water curtain

[opti...@gmail.com]

Hi,

I am trying to create a water curtain over a height of 100m. To do this, I placed nozzles on the top of some structure and points it outwards. By right, I should see the water curtain being created, shooting from top (100m) to the ground. However, I only see it shooting out from 100m to 80m and not all the way to the ground. So is it possible to model such a water curtain from 100m to ground?

My code as such:

&SPEC ID='WATER VAPOR' /
&PART ID='water',SPEC_ID='WATER VAPOR',DIAMETER=300. /

&PROP ID='water spray', PART_ID='water', FLOW_RATE=5., FLOW_TAU=0, PARTICLE_VELOCITY=30., SPRAY_ANGLE=0.,45. /

&DEVC ID='nozzle', PROP_ID='water spray', XYZ=1480,340,100, ORIENTATION=1,0,0, QUANTITY='TIME', SETPOINT=0., ID='noz_11' /
&DEVC ID='nozzle', PROP_ID='water spray', XYZ=1480,360,100, ORIENTATION=1,0,0, QUANTITY='TIME', SETPOINT=0., ID='noz_12' /
&DEVC ID='nozzle', PROP_ID='water spray', XYZ=1480,380,100, ORIENTATION=1,0,0, QUANTITY='TIME', SETPOINT=0., ID='noz_13' /

[opti...@gmail.com]

Grateful if someone can help me with this. I referred to another similar thread but there was no explicit answer. I do not need to get a "sheet" of water, but at least it should flow from top to bottom, somewhat like a waterfall. Anyone has experience modelling this?

https://groups.google.com/forum/#!topic/fds-smv/mTEHAFmPckM

[dr_jfloyd]

It isn't possible to diagnose your problem from the snippet of input you gave.  

Make sure you are using the latest release of FDS and Smokeview.

If the rest of your input file is complicated, I would recommend testing an input file that is nothing but your MESH and the sprinkler inputs.

Another thing to check is are you hitting the default maximum number of droplets (at which point old ones are killed so new can be inserted)?  Try going to two and then one sprinkler.  Do you see drops further down? If so you may need to increase the maximum number of droplets.

If you still have problems after trying the above, create a very simple input demonstrating the problem and post it to the issue tracker.

[Brad Casterline]

Dr. Floyd, could Particle AGE be a factor? Do they 'live' long enough (by default) to go 100m? 

[dr_jfloyd]

The default AGE is 100000 s.

[Jack F.]

I'm very curious what scenario you have with a 100 meter high water curtain at 5 l/min?

[opti...@gmail.com]

Its somewhat like a drencher system...

This is the code that I have written. The spray works fine but does not flow downwards and just disappears in the air. Anyone can advise what's wrong?

&HEAD CHID='scdf2', TITLE='nozzle' /

&MESH IJK=100,200,60, XB=140,160,20,60,0,12 /

&TIME T_END=100 /

&SPEC ID='WATER VAPOR' /
&PART ID='water',SPEC_ID='WATER VAPOR',DIAMETER=300. /

&VENT MB='XMIN', SURF_ID='OPEN' /
&VENT MB='XMAX', SURF_ID='OPEN' /
&VENT MB='YMIN', SURF_ID='OPEN' /
&VENT MB='YMAX', SURF_ID='OPEN' /
&VENT MB='ZMAX', SURF_ID='OPEN' /

&PROP ID='water spray', PART_ID='water', FLOW_RATE=150., FLOW_TAU=0, PARTICLE_VELOCITY=30., SPRAY_ANGLE=30.,80. /

&DEVC ID='nozzle', PROP_ID='water spray', XYZ=148,30,10, ORIENTATION=-1,0,0, QUANTITY='TIME', SETPOINT=0., ID='noz_11' /
&DEVC ID='nozzle', PROP_ID='water spray', XYZ=148,40,10, ORIENTATION=-1,0,0, QUANTITY='TIME', SETPOINT=0., ID='noz_12' /
&DEVC ID='nozzle', PROP_ID='water spray', XYZ=148,50,10, ORIENTATION=-1,0,0, QUANTITY='TIME', SETPOINT=0., ID='noz_13' /

&SLCF PBY=50,  QUANTITY='VELOCITY', VECTOR=.TRUE. /
&SLCF PBX=160, QUANTITY='VELOCITY', VECTOR=.TRUE. /

&TAIL /

[Brad Casterline]

maybe they are evaporating due to friction?

