Turbulence model for Internal flow in vent duct?

Rahul_P1
Rahul_P1
Altair Employee
edited October 2020 in Community Q&A

Hi all,

In Acusolve which turbulence model should be use to simulate steady state of the air flow in vent duct?
Is it Spalart Allmaras or K-omega model?

what is the advantage of Spalart Allmaras and its application?

Thanks

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Answers

  • Rahul_P1
    Rahul_P1
    Altair Employee
    edited February 2015

    What are the advantages and disadvantages of the Spalart-Allmaras model?
    Advantages:
    (a) Computational efficiency:
    The standard k-ε model is a classical model developed by turbulence researchers in the early 1970's, whereas the SA model is a recent model developed in the early 1990's with the objective of numerical efficiency and robustness. The SA model can perform much faster than the k-ε model for the same or better level of accuracy.
    (image/emoticons/default_cool.png' alt='B)'> Accuracy as Low-Re Model:
    Inherently, the SA model is effective as a low-Reynolds number model and provides a superior accuracy than the standard k-ε model for wall-bounded and adverse pressure gradients flows in boundary layers. The k-ε model does not perform well in boundary layers and requires additional terms to be added to the governing equations to produce boundary layer profiles.
    © Mathematics & Numerics:
    The standard k-ε model involves a two equation coupled differential system, which can lead to stiff algebraic system for non-diffusive & accurate flow solver like AcuSolve. Some numerically dissipative solvers can easily handle such stiff differential equations. On the contrary, the SA model possess a well-behaved one equation differential system.
    Disadvantages:
    The primary disadvantage of the Spalart-Allmaras model is seen when applied to free jet flows. For these applications, the rapid change in length scales associated with the transition from wall bounded to free shear proves to be problematic and alternative models may provide better predictions.

    How do I know which turbulence model to use?
    General Applications
    The starting point for most applications should be the steady state Spalart-Allmaras model. For most industrial applications, this model provides sufficient accuracy. For applications involving massive separation, the DES model may be used if a higher level of accuracy is required.
    Unsteady Simulations
    For the simulation of unsteady flows, users have the option of unsteady RANS (URANS), DES, or LES. Depending on the goal of the simulation, different turbulence models may be used. If the unsteadiness in the flow is driven by some type of thermal transient, then the use of URANS (i.e. the Spalart-Allmaras model in unsteady mode) is typically sufficient. If the unsteadiness is due to large scale separation and bluff body vortex shedding, the DES model or LES model should be used. For cases where small scale turbulent structure is of interest, the Dynamic LES model should be used.

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