Questions tagged [cfd]
questions about computational fluid dynamics
98
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Why does CFD over predict shockwave in comparison to wind tunnel?
I ran a CFD simulation of Mach=0.85 flow over an aerofoil and noted that my Cp (coefficient of pressure) plot over predicts the shockwave in comparison to experimental data?
Can someone please explain ...
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56
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SU2 vs OpenFoam for highly unsteady aerodynamics. Suggestions?
I am trying to simulate aerodynamic interactions between high speed propeller downwash and wings of a cruising aircraft. Confused between OpenFoam and SU2. Open to other opensource software ...
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22
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Thermal Undershooting In SLM Simulation on Ansys Fluent
I am creating a SLM simulation of basalt on Ansys Fluent. I have enabled laminar viscosity, solidification and melting, and the energy equation. The heat flux is applied to the top wall through the ...
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How to preserve edge grading of rotated edges in ICEM CFD?
I have a 2D axisymmetric geometry for which I am generating block-structured mesh in ICEM. I am converting this 2D block setup to a 3D block setup by rotating the 2D blocks using a dedicated option in ...
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Which, if any, CFD methods would be best for predicting performance of a sailboat?
I am interested in using a CFD simulator to calculate the performance potential of a sailboat. And not just a single boat, but of multiple boats of different configurations and hull shapes. If I know ...
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Typical Runoff velocity values
I am computing runoff velocities for rainfall falling over an area using St-Venant 1D momentum equation. I wanted to have some idea if my computed velocities are within a reasonable range of what one ...
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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 ...
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Hexamesh of a helical coil in ICEM CFD
I am trying to mesh a helical coil segment in ICEM CFD. My approach is to create a 3d block at the start of the geometry, and then extrude it along the center curve:
However, when I do this I end up ...
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In Ansys ICEM CFD, what do these "cube" symbols on the midpoint of block edges mean?
When I was meshing a helical coil, I've noticed these "cube" symbols located at the midpoint of a the block's edges:
Blocks with these symbols tend to have a lot of strange/unpredictable ...
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Solidworks Particle Injection Modelling - Density has no effect?
I'm modelling a cyclone separator in Solidworks and have ran several different particle studies with particles of different densities. However, density seems to have no impact on how the particles ...
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approximate equation for temperature drop near wall in contact with fluid
I am concerned about the following problem and so far I am not able to find a solution. Let us consider an environment at a temperature $T_a$ and the inner surface of a not insulating wall in contact ...
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Sharp Edged Pipe with Negative Pressure
I want to calculate the 2D pipe flow with sharp edged contraction pipe (below figure). The fluid is water, the model is steady state k-epsilon. The boundary condition is velocity inlet (8.47ft/s = 2....
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66
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Density or Pressure based solver CFD
I’m currently trying to simulate the 2d cross section of a bullet using Ansys Fluent but am really confused about which solver type to use- density or pressure based?
Conditions:
Transonic (M=0.8)
...
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39
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Writing the Reynolds stress in vector form
I am learning about Reynolds Averaged Navier Stokes (RANS) CFD modelling. The Reynolds stress can be written in tensor form as
$$
-\rho\overline{u_i'u_j'}=\mu_t\left(\frac{\partial U_i}{\partial x_j}+\...
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22
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Display Pressure coefficient for multiple points at across the span line of an airfoil in fluent
Learning to use ANSYS Fluent as part of my computational engineering course I have previously modelled a 2D wing and been abled to XY plot for the pressure coefficient against x coordinate.
my ...
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75
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Centrifugal pump head-flow prediction with CFD
Given a volute pump casing, the impeller, and RPM how would one obtain a simulated head-flow graph? As for what I have seen in research papers most methods already assume input flowrate / pressure and ...
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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 ...
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Is there a CFD program that can simulate the motion of a non rigid body through fluid?
Is there a CFD program that can simulate motion of a conveyor belt underwater? Aproximating it as a moving rigid plate is not gonna work.
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How to determine time taken for tyre to deflate using CFD analysis?
I am working on my final year project, and am at a point which requires us to deflate a tyre in 0.8 seconds. This needs to be simulated using CFD. We have drilled a hole into the rim and attached a ...
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183
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Heat transfer coefficient in forced convection and its dependence of temperature
I'm working on a Ansys Fluent of an Aluminium coil annealing furnace with the goal of estimating the heat transfer coefficients at different temperatures and ventilator/fan speed conditions. The ...
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Why am I getting an ever increasing value of power co-efficient (Cp) with the increase of TSR in Vertical axis wind turbine simulation?
I am trying to get the bell-shaped Cp vs TSR graph in my 2D simulation of the H-Darrieus vertical axis wind turbine (using a sliding mesh model). However, I am always getting an ever increase of Cp ...
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101
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Interpretation of dx/dt and u in CFD
I am currently studying CFD and I have a question about how I should interpret the term u and dx/dt. I would like to find that out in the textbook, but I could not.
When I solve 1D Euler Equation with ...
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Isn't the Newton's cooling law for heat convection too macroscopic for CFD simulations?
In CFD (Computational Fluid Dynamics) simulations, the space is discretised into a huge number of tiny cells and, therefore, one has the opportunity to use a model of heat transfer that takes into ...
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259
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How to compute wall heat flux q with just wall temperature
I am doing some simulation for natural circulation loop and have a heat rate q in the heating leg and a fixed temperature for the cooling leg. I know the heat rate for the heating section (128 W) and ...
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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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161
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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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279
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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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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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194
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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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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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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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100
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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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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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594
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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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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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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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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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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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127
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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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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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166
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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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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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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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336
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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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978
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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 ...
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153
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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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101
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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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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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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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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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