CFD Online Logo CFD Online URL
Home > Forums > OpenFOAM Programming & Development

Lagrangian equation in parcel.C

Register Blogs Members List Search Today's Posts Mark Forums Read

Like Tree1Likes
  • 1 Post By zarox

LinkBack Thread Tools Display Modes
Old   October 7, 2014, 04:37
Default Lagrangian equation in parcel.C
New Member
Join Date: Sep 2014
Posts: 7
Rep Power: 2
Cluap is on a distinguished road
Hi everybody,

I'm using OpenFOAM 1.7 with dieselSpray, in order to model gasoline droplets in a turbulent air flow with an Euler approach for the carrier phase and a lagrangian appproach for the droplets.

When I look at the lagrangian equation in parcel.C, I see :

U() = (U() + (timeRatio*Ucorr)+ gcorr*dt)/(1.0 + timeRatio); (Eq 1)

where U() is the droplet velocity, Ucoor the velocity of the gas seen by the droplet and timeRatio=dt/tauMomentum whith tauMomentum the droplet relaxation time.

But this looks very different from any classical lagrangian equation which should be something like :

dUp/dt = (Ug - Up)/Tp + g (Eq 2)

where Up is the velocity of the droplet, Ug the velocity of the gas seen by the droplet ant Tp the droplet relaxation time.

Discretized it should be something like :

U() = (1 - timeRatio)*U() + (timeRatio*Ucorr) + gcorr*dt (Eq 3)

So why does OpenFoam use Eq 1 instead of Eq 3 ?

Any help would be very appreciated.

Thank you.
Cluap is offline   Reply With Quote

Old   February 19, 2015, 11:43
Default Lagrangian particle velocity integration
New Member
Emeline Noel
Join Date: Dec 2013
Location: Paris
Posts: 13
Rep Power: 3
zarox is on a distinguished road
Hi Cluap,

Perhaps, you find the answer but I was asking my self the same question and found the solution so I would like to share with other and also to keep memories of the solution. Perhaps, it is obvious for personn who work in the lagrangian world.

First, I should say I was not aware of the tauMomentum so the Euler integration for parcel of openfoam was very strange for me. But I find that the drag force is can be express thanks to the tauMomentum :

tauMomentum = mp*|Uc-Up|/|Fd|

* Uc : carrier phase velocity
* Fd : Drag Force
* Up : particle velocity
* mp : mass of the particle


dUp/dt = Fd/mp + Fg/mp (1)

Using tauMomentum : Tp

dUp/dt = (Ug - Up)/Tp + g (2)

From there, I think the key is to know that in (2) OpenFOAM use the particle velocity at t+dt

Briefly, taking 1/Tp = A

Up(t+dt) = Up(t) + A*dt*(Ug-Up(t+dt)) + Fg*dt


Up(t+dt) = Up(t) + (A*dt*Ug+Fg*dt)/(1+A*dt)

A*dt = timeRatio

So you find the equation in OpenFOAM :

U() = (U() + (timeRatio*Ucorr)+ gcorr*dt)/(1.0 + timeRatio); (Eq 1)

May it can help someone!

JuanRodriguez likes this.
zarox is offline   Reply With Quote


dieselspray, lagrangian, parcel, particle

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

Similar Threads
Thread Thread Starter Forum Replies Last Post
Some problem of "Qcriterion.mcr& yuyuxuan Tecplot 8 September 23, 2014 11:53
Derivation of Momentum Equation in Integral Form Demonwolf Main CFD Forum 2 October 29, 2009 20:53
mass flow in is not equal to mass flow out saii CFX 2 September 18, 2009 08:07
Need help:about energy equation in CFX Stein CFX 4 July 2, 2009 22:31
Boundary conditions in a Poisson's equation? vincent Main CFD Forum 4 April 16, 1999 02:19

All times are GMT -4. The time now is 12:55.