# Questions tagged [cfd]

questions about computational fluid dynamics

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### What is the Boussinesq approach?

I want to simulate a turbine in Fluent. For this reason, I studied some papers. In these papers, Turbulence is modeled using the realizable k–e model and Non-equilibrium wall functions are used in the ...
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440 views

### Why does the standard $k-\epsilon$ model use zero equation models?

According to Hoffman, the standard $k-\epsilon$ turbulence model incorporates a two-layer approach (inner region and outer region formulations to reperesent mixing length) when it comes to regions ...
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210 views

### Streamlines at the boundary of rotating and stationary domains are malformed

I am simulating a turbine and have divided the mesh into domains: the piping before and after the blade and the turbine blades. The domain containing the blades rotates at 2000 rpm while the other ...
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7k 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 ...
470 views

### How can I set an upper limit on mass imbalance in Fluent?

I studied a paper about simulation of turbines using Fluent that included the following sentence, which I don't understand: All converged solutions had a mass imbalance of less than 0.3% ...
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561 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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330 views

### Wall functions and separation in turbine blade simulation

I am simulating a turbine and I have some question about standard wall function in FLUENT. Standard wall function requires $y^+$ value between 30 to 60 on the blade. but the following quote states: ...
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6k views

### Understanding pressure drop and mass average values

While studying some papers, I didn't understand the following sentences: deltP the pressure drop across the turbine, evaluated using the mass average values at ...
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687 views

### How safe is this assumption for turbulence modelling in porous media?

I am studying the performance of volumetric solar receivers (specifically ceramic foams) versus the change of many parameters: solar flux, surface temperature, porosity, pore diameter, flow pressure ...
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798 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, $\nabla p=0$) ...
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122 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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769 views

### Efficient 3D mesh topology for CFD simulation of turbine blade

I´m developing a tool to generate an openFoam wind tunnel case of a wind turbine. I already have the blade geometry constructed, but I'm really new to CFD and parametric meshing. I found some ...
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173 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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483 views

4k views

### How to force creating a conformal mesh interface between zones in Fluent?

I am trying to perform simple 2D CFD analysis on Fluent having 3 adjacent zones(inlet, porous and outlet). The problem I have is whenever I select non-equilibrium thermal model in porous zone in Cell ...
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193 views

### Imposing/ensuring a constant mass flow rate in turbulent flow simulation

I'm trying to simulate using Finite Elements (non commercial software) the Tube Bundle benchmark problem: http://cfd.mace.manchester.ac.uk/ercoftac/doku.php?id=cases:case078&s[]=tube&s[]=...
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120 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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307 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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196 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 ...
103 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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82 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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917 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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264 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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233 views

### How is the reaction progress variable $c$ coupled with Temperature equation while solving the SIMPLE algorithm in CFD?

While solving the Navier-Stokes equation using SIMPLE algorithm, we solve the transport equation for additional scalar at the last step according to the SIMPLE's procedure. We need to add a new ...
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78 views

### problem in the calculation of pressure drop for an axial turbine

I am simulating an axial turbine. In this turbine, there are two domains. The first domain is the piping before and after the blade and the second domain contains the turbine blades. The domain ...
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416 views

### How to determing convergence in a CFD model [closed]

I am simulating an axial turbine. Under relaxation factors are default. Residuals are as follows: And also, mass flow rate, torque (in direction of Y) and inlet and outlet total pressure are as ...
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35 views

### Is there correlation between friction of boundary layer and values of inlet and outlet pressure? [closed]

Is there correlation between friction of boundary layer(or inertia and viscous forces in boundary layer) and values of inlet and outlet pressure in an axial turbine? For example, when friction of ...
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1 vote
473 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 ...
1 vote
436 views

### Is supersonic flow not possible in a venturi tube?

I'm trying to design a venturi tube that will have a pressure drop of 91525 Pascals where the inlet pressure is at 1 atm and the throat pressure is at 9800 Pascals. I calculated the minimum throat ...
1 vote
348 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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1 vote
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### 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 ...
1 vote
527 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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1 vote
407 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 ...
1 vote
729 views

### What limits my Courant number in Implicit Density based Solver?

As from the derivation we are able to see that the implicit density based solver (such as BTCS) is unconditionally stable for any courant number. So what is it, which limits the upper boundary of CFL ...
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1 vote
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### Why is the turbulent kinetic energy $k=\overline{v_1'^2}+\overline{v_2'^2}+\overline{v_3'^2}$ even in 2D cases?

I'm writing an essay which partly includes writing about the Reynolds stress model where the dissipation term $\varepsilon_{ij}$ is assumed to be isotropic (since dissipation mostly occurs at small ...
1 vote
68 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. ...
1 vote
233 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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1 vote
55 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, ...
1 vote
41 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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1 vote
274 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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1 vote
45 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?
1 vote
461 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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1 vote