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Technical Investigation Department

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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Technical Investigation Department

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  1. Technical Investigation Department

  2. METHOD FOR 3-D MODELLINGOF A MIXED FLOW PUMPUSING PHOENICSD Radosavljevic

  3. Introduction • Background information on the investigation • CFD and PHOENICS role • Modelling with PHOENICS • Results and analysis • Conclusions (simulation, project)

  4. 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.

  5. The Situation

  6. 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.

  7. The Problem

  8. The Problem

  9. 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);

  10. 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).

  11. 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;

  12. Geometry • Not supplied (proprietary vane design) • Perform sectioning of impeller and the bowl in order to take measurements.

  13. 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;

  14. 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).

  15. Modelling in PHOENICS Despite all the Problems !

  16. 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)

  17. 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.

  18. Modelling in PHOENICS Impeller modelling - velocity field

  19. 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.

  20. Modelling in PHOENICS Stator modelling - Ground

  21. 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;

  22. Modelling in PHOENICS Stator modelling - velocity field

  23. 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).

  24. Modelling in PHOENICSTransient pressure field in vaneless space • Effect of the impeller blade passing NOTE: • Contour scaling at plane values

  25. 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;

  26. CONCLUSIONS

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