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5 Stage Single Impeller Analysis

Question asked by Dustin Perreault on Oct 26, 2017
Latest reply on Nov 6, 2017 by Dustin Perreault

Hello,

I am new to SolidWorks Flow Simulation, however I have attempted to do my research before posting here, and searched the forum so if this topic has been covered I appologize.

 

Project Details

5 Stage Pump

1000HP Motor

Inlet Pressure = 130psi (educated guess)

Max Operating Pressure1440psi

Fluid = Gasoline & Diesel

Gasoline

  • Specific Gravity = 0.713 @ 60oF
  • Kinematic Viscosity = 0.795Centistokes @ 60oF

Diesel

  • Specific Gravity = 0.885 @ 60oF
  • Kinematic Viscosity = 4Centistokes @ 100oF

Goal

Flow = 1600GPM/2285 BPH BEP

Top end Ability Flow = 1750GPM/2500BPH

 

I attempted to attach the part file that I am attempting to analyze, however, the file is too large. We received a 5 stage pump and after tearing the pump down we found that the impellers were not the original impellers that were in the pump. I am attempting to calculate the pressure head and the flow rate that the specific impeller can produce. Furthermore, the customer wants to know if the goals can be obtained with using the 1000hp motor.

My attempt at the flow simulation.

Custom fluid was used with a Density of 713kg/m^3 and a dynamic viscosity of 6e-006Pa*s

The inlet and outlet “pipe” was extended greatly because vortices were crossing the boundaries.

A rotating region was created that engulfed the entire impeller with a 0.1” offset to ensure that the rotating region did not lie directly on the impeller edge. Local Region Sliding was selected and then retested with Local Regions Averaging. For sliding the default time parameters were used.

A boundary condition was applied to the “outlet pipe” walls that contacted the fluids, these walls were set to stator.

A “measuring ring” was created in order to measure the bulk average static pressure directly after the fluid leaves the impeller. This component was disabled in the component control settings.

 

After researching it was determined that in this specific scenario the boundary conditions must be set as follows:

Inlet must be flow rate or pressure

Outlet must be pressure

 

In our case, we wish to know the pressure head across the impeller and the output pressure is unknown. Therefore I set the outlet boundary condition to 1000psi and used this as a placeholder so to speak, meaning the pressure drop should remain the same regardless of the value of the output pressure. By doing this is the torque value going to change? Inlet was set to 1800gpm.

 

For the second study, an inlet pressure of 130psi was applied to the inlet face of the pipe and an outlet pressure of 392psi was applied to the inner face of the outlet pipe. ((1440psi-130psi)/5)+130psi which would be the theoretical pressure after the first stage impeller. (With maximum operating pressure of 1440 psi)

Goals

Inlet Volume Flow Rate-surface goal-inlet face

Outlet Volume Flow Rate-surface goal-outlet face

Inlet Mass Flow Rate-surface goal-inlet face

Outlet Mass Flow Rate-surface goal-outlet face

Inlet Average Static Pressure-surface goal-inlet face

Bulk Average Static Pressure-surface goal-inner face of measuring ring directly outside impeller outlet

Torque on impeller (Z)-surface goal-every face of the impeller

Pressure Drop-Equation Goal-{Bulk Average Static Pressure}-{Inlet Average Static Pressure}

Efficiency-Equation Goal-{Pressure Drop}*{Inlet Volume Flow Rate}/{Angular Velocity in Rad/Sec}/{Torque}

Pressure Head-Equation Goal-{Pressure Drop}*{Inlet Volume Flow Rate}/372.8/{Torque on Impeller}

Horse Power-equation goal-{torque on impeller}*8.8507*3560rpm/5252

Where 8.8507 is used for a conversion factor from n*m to lb*in and 5252 is conversion factor as well

Mesh

Global Mesh Level = 6

Local mesh applied to all of the impeller faces in contact with the fluid. Most sliders were advanced at least halfway. Settings top to bottom: 6,6,5,4,3,4

Units were in SI and results were converted to English units.

My flow trajectories were believable, and the cut plots for pressure and what not looked to be located in the correct locations.

I hate attempted many different setups for the study and have yet to obtain believable results. Generally, I seem to get a negative Pressure error, and when I don’t the torque values are much too high which gives me inaccurate horsepower results. Efficiency is generally not realistic either, (sometimes above 1).I know that the software is capable of doing what I want I must just be setting up the simulation incorrectly. If anyone has any pointers or a better way of getting the customer the results they are looking for that would be greatly appreciated.

 

The model is of the impeller only, due to the fact that modelling the pump case is a tedious process that would likely take weeks at best. I set up the study in a similar fashion to the advanced flow simulation tutorial of the centrifugal impeller.

 

Here is a link to download the Zip file from my google drive.

Flow Sim 21024.zip - Google Drive

Also if Jared Conway is still on this forum and ends up reading this I have also uploaded the zip file directly to your Dropbox, and I apologize for the large file size.

 

Thanks in advance,

Dustin Perreault

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