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Questions tagged [cfd]

questions about computational fluid dynamics

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25 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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0answers
10 views

blockMesh fails with Foam::error::printStack

I am trying to generate a mesh using blockMesh. My blockMeshDict looks like this: ...
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1answer
27 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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1answer
54 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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1answer
52 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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26 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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93 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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77 views

While using Transient Time Solver, I am facing many errors such as, a) floating point error b) Temperature AMG divergence c) Reversed flow

Introduction I am doing a Computational Fluid Dynamics Study on Dispersion of gases over buildings. The scenario that is portrayed would be in the event of an explosion, how would the plumes or ...
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0answers
25 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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0answers
49 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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37 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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0answers
21 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
158 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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0answers
128 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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30 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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300 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 ...
4
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1answer
94 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
68 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
132 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
305 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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2answers
36 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 ...
4
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2answers
68 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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71 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
179 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 ...
4
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2answers
3k 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
928 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
218 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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333 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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47 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
292 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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0answers
215 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
56 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 ...
4
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1answer
278 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 ...
4
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2answers
392 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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2answers
92 views

Question about bounday layer thickness?

According to the following figure, boundary layer becomes progressively thicker with downstream distance x . Why? I have an other question as follows: When turbine blade thickness increases, what ...
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1answer
86 views

How to model subcritical open channel flow?

I'm trying to model subcritical flow in an open channel with a side weir of certain small length at the middle of the main channel, so a certain amount of fluid discharges through the weir. I need to ...
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0answers
173 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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0answers
51 views

How do I set Reciprocating and Rotation motion in Fluent or CFX?

I want to model the following case(Attached picture) This case have reciprocating and rotation motion. Is it possible that this case models in Fluent or CFX without writing Code? How i set this ...
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0answers
302 views

How should I set the turbulent prandtl number in a turbulent compressible flow simulation?

I'm working on simulating compressible fluid flow over a flat plate with turbulence. The energy equation for compressible flow with turbulence requires modeling a turbulent heat flux of the form $$...
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1answer
492 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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1answer
3k 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 ...
6
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1answer
135 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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1answer
312 views

Refrigerator temperature - compartment gas volume exchange, time to equilibrate?

I open the door for 30s of a 140L capacity 80W (240VAC, 0.8A) barfridge with a 20L freezer compartment (partition open to main compartment at one end) at a temperature of -5℃ with an internal main ...
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0answers
35 views

How to set up the boundary between volumes in a simulated turbine

I am simulating a turbine and I have some doubts about the correctness of my approach. In this turbine, there are three volumes: The two volumes are the piping before and after the blade and the ...
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0answers
66 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 ...
4
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2answers
532 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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0answers
47 views

periodic rotational conditions in Fluent

I have one question: In Fluent, should be generated same mesh in rotational faces for creating periodic rotational conditions? Is there a way that unmatched meshes are applied for creating periodic ...
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1answer
401 views

What is the numerical diffusion?

I studied many papers and I face with concept of numerical diffusion,but I don't understand it. Can someone explain briefly about numerical diffusion?
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1answer
5k views

Why is there reverse flow in Fluent?

I am simulating a axial turbine and number of cell are about 3000000. Under relaxation factors are as follows: Pressure: 0.1 momentum:0.1 Turbulent kinetic energy: 0.5 Turbulent dissipation rate: ...
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2answers
3k views

How do I set skewness correction in fluent?

I am simulating a turbine that has curves. Mesh is structure completely. But there is high skewness in tip clearance and some parts of around of the blade: When I use SIMPLEC Method, one factor (...