Differences

This shows you the differences between two versions of the page.

--- turbulence_model [2012/07/10 18:18] – marenlie
+++ turbulence_model [2012/07/30 23:15] (current) – removed enviadmin
@@ Line 1: / Line 1: @@
-====== Turbulence Model ======
-===== Turbulence Model in ENVI-met =====
-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:
-{{ ::tke_equation.jpg?nolink |Prognostic equation of Turbulent Kinetic Energy (TKE)}}
-<WRAP centeralign>//Prognostic equation of Turbulent Kinetic Energy (TKE)//</WRAP>
-The second equation is similar but describes the Dissipation Rate of TKE (ε or eps):
-{{ ::eps_equation.jpg?nolink |}}
-<WRAP centeralign>//Prognostic equation of dissipation rate of Turbulent Kinetic Energy (ε)//</WRAP>
-Finally, the Turbulent Exchange Coefficient Km is a result of both:
-{{ ::km_equation.jpg?nolink |Relation of Turbulent exchange Coefficient Km to TKE and ε}}
-<WRAP centeralign>//Relation of Turbulent exchange Coefficient Km to TKE and ε//</WRAP>
-As the result of the TKE-ε 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-ε equation. Once Km begins to be unstable, the TKE-ε 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:
-  * [[Two-Step Calculation Loops (Initialisation)]]
-  * [[Intelligent Troubleshooting via Relaxation]]
-  * [[Range Limiting]]
-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!**