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Questions tagged [cfd]

questions about computational fluid dynamics

94 questions
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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 domains are stationary. The mesh is structure and…
user19061
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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 adjacent to wall surface $(y^+ \approx 30 - 50)$.…
Algo
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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 near wall flow modeling. There are the following…
user19061
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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% What does the mass imbalance of converged solutions…
user19061
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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: When using wall function models, the $y^+$ value…
user19061
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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 please give the basic difference between them.
Pradeep Chada
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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 parameters are already known for a given experiment, I…
Paul
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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 $$q_T=\frac{\mu_T c_p}{Pr_T}\frac{\partial…
Paul
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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 and flow velocity. I have seen two ways in the…
Algo
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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 articles where they mention a C topology to mesh the…
efirvida
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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 the inlet and outlet sections of the computational domain, respectively. What is the…
user19061
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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 $t$>=$\frac{\tau }{2}$ and $E(t)=0$ for $t < \frac…
Gesetzt
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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 these two parameters: growth rate (r) initial…
teepee
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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, $\nabla p=0$) and a pressure outlet condition (p=0, $\nabla…
Paul
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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 standard properties of water I have a Reynolds…
Gesetzt
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