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Questions tagged [fluid-dynamics]

The study of the properties of fluids and gases in motion

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2 votes
2 answers
3k views

openFOAM RAS to LES

I successfully ran a RANS simulation of industrial fan with all wall BCs, pimpleDyMFoam solver and spallart-almaras RAS model. I got results upto some time, I would like to continue that simulation ...
2 votes
0 answers
49 views

Lowest order Raviart Thomas elements

I have questions regarding the implementation of Lowest order Raviart Thomas elements on quadrilaterals, some papers use the basis functions in this form: for example the right edge: $N = \left[\dfrac{...
0 votes
0 answers
39 views

Any resource focusing on choosing the right SPH simulation parameters?

I am a software engineer with no prior experience in numerical and/or physical models (apart from very simple particle simulations). The last few weeks I've been trying to implement a 2D real-time SPH ...
1 vote
1 answer
94 views

Applicability of 1/7 power law for turbulent flow

I am looking to do a CFD study of a turbulent flow through a pipe. I know the average velocity from the flow rate so I decided to use the popular 1/7th power law model for the fully developed ...
0 votes
0 answers
55 views

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 ...
1 vote
1 answer
59 views

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 ...
2 votes
1 answer
270 views

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 ...
1 vote
0 answers
70 views

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 ...
2 votes
2 answers
34 views

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 ...
0 votes
1 answer
60 views

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 ...
1 vote
0 answers
2k views

CFD in Python: Mesh Generation

I am trying to set up a 3D CFD scheme for thermal and flow modelling in Python using the finite volume method. The first concern is to build the geometry and an accompanying mesh that is efficient for ...
0 votes
1 answer
51 views

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} \...
0 votes
1 answer
73 views

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 ...
4 votes
2 answers
166 views

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. ...
0 votes
0 answers
64 views

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°...
2 votes
1 answer
99 views

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: $$ \...
0 votes
1 answer
85 views

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 $\...
2 votes
0 answers
80 views

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{\...
0 votes
0 answers
47 views

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 ...
1 vote
1 answer
210 views

Differential equation for radioactive cooling in fortran

Today I'm trying to evaluate this differential equation for internal energy in a gas in Fortran: $$ \frac{du}{dt} = - \frac{n_H^2}{\rho}\frac{\Lambda}{n_H^2} $$ Where nH is the density of hydrogen in ...
1 vote
1 answer
173 views

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 ...
2 votes
3 answers
223 views

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}),(...
1 vote
1 answer
81 views

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 ...
0 votes
0 answers
20 views

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
2 votes
1 answer
112 views

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 ...
5 votes
0 answers
345 views

Galerkin Least-Squares stabilization for FEM solution advection (hyperbolic) equations

I am playing with Galerkin Least-Squares stabilization to solve advection diffusion problem in the context of the finite element method. This works very well for steady-state advection-diffusion ...
0 votes
0 answers
110 views

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 ...
2 votes
1 answer
118 views

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 ...
0 votes
1 answer
76 views

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{\...
5 votes
1 answer
237 views

Solving simplified 1D plasma fluid equations with finite difference

The following two equations represent a simple model of a plasma where ions are immobile. $$n\frac{\partial u}{\partial t}+nu\frac{\partial u}{\partial x}=n\frac{d\phi}{dx}-\theta\frac{\partial n}{\...
0 votes
0 answers
45 views

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 ...
2 votes
3 answers
2k views

Pressure boundary condition in lid driven cavity using finite element method

Thank you all 1.) I am trying to solve the lid-driven cavity problem for an incompressible Stokes and Navier Stokes equations using the general "Mixed" finite element method. Dirichlet ...
0 votes
1 answer
135 views

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 ...
1 vote
2 answers
614 views

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,...
0 votes
0 answers
60 views

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 ...
0 votes
0 answers
26 views

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 - ...
2 votes
1 answer
1k views

1-D turbulent energy spectra in homogeneous direction (non-isotropic)

I am trying to compute the one-dimensional energy spectra for my channel-flow simulation. I have already written a post-processing script to achieve this; however, I need to validate my code before ...
5 votes
1 answer
587 views

General case Kutta condition

I'm working on a 2D inviscid fluid simulation using a "panel method", with Potential being used to enforce the no-through boundary condition. I'm trying to incorporate the Kutta condition, which says ...
0 votes
0 answers
29 views

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?
0 votes
1 answer
46 views

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 ...
1 vote
1 answer
312 views

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 ...
0 votes
1 answer
61 views

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 ...
0 votes
0 answers
39 views

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 ...
0 votes
0 answers
54 views

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\...
3 votes
1 answer
188 views

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 ...
2 votes
1 answer
124 views

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 ...
0 votes
0 answers
121 views

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....
10 votes
2 answers
1k views

CFL condition in Discontinuous Galerkin schemes

I have implemented an ADER-Discontinuous Galerkin scheme for the resolution of linear systems of conservation laws of the type of $\partial_t U + A \partial_x U + B \partial_y U=0 $ and observed that ...
1 vote
0 answers
79 views

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 ...
1 vote
0 answers
55 views

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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