Questions tagged [fluid-dynamics]

The study of the properties of fluids and gases in motion

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Need help with adaptive meshing code

I am trying to understand adaptive meshing and is using this code (https://github.com/esquivas/amr1d) as a reference. However, there is no documentation for it and thus, it is hard for me to ...
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Bachelor thesis going out of hand, need help [closed]

I am currently working on my bachelor thesis, which aims to enhance the multigrid preconditioned conjugate gradient algorithm proposed by Tatebe in 1993 using Deep Learning. Currently, I am ...
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How to calculate the force of solid applied by fluid? Using finite difference method, DNS, staggered grid, SIMPLE algorithm, immersive boundary

Problem I am using finite difference method to solve classic problem of flow around cylinder, for validation of my group's immersive boundary method. The common way to validate numerical method is ...
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How do we implement the balance of stress on interface in ALE FSI method?

""we aim for a consistent variational-monolithic coupling scheme in which we need all equations defined in the same domain; therefore, $\mathrm{ALE}_{f x}$ was introduced. In variational ...
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Exact Riemann Solver for Multi-Component 1D Euler Model

I am concerned looking for an exact Riemann solver for compressible 1D multi-component Euler equations, supplied with the ideal gases equation of state and under the assumptions: Mechanical ...
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How to implement the interface extension of fluid "displacement" in ALE?

In ALE, we first set a referenced space for fluid, then we extend the boundary fluid displacement to the whole fluid region, take harmonic extension as an example, we need $$\Delta \left ( \hat{u} \...
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Any code on ALE method for N-S equations or advection-diffusion equations?

I'm currently reading the book computational fluid-structure interaction, but the book doesn't provide any code, and I can't understand the ALE method, could you please provide some codes written in ...
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Determining Stainless Steel Pipe Length for Heat Transfer to Reach 1000°C

I'm working on a Uni project where I need to determine the length of a stainless steel pipe that is required to heat a fluid up to 1000°C. The pipe will be placed in an oven that can reach up to 1400°...
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Redefining velocity field to make it divergence free on the grid level

I am currently working with convection equation $\frac{\partial C}{\partial t}+u\frac{\partial C}{\partial x}+v\frac{\partial C}{\partial y}=0$. I assume that the velocity field is incompressible i.e. ...
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Why can the weak forms of the Stokes and continuity equations be combined into a single equation?

Consider this Stokes equations, $$ \left\{ \begin{array}{r} - \mu \Delta \vec{u} + \nabla P = \vec{f} \\ \nabla \cdot \vec{u} = 0 \end{array} \right. $$ Weak form I is: $$ \...
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shooting method to compute the interface shape

I am trying to use a shooting method to compute the shape of liquid-gas interface given by the following differential equation: $$ \frac{d^2 \theta}{ds^2} = \frac{f(\theta)}{h(h + 3\lambda)} $$ with $\...
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Preventing an Overflow in Exponential Integrating Factor

The following is the Discrete Spectral Vorticity Evolution PDE for incompressible flow: $$ \frac{\partial \Omega_{pq}}{\partial t} = \nu \left( \frac{\partial^2 \Omega_{pq}}{\partial x^2} + \frac{\...
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Drag hydrodynamic force for low particle Reynolds numbers

Suppose we have a fluid particle mixture, where the particle have cylindrical shape, no gravitation force, flow is laminar (let's say $Re_f=100$), and we want to do numerical simulations, and we are ...
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Symmetry axis boundary condition

I was wondering about the symmetry axis boundary condition in commercial CFD solvers such as ANSYS Fluent. If the problem is the flow through a round pipe or out of a round nozzle, it is natural to ...
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Approximation of derivatives in the finite volume method

I am looking into the finite volume method and I have come to a problem with discritisation. Suppose I am looking at a particular cell(I'm dealing) with cartesian grid. at the points $(X_{i},Y_{j}),(...
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Is the weak form on this book about a level set FSI problem wrong?

I'm trying to repeat a level set FSI problem on the book <Level Set Methods for Fluid-Structure Interaction>, on the page 89, the provided freefem code define a weak form of the discretized ...
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Is there any papers about simulating material damage under supersonic combustion?

