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Home / Examples / Fluid Analysis [Bernoulli] / Example 16: Capillary Action Analysis
Example 16: Capillary Action Analysis
General
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The model is two parallel plates and water sandwiched between them. Water rising by surface tension is solved with the VOF method.
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The volume fractions of air and water are solved.
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Unless specified in the list below, the default conditions are applied.
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Simulation Time: around 50 min
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Two methods are compared: manually specified timestep and automatically specified timestep.
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Obtain this session's project file. (Right-click and choose 'Save link as')
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Results will vary depending on Femtet version and the PC environment.
Analysis Space
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Item |
Settings |
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Analysis Space |
2D |
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Model Unit |
mm |
Analysis Conditions
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Item |
Tab |
Settings |
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Solver |
Solver Selection |
Fluid Analysis [Bernoulli] |
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Analysis Type |
Fluid Analysis |
Transient Analysis |
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Free Surface Analysis (VOF Method) |
Fluid Analysis |
Free Surface Analysis (VOF Method): Select |
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Free Surface Analysis (VOF Method) Setting |
Fluid Analysis |
Phase Setting: Register [000_Air] and [100_Water].
Take into account weight: Select Take into account surface tension: Select Phase Pair Setting:
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Detailed Settings |
Fluid Analysis Setup Details |
Volume Control Type: Cell-centered Base |
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Timestep [Manual] |
Transient Analysis |
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Timestep [Automatic]
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Transient Analysis |
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Meshing Setup |
Mesh |
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Model
Body Attributes and Materials
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Body Number/Type |
Body Attribute Name |
Material Name |
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0/Face |
Wall |
Wall |
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1/Face |
Wall |
Wall |
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2/Face |
Water |
100_Water * |
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3/Face |
Air |
000_Air * |
* Available from the material DB
The material property of "Wall" is set as follows.
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Material Name |
Tab |
Settings |
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Wall |
Solid/Fluid |
Solid |
Contact Angle is set in the body attributes of "Wall".
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Body Attribute Name |
Tab |
Settings |
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Wall |
Solid |
Multiphase Flow Setting (Contact Angle Setting): Specify for each body attribute: Select Phase Pair Setting:
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Boundary Condition
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Boundary Condition Name/Topology |
Tab |
Boundary Condition Type |
Settings |
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WaterInlet/Edge |
Fluid |
Inlet/Outlet |
Natural Inflow/ Natural Outflow Multiphase Flow Setting: Inflow Phase [100_Water] |
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AirInlet/Edge |
Fluid |
Inlet/Outlet |
Natural Inflow/ Natural Outflow Multiphase Flow Setting: Inflow Phase [000_Air] |
Results
The volume fraction contours of phase 2 at 0, 0.1 [s], 0.2 [s], 0.3 [s], 0.4 [s], and 0.5 [s] are shown below.
Phase 2 (Water) is indicated in red.
The diagram indicates that the water level initially increases up to 0.1 seconds and over time, it fluctuates and appears to be approaching a constant height.
However, within the given time range of 0 to 0.5 seconds, the water level has not yet converged to a constant value.
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Time: 0 [s] |
Time: 0.1 [s] |
Time: 0.2 [s] |
Time: 0.3 [s] |
Time: 0.4 [s] |
Time: 0.5 [s] |
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With contact angles taken into account, the calculation may not converge due to boundary oscillations.
About 10 times larger viscosity can suppress the undesired oscillations.
The steady-state is calculated where the surface tension and the weight are balanced.
Then, the change in viscosity does not affect the calculation of the steady-state.
Water level can be obtained from the equations below, which indicates water level does not depend on viscosity.
H [m]: Water Level, σ [N/m]: Coefficient of Surface Tension, θ: Contact Angle, ρ [kg/m3]: Water Density, g [m/s2]: Gravitational Acceleration, L [m]: Distance between the parallel plates
The calculation results with 10 times higher viscosity are shown below.
Water level converges to a certain value.
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Time: 0 [s] |
Time: 0.1 [s] |
Time: 0.2 [s] |
Time: 0.3 [s] |
Time: 0.4 [s] |
Time: 0.5 [s] |
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The water levels of the two models are acquired by [VOF CaptureBoundary Macro.xlsm] and shown in the graph below.
The water level converges to about 6.1 [mm].
The theoretical value of water level is,
h = 2 * 0.07 * 0.5 / (997 * 9.8 * 0.1e-3 ) = 7.16 [mm].
The theoretical water level is slightly higher than the calculated level.
In addition, for the viscosity set to 10 times, compare the result with that obtained using the automatic timestep setting of [Adjust referring to Courant number].
It is observed that almost the same results are obtained.
When [Manual] is set for the timestep, 5,000 steps are required for calculations; whereas if [Automatic] is set, about 1,600 steps are required. Setting to [Automatic] can lead to shorter calculation times.
