# Questions tagged [fluid-dynamics]

The study of the properties of fluids and gases in motion

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### Good non oscilliatory derivatives for an exsisting grid

I'm calculating the entropy production of a shockwave by utilizing the equations: \begin{equation} \sigma = J'_q\frac{\partial}{\partial x}\left(\frac{1}{T}\right) +\frac{1}{T}\frac{4\eta}{3}\left(\...
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### Jos Stam's stable fluids — why is the timestep multiplied by the number of grid cells?

One more question about Jos Stam's GDC tutorial on stable fluids: in the advection step on page 8, the timestep for each dimension is implemented as dt * N, where <...
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### Jos Stam's stable fluids — why multiply by the grid size when subtracting out the curl-free part?

Considering page 10 of Jos Stam's GDC tutorial on stable fluids, the function project() first obtains the divergence of the velocity field: ¹ ...
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### Simulating the behavior of falling peas

I hope this is the right place for my question. I am a university student who designed a pea-pouring machine.Now I‘m really interested in simulating the behavior of those peas. Basically, they are ...
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### Discretizing the viscous component in 1 - D Navier stokes compressive flow

I've been working on modelling the NS equations in order to simulate shock waves. The equations are set up on the form: \begin{equation} \frac{\partial U}{\partial t} + \frac{\partial F(U)}{\partial x}...
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### Non-reflective boundary condition

I'm currently solving incompressible Navier-Stokes system of equations with periodic flow and high viscosity. Is there any outlet boundary types that avoids the reflection of flow from the outlet back ...
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### Multigrid method: linear solver and modified residual

I am trying to better understand the FAS multigrid algorithm for Euler equation in FV discretization. The usage of the modified residual (the residual with forcing) inside the different cases: ...
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### Filter size of large eddy simulation with Smagorinsky sub-grid stress model

I am trying to implement Large eddy simulation for solving air flow simulation with large Reynolds number using Smagorinsky sub-grid stress model. I read that the filter size should be calculated ...
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### Weird "oscillatory" modes appearing in FEM simulations

I am using COMSOL to solve a mathematical model involving thermoelectric hydrodynamic (TEMHD) flow. I am running a very large parameter sweep and using the solutions obtained to make some plots. ...
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### Is it possible to shift the numerical results in order to compare it with the analytical solution?

I'm using lattice Boltzmann method (LBM) to do simulation of flow in a pipe. The diameter of the pipe is 0.02 m and its height is 0.1 m. I put a parabolic velocity profile at the inlet: \mathbf{u}(\...
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### Finding a CFD paper with extra degree of freedom variable in mass conservation

I am trying to find a paper that I saw about a year ago. I am not sure of the actual date of the paper. I believe it was a finite difference CFD paper. The interesting part of the paper was the ...
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### Imposing pressure variation instead of Dirichlet boundary conditions on Finite Element Method

I always see Finite Element codes solving PDE with Dirichlet or Neumann boundary conditions. But, I have a problem now consisting of a straight cylinder with a circular base (a simple 3D tube), with ...
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### Understading memory sharing in a GPGPU using a lattice example

I am new in the GPUs world, I used them in Matlab ambient so I didn't need to appreciate the subtleties of these devices. I know that a GPU can be divided into multiprocessors (also called Streaming ...
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### How to calculate the average velocity over a surface through time using paraview?

My problem is a little more complex, but here is a simplified similar model. Let us consider a fire source inside a box and the hot gases (burnt or unburnt) from the combustion are going out of the ...
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### computing time scale and steady state concentration in microfluidic channels

I have been performing convection-diffusion transport studies on microfluidic channels like the following The inlet concentration is specific and I obtain the time-dependent concentration profiles of ...
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### Would modeling a fluid flow that decreases in magnitude violate conservation of mass?

If I make a quasi-steady assumption in a model such as keeping the fluid density constant and assuming the flow is incompressible, does modeling a flow with decreasing velocity / magnitude, say, as ...
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### Understanding STRUCTURED_POINTS dataset in VTK

Based on my readings this is what I have gathered: Dimensions: Number of data points in the x, y, z directions Spacing: Space between points in each dimension Origin: Location of origin Cell data: ...
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### Grid Independence Study

Is the change in time step necessary for the grid independent study? As the CFL is based on the relation between dt and dx. In mesh independent study, only change should be mesh i.e, dx isn't it so?