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Technical Investigation Department. METHOD FOR 3-D MODELLING OF A MIXED FLOW PUMP USING PHOENICS D Radosavljevic. Introduction. Background information on the investigation CFD and PHOENICS role Modelling with PHOENICS Results and analysis Conclusions (simulation, project) . The Situation.

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Presentation Transcript
introduction
Introduction
  • Background information on the investigation
  • CFD and PHOENICS role
  • Modelling with PHOENICS
  • Results and analysis
  • Conclusions (simulation, project)
the situation
The Situation
  • A major water supply project located in North Africa (484 pumps).
  • Pumps reported to have been unused when first put into service on this project.
  • The type of pump is defined as a wellpump of the vertical submersible turbine type (7 stages).
  • Pumps were specified to meet a range of duties for 25 years in relation to the envisaged drawdown schedule.
the problem
The Problem
  • During the course of approximately 3 years of operation, pump performance problems were encountered in a number of wells.
  • Upon withdrawal from the well, a pump was observed to exhibit severe cracking and corrosion, in particular in the region of the upper pump bowl.
  • Cracking was also observed in the corresponding corroded impeller.
approach
Approach
  • Identifying the nature of the processes involved. The primary ones may be categorised as:
      • - physical (clogging and abrasion);
      • - chemical (clogging and electro-chemical corrosion);
      • - microbial (clogging and microbially-induced corrosion);
approach1
Approach
  • Identifying the nature of the processes involved. Important subsidiary factors:
      • - operational (steady loads (static water head), unsteady loads (water hammer), intermittent pumping and over-abstraction ;
      • - structural and mechanical (design/construction and materials).
approach2
Approach

A number of separate studies defined including objectives to:

  • determine quasi-steady hydrodynamically-induced loadings, using CFD analysis (PHOENICS);
  • determine other loadings from specification, such as self-weight, torque and centrifugal;
  • apply all loadings to finite element analysis model and determine individual and combined stresses;
geometry
Geometry
  • Not supplied (proprietary vane design)
  • Perform sectioning of impeller and the bowl in order to take measurements.
modelling in phoenics
Modelling in PHOENICS
  • Model one full stage of the pump as a single device;
  • Apply sliding grid with Multiblock. Rotating block - impeller and stationary block - bowl;

Advantage

  • Capture of full transient effects and (true) dynamic loading;
modelling in phoenics1
Modelling in PHOENICS

Problems (constraints of sliding MB)

  • no surface porosities allowed (vanes?);
  • only uniform grid in circumferential direction allowed;
  • only clock-wise rotation is allowed (pump rotates anti-clockwise).
modelling in phoenics2
Modelling in PHOENICS

Despite all the Problems !

modelling in phoenics3
Modelling in PHOENICS

Compromise approach

  • Treat impeller and the bowl as separate components;
  • Steady simulation of the impeller;
  • Transient simulation of the diffuser with the correct input flow field (impeller exit). (More accurate rotor-stator interaction)
modelling in phoenics4
Modelling in PHOENICS

Impeller modelling

  • Steady;
  • BFC grid;
  • Single passage (1/6 of the flow volume);
  • Cyclic boundary at the exit (vaneless space);
  • 2900 rpm (ROTA patch for rotational forces);
  • Wall friction, k-e model;
  • Outlet flow field data saved in a file.
modelling in phoenics5
Modelling in PHOENICS

Impeller modelling - velocity field

modelling in phoenics6
Modelling in PHOENICS

Stator modelling

  • Transient;
  • Inlet flow field cycles through impeller exit data;
  • BFC grid;
  • Single passage (1/7 of the flow volume);
  • Cyclic boundary at the exit and inlet (vaneless space);
  • Wall friction, k-e model.
modelling in phoenics7
Modelling in PHOENICS

Stator modelling - Ground

modelling in phoenics8
Modelling in PHOENICS

Stator modelling - Numerics

  • Convergence generally within 500sw(/tstep);
  • Stator - start from steady solution in ‘aligned’ position;
  • 10 hours CPU for the transient run;
modelling in phoenics9
Modelling in PHOENICS

Stator modelling - velocity field

modelling in phoenics10
Modelling in PHOENICS

Stator modelling - Assumptions

  • Impeller flow calculated in isolation - no interaction with the stator;
  • Cyclic condition ahead of stator inlet;

Assessment of accuracy

  • Pressure increase within impeller 3.6 bar;
  • Pressure increase within stator 2-3 bar;
  • 5.71 bar per stage;
  • Torque 98.7 kW vs. 103kW (GXDRAG).
modelling in phoenics transient pressure field in vaneless space
Modelling in PHOENICSTransient pressure field in vaneless space
  • Effect of the impeller blade passing

NOTE:

  • Contour scaling at plane values
conclusions
CONCLUSIONS

PHOENICS

  • GROUND proved extremely valuable;
  • Allowed extensive modification to the calculation procedure;

Pump

  • Obtained estimates of the hydrodynamic loading within the pump;
  • Results do not identify any pronounced local peaks in pressure;