[ismael.s]

Hello,

I am working in a centrifugal pump simulation, but I am having differences between the numerical and experimental results.

I´ve made 4 designs of centrifugal pump on CFX, 1 is equal my simulation so it's ok, other I have difference in experimental results but it´s ok too, it´s near the real results.

But now the question, I am having problem in 2 simulations, with a big difference between Numerical and Experimental results.

First I thought that would be cavitation problems, so I've made some studies in CFX with multiphase simulation using cavitation, I´ve reduced the cavitation as much as possible, then I made a new prototype, and I still had a big difference between results.

Some numbers to you have an idea of the difference.

- Numerical results with cavitation
1953 m³/h, 42m of head, 344hp and 87.9% hydraulic performance.

- Experimental results
1953 m³/h, 21.5m of head, 324hp and 51.4% hidraulic performance.

About the simulation. I've simulated a periodic impeller and periodic vanned diffuser, then full geometry.

This flowrate is supposed to dont have much cavitation since it's 2/3 of maximum flowrate of the pumps.

The best design point is to the pump works with 2500m³/h and 32m of head, and the maximum flow at 0 head more than 3000 m³/h of flowrate, but the maximum flow in the empirical results is 2100 m³/h at 0m of head.

So what I did to try to solve this:

I've changed the turbulence model, used k-e e k-omega (sst), I've changed the saturation pressure of water at 25°C (used 3574pa and 3169pa to see if there was any difference between them), I tried to use another methods to simulate cavitation with SST and k-e , I've tried to change steady state to transient, changed the size and quality of mesh now as last resource I am trying to simulate Transient with Cavitation.

With all those simulations I've reached the same results, 1953m³/h 41-42m of head....not even near of the 21.5m of head in experimental results.

So I´ve started to think that is not my simulation, but I really dont know.

The success pump design was done with the same way, k-e periodic geometry of impeller and diffuser, then k-w with rough mesh (I was starting cavitation simulations here), then k-e with full impeller, diffuser and return chambers to analyse losses.

I thought that I could have problem in my bench test at higher flowrates, but we had a problem with another 2 pumps, 1 centrifugal with lower flowrate and other semi-axial with high flowrate too.

Maybe it's still cavitation, because the behavior of the pump in the bench test is strange, when we start the pump, it is pumping like 2800m°3/h, then it starts to fall slowly until it reach around 2100 m³/h at o head. Those 3 problematic pumps I told you about with the same problem.

1 Centrifugal high flowrate, another centrifugal lower flowrate and the semi-axial with high flowrate and lower head.

I know it's a lot of information to start, but I guess it is better to have an ideia of the whole situation.

I would appreciate any suggestions, ideias, thoughts, and if necessary I can give you more information.

Forgive me for any gramatical problems, but english it's not my main language, I am an portuguese speaker.

And here I dont know about much more people that uses CFX to turbomachinery application, I guess the company I work is one of the first.

Thank you again.

You can talk to me by email too if you want, ismael.schroer@gmail.com