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Rational Design of a Pump-Sump and its Model Testing

Z. Ahmad1; B. Jain2; S. Kumar 3; and M. K. Mittal4

Abstract: Water pumps used in pumped storage plant, drainage, agriculture, and industrial process experience operational problems such as

vibration, impeller damage, and wear of bearing caused by nonaxial inflow of water in the suction pipe. Rational design of pump-sump and

vortex breaker aligns the nonaxial flow in the axial direction and reduces these operational problems in the pump. This paper deals with state-

of-the-art-design of a pump-sump and the criteria for its model testing. A 1 ∶10 scaled model of a pump-sump with five cooling water pumps

and three auxiliary cooling water pumps was tested, and the model results related to separation of flow, dead zones, surface and subsurface

vortices, swirl angle, etc., are reported in this paper. No surface vortices were observed in any of the tests; however, Type-2 (dye core)

subsurface vortices and a swirl angle that is more than the permissible value were noticed in most of the tests without vortex breaker.

A conical vortex breaker with eight fins was very effective in reducing the swirl angle. Tests conducted at higher Froude numbers and

velocity ratios for different combinations of pumps and water surface levels indicate a minor increase in the swirl angle, which is mainly

attributed to high turbulence rather than the swirl in the flow. DOI: 10.1061/(ASCE)PS.1949-1204.0000074. © 2011 American Society of

Civil Engineers.

CE Database subject headings: Pumps; Vortices; Turbulence; Model tests; Rotation; Design.

Author keywords: Pump-sump; Vortex breaker; Subsurface vortices; Swirl angle; Turbulence.

Introduction

Water pumps used in drainage, agriculture, and industrial processoften experience operational problems such as vibration, impeller damage caused by cavitations, and excessive wear of bearings. Thisnot only results in severe deterioration of their performance but alsoleads to a significant increase in operational and maintenance costs.These problems probably result from nonaxial flow of water in thesuction pipe because of poor pump-sump design. The rational de-sign of pump-sump is governed by the nature of flow pattern in it,which has been studied experimentally and numerically by many

researchers (Padmanabhan and Hecker 1984; Nakato 1990; Con-stantinescu et al. 1997). Unfortunately, the phenomena are so com-plex and diverse that there is no comprehensive theoretical model topredict them. Existing design guides usually contain little morethan rules of thumb for pump performance. The common problemsencountered in the pump-sump are (Karassik et al. 2001) asfollows:• Free-surface vortices—the air may be drawn from the surface

into the pump. These vortices cause unbalanced loading on

the impeller and periodic vibrations, thereby reducing pump ca-pacity. Furthermore, other nonair entraining vortices induce cir-culation in the flow approaching the bell mouth.

• Subsurface vortices, which may emanate from the floor, sideand back walls of the sump, or a combination of these. Thesealso induce circulation to the flow entering the bell mouth.

• Nonuniform velocity distribution in bays, which results in pre-rotation of flow entering the bell mouth.

• An uneven distribution of flow at the pump throat which mayresult in unequal loading of pump impeller and the vibration.

• Cavitations that can cause damage to the underside of a mixed

flow impeller.These problems encountered in the pump-sump will affect the

pump performance and significantly increase the operational andmaintenance costs. Various relationships are available in the liter-ature to compute the minimum submergence required to avoid the

surface vortices [Ahmad et al. 2008; Durai et al. 2007; Jain et al.1978; American National Standards Institute (ANSI) 2001;Gulliver et al. 1986]. According to the guidelines suggested byASCE (1995), dimensionless critical submergence S C =d ¼0:5 þ 2F, where d = diameter of suction pipe; and F = Froude num-ber in the suction pipe. For a vertical intake, Durai et al. (2007)proposed S c=d ¼ 0:44F0:53 by using data from Jain et al.(1978). Recently, Graber (2010) studied flow in manifold, andSingh and Adachi (2010) found that concrete cylinder pipes were

more inefficient than ductile iron, cast iron, and PVC pipes.Formation of subsurface vortices is mainly attributable the sep-

aration of flow near the bell mouth. This could be controlled bykeeping the velocity of flow in the bay to 0:3 m =s (ANSI 1998)and fixing the dimensions of suction pipe, bell mouth, and baysaccording to standards indicated in IS 15310 [Bureau of Indian

Standards (BIS) 2003], ANSI/HI 9.8 (ANSI 1998), BritishHydromechanics Research Association (BHRA) (Prosser 1977),Padmanabhan and Hecker (1984), and Knauss (1987).

