogallo's procedure is carried out exactly to build up initial conditions for DNS simulations for Homogeneous Isotropic Turbulence ?
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11 views

Predict liquid film thickness outside a cylinder, under the influence of a) external gas flow and b) heating of the cylinder

I'm very perplexed with respect to which would be the correct Stack Exchange site for this question. In the end I decided to post here. Hopefully I took the right decision. Consider a semicylinder ...
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1answer
71 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 ...
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48 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 ...
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1answer
48 views

Recovering pressure from velocity or streamfunction fields

I am interested in 2D channel flow of an incompressible Stokes fluid (Re = 0), with periodic boundary conditions in the x-direction and no-slip at the walls in the y-direction. I have existing code ...
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3answers
160 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 ...
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0answers
37 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 ...
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1answer
39 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 ...
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1answer
93 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 ...
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0answers
23 views

what's the optimal parameters to reach the maximum speed of GAMG algorithm

everyone! As the GAMG algorithm has many parameters to set, how can I reach the maximum speed? Is there any optimal parameters range for any CFD models? or I have to try every parameters to reach the ...
4
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1answer
83 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
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1answer
99 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^...
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1answer
97 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 ...
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0answers
71 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, ...
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3answers
96 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 ...
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1answer
40 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
94 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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0answers
70 views

Solving Lid-driven Cavity on a Collocated grid

I want to solve the two dimensional lid driven cavity flow on a collocated grid. I already have used a staggered grid and validated my results with Ghia (1982). Recently, I came across this paper (...
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3answers
161 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
42 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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41 views

Using Periodic BC for Taylor Green Vortex Flow Simulation

I want to solve the very simple case of two dimensional Taylor Green Vortex Flow. I am using incompressible Navier Stokes equations and Artificial Compressibility Method as my solver where I introduce ...
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49 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 ...
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1answer
104 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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261 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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1answer
130 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 ...
3
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1answer
80 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
51 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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54 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 ...
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1answer
147 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
135 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
109 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
154 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
76 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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81 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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46 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
207 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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33 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
120 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
52 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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54 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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28 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 ...
3
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1answer
180 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
54 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
108 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
117 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 ...