 

(thanks Dr Floyd, it is not like me to NOT look something like default age up in the guide)

 

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[Andrew Louie]

Your sprinklers are pointing toward the XMIN boundary, 8m away from
it. Perhaps what you are seeing is the water is disappearing after it
crosses the XMIN boundary.

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[dr_jfloyd]

The most friction heating could possibly be would be the initial kinetic energy of the drop plus its potential energy.  This is ~1 kJ/kg of droplets.  This would raise the temperature by < 1 K.

[dr_jfloyd]

What version of FDS and Smokeview are you using?  Running the input you show above with FDS 6.1.2 SVN 20564 Win64 and Smokeview SVN 21966 after a couple of seconds I show drops all the way to the bottom as shown in the attached.

[Brad Casterline]

I apologize for keep piping in but I changed the Mesh to this:

 

&MESH IJK=25,50,125, XB=140,160,20,60,0,100 /

 

and the device lines to this:

 

/&DEVC ID='nozzle', PROP_ID='water spray', XYZ=148,30,98, ORIENTATION=-1,0,0, QUANTITY='TIME', SETPOINT=0., ID='noz_11' /

&DEVC ID='nozzle', PROP_ID='water spray', XYZ=148,40,98, ORIENTATION=-1,0,0, QUANTITY='TIME', SETPOINT=0., ID='noz_12' /

/&DEVC ID='nozzle', PROP_ID='water spray', XYZ=148,50,98, ORIENTATION=-1,0,0, QUANTITY='TIME', SETPOINT=0., ID='noz_13' /

 

and it reaches the floor.

 

I got access violation flowing all three, and I did not try the original stated 5 LPM.

 

Brad

---

From: fds...@googlegroups.com [mailto:fds...@googlegroups.com] On Behalf Of dr_jfloyd
Sent: Friday, March 20, 2015 2:38 PM
To: fds...@googlegroups.com
Subject: [fds-smv] Re: water curtain

 

What version of FDS and Smokeview are you using?  Running the input you show above with FDS 6.1.2 SVN 20564 Win64 and Smokeview SVN 21966 after a couple of seconds I show drops all the way to the bottom as shown in the attached.

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[dr_jfloyd]

Brad,

I ran the following with the 6.1.2 and stop at 25 s with no error (and particles went to the floor).  What version of FDS are you running and when did you see the error?

&HEAD CHID='scdf2', TITLE='nozzle' /

&MESH IJK=25,50,125, XB=140,160,20,60,0,100 /

&TIME T_END=100 /

&SPEC ID='WATER VAPOR' /

&PART ID='water',SPEC_ID='WATER VAPOR',DIAMETER=300. /

&VENT MB='XMIN', SURF_ID='OPEN' / 

&VENT MB='XMAX', SURF_ID='OPEN' / 

&VENT MB='YMIN', SURF_ID='OPEN' / 

&VENT MB='YMAX', SURF_ID='OPEN' / 

&VENT MB='ZMAX', SURF_ID='OPEN' /

&PROP ID='water spray', PART_ID='water', FLOW_RATE=150., FLOW_TAU=0, PARTICLE_VELOCITY=30., SPRAY_ANGLE=30.,80. /

&DEVC ID='nozzle', PROP_ID='water spray', XYZ=148,30,98, ORIENTATION=-1,0,0, QUANTITY='TIME', SETPOINT=0., ID='noz_11' /

&DEVC ID='nozzle', PROP_ID='water spray', XYZ=148,40,98, ORIENTATION=-1,0,0, QUANTITY='TIME', SETPOINT=0., ID='noz_12' /

&DEVC ID='nozzle', PROP_ID='water spray', XYZ=148,50,98, ORIENTATION=-1,0,0, QUANTITY='TIME', SETPOINT=0., ID='noz_13' /

&SLCF PBY=50,  QUANTITY='VELOCITY', VECTOR=.TRUE. / 

&SLCF PBX=160, QUANTITY='VELOCITY', VECTOR=.TRUE. /

&TAIL / 

[opti...@gmail.com]

Thanks, problem solved! I actually ran with a coarser mesh, but upon switching to the one I posted, it worked!

