Waterfall CFD Simulation Using Two-Phase Flow

Description

Introduction

Flow separation from a surface or separation of two-phase flows (natural waterfall) is one of the most important issues in fluid mechanics. Flow separation due to the specific shape of the geometry or flow can have positive or negative effects on its surroundings. Therefore, it has always been tried to control this phenomenon as much as possible and to investigate the possible effects and consequences.

Project Description

In this project, the separation of laminar fluid flow from a surface which is easily seen in a natural waterfall is investigated and analyzed. This separation occurs only due to gravity and the difference in height between the two surfaces. Water enters the fluid domain with a mass flow of 20 Kg/s and falls when the lower bed is finished, converting into a waterfall. K-epsilon and implicit VOF models are activated to analyze this flow.

waterfall Geometry & Mesh

The geometry and the mesh for this project are created inside Gambit®. The geometry includes a mass-flow inlet, 3 pressure outlets, several symmetry and wall boundary conditions and 9 different partitions.  The mesh type used for this geometry is structured and the element number is 626400.

Waterfall CFD Simulation Settings

The key assumptions considered in this project are:

• Simulation is done using pressure-based solver.
• The present simulation and its results are considered to be steady and do not change as a function time.
• The effect of gravity has been taken into account and is equal to -9.81 in Y direction.

The applied settings are summarized in the following table.

	Models
Viscous model		k-epsilon
	k-epsilon model	RNG
	near wall treatment	standard wall function
Multi phase		VOF
	Formulation	Implicit
	Phase 1	Air
	Phase 2	Water
	Boundary conditions
Inlet		Mass-flow inlet
	Water mass-flow rate	20 Kg/s
	Turbulent kinetic energy	1 m2/s2
	Turbulent dissipation rate	1 m2/s3
Outlets		Pressure outlet
	Gauge pressure	0 Pa
	Turbulent kinetic energy	1 m2/s2
	Turbulent dissipation rate	1 m2/s3
Walls
	wall motion	stationary wall
	Solution Methods
Pressure-velocity coupling		Simple
Spatial discretization	pressure	PRESTO!
	Volume fraction	Modified HRIC
	momentum	second order upwind
	Turbulent kinetic energy	first order upwind
	Turbulent dissipation rate	first order upwind
	Initialization
Initialization method		Standard
	gauge pressure	0 Pa
	velocity (x,y,z)	(0,0,0) m/s
	water volume fraction	0
	Turbulent kinetic energy	1 m2/s2
	Turbulent dissipation rate	1 m2/s3

Results

Contours of pressure, velocity, volume fraction, etc. are presented.

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