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Pump Design and the Role of Computational Fluid Dynamics

pump design

Pumps are essential in a large variety of applications. Pumps are a vital equipment for any system that deals with water, from heating circulating flows, to consumer or industrial water supply, fountains, fire protection systems, and washing machines.

Which are the main pump types?

In a simple classification, pumps have two major types: centrifugal pumps (or rotodynamic pumps) and positive displacement pumps [1].

Centrifugal Pumps produce a head and a flow by increasing the velocity of the liquid through the machine due to the help of a rotating vane impeller. These pumps include radial, axial and mixed flow units. Centrifugal pumps can further be classified as:

• end suction pumps

• in-line pumps

• double suction pumps

• vertical multi-stage pumps

• horizontal multi-stage pumps

• submersible pumps

• self-priming pumps

• axial-flow pumps

• regenerative pumps

Positive displacement pumps operate by alternating of filling a cavity and then displacing a given volume of liquid. The positive displacement pump delivers a constant volume of liquid for each cycle against varying discharge pressure or head. The positive displacement pumps can be classified as:

• Reciprocating pumps – piston, plunger and diaphragm

• Power pumps

• Steam pumps

• Rotary pumps – gear, lobe, screw, vane, regenerative (peripheral) and progressive cavity

Pump Design and its Potential

ss040-coverGlobal demand for fluid handling pumps will increase 5.5 percent annually to $84 billion in 2018, according to the Freedonia Group research [2].

Pump design needs continuous improvement in all product development stages, from concept to design, testing laboratories and engineering validation and finally manufacturing.

Crucial in pump design is making sure it fits the efficiency parameters. For a heating circulating pump, the total efficiency results by multiplying the motor efficiency and the hydraulic efficiency.

Depending on the pump type and size, the efficiency can vary. For glandless pumps, the total efficiency can vary from 5% to 54%, comparing with pumps with glands where the same factor is between 30% and 80% [3].

Why is simulation important for pump design?

Any design and optimization process should be based on a complex set of solid mechanics, fluid dynamics,  and thermal simulations. The main advantage of engineering simulation is that it allows you to virtually test your CAD model early in the design process, and consequently iterate until finding the best possible version. As simulations can be done with a computer, the number of physical prototypes required is massively reduced.

What SimScale brings is the possibility, for the first time in history, to create these simulations in the Cloud, by only using a web browser and without the need to invest in a powerful computer or licenses.

Used by pumps designer worldwide, SimSale has the same web-based environment for all the simulation features, enabling you to validate experimental results, run parametric studies and optimize your designs.

Let’s see a few example of pump simulation projects:

Centrifugal Pump with MRF

This is a simulation project for a centrifugal water pump using the Steady State, Multi-Reference-Frame method (MRF) and K-Omega SST turbulence model.

centrifugal pump with MRF

The velocity streamlines in a centrifugal water pump

The MRF model is one of the two approaches for multiple zones. MRF is a steady-state approximation in which individual cell zones can be assigned different rotational and/or translational speeds.

Performing MRF simulations is computationally much less demanding than transient modelling. MRF provides good approximations with less computational effort and considerably less computation times. Center of rotation, rotation axis, and angular velocity define the MRF rotation.

In this case, the geometry includes a standard backwards type pump impeller and volute casing. The flow intake axially from the inlet pipe and exit from the shown outlet. In addition, a separate region specifies the MRF zone in the vicinity of the impeller. For a given pump we need to know the flow parameters in order to attain the accurate pressure rise. Here arbitrary values were used to demonstrate an operation example. The simulation analyses the mean velocity and pressure field in the pump.

The results therefore show the velocity vectors and pressure rise at the outlet for a cut section of the pump. The simulation provides insight as to how much pressure rise the pump creates for a given mass flow and rotational speeds.

Centrifugal Pump with AMI

This project simulates a transient analysis of a centrifugal pump with a rotating mesh using the Arbitrary Mesh Interface (AMI) approach and K-Omega SST turbulence model.

centrifugal pump with AMI

Pressure contours in a centrifugal pump with AMI

In the AMI approach, a mesh interface is created between the moving and stationary parts of the mesh. AMI simulations are full “Transient” and therefore are computationally much more expensive than MRF. Also they take all transient effects into account and are usually sensitive to the time step length. In addition, AMI could be specified as oscillating or full rotating motion.

In this case, the geometry has a backwards type pump impeller with a volute casing around it. The flow enters the domain from the inlet and exits from the outlet shown. An AMI zone created around the impeller defines the rotating mesh region.

The simulation analyses the instantaneous flow in the pump. The computed results show the instantaneous velocity field and instantaneous pressure profile for a section plane. The simulation provides insight into the time-dependent changes in the flow.

Just upload a design and improve it!

SimScale’s Public Project library is an open collaborative platform offering different models of pumps and suggested simulations. Basic pump design simulations are available for free and any engineer or designer can use and modify it for free:

pump simulations

A “pump” simple search in SimScale’s Public Projects

Here are a few links to some of the most interesting pump projects in the SimScale Public Project library:

Just sign up for the 14-day free trial and copy any of these projects to get started.


References

[1] – Classifications of Pumps, Legacy Chiller Systems.

[2] – World Pumps – Demand and Sales Forecasts, Market Share, Market Size, Market Leaders, The Freedonia Group, 2013.

[3] – Fundamental principles of pump technology, Wilo Pump Basics, 2005.

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