[opti...@gmail.com]

Hi, i wanna ask whether FDS is capable of simulating the interaction between the water curtain and a gas eg chlorine. that is, if chlorine is in contact with the water curtain, will some of it be dissolved in the water?

[Kevin]

No

[Brad Casterline]

Jason, I ran that with 6.1.1 SVN 19882 Compile Date Thu, 10 Jul 2014.

I know it is not the latest, but for various reasons that is installed on the computer I used.

 

thanks, Brad

To view this discussion on the web visit https://groups.google.com/d/msgid/fds-smv/05389ea0-1d3d-4cdc-b391-76b57854d393%40googlegroups.com.

[Brad Casterline]

Oops... I got the error around 14 sec If I remember right, But, I just ran the input below on the same machine and it is fine! I have v5 and v6 and I thought the access  violation was due to opening in SMV5 , then SMV6, while it was running, but I cannot produce the same error again!!!  

 

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[opti...@gmail.com]

Dear All,

I need your help in my scenario:

I am simulating a water curtain (produced by nozzles) to protect an installation against gas leak (ammonia). For protection using water curtains, the gas leak is usually diluted via dispersion and dissolution. I understand that FDS is not able to simulate the dissolution portion. However, when I run the simulations, and evaluated the concentrations, it seems that the concentration with the water curtain at a particular point and the concentration w/o the water curtain is about the same, except that there is a time delay for the simulation with the water curtain, ie it takes longer for the same concentration to reach a particular point.

I would like to ask whether FDS is able to simulate the 'dispersion' of the gas leak. By right it should, otherwise how would it affect smoke movement. If yes, why didn't the concentration decrease?

Grateful for any good advice/guidance here.

[Kevin]

Yes, FDS simulates the transport of specified gases. I suggest you create a simple test case involving just the gas leak to ensure that FDS is doing what you think it should. Best to create a case that you can compare to an actual experiment or some analytical solution to a simple flow problem.

[opti...@gmail.com]

Hi Kevin,

Thanks for yr reply. I have actually created the simulation involving gas leak and water curtain. The simulation is as per what I envisaged, but the results are not. Meaning I thought the gas concentration will be significantly reduced by the water curtain, but it did not. In actual physical experiments, it was proven that the concentration will be reduced by dispersion and dissolution.

Right now, I was hoping FDS can simulate the dispersion portion, but it somehow did not... Therefore I need advice on why the dispersion did not occur for FDS or whether I should simulate the scenario differently.

Thanks.

[F-Sim.de]

Thanks for yr reply. I have actually created the simulation involving gas leak and water curtain. The simulation is as per what I envisaged, but the results are not. Meaning I thought the gas concentration will be significantly reduced by the water curtain, but it did not. In actual physical experiments, it was proven that the concentration will be reduced by dispersion and dissolution.

Right now, I was hoping FDS can simulate the dispersion portion, but it somehow did not... Therefore I need advice on why the dispersion did not occur for FDS or whether I should simulate the scenario differently.

 
Your description of your problem is far too vague. If you want someone to be able to help you, like Kevin suggested: create a very simple test case showing your problem.

[opti...@gmail.com]

Actually, my question is simple, whether the water curtain will interact with the gas and cause it to disperse or move away....

Nonetheless, will try to share my script later. Thanks.

[Simo]

Actually, you presented two questions.

First one it simple: Yes, the water curtain will interact with the gas. In FDS the droplets exchange momentum, heat (convective and radiation) and evaporate. Condencation or dissolution, among many other things are not included in the model, howeer.

The second question (Does this interaction cause the gas to disperse or move away?) is not simple. The answer depends on the conditions and scenario. Therefore you need to prepare the test case where you have a reason to expect that something happens, and demonstrate that FDS is not doing what is should.

[opti...@gmail.com]

This is the case. Thanks Simon for clarifying on the first part. After running the case, it seems that the concentration of chlorine is not reduced, which should be expected if the water causes dispersion of the gas. Can anyone explain why the concentration is not reduced?

Grateful for help.

