Questions tagged [cfd]

questions about computational fluid dynamics

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26 views

Analytical solution for the 1D convection-diffusion equation

The Ogata and Banks analytical solution of the convection-diffusion equation for a continuous source of infinite duration and a 1D domain: where C [mol/L] is the ...
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2answers
82 views

How to determine the force to empty a syringe containing high-viscosity fluid?

I am trying to determine the force it would take to fully empty a syringe using a long nozzle, that contains a high-viscosity fluid. Specifications I'm using: I'm trying to determine the force ...
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1answer
24 views

What is the side way force on a flat membrane place perpendicular to the flow of current on one side, and stagnant water on the other

So basically imagine a plate being placed parallel to the direction of flow of water with water flowing with a certain velocity on one side of the plate and on the other side it is almost stagnant. ...
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59 views

Can we run ANSYS Fluent/OpenFOAM simulations in AWS or any free server?

I was planning to run some FSI related simulations. But the computation capacity that I have is not sufficient. But I had heard that there is a possibility to create instances in the Amazon EC2 or the ...
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25 views

Where is Wizard in Solidworks Flow simulation?

would anyone knows why my wizard in Solidworks 2016 flow simulation is missing, I am starting to learn flow simulation because of my study, I am still a beginner, I tried testing it 1 time with my ...
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1answer
47 views

How to compute velocity distribution in the developing boundary layer on the cylinder

Air flows perpendicular to the axis of a cylinder $a=1$ cm in diameter. Air speed upstream of the cylinder is $U=6.72$ mm/s and its kinematic viscosity is $2.1×10^{-5}$ at 350 K. I want to obtain the ...
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17 views

Finding the momentum source using divergence theorem

I have the following question: I understand how to use the divergence theorem but I'm not sure how I would find the momentum source, am I supposed to find the integral of grad U?
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1answer
41 views

Pressure drop in a CFD simulation of an air flow too small

I am simulating a turbulent air flow through a rectangular channel with the goal to match measured velocity profiles and the static pressure at certain points. My problem is that the pressure drop in ...
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0answers
31 views

Convergence problem in RANS simulation of unsteady flow

I am simulating an air flow through a two dimensional rectangular channel. The channel splits into two channels, one of them is followed by a 90 degree bend downwards and leads into a cylindrical ...
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19 views

Why is CGNS not used in CSM?

The CGNS format appears to be only applied in CFD (computational fluid dynamics). Why is it not applied in CSM (computational solid mechanics)? Is there any technical reason? The hierarchical ...
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1answer
204 views

Velocity inlet boundary condition in Ansys Fluent

Ansys Fluent offers a very simplified version of boundary conditions. So if I know the velocity at the inlet, I need not care about pressure and vice versa. What I am having trouble with is that I ...
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21 views

Why does Roe Average use enthalpy?

If my understanding is correct, Roe averaging is supposed to be a linearization of the nonlinear flux jacobian. For the Euler equations, one can compute the roe average as depending on density, ...
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1answer
37 views

Boundary layer momentum equation

How does the author get that formula(d alpha formula) using the momentum equation . The book here is Mechanics and thermodynamics of propulsion by Philip Hill and Carl Peterson.
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144 views

OpenFOAM simpleFoam calculation of flow around object leads to strange result

I calculated the flow around an object using OpenFOAM's simpleFoam and wanted to evaluate it's drag coefficent. Actually the drag coefficient is in a reasonable ...
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24 views

Solution diverges for Converging-Diverging Nozzle

I am trying to run a CFD simulation for an ASTAR nozzle but cannot get the solution to converge. These are the steps I took to try and run the simulation. I made the geometry in Solidworks and ...
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0answers
32 views

Assign a name to surface in CAD STEP file

I have a CAD model designed in FreeCAD and need to export it to a STEP file (neutral CAD format) to be used in numerical anaysis software. I would like to assign names to selected surfaces in order to ...
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1answer
24 views

How to deal with time derivative of speed toward time in staggered grid in CFD?

