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RE: Secondary flow

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Abdelrahman Abdou, modified 1 Month ago.

Secondary flow

Keen Forecaster Posts: 6 Join Date: 9/2/20 Recent Posts
I have a question about simulating spiral flow.My case is 2DH simulation of a straight channel and I want to activate the spiral flow in my model. I activated the secondary flow in the process window but when I generate *.mor file to change Espir (calibration factor of spiral flow) it is not there, however, I checked another model used  and I opened the *.mor file and the Espir is addressed there. Is it a problem of the different versions or should I do something to my model?
here is a link to the photo of different *.mor files : https://drive.google.com/file/d/1LC4bYZcRzdrlpGpILnmlFn2tob9hKfJt/view?usp=sharing
what about the initial value of secondary flow in the initial condition, I put it (v=0m/s), is it ok?What is the appropriate value for Espir?
Victor Chavarrias, modified 1 Month ago.

RE: Secondary flow

Famous Fortune teller Posts: 41 Join Date: 4/24/20 Recent Posts
[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. 
Victor Chavarrias, modified 1 Month ago.

RE: Secondary flow

Famous Fortune teller Posts: 41 Join Date: 4/24/20 Recent Posts
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?
Victor Chavarrias, modified 1 Month ago.

RE: Secondary flow

Famous Fortune teller Posts: 41 Join Date: 4/24/20 Recent Posts
[date incorrect, post copied after moving to new threat]---


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

RE: Secondary flow

Famous Fortune teller Posts: 41 Join Date: 4/24/20 Recent Posts
Abdelrahman Abdou, modified 9 Minutes ago.


It works well.Thank you for your help emoticon