&HEAD CHID='water curtain', TITLE='chlorine_without obstructions' /

&MESH IJK=40,120,40, XB=0,20,20,80,0,20 /
&MESH IJK=60,30,10, XB=20,140,20,80,0,20 /
&MESH IJK=50,120,40, XB=140,165,20,80,0,20 /

&TIME T_END=600 /

&SPEC ID='CHLORINE',MW=71, MASS_EXTINCTION_COEFFICIENT=8700. /
&SURF ID='CHLORINE RELEASE', MASS_FLUX(1)=0.04, SPEC_ID(1)='CHLORINE'/
&VENT XB=3,4,50,51,0,0, SURF_ID='CHLORINE RELEASE', COLOR='RED'  /

&DUMP SMOKE3D_QUANTITY='MASS FRACTION', SMOKE3D_SPEC_ID='CHLORINE' /

&SPEC ID='WATER VAPOR' /
&PART ID='water',SPEC_ID='WATER VAPOR',DIAMETER=300. /

&VENT MB='XMIN', SURF_ID='OPEN' /
&VENT MB='XMAX', SURF_ID='OPEN' /
&VENT MB='YMIN', SURF_ID='OPEN' /
&VENT MB='YMAX', SURF_ID='OPEN' /
&VENT MB='ZMAX', SURF_ID='OPEN' /

&MISC MEAN_FORCING(1:2)=.TRUE.,.TRUE., U0=0.5 /

&PROP ID='water spray', PART_ID='water', FLOW_RATE=0.05, FLOW_TAU=0, PARTICLE_VELOCITY=10., SPRAY_ANGLE=40.,60. /

&DEVC ID='nozzle', PROP_ID='water spray', XYZ=149,38,10, ORIENTATION=-1,0,0, QUANTITY='TIME', SETPOINT=0., ID='noz_11' /
&DEVC ID='nozzle', PROP_ID='water spray', XYZ=149,40,10, ORIENTATION=-1,0,0, QUANTITY='TIME', SETPOINT=0., ID='noz_13' /
&DEVC ID='nozzle', PROP_ID='water spray', XYZ=149,42,10, ORIENTATION=-1,0,0, QUANTITY='TIME', SETPOINT=0., ID='noz_15' /

&DEVC ID='nozzle', PROP_ID='water spray', XYZ=149,48,10, ORIENTATION=-1,0,0, QUANTITY='TIME', SETPOINT=0., ID='noz_21' /
&DEVC ID='nozzle', PROP_ID='water spray', XYZ=149,50,10, ORIENTATION=-1,0,0, QUANTITY='TIME', SETPOINT=0., ID='noz_23' /
&DEVC ID='nozzle', PROP_ID='water spray', XYZ=149,52,10, ORIENTATION=-1,0,0, QUANTITY='TIME', SETPOINT=0., ID='noz_25' /

&DEVC ID='nozzle', PROP_ID='water spray', XYZ=149,58,10, ORIENTATION=-1,0,0, QUANTITY='TIME', SETPOINT=0., ID='noz_31' /
&DEVC ID='nozzle', PROP_ID='water spray', XYZ=149,60,10, ORIENTATION=-1,0,0, QUANTITY='TIME', SETPOINT=0., ID='noz_33' /
&DEVC ID='nozzle', PROP_ID='water spray', XYZ=149,62,10, ORIENTATION=-1,0,0, QUANTITY='TIME', SETPOINT=0., ID='noz_35' /

&DEVC ID='ammonia', QUANTITY='VOLUME FRACTION', SPEC_ID='CHLORINE', XYZ=130,50,8, ID='front' /
&DEVC ID='ammonia', QUANTITY='VOLUME FRACTION', SPEC_ID='CHLORINE', XYZ=130,50,2, ID='front_bottom' /
&DEVC ID='ammonia', QUANTITY='VOLUME FRACTION', SPEC_ID='CHLORINE', XYZ=160,45,8, ID='bet12' /
&DEVC ID='ammonia', QUANTITY='VOLUME FRACTION', SPEC_ID='CHLORINE', XYZ=160,45,2, ID='bet12_bottom' /
&DEVC ID='ammonia', QUANTITY='VOLUME FRACTION', SPEC_ID='CHLORINE', XYZ=160,55,8, ID='bet23' /
&DEVC ID='ammonia', QUANTITY='VOLUME FRACTION', SPEC_ID='CHLORINE', XYZ=160,55,2, ID='bet23_bottom' /
&DEVC ID='ammonia', QUANTITY='VOLUME FRACTION', SPEC_ID='CHLORINE', XYZ=160,35,8, ID='1' /
&DEVC ID='ammonia', QUANTITY='VOLUME FRACTION', SPEC_ID='CHLORINE', XYZ=160,66,8, ID='3' /
&SLCF PBX=160, QUANTITY='VOLUME FRACTION', SPEC_ID='CHLORINE', CELL_CENTERED=.TRUE. /
&SLCF PBX=140, QUANTITY='VOLUME FRACTION', SPEC_ID='CHLORINE', CELL_CENTERED=.TRUE. /