This paper deals with the rational design of a pump-sump andthe design criteria for its model testing. A 1∶10 scaled model of a pump-sump with five cooling water pumps and three auxiliary

1Associate Professor, Dept. of Civil Engineering, Indian Institute of Technology Roorkee, Roorkee-247667 (UA), India (corresponding author).E-mail: [email protected]

2Research Scholar, Dept. of Civil Engineering, Indian Institute of Tech-

nology Roorkee, Roorkee-247667 (UA), India. E-mail: [email protected] 3Research Scholar, Dept. of Civil Engineering, Indian Institute of Tech-

nology Roorkee, Roorkee-247667 (UA), India. E-mail: [email protected]

4Emeritus Fellow, Dept. of Civil Engineering, Indian Institute of Tech-nology Roorkee, Roorkee-247667 (UA), India. E-mail: mknsnfce@iitr .ernet.in

Note. This manuscript was submitted on June 14, 2010; approved onOctober 24, 2010; published online on October 27, 2010. Discussion periodopen until October 1, 2011; separate discussions must be submitted for individual papers. This paper is part of the Journal of Pipeline Systems

Engineering and Practice, Vol. 2, No. 2, May 1, 2011. ©ASCE, ISSN1949-1190/2011/2-0–0/$25.00.

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JOURNAL OF PIPELINE SYSTEMS ENGINEERING AND PRACTICE © ASCE / MAY 2011 / 1

http://dx.doi.org/10.1061/(ASCE)PS.1949-1204.0000074







cooling water pumps is tested, and the model results related to sep-aration of flow, dead zones, surface and subsurface vortices, swirlangle, etc., are presented.

Dimensions of Pump-Sump

The various dimensions of the model as recommended by variousstandards indicated in IS 15310 (BIS 2003), ANSI/HI 9.8 (ANSI1998), BHRA (Prosser 1977), Padmanabhan and Hecker (1984),and Knauss (1987) are summarized in Table 1.

Criteria for Model Testing

Selection of Geometric Scale

A large geometric scale, which gives greater confidence in the scal-ing of vortex effects, is desired. As long as testing difficulties arenot increased, it is better that the model is as large as possible subject to the consideration of the cost of model construction (Prosser

1977). A reasonably large scale is selected to minimize the viscousand surface tension scale effects and to reproduce the flow patternnear the intake. Also, the model should be large enough to allowvisual observations of flow patterns, accurate measurements of swirl and velocity distribution, and sufficient dimensional control.Furthermore, to ensure minimum scale effects, the model geometric

scale is chosen so that the model bell entrance Reynolds number and Weber number are more than 6 × 104 and 240, respectively, for the test conditions based on Froude similarity (ANSI 1998). Anwar et al. (1978), Daggelt and Kelugan (1974), and Jain et al.(1978) found that viscous force has minimal effect on vorticesfor Reynolds number greater than 3 × 104.

Similitude Law

The flow in the pump-sump is mainly governed by gravitationaland inertial forces. Therefore, Froudian similarity law is consid-ered, which requires equal Froude number F both in the modeland in the prototype. The velocity, discharge, and time scale can

be written in terms of length scale as V r ¼ ffiffiffiffiffi

L r p ; Qr ¼ L 2:5r ; and

T r ¼ ffiffiffiffiffi

L r

p , respectively.

Flow Conditions

Vortices are most severe at maximum flows and minimum water

level. Accordingly, model tests are conducted under the design dis-

charge and minimum water level. However, there are instances

where stronger vortices may occur at higher water level and lower

flows, perhaps because of less turbulence. Tests should also be per-

formed at minimum, intermediate, and maximum water levels

(ANSI 1998). Although no significant scale effect is found once

the model study is carried out on the basis of Froude similarity,

a few tests for the final design of a free surface intake should

be conducted at 1.5 times the Froude-scaled flows to compensate

for any possible scale effects on the free surface vortices. Tests at

the prototype velocities are not recommended, as this will distort

flow patterns and unduly exaggerate flow disturbances (e.g., vor-

tices) in the model (ANSI 1998). The concept of equal velocity

modeling seems relevant only to large models (at least 1∶4 scale)

for which a small increase in flow in the model results in equal

velocities in the model and the prototype (Hecker 1981). Rahiman

et al. (2003) found that swirl angle does not increase with an in-

crease in Froude number.However, studies before 1970 mention that if tests at Froude

scale show very limited or no vortex action, tests are to be repeated

for higher flow velocities, say at two or three times the Froude

scale, to give a margin of safety with respect to air entraining vor-tices because some may have been missed at Froude scale ( Prosser

1977). However, Rohan (1966) and Chang (1979) suggest that

model velocities should be increased above Froude scale by an

amount depending on the ratio of prototype and model Reynolds

number. Anwar (1965, 1966) found that excessive surface rough-

ness on the tank reduces tangential velocities and could even sup-

press vortex formation. Denny (1956) and Denny and Young

(1957) advocate the testing of a geometric model at the same veloc-

ity as in the prototype. Kenn and Zenker (1967) try to interpret the

equal velocity concept as the equality of the ratio of the Weber and

Reynolds number, also called dimensionless capillary number .

