Scientific Bulletin of thePolitehnica University of Timisoara

Transactions on Mechanics Special issue

Workshop onVortex Dominated Flows –

Achievements and Open ProblemsTimisoara, Romania, June 10 - 11, 2005

SWIRLING FLOWS IN THE SUCTION SUMPS OFVERTICAL PUMPS. THEORETICAL APPROACH

Eugen Constantin ISBASOIU, Prof*Department of Hydraulic Machinery“Politehnica” University of Bucharest

Tiberiu MUNTEAN, Assist.Department of Hydraulic Machinery“Politehnica” University of Bucharest

Carmen Anca SAFTA, Assist. ProfDepartment of Hydraulic Machinery“Politehnica” University of Bucharest

Petrisor STANESCU, MEng.S.C. AVERSA S.A. Bucuresti

*Corresponding author: 313 Splaiul Independentei, 060024, Bucuresti, RomaniaTel.: (+40) 21 4029 523, Fax: (+40) 21 4029 523, Email: codin@hyd.pub.ro

ABSTRACTThe paper is the beginning of a study regarding

the swirling flows in the intake channel suctionsump pump. The goal of the study is to observe theinfluence of the level upstream the suction pump andthe developed of the swirling flow in the sump pump.

Vortex types are described. The suction sump di-mensions are presented based on the two standardsof Hydraulic Institute Standards and British Hydrome-chanics Research Association. Types of eddy flowprevention devices are described. Some preliminaryresults of the numerical simulation of the flow in theintake channel suction sump of a large-bore wereobtained. The numerical results indicated that theflow inside the suction sump is highly vertical.

KEYWORDSSuction sump, large-bore axial pump, k-ε method,

eddy flow prevention devices

1. INTRODUCTIONSuction sumps receive water flowing from the intake

channel and must direct it smoothly to the pump suctionopening. If suction sumps are improperly shaped orsized, air-entraining vortexes or submerged vortexes aredeveloped. This may greatly affect pump operation ifvortexes grow to extent. In the design of a conventionalsump there are standards [1, 2, 3], each having sufficientinformation in the aids of the designers. For specialapplications and particularly for large high-capacitypump installations, sump designs needed a compre-hensive model test.

2. VORTEX TYPESVortexes and water surface turbulence may produce

adverse effects on the pump such as: generation of

vibration and noise; suction of air, causing pumpperformance to deteriorate the pump or pump failure;generation of unstable swirling flows at the impellerentrance that to cause a motor overland due to excessivedischarge; impeller erosion and submerged bearingwear; vibration, surging and air hammer in water supplypipes because of the entrained air in pumped water

Vortexes developing in a pump suction sump witha free water surface are classified into five types; seeFigure 1, [3]. A dimple vortex is produced on the watersurface, without suction of air. If the dimple on thewater surface grows, and its tip intermittently causessuction of air, an intermittent air entraining vortex willappear. When air is continuously entrained a con-tinuous air entraining vortex is developed. A shallowdepth of submergence continuously entrains a largeamount of air, causing deterioration of pump per-formance and generates vibration and noise. Thesethree types of vortexes are called surface vortexes,[1]. The fourth type of vortex is the coaxial vortex.It is developed when the water surface is decreasedbelow the level at which the continuous air entrainingvortex develops. The center of vortex coincides withthe center of the suction bell mouth. A large amountof air is entrained from around the bell mouth. As aresult, pump performance deteriorates to an extremedegree and pump failed. The last type of vortex isthe submerged vortex. A vortex of this type has nodirect relation with the submerged depth of the bellmouth. Such vortex develops in the water, beginningfrom the side or bottom wall of the sump, with avapor cone produced in its center. When the vaporcrosses the impeller of a vertical shaft type mixedflow or axial flow pump, irregular vibration or noisemay be produced. The swirling flow around thesuction bell mouth is caused by increased velocity

Proceedings of the Workshop on VORTEX DOMINATED FLOWS. ACHIEVEMENTS AND OPEN PROBLEMS, Timisoara, Romania, June 10-11, 200518

of pump-approach flow, non-uniform flow and driftflow in the suction sump, Figure 2.

