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Improved Centrifugal Pump Design with CFD Simulation

centrifugal pump design with cfd analysis

The growth and improvement of many key industrial processes have been always linked to the improvements in the pumping equipment. Centrifugal pumps play a particularly important role due to their capacity to handle high flows. They constitute more than 85% of the world’s production of pumps and are used in sewage, food processing, water treatment and manufacturing plants, as well as the chemical and petroleum industries, finding their applications in pumping all types of low viscosity fluids. They can also easily handle liquids having high proportions of suspended solids present in them.

With the many varieties of available pump configurations, a proper design is the most important requirement for any facility. 20% of the total energy consumed globally is used to run a pump of one sort or another—yet, 2/3 of these pumps use 60% more energy than is required. To ensure energy efficiency and prevent equipment failure, it is important to be able to predict and evaluate its performance under different operating conditions. This is where computational fluid dynamics (CFD) tools come to your aid.

To illustrate how CFD or flow simulation can help pump engineers improve the performance of a centrifugal pump design, we will host a free 30-minute webinar on December 12th, 2017:

Why You Should Care About Simulation

centrifugal pump design process - product cost performance and product design process timeline

The cost and performance of any physical product are generally determined quite early on in the design process. The stage when you begin to explore the design space and define your product concept is when the most impactful design decisions are made. After that, the rate at which the production costs are realized is much slower.

Simulation is one of the tools that play a fundamental role in those early product development stages, allowing engineers to make more informed design decisions earlier in the process. For the final product, this can mean lower production costs, more efficient energy consumption, lower failure risk, and more.

Why SimScale?

So why aren’t all designers using simulation yet? Several barriers have prevented a more widespread adoption of simulation software by engineers and designers—and here’s how SimScale is aiming to change this:

  • multiphysics simulation analysis types, cfd, fea thermal analysis software

    Accessibility: Traditional software needs to be installed locally on expensive high-performing computers, which are idle most of the time. With SimScale, all computations are cloud-based—all you need is a web browser.

  • Operating costs: Standard commercial simulation software packages are notoriously expensive. With SimScale, there is an option to start simulating right away with a free Community Plan or a 14-day trial for the Professional Plan.

  • Know-how: Most modern tools are designed for experts and experienced simulation engineers. To bridge that knowledge gap, SimScale offers a large public projects libraryfree training, and live support chat.

Engineering Problem

centrifugal pump design pump components

A centrifugal pump essentially consists of an impeller rotating in a casing called volute. Fluid enters the eye (center) of the impeller and exits through the space between the impeller blades to the space between the impeller and casing walls. The velocity of fluid elements is in both tangential and radial directions, as the impeller rotates. The velocity as well as the pressure, both increase, as the fluid flows through the impeller. Since the rotational mechanical energy is transferred to the fluid, at the discharge side of the impeller both the pressure and kinetic energy of the water will rise. At the suction side, water is getting displaced, so a negative pressure will be induced at the eye. Such low pressure helps to suck fresh water stream into the system again, and this process continues.

The impeller is the most vital part of a centrifugal pump design. Successful impellers have been developed with many years of analysis and developmental work. The vanes (blades) of the impeller are backward-curved. Backward-curved vanes have the blade angle less than 90 degrees and are the most preferred vane type in the industry due to its self-stabilizing power consumption characteristics. This means that with an increase in flow rate, the power consumption of the pump stabilizes after a limit.

centrifugal pump vanes blade angle, forward-facing vanes, radial vanes, backward-facing vanes

Centrifugal Pump Design Optimization Study

The complexity of the flow in a turbomachine is primarily due to the 3D developed structures involving turbulence, secondary flows, unsteadiness, etc. Initially, the centrifugal pump design process was mainly based on empirical correlation, a combination of model testing, and engineering experience. Nowadays, the design demands a detailed understanding of the internal flow, possible with the aid of CFD.

CFD simulation makes it possible to visualize the flow conditions inside a centrifugal pump and provides valuable information about the pump’s hydraulic design. Simulation results are used to calculate and predict the performance of a centrifugal pump replacing lengthy physical experiments. A great deal of work is saved, in addition to shortening the design cycle.

Project Overview

For our case study, we will use the following simulation project as a template: Centrifugal Pump Design Optimization with CFD.

This project simulates a typical centrifugal water pump using the steady state, Multiple Reference Frame (MRF) method and the k-omega SST turbulence model. The pressure-velocity coupling is performed through the SIMPLE algorithm. The MRF zone is assigned a rotational velocity of 157.08 rad/s (1500 rpm). The project is concerned with the influence of (1) the outlet blade angle and (2) the number of blades on the performance of a centrifugal water pump. The performance characteristic curves, as well as the local and global flow variables, are numerically predicted using SimScale for impellers with 3 different outlet blade angles, i.e. 13, 23 and 33 degrees and 3 different numbers of blades i.e. 6, 8 and 10.

