Hey guys
i tried many times to solve 3D steady state model flow move in room with inlet and outlet by k-e model
the first iteration for k-e model starts with 1e+8 and 1e+10 then diverge what's wrong however N.S converge and Heat eqn converge ?
and when i solve this model transient it had been solved and get results but take much time computational effort.
any one help me please this my sif file.
I can't solve 3D steady state turbulent Model (N.S & K-e)
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Ahmed 7afezz
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I can't solve 3D steady state turbulent Model (N.S & K-e)
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kevinarden
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Re: I can't solve 3D steady state turbulent Model (N.S & K-e)
I would say the flow is much too turbulent to have a steady state at least in the domain of your model. It is too fast, viscosity too low, not enough energy dissipation. If it is too turbulent it will not have a steady state.
From wiki fluid dynamics page:
Steady vs unsteady flow
A flow that is not a function of time is called steady flow. Steady-state flow refers to the condition where the fluid properties at a point in the system do not change over time. Time dependent flow is known as unsteady (also called transient[6]). Whether a particular flow is steady or unsteady, can depend on the chosen frame of reference. For instance, laminar flow over a sphere is steady in the frame of reference that is stationary with respect to the sphere. In a frame of reference that is stationary with respect to a background flow, the flow is unsteady.
Turbulent flows are unsteady by definition. A turbulent flow can, however, be statistically stationary. According to Pope:[7]
The random field U(x,t) is statistically stationary if all statistics are invariant under a shift in time.
This roughly means that all statistical properties are constant in time. Often, the mean field is the object of interest, and this is constant too in a statistically stationary flow.
Steady flows are often more tractable than otherwise similar unsteady flows. The governing equations of a steady problem have one dimension fewer (time) than the governing equations of the same problem without taking advantage of the steadiness of the flow field.
From wiki fluid dynamics page:
Steady vs unsteady flow
A flow that is not a function of time is called steady flow. Steady-state flow refers to the condition where the fluid properties at a point in the system do not change over time. Time dependent flow is known as unsteady (also called transient[6]). Whether a particular flow is steady or unsteady, can depend on the chosen frame of reference. For instance, laminar flow over a sphere is steady in the frame of reference that is stationary with respect to the sphere. In a frame of reference that is stationary with respect to a background flow, the flow is unsteady.
Turbulent flows are unsteady by definition. A turbulent flow can, however, be statistically stationary. According to Pope:[7]
The random field U(x,t) is statistically stationary if all statistics are invariant under a shift in time.
This roughly means that all statistical properties are constant in time. Often, the mean field is the object of interest, and this is constant too in a statistically stationary flow.
Steady flows are often more tractable than otherwise similar unsteady flows. The governing equations of a steady problem have one dimension fewer (time) than the governing equations of the same problem without taking advantage of the steadiness of the flow field.
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Ahmed 7afezz
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Re: I can't solve 3D steady state turbulent Model (N.S & K-e)
Thanks a lot for reply
but the same model is solved steady with Ansys and get perfect results with comparison by experimental data.
my velocity is 0.04 m/sec is not very high ?
but the same model is solved steady with Ansys and get perfect results with comparison by experimental data.
my velocity is 0.04 m/sec is not very high ?
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kevinarden
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Re: I can't solve 3D steady state turbulent Model (N.S & K-e)
I have noticed that in comparison with commercial codes that Elmer requires finer meshes for similar problems.
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raback
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Re: I can't solve 3D steady state turbulent Model (N.S & K-e)
Hi
Elmer development follows the projects related to it to rather large extent. Over the years there has been a plethora of projects with almost complete exception of turbulence. It is the real-world cases that are needed to trim the code. I would think one reason is that OpenFOAM sucks those applications quite efficiently. Also FVM is conservative by construction which is well suited for fluid mechanics. FEM can be made conservative also but with a higher price.
The thing with the turbulence models is the transport equation k and e, for example, are very nonlinear (and include division by k). Therefore the route for convergence can be quite rough since FEM does not ensure monotonicity by construction. Perhaps using FCT (flux corrected transport) for the turbulent transport would help. We may look to improve the FCT features in Elmer in coming months. But I feel your pain.
-Peter
Elmer development follows the projects related to it to rather large extent. Over the years there has been a plethora of projects with almost complete exception of turbulence. It is the real-world cases that are needed to trim the code. I would think one reason is that OpenFOAM sucks those applications quite efficiently. Also FVM is conservative by construction which is well suited for fluid mechanics. FEM can be made conservative also but with a higher price.
The thing with the turbulence models is the transport equation k and e, for example, are very nonlinear (and include division by k). Therefore the route for convergence can be quite rough since FEM does not ensure monotonicity by construction. Perhaps using FCT (flux corrected transport) for the turbulent transport would help. We may look to improve the FCT features in Elmer in coming months. But I feel your pain.
-Peter