&SLCF PBY=50,  QUANTITY='VELOCITY', VECTOR=.TRUE. /
&SLCF PBX=160, QUANTITY='VELOCITY', VECTOR=.TRUE. /

&TAIL /

[opti...@gmail.com]

Hi, I have posted, grateful for some advice, thanks

[dr_jfloyd]

Units for FLOW_RATE on PROP per the User's Guide are L/min (not kg/s).  FLOW_RATE=0.05 means each head is flowing less than a gram of water per second.  

[opti...@gmail.com]

Hi, this model is a scaled down model of 0.1. Meaning I reduced the distance by dividing by 10 so that the analysis time can be faster. Consequently, the flow rate of the water is reduced by 1000 times since volume = distance^3. That explains the low flow rate. But nonetheless smoke view is giving me a very good water curtain.

Hence I do not think that the low flow rate is the reason for the gas concentration to remain high.

Any other advice is appreciated. Thks

[dr_jfloyd]

With your flow speed of 0.5 m/s you are trying to influence the movement of ~720 kg/s of gas (20 m high x 60 m wide x 0.5 m/s x 1.2 kg/m^3)  with 0.075 kg/s of water.  On what basis do you feel you will see any significant impact on the gas via momentum interacations with the water?

[opti...@gmail.com]

Hi, can u elaborate more on how u obtained 720kg/s? I thought my gas production rate is just 0.04x1x1=0.04kg/s?

[dr_jfloyd]

The water spray does not act on the chlorine alone.  The water spray interacts via momentum exchange with the entire volume of air flowing through your domain.  You have specified an ambient flow of 0.5 m/s in the u-direction.  Therefore you have air moving at 0.5 m/s through a domain that measures 20 m x 60 m.  At ambient temperature and pressure, air has a density of ~1.2 kg/m^3.  So you have 20 m x 60 m x 0.5 m/s x 1.2 kg/m^3 = 720 kg/s of gas flowing through your domain.  You are trying to influence that with 0.075 kg/s of water. 

[opti...@gmail.com]

Hi, thanks for the enlightenment. Can you advise on a minimum flow rate to be used for the nozzles such that the water curtain is able to create the dispersion effect?

[dr_jfloyd]

I suggest you research the literature on the subject.  What has prior research shown works in terms of spray density (both flow rate and particle size)?  To what extent can you replicate the results of any prior research with FDS? 

You should probably also consider your domain and boundary conditions.  If you cover the entire width of your domain with spray nozzles and impose mean forcing, you will force FDS to drive air through the water curtain (it is what you have told it to do)

[opti...@gmail.com]

Hi, the literature research was already done before I began the simulation. The actual flow rate of a nozzle is about 50L/min, but with a scale factor of 0.1, it was reduced 1000 times to 0.05L/min. I can try increasing the flow rate to gauge the effects.

You brought up another interesting point. Actually I was merely trying to simulate wind in the x direction by using the mean forcing code. Is there any other way of having wind but not 'forcing' the gas through the water curtain?

Thanks

[dr_jfloyd]

I don't think your assumption that the spray flow rate scales with volume is correct. 

The real experiment had a 600 m long row of nozzles at a height of 100 m? That is an impressive experimental setup.

You haven't given the wind any place to divert around the spray as the spray goes across then entire width of the domian.  You may need to move the domain boundaries out.

[Simo]

Also, you may want to consider specifying the wind as a vertical velocity boundary condition to make sure that the 'forcing' is not making too much violence to the flow field inside the spray region.

[opti...@gmail.com]

What do you mean by moving the domain boundaries out? Ymax, Ymin and Zmax are all open boundaries, so why cant the wind go beyond the boundaries?