In [2] the coaxial vortex and the submerged oneare called ‘subsurface’ vortexes and are described asType C, Type B and Type A. Type C and type A are

the same as the coaxial vortex and the submergedvortex, see [1]. Type B is similar in formation andmovement to the Type C vortex but of grater magnitudeor intensity. Type B vortexes may be either periodicor continuous.

a) Dimple vortex b) Intermittent air entraining vortex c) Continuous air entraining vortex

d) Coaxial vortex e) Submerged vortexesFigure 1. Vortexes types, a, b, c, d, e

Figure 2. Submerged vortex at the entrance of theimpeller from sump bottom

3. STANDARD CONFIGURATIONFOR A SUCTION SUMP

A good sump design must be capable of deliveringthe pumped liquid from a channel or pipeline to thepump intake with an acceptable efficiency, without anydetrimental effect on the pump hydraulic or mechani-cal performance. Is considered the submergence, Zi,minimum vortex submergence only, see Figure 3.

Sump design parameters are given in ratios of suctionbell diameter D or as a function of a basicvelocity,for example the approach velocity, Vch, [4]. It isassumed this in the limiting value of the net positivesuction head available (NPSHA), defined as:

Figure 3. Standard sump configuration, [4]

svpaa ZhhNPSHA +−= (1)

where: ha is atmospheric pressure, (m), absolute;hvpa is vapor pressure of pumped liquid, (m),

absolute at pumping temperature;Zs is water depth over impeller eye, (m).

Proceedings of the Workshop on VORTEX DOMINATED FLOWS. ACHIEVEMENTS AND OPEN PROBLEMS, Timisoara, Romania, June 10-11, 2005 19

The Hydraulic Institute Standards, [1] and theBritish Hydromechanics Research Association, [2]recommended sump dimensions versus flow and inratios of pump suction bell diameter, see Table 1.

Japan Association of Agricultural EngineeringEnterprises, [3] shows recommended sump dimensionsfor different types of sumps according with pumpbore size. JAAEE considered the sump dimensionsnot only for sump with free water surface but alsofor intake channel to the suction sump. In this casethe following considerations should be taken intoaccount:• the intake channel to the suction sump should be

straight;• flow velocity should be about 0.5 to 0.7 m/s in

the intake channel upstream of the sump;• distribution of flow velocity into each sump should

be as uniform as possible;• for a pumping station with many pumps, suction

pipe arrangement for each pump should be studied;• drift flow and swirling flow due to accumulations

of earth and sand must be prevented.

Standard dimensions of large-bore pumps withintake channels to the suction sump are presented inFigure 4 and Table 2.

Figure 4. Standard dimensions of large-bore axialflow pumps, [3]

Table 1. Basic sump dimensions

Standard Pump capacity,(m3/h)

Bottom clearanceZC/D*

Back wall clearancelB/D*

Minimum vortexsubmergence,

Zi/D*

Hydraulic Institute 2,27022,700

0.62-0.730.45-0.53

0.84-1.000.88-1.04

1.52-1.801.33-1.57

BHRA All flows 0.5 0.75 1.5* First number is for an assumed suction bell velocity of 1.3 m/s; second number is for an assumed bell velocity of 1.8 m/s.

Table 2. Standard dimensions of large-bore axial flow pumps, JAAEEPrincipal dimensions (mm)Bore size

(mm) φφφφC D F G H I J K2200 3000 3000 3200 6000 4200 1800 4200 40002400 3200 3300 3500 6600 4600 2000 4600 43002600 3400 3500 3900 7000 5000 2200 5000 46002800 3600 3800 4200 7600 500 2400 5600 5000

4. EDDY FLOW PREVENTION DEVICESVarious effective types of eddy flow prevention

devices have been used to prevent vortexes andswirling flows generated by installation conditions.For large-bore pumps, such devices are often installedto decrease the depth of submergence of the suctionbellmouth and to reduce the required excavation forthe suction sump. Suction cone, the cruciform guideor vertical splitter are such devices.