In my control equation, there is a term $$ \frac{\partial \rho u}{\partial t}+\frac{\partial \rho u^2}{\partial x}+\cdots=\frac{\partial p}{\partial x} $$ How to discretize it in staggered grid? ...
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89 views

Airfoil meshing using ANSYS

Logged in a little time ago i have a new question. So I am trying to mesh an arifoil geometry using ANSYS meshing. Airfoil number is NACA 84-M profile. Running 2-D simulation my main objective is to ...
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1answer
49 views

VTOL Aircraft Take-Off Mechanics Question

These question(s) could be potentially trivial, but its difficult to find visuals on CFD of VTOL aircraft. While watching a video of the f-35 performing its vertical take-off/hovering, I noticed the ...
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1answer
69 views

Pressure Coefficient with a Minima of 0 on Compressor Airfoils in Cascade

I am a relatively recent BSME graduate working on reproducing the results of a technical paper to strengthen my ANSYS CFX skills. The paper is "Effect of Section Thickness and Trailing Edge Radius on ...
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2answers
195 views

Why is Rocket Nozzle CFD done in 2D instead of 3D?

Why do I see rocket nozzle CFD like the one here in this SpaceX video done in 2D? Real Fluid flow is three dimensional and involves an x, y and z axis. Is fluid flow done in 2D only because computers ...
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3answers
533 views

How do drag and downforce in a rear spoiler of a car vary with angle of attack?

I ran an two aerodynamic simulations, one for a spoiler angle of 0 deg and the other for the same spoiler declined at 30 deg. The results showed a considerable increase in downforce, but only a slight ...
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75 views

Interpolation at a face, Finite Volume Method in Computational Fluid Dynamics

I am learning CFD and I have come across an example in which the thermal conductivity needs to be interpolated at a face between two rectangular cells. The face weighting factor is given as: $$g = \...
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285 views

ANSYS Fluent - Using Patch to set initial conditions, should I set the pressure and velocity or only one property to generate shock waves in a pipe?

I am fairly new to CFD and I am working in ANSYS Fluent. I am trying to model two specific shock waves in opposite directions in a length pipe. The shock waves need to be traveling at specific Mach ...
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0answers
58 views

Regarding the ITTC Guidelines for Ship CFD applications

I was reading through the ITTC – Recommended Procedures and Guidelines - Practical Guidelines for Ship CFD Applications (https://ittc.info/media/4196/75-03-02-03.pdf) document and this little thing ...
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60 views

Flow rate at the vent exit

I am working on a vent. The vent is attached to a box and is designed to extract air out of the box using the venturi effect. Air is made to flow over the vent which creates a significant pressure ...
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57 views

Tempreture distribution in a furnace

I am simulating a furnace as follows: Is it possible to capture temperature distribution in this furnace without designing intake fan? Which kind of boundary conditions can replace with intake fan? ...
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22 views

How to unserstand Correct boundary condition at outlet for incompressible flow?

I am simulating flow around a model. This model have an inlet and an outlet. Flow is incompressible. I know that value of pressure at the outlet is very much different from ambient pressure(Operating ...
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3answers
280 views

What does mesh topology mean?

What is a mesh topology? I have read this term being used in a lot of articles dealing with meshing the computational domain, but could not understand its intuitive meaning. And why is topology called ...
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198 views

How to solve mesh error for narrow surfaces in Ansys Meshing?

I am simulating a spherical grooved bearing….e.g. A bearing that has spiral grooves on the ball. Please see the following figures. There is a kind of lubricant between ball and cup, so as to prevent ...
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38 views

Is RotCFD or Ansys Fluent better to capture the wake pattern far downstream of a flow in the case of a rotating blade?

My main constraint is that the wake pattern to be worked on is far downstream. Which one will give me more accurate results? Will these two work well for the far wake at all?
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615 views

How to simulate an exhaust fan condition in ANSYS Fluent?

I'm trying to simulate a model which has one inlet and three outlets, and I'm passing air through it. Now, I want one of the outlets to have exhaust fan. I see options of exhaust fan and outlet-vent ...
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1answer
117 views

Convolution with RTD laminar flow

I have laminar flow in a tube. Consider the tube to be 0.2 m long and with an average velocity of 0.05 m/s. The analytical expression for my transfer function is: $E(t)= \frac{\tau^2}{2*t^3}$ for $t$>=...
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2answers
84 views

Turbulence model for low reynolds problem

I'm simulating the flow in a capillary with a sudden expansion. The small capillary has a diamater of 250 µm. The big capillar has a diamater of 1000 µm. My flow rate ist $ 1\frac{ml}{min} $. Using ...
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3answers
252 views

What is the best method to generate heat from a compressed air canister?

