Francis Turbine CFD Simulation

Description

Project Description

The present problem simulates the water flow inside a Francis water turbine. Water turbine is a turbomachinery that convert kinetic energy from water flow or potential energy from water height differences into rotational motion. Francis turbines are one of the types of water turbines that have the ability to use both kinetic and potential energy for power generation at the same time due to the location of their blades.

In this type of turbine, water flows into the helical chamber, because due to the circular structure of the blades, in order to improve the operational efficiency of the system, the flow of fluid colliding with the blades must be rotational. The water flow is then transferred to the turbine runner blades with a certain flow rate, and as a result, by rotating these blades by the water flow, the desired work is produced. Finally, the outflow of water from the turbine runner blades will be axial.

Project Description

In the present simulation, a flow of water with a flow rate of 1.996 kg.s-1 enters the inner chamber of the turbine. Frame motion is used to define the rotation of the blades inside the chamber and to create the resulting rotational flow around the blades. In fact, it is assumed that the area of water flow around the blades has a rotational motion relative to the blades; While the rotating blades have a rotational speed of zero relative to this rotating area.

Therefore, for the area related to water flow around the blades, the frame motion technique with a rotational speed of 158 rpm has been used, and for the blade walls, a moving wall boundary condition with a zero rotational speed ( The blade speed is used relative to the area in which it is located) is defined. The following figure shows a view of the Francis water turbine.

Francis Turbine Geometry & Mesh

The geometry is designed using Design Modeler software. In the design of the present model, two main parts have been considered, which include fixed walls that have fixed vanes with fixed angles, and moving walls that have rotating vanes. The following figure shows a view of the geometry.

The meshing of the model has been done using ANSYS Meshing software and the mesh type is unstructured. The element number is 4653160. Also, the quality of the mesh is considered finer in the areas close to the blades. The following figure shows the mesh.

Francis Water Turbine CFD Simulation

To simulate the present model, several assumptions are considered:

• We perform a pressure-based solver.
• The simulation is steady.
• The gravity effect on the fluid is equal to -9.81 m.s-2 along the z-axis.

A summary of the defining steps of the problem and its solution is given in the following table:

	Models
Viscous model		k-epsilon
	k-epsilon model	RNG
	near-wall treatment	standard wall function
	Boundary conditions
Inlet		Mass flow inlet
	mass flow rate	1.996 kg.s-1
Outlet		Pressure outlet
	gauge pressure	0 Pascal
Outer walls		Wall
	wall motion	stationary wall
Inner blades
	wall motion	moving wall
	Solution Methods
Pressure-velocity coupling		SIMPLE
Spatial discretization	pressure	PRESTO
	momentum	second order upwind
	turbulent kinetic energy	first order upwind
	turbulent dissipation rate	first order upwind
	Initialization
Initialization method		Standard
	gauge pressure	0 pascal
	y-velocity	0.5952913 m.s-1
	x-velocity, y-velocity	0 m.s-1

Results

At the end of the solution process, two-dimensional and three-dimensional contours related to pressure, velocity, as well as path lines and velocity vectors are obtained. They are plotted in X-Z and Y-Z sections. Also, the pressure distribution contour on the wall surfaces is obtained.

There is a mesh file in this product. By the way, the Training File presents how to solve the problem and extract all desired results.