Table 1. Recommended Dimensions of Pump Sump

S. No. Description Recommended value References

1 Bell mouth diameter, D 1:5–1:8d a

Prosser (1977)

2 Distance from the pump bell mouth center line to the bay entrance 5 D ANSI (1998)

3 Distance from the back wall to the pump bell mouth center line 0:75 D ANSI (1998)

4 Distance between the bell mouth and floor 0:3 D–0:5 D ANSI (1998)

5 Minimum pump bell mouth submergence S ¼ Dð1:0 þ 2:3F DÞbANSI (1998)

6 Pump inlet bay entrance width > 2 D ANSI (1998)

7 Pump inlet bay length > 5 D ANSI (1998)

8 Distance from pump bell mouth center line to the through-flow traveling screen > 4 D ANSI (1998)

9 Distance from pump bell mouth center line to sloping area > 5 D HIS (1998)

10 Angle of floor slope 10° to þ10° ANSI (1998)

11 Angle of divergent < 10° ANSI (1998)

< 20° Padmanabhan and Hecker (1984)

and Prosser (1977)

12 Approach flow velocity to bay < 0:3 m =s Padmanabhan and Hecker (1984)

and Prosser (1977)

< 0:5 m =s ANSI (1998)a d = diameter of the suction pipe.

bF D = Froude number with reference to D.

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Acceptance Criteria

The acceptance criteria for the model test as per ANSI (1998), Iowa Institute of Hydraulic Research (IIHR) (Nakato 1990), and other standards are as follows:• Free-surface and subsurface vortices entering the pump must be

less severe than those with coherent dye cores, i.e., Type-3 for free-surface vortices and Type-2 for subsurface vortices;

• Swirl angle must be less than 5°; however, the maximum short-term swirl angles up to 7° are acceptable only if they occur less than 10% of the time for infrequent pump-operating

conditions;• Depth-averaged pump-bay intake velocities, measured at two-

bay width upstream from the center line of pump bell mouth,should not deviate by more than 20% from the area-averagedpump-bay velocity over the central 75% of the bay width;

• Velocities in the throat of the bell should be within 10% of thecross-sectional area average velocity; and

• There should be no detectable, large-scale, persistent “unsteadi-ness” or waviness in the pump bell mouth approach flows andno indication of persistent large-scale turbulence.

Modeling of Screen and Bell Mouth

Geometric similarity is not followed for modeling the screen. How-

ever, the screen head-loss coefficient in the model and in the proto-type is kept the same by taking the blockage ratio for both themodel and the prototype equal.

The inside geometry of the bell mouth up to the bell throat isscaled, including any hub located between the bell entrance and thethroat. The impeller is not included in hydraulic models, as the ob- jective is to evaluate the effect of the intake design on the flow pat-tern approaching the impeller. A straight pipe of size equal to thethroat diameter or pump suction diameter extends at least five diam-eters downstream from the throat or pump suction.

Measurement of Swirl Angle

The intensity of flow rotation was measured using a vortimeter con-

sisting of a straight vane propeller with four vanes mounted on a shaft with low-friction bearings. The diameter and height of thevortimeter are assumed to be 0.75 and 0.60 times of suction pipediameter, respectively. The revolutions per unit time of the swirlmeter are used to calculate the swirl angle, θ, which indicatesthe intensity of flow rotation. The rotational flow indicator inthe suction line is generally expressed in terms of the angular veloc-ity of the vortimeter tip and the average axial velocity V z in thesuction pipe. The swirl angle is defined by

θ ¼ tan1

V θ

V z

ð1Þ

where V θ ¼ π d ω=60 = tangential velocity at the tip of the vorti-

meter blade; and ω = angular velocity of vortimeter in revolutionsper minute (rpm).

