Centrifugal pump design and analysis

Aim: To design and perform the flow analysis of a centrifugal pump.

Description:

COMPUTATIONAL FLUID DYNAMICS: The field of study devoted to the solution of the equations of fluid flow through the use of a computer (or, more recently, several computers working in parallel). Modern engineers apply both experimental and CFD analyses and the two complement each other.

Reynolds Number

The transition from laminar to turbulent flow depends on the geometry, surface roughness, flow velocity, surface temperature, and type of fluid, among other things. After exhaustive experiments in the 1880s, Osborne Reynolds discovered that the flow regime depends mainly on the ratio of inertial forces to viscous forces in the fluid. This ratio is called the Reynolds number and is expressed for internal flow in a circular pipe as

Re=`ρVD/μ`,

Where V= average flow velocity (m/s),

D =characteristic length of the geometry (diameter in this case, in m),

= Density(kgm^-3)

μ = Dynamic viscosity of the fluid (Pa s)

• Re `<=`2300 laminar flow
• 2300`<=` Re `<=`4000 transitional flow
• Re 4000 turbulent flow

Turbomachines: Turbomachines are mechanical devices that either extract energy from a fluid turbine or add energy to a fluid pump as a result of dynamic interactions between the device and the fluid.

Pump: The purpose of a pump is to add energy to a fluid, resulting in an increase in fluid pressure, not necessarily an increase of fluid speed across the pump.

Centrifugal Pump:

One of the most common radial-flow turbomachines is the centrifugal pump. This type of pump has two main components: an impeller attached to a rotating shaft, and a stationary casing, housing, or volute enclosing the impeller. The impeller consists of a number of blades usually curved, also sometimes called vanes, arranged in a regular pattern around the shaft. As the impeller rotates, fluid

is sucked in through the eye of the casing and flows radially outward. Energy is added to the fluid by the rotating blades, and both pressure and absolute velocity are increased as the fluid flows from the eye to the periphery of the blades.

Figure 1: A side view and frontal view of a typical centrifugal pump. Fluid enters axially in the middle of the pump (the eye), is flung around to the outside by the rotating blade assembly (impeller), is diffused in the expanding diffuser (scroll), and is discharged out the side of the pump. We define r1 and r2 as the

radial locations of the impeller blade inlet and outlet, respectively; b1 and b2 are the axial blade widths at the impeller blade inlet and outlet, respectively

Performance Curve

The characteristic/performance curve of a pump is the interaction of two variables that describe its performance:

• HEAD: the energy by the unit of mass that the pump can supply to the fluid
• FLOW RATE: The quantity of fluid that goes through a section in a certain period of time

Objective:

• To obtain the Performance diagram.
• To obtain the relationship between Pressure ratio and mass flow rate.

Figure 2: Flow of the project.

Steps Followed:

• A centrifugal pump geometry is created using the video provided by skill Lync.
• Flow simulation is opened.
• Then some initial conditions are provided such as Fluid type, thermodynamic parameters, analysis type, rotation, etc.
• The flow domain is setup.
• Boundary conditions are provided.
• The discretization is done(meshing).
• For results the plots are created at required positions are created the cut plots.
• Then flow simulation is run.
• Desired outputs are saved.
• A parametric study is done for different velocities.
• Plots are exported and saved.

Results:

Velocity=10m/s

Figure 3: Velocity plot

Figure 4: Flow trajectory

Velocity=17.5m/s

Figure 5: Velocity plot

Figure 6: Flow trajectory

Velocity=25m/s

Figure 7: Velocity plot

Figure 8: Flow trajectory

Velocity=32.5m/s

Figure 9: Velocity plot

Figure 10: Flow trajectory

Velocity=40m/s

Figure 11: Velocity plot

Figure 12: Flow trajectory

Conclusions:

• As the mass flow rate increases the outlet pressure also increases, but it doesn’t follow any pattern.

• As the mass flow rate decreases the pressure ratio increases.

Link for CAD files:https://drive.google.com/file/d/1ChXVyudIKvbZqD3TAu_qnlnL2HQ-DfDL/view?usp=sharing