Cohesion and Adhesion Effect on the Fluid, CFD Simulation

Description

Project Description

The present problem simulates the effect of cohesion and adhesion on a fluid using ANSYS Fluent software. In this project, it is assumed that there is a T-shaped computational domain; So that the fluid flow enters from the bottom and exits from the top. Initially, this area consists of only air, and then water flows at a rate of 0.001 m.s-1 vertically and upward into the computational domain. In this case, the water flow is in contact to the air flow and the wall surfaces. Therefore, the property of cohesion in water flow and adhesion property between the solid surfaces of the model and water flow will affect the kinetic behavior of water flow. The simulation is transient; So that the time step size is equal to 0.001 s.

Also, since this simulation is necessary to define two phases of air and water, the multiphase flow model is used. The multiphase model used in this simulation is the VOF model; Because this model can distinguish the interface between two fluids.

Geometry & Mesh

The present model is designed in two dimensions using Design Modeler software. The model’s geometry consists of a T-shaped computational region whose lower boundary with a smaller cross-section is defined as the flow input. Its upper boundary with a larger cross-section is defined as the output.

We carry out the model’s meshing using ANSYS Meshing software, and the mesh type is structured. The element number is 3024. The following figure shows the mesh.

Cohesion and Adhesion CFD Simulation

We consider several assumptions to simulate the present model:

• We perform a pressure-based solver.
• The simulation is unsteady.
• The gravity effect on the fluid is ignored.

The following table represents a summary of the defining steps of the problem and its solution:

Models
Viscous		Laminar
Multiphase Model		VOF
	formulation	implicit
	number of eulerian phases	2 (water & air)
	interface modeling	sharp
Boundary conditions
Inlet		Velocity Inlet
	velocity magnitude	0.001 m.s-1
	water volume fraction	1
	air volume fraction	0
Outlet		Pressure Outlet
	gauge pressure	0 pascal
	wall motion	stationary wall
Methods
Pressure-Velocity Coupling		SIMPLE
	Pressure	PRESTO
	momentum	second-order upwind
	volume fraction	compressive
Initialization
Initialization methods		Standard
	gauge pressure	0 pascal
	x-velocity & y-velocity	0 m.s-1
	water volume fraction	0

Cohesion and Adhesion Results & Discussions

At the end of the solution process, two-dimensional contours related to the volume fraction of each water and air phase are obtained. The performed solver is unsteady, and the total simulation time is defined as 0.1 s. Contours related to the volume fraction of water and air were obtained at different time intervals of 0.01 s. The images show that in both sections, which have a smaller and larger cross-section than the model, the flow cohesion is higher than the water adhesion on the wall surfaces. For this reason, the water flow tries to maintain its uniform shape and resist complete dispersion on solid surfaces.

There are a Mesh file and a comprehensive Training Movie that presents how to solve the problem and extract all desired results.