Also, referring to your earlier reply, I am exploring other ways to specify wind so that the wind will not be 'forced' to go through the water curtain. Will this be better?

&MISC TMPA=34., LAPSE_RATE=-0.01, U0 = 0.5. /

[opti...@gmail.com]

May I ask how do I do that? This is my wind script:

&MISC MEAN_FORCING(1:2)=.TRUE.,.TRUE., U0=0.5 /

[dr_jfloyd]

Take a look at the attached image.  The blue oval is your water curtain.  The water curtain is going to act like an obstruction to the wind. Some of the wind will divert around the curtain as indicated by the streamlines. You have drawn your computational domain as shown with the dotted line.  Think if the water curtain were actually a solid wall.  In real life you would form a recirculation region downstream of the wall.  But if the domain boundary is exactly as big as the wall, how will that happen?  The CFD model only knows what is happening inside the domain, it doesn't know anything about flow outside of the domain. If you move the boundary away from the wall at some point the open boundary will be far enough that it no longer prevents you from getting a reasonable flow solution downstream of the wall.  

[opti...@gmail.com]

Thanks for yr detailed explanation, I know what you mean. I will expand the sides and top boundaries.

For a more realistic wind just like the atmosphere, should I remove the mean forcing?

[dr_jfloyd]

This is not a use that we have experience with (there are no water curtain examples in the V&V guides). You will have to experiment with different approaches to determine what works.

[Eric Wang]

Hi jfloyd

            I am looking for thr related issur about the effectness of water curtain to dilute chemicals concentration. In fact , I had done a case to evaluate the performance of water curtain to diluate HCl gas dispersion by FDS.

            Until today, to my suprise, I saw that you writted before " there are no water curtain examples in the V&V guides".

            Is it means that we use FDS to predict the performance of water curtain is not correct? especial in dilution application?

            Because the model of water curtain is not pass V&V approve. 

dr_jfloyd於 2015年4月14日星期二 UTC+8下午11時17分38秒寫道：

[Kevin]

There are two examples of radiation attenuation by water sprays in the FDS Validation Guide, called LEMTA and BRE Sprays.

[Simo]

Plus VTT_Sprays, which represents attenuation in water mist

[dr_jfloyd]

Water spray in fds will not adsorb soluable species.

[Eric Wang]

TO jfloyd

              So the concrntration of HCl, NH3...that  after water curtain will reduced and this phenomenon is not "diluation"? 

              Although in real world, hydrogen chloride can be removed by rain. And most of factories, we use water curtain to

              remove hydrogen chloride.

              I just want to clear to know that there is no adsorb behavior between HCl vapor and water in FDS model. But in real case,

              HCl vapor does dissolved by water. right?

              And what kind of mechanism and/or mathmatic model in FDS?

              Thanks for your reply.

dr_jfloyd於 2015年12月8日星期二 UTC+8上午3時56分34秒寫道：

[dr_jfloyd]

Water droplets in FDS do not absorb species. Read the Technical manual for a detailed discussion of the equations solved for droplet transport, evaporation, and heat transfer.

[Eric Wang]

   Thank you, jfloyd
    I have search many paper about this issue. Share with you as bellow.

   

Experimental study of effective water spray curtain application in dispersing liquefied natural gas vapor clouds

1. Morshed A. Rana,
2. Benjamin R. Cormier,
3. Jaffee A. Suardin,
4. Yingchun Zhang and
5. M. Sam Mannan^*

Article first published online: 28 OCT 2008

      In this paper, they list 4 mechanisms for water curtain how to reduce concentration. And the absorption is one of mechanisms, but the effectiveness is less than others. And the movement of water curtain is the main factor to stop the gas dispersion( in confined space).

      Based on these reasons, that's why we still can use FDS to predict the performance of water curtain. right?

     

     
dr_jfloyd於 2015年12月8日星期二 UTC+8上午9時59分11秒寫道：

[dr_jfloyd]

FDS will predict the effects of drag. This requires that you be able to accurately describe the spray distribution (drop size distribution and spray pattern) from the nozzles. For a species like natural gas where absorption is not the primary mechanism, provided you can accurately define the spray, then FDS would be capable of modeling the drag effects. 

[Eric Wang]

Thanks!

dr_jfloyd於 2015年12月8日星期二 UTC+8下午8時20分35秒寫道：