The suction cone, Figure 5, is installed in the sumpunder the pump suction bell. The dimensions are inaccording with suction bell diameter, D. The cruciform

or X-shaped, guide is installed under the pump suction,Figure 6. It improves the flow path into the suctionwhen a sump is too short or is subject to upstreamdisturbers.

5. PRELIMINARY NUMERICAL RESULTSOF THE FLOW IN THE SUCTION SUMP

A theoretical approach of the flow in the suctionsump was beginning. It was considered the practicaldimensions of the suction sump of a large-bore axialpump. The goal of this approach is to find the influenceof the level upstream the intake channel to the suctionsump in the swirling flow development.

Proceedings of the Workshop on VORTEX DOMINATED FLOWS. ACHIEVEMENTS AND OPEN PROBLEMS, Timisoara, Romania, June 10-11, 200520

Figure 5. Suction cone, [4]

It was considered an intake channel to the suctionsump for a large-bore axial and vertical pump. Thesuction sump was with out suction cone and verticalsplitter. A computational grid for pump sump was of141,754 tetrahedral elements of TGrid type. A finemesh was generated around the suction pipe. Calcu-lations of the flow were made with k-ε model, usingFLUENT, CFD code.

The solution domain is bounded by the entranceboundary, the annular exit and the sump wall.

Boundary conditions for the entrance boundary werethe velocity inlet calculated for a flow rate of 1 m3/sand then for 10 m3/s, and for the exit, the flow ratewas constantly maintained. A no-slip condition isapplied to the stationary suction sump walls.

The boundary conditions for the turbulence quan-tities, turbulence kinetic energy and turbulent dissi-pation rate are considered to be predefine, at thebeginning, [6].

Some numerical results are given below.

Figure 6. Cruciform used for inlet flow improvement

Figure 7. Pathlines for 10 m3/s flow range.

Proceedings of the Workshop on VORTEX DOMINATED FLOWS. ACHIEVEMENTS AND OPEN PROBLEMS, Timisoara, Romania, June 10-11, 2005 21

Figure 8. Pathlines for 1 m3/s flow range.

Figure 9. Velocity vectors in horizontal sections for 1 m3/s flow range.

Figure 10. Velocity vectors in vertical section for 1 m3/s flow range

Proceedings of the Workshop on VORTEX DOMINATED FLOWS. ACHIEVEMENTS AND OPEN PROBLEMS, Timisoara, Romania, June 10-11, 200522

Figure 11. Velocity vectors and the swirl at the entrance of the pump, for 10 m3/s flow range

6. CONCLUSIONSIn the theoretical and experimental approach of

the swirling flow in the suction sump of the pumpsome practical problems were described. The suctionsump dimensions were presented based on the twostandards of Hydraulic Institute Standards, [1] andBritish Hydromechanics Research Association, [2].Also the vortex types were described. Some preliminaryresults of the numerical simulation of the flow in theintake channel suction sump of a large-bore wereobtained. The numerical results indicated that theflow inside the suction sump is highly vertical. Thefuture step in this study is to improve the numericalmodel and even the geometry and the mesh of thesuction sump. The goal of this study is to see theinfluence of the level of upstream intake of the suctionpump concerning the pump efficiency.

BIBLIOGRAPHY1.***, Hydraulic Institute Standards, 14th ed., Hydraulic

Institute, 14600 Detroit Ave., Cleveland, Ohio 44107,1983

2.M.J. Prosser, The Hydraulic Design of Pump Sumps andIntakes, British Hydromechanics Research Association,Cranfield, Bedford, England, 1977

3.***, Pumping Station Engineering Handbook, JapanAssociation of Agricultural Engineering Enterprises,1990

4.J.L. Dicmas, Vertical Turbine, Mixed Flow and PropellerPumps, McGraw-Hill Book Co., 1989

5.R. Iwano, T. Shibata, Numerical prediction of the sub-merged vortex and its application to the flow in pumpsumps with and without a baffle plate, 9th InternationalSymposium on Transport Phenomena and dynamics ofRotating Machinery, Honolulu, Hawaii, 2002

6.*** FLUENT 5 User’s Guide, FLUENT Inc., 1998