I'm quite interested in this field, Is there any papers about simulating the damage of material(such as alloy) under supersonic combustion, after searching for a while, I didn't find anything
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Where has my implementation of the SHAS2D (Book and Boris, 1975) model gone wrong?

I am new to computational fluid dynamics, and am having a tough time implementing the Book and Boris flux limiter SHAS2D model. I am attempting to re-create the SHAS2D fluid code to solve the Euler ...
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FENICSx or deal.ii for modeling fluid structure interaction of cylindrical energy harvesters in various arrangements

I'm trying to model fluid-structure interaction of cylindrical energy harvesters in various arrangements. I have chosen OpenFOAM for the fluid part but I have no clue which framework to use for the ...
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AMR framework for efficient simulation of PDEs, potentially with boundary layers

I am aiming at developing a simulation software mostly aimed at reactive fluid flows applications. Here are a simplified list of points to drive the initial choices (code structure, libraries...): I ...
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In level set fluid structure interaction method why can we rewrite the elastic force in this form while there is no shear force?

when we consider a Immersed Membrane Without Shear, we can define a regularized elastic energy as $$\mathcal{E}(\varphi)=\int_{\Omega} E(|\nabla \varphi|) \frac{1}{\varepsilon} \zeta\left(\frac{\...
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OpenFOAM- write interval changed after restarting simulation

I am running a pimpleFoam simulation on a supercomputer. I have to submit it as a job which has an allocated time. The simulation I was running ran out of this allocated time. So then I restarted it ...
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Lattice Boltzmann method parallelization

I'm learning about the lattice Boltzmann method (LBM) and how it can be parallelized. On Wikipedia, they say, "The LBM was designed from scratch to run efficiently on massively parallel ...
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What happens at the interface between a solid and a fluid?

I am doing an MPM simulation of water colliding against a solid, I am currently encoding the model for collision forces and I am realising something isn't clicking. Let us assume the fluid experiences ...
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Error - Getting negative temperature while solving Quasi 1D flow in a Nozzle (JD Anderson Book)

I am currently trying to solve Nozzle Flow problem from JD Anderson Book. Here's my entire python code - ...
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How should I solve generalized eigenvalue problems in Python? (Orr-Sommerfeld equation)

I am trying to solve the Orr-Sommerfeld equation numerically, using the techniques given in this article. This leads to solving a generalized eigenvalue problem, that is, given two matrices $\mathbf A,...
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How can i model upward natural convection in various angles (0 - 90)?

I am looking for a way to numerically solve the Naiver-Stokes equations for steady incompressible flow using FDM over a surface with various angles?
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How to address the element face adjacent to boundaries when the finite difference method and marker-and-cell scheme are used to solve the Stokes flow?

The Stokes equations are $$-\Delta \mathbf u + \nabla p = f \text{, in }\Omega,$$ and $$ -\nabla \cdot \mathbf u = g, \text{ in } \Omega$$ where $\mathbf u = \left( u, v \right)$ is the flow ...
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How can we use the two boundary conditions for the Taylor-Maccoll Equations for Cone Shock Waves?

The Taylor-Maccoll equations below govern the gas dynamics around a supersonic, axially oriented cone. Using the notation from Anderson's Fundamentals of Aerodynamics, which uses a dimensionless ...
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MPM course, implicit updat clarifification

In the 2016 SIGGRAPH notes on MPM the authors explain how to do an implicit update in section 11.4 throguh by this formula: It is not clear to me what the $j$ is over in this case (for eq 202), is it ...
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Resultant Lift Direction Confusion

Quite a small scale question but I have gotten myself confused. Inside Ansys Fluent I am simulating a wing at different angle of attacks, instead of rotating the airfoil I have rotated the inlet ...
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Why do we use modified pressure in incompressible multiphase solvers with gravity?

The context of my question is two-phase incompressible solvers such as interFoam in OpenFOAM, but I have seen this trick used ...
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Fluent Induced Drag Aerofoil Convergence Error

I am currently modelling what happens, to lift induced drag, when you apply washout to a wing (Twist). However I have a few issues the drag values I calculate are into the 1000s the drag values ...
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Energy potential involvign pressure and viscoscity?

Making a really long explanation short. I am looking for an energy density function for an incompressible isotropic fluid that involves both viscoscity and pressure. The reason is, there is a way to ...
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Solving a minimization problem without flattening inputs?

