Pump design – Discover Dredging

Graduation Of Alex De Rooij: Pumps Actually Fly Like An Unusual Airplane

Alex de Rooij receiving flowers from Suman Sapkota for his graduation

When you hire a carpenter, he repairs everything with a hammer. So, what happens when you ask an aeronautical student to solve some issues in a dredge pump? He models the pump as a badly behaving airplane. And with success, Alex de Rooij joined our company as a graduation student and recently graduated on the topic of ‘Numerical Study on NACA Profiles Sensitivity in Dredge Pump Impellers’.

The normal procedure for designing pumps is relatively straight forward. Set the performance specifications and try to hit that mark with the simulated behaviour from an iteratively improved design. This is well documented and I’ve been writing about this process before.1

Pump design workflow (inspired by Suman Sapkota)

One of the design parameters is the NPSHr. This is basically the amount of absolute pre-pressure the pump requires to operate.2 The system and operating conditions will result in a certain available pre-pressure: NPSHa. When the NPSHa drops below the NPSHr, the pump will experience cavitation at the low pressure side of the blade. The flow of the medium will be disturbed and the performance of the pump will abruptly crash. There is some warning. Operating near the NPSHr, there will be an incipient cavitation where the vapour bubbles start to form, but do not cause any issue. The imploding vapour bubbles may be detected audibly for the trained listener.3 Next will be a stage on the NPSHr, where the bubbles get larger and they loudly implode. At this stage, the pump sounds like it is tumbling nuts and bolts inside. These imploding bubbles will definitely cause damage to the impeller. At last, working below the NPSHr, the bubbles will become so large, they will block the passage between the blades. The result is an immediate drop in delivered head.

Explanation of NSPHr, NPSHa and cavitation

The flow of the medium through the impeller can be simulated in a CFD program. Specifically for impellers, you will need to model a rotating frame of reference. And that is the usual representation of the results. However, with mathematics being one of the most powerful tools invented by humanity, we can have an alternative view on these results. We can cut the impeller along a radial and stretch open the meridional passage and the blades to a row of foils. And that is exactly where our young aspiring engineer comes in. In literature, the blades in the impeller are modelled having a constant thickness. But, Alex has been investigating what the influence will be when we model the blades as foils. Selecting a proper profile makes the blade less sensitive to stalling.

Conversion of axial view to blade to blade view

Alex, thank you very much for your work here at Damen. We’ve learned the influence of certain profiles on the performance and geometry of the pumps. You have the right mindset to pass your time at the TU Delft and graduate successfully over there also. And whenever you have some days of the month left after you spend your allowance, know that we can give you a warm reception at our office.

Alex working at the reception desk at Damen Dredging Equipment

References

CEDA Dredging Days 2021: Sustainable Dredging And Innovation

Promotional banner of the CEDA Dredging Days 2021 (Credit: CEDA)

Tomorrow, another event with a long tradition will start: the CEDA Dredging Days1. Due to the Covid issues, this time, it will be a virtual event, just as a lot of other regular happenings. Hopefully, it will be the last days of this dreadful period. I can’t wait to meet people again in real life. Back at the office, we are slowly starting to get back. But meetings with people far outside the regular circle were difficult. For instance, I was a member of the Technical Paper & Program Committee and the preparation was completely digital.

Home page of your CEDA Dredging Days on the Swapcard platform (Credit: CEDA)

Now, the event itself is also digital. Of course, this is still not the real thing. Having a coffee and a chat in the lobby is a much more enjoyable experience than sitting in front of your screen. I have to say that with the Sawpcard platform2 selected by the organising committee, it is much easier to arrange your own program, adapted to your personal interests. Moreover, it will also facilitate meeting people with the same interest. In a sense, this might be an opportunity to approach those. In the real world, people will not get seated next to you when they have the same interest. And certainly don’t have them captioned on their chest.

As member of the TPPC, I had the opportunity of a sneak preview of the articles and presentations and I can guarantee there are a lot of interesting sessions. For starters, there are three presentations by my colleagues. Suman Sapkota will have presentation on his research in various novel methods to apply numerical research into the design of dredge pumps3. We are happy to share with you some experiences and insights on the Dredging Days.

