[date incorrect, post copied after moving to new threat]---
Hi Abdelrahman,
When you 'activate secondary flow' (i.e., in the mdf-file or mdu-file), you are accounting for secondary flow in the solving the flow equations and you are solving the advection-diffusion equation for the secondary flow intensity. If also accounting for morphodynamic development, the flag 'Espir' in the mor-file is of interest, as it wheights the effect of the secondary flow intensity in changing the direction of the near-bed flow velocity, which is used in computing the direction of the bed-load sediment transport. 
The GUI generates the basic files for running a simulation. Nevertheless, there is much more input than written by the GUI. In all files in Delft3D, there is no specific order in the input and if something is not specified is left to the default value. The flag 'Espir' in the mor-file does not appear automatically when you active secondary flow. Hence, you are using the default value which is 0. This means that, by default, the near-bed velocity has the same direction as the depth-averaged flow velocity. A value of 'Espir' equal to 1 causes the near-bed flow velocity to be deflected by the theoretical value of the secondary flow intensity. As the input is double, a value equal to 0.5 reduces the theoretical value by 50%. When you run a simulation, chek in the dia-file (from diagnosis) that the values that you input are read by Delft3D. 
You are modelling a straight channel and I assume that the initial condition is something like normal flow or no flow. In this case, the curvature of the streamlines is 0 and the initial secondary flow intensity is also 0. Hence, it is reasonable to use as initial condition 0 secondary flow intensity. I do not know the details of your simulation but it is relevant to consider the following. If your simulation is a straigth channel, secondary flow can only arise if a pattern of bars appears in your model causing curvature of the streamlines. This will occur in a sufficiently wide channel. Consider also that, as secondary flow is considered a constituent (such as salinity and temperature) the diffusion coefficient employed in computing the advection-diffusion equation is the diffusivity and not the viscosity. 

Abdelrahman Abdou, 


Hi Victor,

Thanks for your explanation it helps a lot.In my case, I have a wide straight channel and I expect multiple bar formation as (m>3).I checked the dia.file and I found Espir =0. so I think I need to change the value of Espir to 1 instead of the default value(=0).how can I change it while it is not flagged in the *mor file?

[date incorrect, post copied after moving to new threat]---


simply add it to the mor-file under the block [Morphology]. E.g.:
----

	1 [MorphologyFileInformation]
	1    FileCreatedBy    = V
	1    FileCreationDate = today :)
	1    FileVersion      = 02.00
	1
	1 [Morphology]
	1    EpsPar           = false                         Vertical mixing distribution according to van Rijn (overrules k-epsilon model)
	1    IopKCW           = 1                             Flag for determining Rc and Rw
	1    RDC              = 0.01                 [m]      Current related roughness height (only used if IopKCW <> 1)
	1    RDW              = 0.02                 [m]      Wave related roughness height (only used if IopKCW <> 1)
	1    MorFac           =  1.0000000E+00               [-]      Morphological scale factor
	1    MorStt           =  7.2000000E+03                     Spin-up interval from TStart till start of morphological changes
	1    Thresh           =  1.0000000e-003      [m]      Threshold sediment thickness for transport and erosion reduction
	1    BedUpd           = true                            Update bed levels during FLOW simulation
	1    UpdInf           = true                            Update bed levels at inflow boundaries during FLOW simulation
	1    CmpUpd           = false                            Update bed composition during flow run
	1    EqmBc            = true                          Equilibrium sand concentration profile at inflow boundaries
	1    DensIn           = false                         Include effect of sediment concentration on fluid density
	1    AksFac           =  1.0000000e+000      [-]      van Rijn's reference height = AKSFAC * KS
	1    RWave            =  1.0000000e+000      [-]      Wave related roughness = RWAVE * estimated ripple height. Van Rijn Recommends range 1-3
	1    AlfaBs           =  0.0000000e+000      [-]      Streamwise bed gradient factor for bed load transport
	1    AlfaBn           =  0.0000000e+000      [-]      Transverse bed gradient factor for bed load transport
	1    Sus              =  1.0000000e+000      [-]      Multiplication factor for suspended sediment reference concentration
	1    Bed              =  1.0000000e+000      [-]      Multiplication factor for bed-load transport vector magnitude
	1    SusW             =  1.0000000e+000      [-]      Wave-related suspended sed. transport factor
	1    BedW             =  1.0000000e+000      [-]      Wave-related bed-load sed. transport factor
	1    SedThr           =  1.0000000e-003      [m]      Minimum water depth for sediment computations
	1    ThetSD           =  0.0000000e+000      [-]      Factor for erosion of adjacent dry cells
	1    HMaxTH           =  1.5000000e+000      [m]      Max depth for variable THETSD. Set < SEDTHR to use global value only
	1    FWFac            =  1.0000000e+000      [-]      Vertical mixing distribution according to van Rijn (overrules k-epsilon model)
	1    EpsPar = false     [T/F] Only for waves in combination with k-epsilon turbulence model
	1                             TRUE : Van Rijn's parabolic-linear mixing distribution for current-related mixing
	1                             FALSE: Vertical sediment mixing values from K-epsilon turbulence model
	1    IopKCW = 1         [ - ] Flag for determining Rc and Rw
	1                             1 (default): Rc from flow, Rw=RWAVE*0.025
	1                             2          : Rc=RDC and Rw=RDW as read from this file
	1                             3          : Rc=Rw determined from mobility
	1    RDC    = 0.01      [ - ] Rc in case IopKCW = 2
	1    RDW    = 0.02      [ - ] Rw in case IopKCW = 2
	1    Espir  = 1.0       [ - ] Calibration factor spiral flow
	1    ISlope = 3         [ - ] Flag for bed slope effect
	1                             1          : None
	1                             2 (default): Bagnold
	1                             3          : Koch & Flokstra
	1    AShld  = 0.850000       [ - ] Bed slope parameter Koch & Flokstra
	1    BShld  = 0.500000       [ - ] Bed slope parameter Koch & Flokstra
	1    CShld  = 0.000000       [ - ] Bed slope parameter Koch & Flokstra
	1    DShld  = 0.000000       [ - ] Bed slope parameter Koch & Flokstra
	1    IHidExp= 1        [ - ] Flag for hiding & exposure
	1                             1 (default): none
	1                             2          : Egiazaroff
	1                             3          : Ashida & Michiue, modified Egiazaroff
	1                             4          : Soehngen, Kellermann, Loy
	1                             5          : Wu, Wang, Jia
	1    BcFil  = bcm.bcm
	1    ASKLHE = 0.0000000E+00

Abdelrahman Abdou, modified 9 Minutes ago.


It works well.Thank you for your help