I am reading this paper on improving time steps for solving simulation problems: https://www.math.ucla.edu/~jteran/papers/GSSJT15.pdf The authors developed this energy function: $$E(x) = \frac{1}{2\...
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MPM implicit integration

Setup I am having a hard time translating the formulas in the 2016 MPM course from siggraph into algorithmic computations. In particular we have equations 200 and 201 $$h(v^{n+1}) = Mv^{n+1} - \Delta ...
Makogan's user avatar
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Projection (or fractional-step) methods Vs coupled method for incompressible Navier-Stokes

My question is in the context of the finite element method. Incompressible Navier-Stokes equations can be solved using the coupled method or projection/fractional step methods. Each method has its ...
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How do the navier stoke equations model materials who "forget" their original form?

Sorry for the screenshot but I don't want to try to format this on latex: We have this annotation of the Navier-Stokes equations: I am particularly puzzled by the viscosity/stress term. For an ...
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Adding stability to MPM simulation?

I am writing a 2D implementation of MLS-MPM, I have fluids working perfetly fine, solids technically work as well, at low time steps. This is the fluid simulation at a large time step: https://i.stack....
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SPH example codes for solving differential equations

I'm quite new to the smoothed particle hydrodynamics method, so I'm trying to find Matlab or Python code to help me understand it. Specifically, I want to know how to solve the one-dimensional ...
Medulla Oblongata's user avatar
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How to calculate the reynolds number for airborne wind energy system?

I am asking for some help on how to calculate the reynolds number for an AWES. I know the formula of Re=rhovl/viscosity. I have selected the air foil as Clark y with chord length 3.72m (which will be ...
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discrete definition of curl $ \nabla \times \vec{A}$ on a 3D grid?

I have the data for 3D vector field $\vec{A}$ (with components $\vec{A_1}$, $\vec{A_2}$ and $\vec{A_3}$) sampled on a 3D grid with integer indices i, j and k. Assuming that only the third component $\...
rockonkl's user avatar
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Fortran - Lid-Driven Cavity Boundary Conditions Error when using SIMPLE method

I am studying Numerical Methods for incompressible flows. part of the tasks is to model the lid driven cavity problem in 2D using the SIMPLE method. I have been provided with Fortran code that is ...
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books/paper recommendation on computational thermal-turbulence by using FEM

I have just learned basic FEM for 2D N-S euqation, now my teacher let me to do the following problem, the document of this problem is in large fluid problem, the system of equations is listed in that ...
吴yuer's user avatar
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How to implement pressure stabilization in matlab while solving steady stokes equation

the equation is $$ \left\{\begin{array}{l} -\nabla \cdot \mathbb{T}(\mathbf{u}, p)=\mathbf{f} \text { in } \Omega, \\ \nabla \cdot \mathbf{u}=0 \text { in } \Omega, \\ \mathbf{u}=\mathbf{g} \text { on ...
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How to specify the value of pressure in a point in solving steady stokes equation numerically?

I try to solve the steady-Stokes equation numerically on , that is \begin{aligned} -\nabla \cdot \mathbb{T}(\mathbf{u}, p) & =\mathbf{f} \quad \text { on } \Omega=[0,1]*[-0.25,0], \\ \nabla \cdot \...
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Once a method is implemented in a computer program, then does learning the theory become less useful use of time?

Once a method is implemented in a computer program, then does learning the theory become less useful use of time? This has confused me. I used to view that all things should be studied from first ...
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How to combine multigrid preconditioner with jacobi preconditioner?

I have not found any relevant information in the literature on the following rather simple problem: How to combine (geometric) multigrid preconditioned conjugate gradient (MGPCG) with an additional ...
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Starting point to use Trilinos linear algebra packages?

I have experience with classical linear algebra packages in C++ like Eigen, Blaze, etc. I have never wrote my own PetSC back-end solver but I used/modified several of them. In a new project I would ...
Kürşat Yurt's user avatar
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Problem with my Octave code (unsteady heat equation with FEM)

I want help with my Octave code regarding the unsteady heat equation. My geometry and mesh are generated with FreeFEM++, so there is no problem with that (I tried it with the steady problem with no ...
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