Model Test of Pump-Sump

Description of Prototype

The prototype pump-sump was designed with five cooling water (CW) pumps and three auxiliary cooling water (ACW) pumps,based on the recommended dimensions given in Table 1. It wasproposed to supply water to the pump-sump through two CW ducts(each of 6 m width and 4 m height) and one ACW duct (1.75 m

width and 1.0 m height). The width of the forebay at inlet was

14.75 m, and both side walls of this forebay were diverted by20°; however, the bottom floor had 9° of downward slope. The in-vert level of CW duct was 6:0 m, whereas that of ACW duct was

3:0 m. The floor of the sump was at a level of 8:7 m, and themaximum and minimum water levels in the sump were fixed at levels of 0:5 and 1:7 m, respectively. Five bays, each of length14.65 m and width 4.5 m with 1-m pier thickness, were providedfor five CW pumps; and three bays, each of length 12.257 m andwidth 1.4 m with 0.5-m pier thickness, were provided for ACWpumps. A vertical screen consisting of 20-mm circular diameter bars with a 50-mm clear spacing between them was provided at the entrance of each bay. Details of CW and ACW pumps are given

in Table 2.

Model Layout

A 1∶10 geometric scale was chosen for the model study of thepump-sump. For this scale, the bell entrance Reynolds and Weber numbers were 10:4 × 104 and 685, respectively, which are higher than the limits prescribed by ANSI (1998) for neglecting the effect of viscosity and surface tension. The model consisted of an intakechamber, channel section, tunnel section, forebay, bays, and pumpassembly with a bell mouth suction pipe (Fig. 1). Suitable arrange-ments of perforated walls, flow straighteners, and wave suppressorswere provided in the intake chamber and channel section to stabi-lize the flow without any disturbance in the inflow. An emergency

sluice gate and a rectangular weir were provided on the side wall of the intake chamber to spill the water from the tank once it is not needed in the sump or when flow regulation is required. A 35-hppump was used to supply the water from an underground sump tothe intake chamber through a 200-mm supply pipe. The model wasmade of concrete except the floor and the front view of the bays,which were of transparent glass to visualize the flow. The bellmouth and suction pipe of up to 600 mm were also fabricatedof transparent plastic. A vortimeter was fitted in the suction pipeto measure the swirl angle of the flow. Screens were made of 10-mm circular bars placed at a clear spacing of 25 mm and fittedat the entrance of each bays. A photograph of the model is shownin Fig. 2.

Water entered in each suction line through a transparent bell

mouth and passed through a transparent acrylic pipe, a 90° elbow,a 1,200-mm-long straight pipe, a 90° bend, and a valve. The bendwas used to measure the discharge, whereas the valve was used toregulate the flow in the suction line. Each suction line was con-nected to a 203-mm-diameter pipe, which was connected to a 50-hp centrifugal pump. The delivery pipe of the pump was152 mm, and the valve was fitted in this pipe to regulate the dis-charge. The pump was placed at a level lower than the minimum water level in the sump to avoid the priming problem in them. The

delivered water from the pumps was returned to the undergroundsump through a return drain to maintain continuous recirculation of water in the model.

Table 2. Details of CW and ACW Pumps

Description CW pumps ACW pumps

Number of working pumps 4 2

Number of pumps standby 1 1

Total number of pumps 5 3

Design flow per pump 20;000 m 3=h 1;400 m 3=h

Maximum flow per pump 24;000 m 3=hr 1;680 m 3=h

4




An ultrasonic flow meter (Panametric P878) was used to mea-sure the discharge in the suction pipe of each pump. A bend meter fitted in each suction pipe was calibrated by measuring the gaugepressure in its outer bend for different discharges. A digital point gauge of 0.01-mm accuracy was used to measure the water level inthe sump. A Nortek 10-MHz acoustic Doppler velocity (ADV) witha down-looking probe was used to measure three-dimensional (3D)velocities in the bays. Flow visualization was achieved by using

food dye injected through a hypodermic needle and placed at de-sired points in the flow field. Flow patterns were photographed andvideotaped using a high-resolution camera. A four-blade vortimeter supported with low-friction pivoted shaft was used to measure theswirl angle in the suction pipe at impeller level. A Prandtl-type pitot tube attached to a vertical manometer was used to measure axialvelocities along two perpendicular axes at the throat of thebell mouth.

Test Procedure

The procedure for the model study involved, first, starting the sup-ply pump and allowing the water to flow in the model. The valve,

fitted in the supply pipe, was regulated to ensure the desired dis-

charge in the system. Once the water level in the sump reaches thedesired level, the required number of CW and ACW pumps were

started. The valves fitted in the suction lines were regulated to

maintain the designed discharge of each suction line. Once the flow

in the model was stabilized after a suitable time, the following were

observed:1. With the help of dye, the flow in the sump was visualized to

identify the separation of flow and dead zones.2. Surface vortices were inspected by visually, and types of vor-

tices were identified with the help of dye injection.3. The possible existence of subsurface vortices was explored by

dye injection at selected locations on the wall and floor near thebell mouth, where a vortex may form.

