# Tagged Questions

The study of the properties of fluids and gases in motion

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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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 ...
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### 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 ...
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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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 ...
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### 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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### 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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### 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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### 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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### 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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### 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 ...