View Issue Details
| ID | Project | Category | View Status | Date Submitted | Last Update |
|---|---|---|---|---|---|
| 0000822 | OpenFOAM | Bug | public | 2013-04-22 08:27 | 2013-05-13 17:30 |
| Reporter | Assigned To | ||||
| Priority | normal | Severity | major | Reproducibility | always |
| Status | resolved | Resolution | fixed | ||
| Summary | 0000822: Error in definition of lift force on Lagrangian particle | ||||
| Description | In src/lagrangian/intermediate/submodels/Kinematic/ParticleForces/Lift/LiftForce/LiftForce.C, line 144, the lift force on a discrete, Lagrangian particle is defined as: value.Su() = mass/p.rho()*p.d()/2.0*p.rhoc()*Cl*((p.Uc() - p.U())^curlUc); This cannot be correct, for two reasons. The first is that the units/dimensions of the expression is wrong. If I apply the standard SI units to the respective physical quantities, I get that the force gets units of kg*m^2/s^2, witch does not correspond to the (correct) dimension of force, that is mass times acceleration, with units kg*m/s^2. The second reason for this being incorrect, is that other sources, for example the paper "Transverse migration of single bubbles in simple shear flows" by Tomiyama et.al. (DOI: http://dx.doi.org/10.1016/S0009-2509(02)00085-4) clearly define the lift coefficient differently. I think the following definition from Tomiyama is what you have tried to use: F_L = - C_L*rho_c*pi*d^3/6*(V-U)^(curl(U)) where rho_c is the fluid/carrying phase density, V is the particle/bubble velocity and U is the fluid velocity. If I take your definition in LiftForce.C, and manipulate it a little bit, using that mass/p.rho() = volume = (4/3)*pi*(d/2)^3, I get that you actually have implemented: F_L = C_L*rho_c*pi*d^4/6*(U-V)^(curl(U)) and see that the expression is multiplied with one diameter "extra". In many cases, where the diameter is small (d<<1), this will lead to vanishingly small lift forces. My conclusion is that the following must be the correct expression for particle lift force: value.Su() = mass/p.rho()*p.rhoc()/2*Cl*((p.Uc() - p.U())^curlUc); This will give the correct dimension of force = mass * acceleration | ||||
| Tags | No tags attached. | ||||
| Date Modified | Username | Field | Change |
|---|---|---|---|
| 2013-04-22 08:27 |
|
New Issue | |
| 2013-05-13 17:30 |
|
Note Added: 0002193 | |
| 2013-05-13 17:30 |
|
Status | new => resolved |
| 2013-05-13 17:30 |
|
Fixed in Version | => 2.2.x |
| 2013-05-13 17:30 |
|
Resolution | open => fixed |
| 2013-05-13 17:30 |
|
Assigned To | => user2 |