Testing the non-radioactive density sensor

Another presentation will be by Frank Bosman4. He has been active in the development of an instrument that will measure the mixture density, without using a radio-active source. This intelligent solution is not only more sustainable, but will also provide easier access to this information. If you don’t know the density, you are very likely to underperform with your dredge. He will present some experiences and data gathered on the performance of this system.

Example of recent electric DOP dredge family

Our last presentation will be by René Sens3. Less technical, but surely an interesting perspective on the future of dredging equipment. Everyone in the dredging community is aware of the necessity to change and adapt to a more sustainable approach of our dredging business. There is an urgency to reach the goals set by the UN to leave the world behind as a better place than we received it. Although usually an increase in size also increases the efficiency of a dredge, the UN goals look beyond that single parameter. With that in mind, small and medium size dredges will be far more interesting than at first sight.

Session 7: Young CEDA ask a CEO (Credit: CEDA)

There will be a lot more going on and I could produce a long list of other interesting presentations. I think you should also check out: Edwin de Hoog and Joep Goeree, Basel Yousef and Jeroen van Stappen, and if you really want to get academic: Janek Gundlach, Ebi Shahmirzadi and Arno Talmon. You can just add to your own list and see who also joins in in the audience. Other interesting sessions will be the student ‘Flash Talks’5 and the ‘Young CEDA ask a CEO’ session6 with Peter Berdovski and Kees van de Graaf. And I am very curious what the other working groups and commissions of CEDA have to present about their work.

Thursday evening is the big get together of the dredging community; meet you there! (Credit: CEDA) — Dredging Days as a they used to be: personal interaction (Credit: CEDA)

References

Graduation Of Wim Kleermaker: Measuring And Predicting Wear In Impellers

Wim Kleermaker during the practical phase of his graduation in dredging

Yesterday, Wim Kleermaker graduated at the TU Delft on a research project he conducted on our slurry test circuit at Damen Dredging Equipment. Specifically, he was investigating the wear behaviour in our dredge pumps. The noteworthy aspect of this project, was that Wim was supervised by our colleague Suman Sapkota. As long time readers in the audience might remember Suman was my own pupil some years ago1.

Example of a worn impeller at the Damen Dredging Experience

Wear is a very common process in the dredging industry and one of the main cost factors in a project2. It is beneficial to know the amount of wear to expect in a certain condition and be able to predict the budget to reserve for this nuisance. This is only possible when we as a manufacturer will be able to predict the wear rate and pattern can provide the information to the operator for his estimates. We do have historical data that will allow us to provide a ball park figure, but a more analytical approach might assist us in particular unusual cases. Furthermore, it will also provide us insight in the impact of certain design decisions for the wear performance of a certain pump design. For Wim’s graduation, he had to approach this academically: come up with a simulation model and verify this with measurements.

Damen dredge pump slurry test circuit on the outfitting quay in Nijkerk

The measurements were done in our slurry pump test circuit. This circuit has been highlighted a couple of posts back3. For Wim’s experiments, he used an impeller under a certain operating condition and mixture properties. Before and after a representative period, the condition of the impeller was measured and the difference is a measure of the wear experienced.

Wear (or scientifically: erosion) is related to the impact of the particles on the material surface. In order to know the kinetic energy of the particles, the flow field has to be known. As the flow fleild cannot be measured directly at the test circuit, we have to resort to Computation Fluid Dynamics. We already know of Suman’s graduation, to look for patterns in the flow lines, but Wim has extended the procedure to also quantitively estimate the related erosion.

Comparing CFD results (l) with measured erosion (r)

Although there is only a limited amount of data available, comparing the results of the CFD estimation and the measured erosion are looking promising. This is certainly a workflow that will provide us the unique tools for engineering better pumps and assisting customers in their specific projects.
Although Wim will not join our ranks in the dredging community and pursue a different career in another interesting industry, we are sure he will be constructive and dedicated colleague at Marin.

Tag: Pump design

Graduation Of Alex De Rooij: Pumps Actually Fly Like An Unusual Airplane

References

See also

CEDA Dredging Days 2021: Sustainable Dredging And Innovation

References

See also

Graduation Of Wim Kleermaker: Measuring And Predicting Wear In Impellers

References

See also