I want to convert the pressured air exiting a valve to heat. I know that a vortex tube can be used to do this, but I am wondering if I need to make modifications to the vortex tube to make it more ...
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3answers
448 views

Smoothed Particle Hydrodynamics (SPH) Vs. Large Eddy Simulation (LES) for Gearboxes

In the not too distant future I will be looking to simulate lubricant oil flows in a gear box, with rotating gears located in a bath of oil. I will be looking at the distributions at various angles of ...
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45 views

How to model the inside of a server for CFD and thermal studies?

At my workplace I have been assigned to create an accurate 3D model of our Dell PowerEdge R820 servers so we can insert our custom cards and run a CFD and thermal analysis on them. The end goal is to ...
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2answers
73 views

What is a good method (equation) for locally refining a 1D grid at each end?

I have a grid that I plan to discretize in 1D. It extends from 0 to L using N nodes, and I need to refine it at each end. I plan to have something that looks as follows: I have tried the to specify ...
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135 views

What is the exact meaning of “static and dynamic torque”?

I have the following parameters in my project. enter link description here I submitted a paper. Now, one of the Reviewer's comments is as follows: Validation is not enough and convincing. The CFD ...
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2answers
338 views

Steady state approximation for compressible fluid flow (manifolds and other pressure vessels)

I've been puzzling over a question / class of questions I'd like to solve via rough estimate before turning to CFD analysis. Say I have a pressure vessel with one inlet and one outlet. The pressure ...
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2answers
5k views

What is the difference between FEA and CFD?

Many of us think FEA is used for structural problems and CFD is used for fluid dynamics problems. But I have read that the above statement is wrong. So please explain the exact usage of those two.Also ...
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1answer
1k views

Boundary conditions for Stream function-Vorticity method

I have used a MATLAB finite difference code to solve a lid driven cavity flow, based on a Stream function-Vorticity formulation of the viscous, incompressible Navier Stokes equations. Details about ...
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1answer
286 views

Difference between strong, weak and differential forms?

We recently covered fundamental laws in our Computational Continuum Mechanics course last term. There are many forms of these laws and I am confused which one to use and when. For instance in mass ...
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362 views

Why is there negative static pressure in contour?

I studied a paper about turbine and i seen that there is negative static pressure in contour. Why does this happen? Wave Energy Harvesting Turbine: Performance Enhancement
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52 views

Flow through manifold: convergence issues

I try to simulate flow through a manifold with multiple inlets & outlets but I'm facing convergence issues. I know that it may be due to poor quality mesh, but my mesh statistics are: Minimum ...
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2answers
353 views

What is reason of low axial velocity at tip and hub of an axial turbine?

I am analyzing results of my turbine simulation. I have created one line from hub to casing at downstream of the flow...please see the following figures. I want to investigate along this line how the ...
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242 views

Obtaining the correct flat plate turbulent boundary layer thickness in a CFD simulation

I used a commercial CFD software to simulate incompressible turbulent flow of air over a flat plate. I setup a 2D domain 1.5m long in the x direction and .2m in the y direction. The boundary ...
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0answers
59 views

Is it possible that entropy generation decreases with decreasing turbine efficiency(First Low efficiency )?

I simulated an axial turbine(Wells turbine). Now I have faced with strange problem. Performance of any turbine can be improved if the losses are identified and minimized. Several losses can be ...
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1answer
437 views

How to measure turbulence parameters experimentally?

When running CFD simulations with turbulence on, I often need to specify inlet parameters such as the turbulent intensity, turbulent viscosity ratio and/or the turbulent length scale. If these ...
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2answers
575 views

Should I expect fluid velocity within a pipe to increase beyond the inlet velocity?

I'm using commercial software to simulate unsteady incompressible flow of air through a 1m long rectangular pipe with cross section 0.2mx1m. I have a velocity inlet condition (u=100m/s, $\nabla p=0$) ...