$$$$ KEPSILON NOTICE CHAT 11/09/12 21:16:43 7124 DATE 11/09/12 Procedure KEPSILON Voir aussi : ------------------ SYNTAXE ( EQEX ) : Cf operateur EQEX _________________ 'OPER' 'KEPSILON' RO UN MU DT (RGB TN) 'INCO' 'KN' 'EN' Description : _____________ This procedure computes the effective (turbulent + molecular) viscosity obtained by the transient solution (one time step) of the K-epsilon model. The result is stored in the 'INCO' table at the entry MUF' for effective dynamic viscosity. For standard version (high Reynolds model) the Production/dissipation ratio is limited to 10 (proposed by Menter). Warning: when the aspect ratio of mesh cells is greater than 20, lack of convergence may occur. Comments : __________ RO Density FLOTTANT or MOT UN Velocity field CHPOINT VECT SOMMET or MOT MU dynamic viscosity (Kg/m/s) FLOTTANT or MOT DT Time step FLOTTANT or MOT RGB Coefficient for the buoyancy term VECTEUR or MOT TN Temperature field CHPOINT SCAL SOMMET ou MOT A type MOT coefficient indicates that the operator search for the coefficient in the INCO table referenced by the given MOT. The options of this procedure are taken in a LISTMOTS object referenced at 'ALGO_KEPSILON' entry of rv procedure. ex : RV.'ALGO_KEPSILON'= MOTS 'Bw' 'Cnu'; If this entry does'nt exist the default values are taken. The list of availlable options is: IMPR,RNG,Filtre,Bw,Cnu,Nut,Fi, M2M,CSTE,Ret,KL,KLbr,Chien,Sharma,Jones,Lam The default options are : Nut and the standard k - epsilon model IMPR: Print options RNG : RNG k - epsilon model Filtre : Filtered K-epsilon model. The length scale is filtered by a value given in RV.'INCO'.'Echl'. This model allows to better capture instationarities or large scale instabilities (greater than the size filter). The size of the filter can be taken to the size of a mesh element. Bw : A realisability condition is imposed on the maximum turbulent shear stresses. (u'v')/k < 0.3 (Bradshaw) DEFAULT = FAUX Cnu : The so called Cnu 'constant' is related to the equilibrium coefficient Ksi=(Nut P)/epsilon : Cnu = F(1./Ksi) (See Rodi) For Ksi = 1 Cnu=0.09. DEFAULT = FAUX Nut : The intermediate variables used are Teta and Nut DEFAULT = VRAI Fi : The intermediate variables used are Teta and Fi DEFAULT = FAUX M2M : Constantes of Mohammadi and Medic. DEFAUT = FAUX. CSTE: The constants of the model are taken in the INCO table at entries 'cnu' 'c2' 'sgk' 'sge' and c1 constant being deduced. DEFAUT = FAUX. KL : K-L model. The turbulence length scale has to be specified 'Echl' entry in 'INCO' table (FLOTTANT or CHPOINT SCAL SOMMET). Numerically this model is obtained replacing the PDE for epsilon by epsilon = k**1.5 / L. The inputs have to be completed like the K-epsilon model. In particular it is necessary to specify the epsilon unknown and the boundary conditions on espilon must verify the above relationship with the length scale. KLbr: Low-Reynols K-L model. It is the model proposed by Wolfshtein (1967) and Yap (1987). Instead of lengthscale we have to specify the distance to the walls: 'dparoi' entry (CHPOINT SCAL SOMMET) in 'INCO' table. The boundary conditions at the wall are U=0,K=0 and Epsilon=0. The first cell must be in the viscous sublayer (y+ < 1). Chien: Low-Reynolds k-epsilon model of Chien. This model requires the distance to the wall for each grid point: entry 'INCO'.'dparoi' (same support as k or epsilon), and the computation of y+ (entry 'INCO' 'yplus'). This last entry needs to be computed at each time step via a procedure. The boundary conditions and the mesh requirement are the same as previous. See as example canal-Chien.dgibi Sharma: Low-Reynolds k-epsilon model of Launder and Sharma. This model does'nt require any additional information which is a certain advantage. The boundary conditions and the mesh requirement are the same as previous. See as example canal-Sharma.dgibi Jones: Low-Reynolds k-epsilon model of Jones and Launder. This model is almost the same as Launder-Sharma except the values of the constants. Lam: Low-Reynolds k-epsilon model of Lam and Bremhorst. (in test) *-------------------------- in progress -------------------------------- Chien: Low-Reynolds k-epsilon model of Chien. This model requires the distance to the wall for each grid point: entry 'INCO'.'Yparoi' (same support as k or epsilon). *-------------------------- in progress -------------------------------- List of CHPOINTs (SCAL SOMMET) created in the 'INCO' table TKTE teta=k/epsilon NUTI intermediate value of NUT FI Fi unknown PRODT turbulent Prodution / NUT = (grad U + grad^t U)grad U TKTI teta=k/epsilon intermediate Ksi factor : nut PRODT / epsilon MUF effective dynamic viscosity (turbulent+molecular)
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