The centrifugal pump design under consideration has inlet and outlet diameters of 150mm and 151.5mm respectively, and its impeller diameter is 340mm. The domain is the geometry, which was meshed using the ‘Snappy-Hex-Mesh’ on the SimScale platform. The resulting mesh consists of approximately 4.5 million cells and is shown in the figure below.

Centrifugal Pump model meshCentrifugal Pump model mesh Centrifugal Pump model mesh

(1) Effect of Outlet Blade Angle Variation

centrifugal pump Outlet Blade Angle 13 degreescentrifugal pump Outlet Blade Angle 23 degrees centrifugal pump Outlet Blade Angle 33 degrees

    Outlet Blade Angle – 13 degrees                                              23 degrees                                                         33 degrees

Flow Parameters

  • Number of Blades = 8
  • K-Omega SST Turbulence Model
  • Steady State, Incompressible Flow
  • Multi-Reference-Frame (MRF) Method
  • Impeller Rotational Velocity = 1500 rpm
  • Inlet Volumetric Flow Rate = 540 cubic meters per hour
  • Volute Casing Outlet Face — Pressure Outlet (0 Gauge Pressure)

centrifugal pump pressure contours cfd analysis

 

centrifugal pump pressure contours cfd analysis

Pressure Contours

centrifugal pump pressure difference depending on blade angle

 

The pressure contour results show that maximum pressure difference (208.4 KPa) between the pump inlet and outlet occurs in the pump with blade outlet angle of 33 degrees and least for 13 degrees (116.6 KPa), pump outlet is set as Pressure Outlet with fixed value, 0 Gauge Pressure boundary condition.

 

 

(2) Effect of Variation of Number of Blades

centrifugal pump blade number 6 centrifugal pump blade number 8centrifugal pump blade number 10

    Number of Blades – 6 blades                                                 8 blades                                                              10 blades

Flow Parameters

  • Outlet Blade Angle = 33 Deg
  • K-Omega SST Turbulence Model
  • Steady State, Incompressible Flow
  • Multi-Reference-Frame (MRF) method
  • Impeller Rotational Velocity = 1500 rpm
  • Inlet Volumetric Flow Rate = 540 cubic meters per hour
  • Volute Casing Outlet Face — Pressure Outlet (0 Gauge Pressure)

centrifugal pump pressure contours cfd simulation

centrifugal pump pressure contours cfd simulation

Pressure Contours

centrifugal pump pressure difference depending on blade number

 

From the pressure contour results, it can be seen that maximum pressure difference (230.5 KPa) between the pump inlet and outlet occurs in the pump with 10 blades and least for 6 blades (161.04 KPa).

 

 

 

Performance Comparison Between Pumps With 8 and 10 Blades
(Blade Angle 30 Degrees)

Best Efficiency Point

Best Efficiency Point (BEP) is the flow at which the pump operates at the highest or optimum efficiency for a given impeller diameter. BEP for this pump is obtained at the flow rate of 432 cubic meters per hour. And, the maximum efficiencies obtained for pumps with 8 blades and 10 blades are 60.5% and 62.04% respectively.

centrifugal pump best efficiency point

Head at Best Efficiency Point

Since the BEP occurs at a flow rate of 432 units, that flow rate also intersects the pump curve at a point equal to head of 26.65 meters and 28.33 meters for pumps with 8 blades and 10 blades respectively.

centrifugal pump head at best efficiency point

Conclusion

The centrifugal pump is a simple but essential device as we have seen above. Seemingly minor design changes, such as the outlet blade angle or the number of blades, can substantially impact the performance of the pump. With the multitude of available centrifugal pump design configurations, physically testing each one of them or relying on experience alone would make the design process unnecessarily long and expensive. The same design experiments can be carried out using numerical analysis and simulation, achieving equally accurate results within a few minutes or hours.

This is just one example of how CFD tools can help engineers evaluate their pumping equipment designs. The SimScale Public Projects Library has a wide selection of simulation templates covering various design aspects of industrial equipment and machinerycommercial and industrial fans, valves, and many more.

Explore them by creating a free Community account or discover the perks of our Professional Plan by signing up for the 14-day trial. Sign up for the free webinar to learn more:


References

1. http://www.sciencedirect.com/science/article/pii/S1877705813001033
2. http://ieeexplore.ieee.org/document/7124063/?reload=true
3. http://publications.lib.chalmers.se/records/fulltext/163168.pdf
4. http://publications.lib.chalmers.se/records/fulltext/179797/local_179797.pdf
5. http://publications.lib.chalmers.se/publication/101019-the-ercoftac-centrifugal-pump-openfoam-case-study

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