A holistic microclimate model

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turbulence_model [2012/07/10 18:11] – created marenlieturbulence_model [2012/07/30 23:15] (current) – removed enviadmin
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-====== Turbulence Model ====== 
  
-===== Turbulence Model in ENVI-met ===== 
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-ENVI-met uses the so-called 2-equation Turbulence Kinetic Energy (TKE) Model to predict the turbulence in the air. \\ 
-The first equation describes the distribution of the kinetic energy (E) in the air depending on production, advection, diffusion and destruction: 
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-Prognostic equation of Turbulent Kinetic Energy (TKE) 
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-The second equation is similar but describes the Dissipation Rate of TKE (e or eps): 
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-Prognostic equation of dissipation rate of Turbulent Kinetic Energy (e) 
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-Finally, the Turbulent Exchange Coefficient Km is a result of both: 
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-Relation of Turbulent exchange Coefficient Km to TKE and e 
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-As the result of the TKE-e equation Km (via Ke and directly) is used as input data for the next calculation cycle, there is a non-linear feedback loop between the turbulent exchange coefficient and the TKE-e equation. Once Km begins to be unstable, the TKE-e equation system will get unstable too, producing even more unstable Km's in the next loop.\\ 
-To avoid numerical problems, several mechanisms have been introduced in ENVI-met making the turbulence model more reliable: 
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-  * [[Two-Step Calculation Loops (Initialisation)]] 
-  * [[Intelligent Troubleshooting via Relaxation]]  
-  * [[Range Limiting]] 
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-In previous ENVI-met versions, it was suggested to calculate the turbulence field using the "Update" method (Turbulence mode=1, see [[[TURBULENCE]]]-Section). In this mode, the TKE-e equation system was only solved in fixed time intervals until a stationary solution was found. This method was only introduced to keep the model executable on older computers. \\ 
-Today, we do not suggest to use the "Update" mode any longer!\\ 
-Recent computers are strong enough to use the "[[[TURBULENCE]|Continuous Mode]]" (2)!\\ 
-**As the old update method was a huge source of error and frustration, we have decided not to support it any longer in ENVI-met!**