4. For each run, the revolutions per minute of the vortimeter

was counted, and the swirl angle was calculated for eachpump.

5. The combination of pumps in operations giving high swirl an-gle is considered as a stringent combination of pumps. For thisstringent condition, measurements were taken for the cross-sectional and axial velocity, as mentioned in 6 and 7.

6. At a distance of 900 mm upstream of the pump center line, thecross-sectional velocity profile of the approach flow was mea-sured at three verticals. For each vertical, the velocity was mea-sured at three points for one of the stringent combinations of CW and ACW pumps in operations.

7. The axial velocity at the throat of the bell mouth was measuredat two perpendicular axes for one of the stringent combinationsof CW and ACW pumps in operations.

The model study was conducted for the following flow con-ditions:

1. Design discharge and minimum water level, i.e, 1:7 m;2. Design discharge and normal (intermediate) water level,

i.e, 1:1 m;3. Design discharge and maximum water level, i.e, 0:5 m;4. Higher discharges and minimum water level;5. Higher discharges and normal (intermediate) water level; and6. Higher discharges and maximum water level.

Different combinations of the CW and ACW pumps were

chosen considering the symmetry of flow in the system and the time

required to run the model.

Fig. 1. Layout of pump-sump model

Fig. 2. View of pump-sump model




Test Results

Test Results without Vortex Breakers

Tests were conducted for the following five operational combina-tions of CW and ACW pumps at design discharge and minimum water level without vortex breakers:

1. CW pumps 1, 2, 4, and 5; and ACW pumps 1 and 2;2. CW pumps 1, 2, 3, and 4; and ACW pumps 1 and 2;3. CW pumps 1 and 5 and ACW pumps 1 and 2;

4. CW pumps 2 and 3 and ACW pumps 1 and 2; and5. CW pumps 3 and 4 and ACW pumps 1 and 2.Flow was visualized in the forebay to identify flow separation

and dead zones. No separation of flow and dead zones were noticedin any of the tests. Furthermore, no separation of flow was observedwhen the dye was injected on the bed of the forebay. This confirmsthat a 20° diversion of side wall and 9° downward slopes are suf-ficient for negligible flow separation in the forebay. The flow ap-proaching the bay was straight. Virtually no surface vortices werefound in any of the tests. However, Type-2 (dye core) subsurfacevortices were noticed in most of the tests. For one of the stringent combinations of the pumps, i.e., CW 1, 2, 3, and 4, the flow near thebell mouth of CW 1was visualized by injecting the dye from the left and right sides. It was noticed that the flow had a clockwise spiral

motion. The results of the swirl angle are listed in Table 3. A clock-wise rotation of the vortimeter (looking down) was taken as pos-itive, and a counterclockwise as negative. The model vortimeter readings were obtained by averaging three 2-min readings. Except for Run 3, other runs showed high swirl angles, i.e., greater than 3°.Thus, vortex breakers were needed to limit the swirl angle for allthe five runs for which the model was tested. The swirl angles inACW pumps were negligible.

Proposed Vortex Breaker

On the basis of the visualization of flow pattern near the bell mouthand the number of trials, the size and shape of the vortex breaker, i.e., a conical vortex breaker (165-mm diameter and 82.5-mm height)

with splitter plates was proposed, as shown in Fig. 3. The plate wasof the shape of a right-angled triangle, with 82.5-mm-long right-angled arms, and fabricated by 5-mm-thick acrylic sheet. Such

eight plates were fitted on the slanted surface of the cone at equalintervals, i.e, at 45°. One splitter plate was extended to thefront wall.

Test Results with Vortex Breakers

Tests were conducted for five operational combinations of CW andACW pumps, as previously mentioned in subsection “Test Resultswithout Vortex Breakers,” at design discharge and minimum water

level with proposed vortex breakers. For the combination of pumps,i.e., CW 1, 2, 3, and 4, the flow near the bell mouth of CW 1 wasvisualized by dye injection from the left and right sides. It wasnoticed that the vortex breaker guides the flow to follow an axialdirection in the bell mouth. The results of the swirl angle are givenin Table 3. It is clear that the provision of vortex breakers is veryeffective in substantially reducing the swirl angle. Thus, it is rec-ommended to use the proposed vortex breaker to limit the swirlangle to 3°.

This study indicates that fixing the dimensions of a pump-sumpas recommended by various standards is merely a guideline. Apump-sump designed according to these standards may have a swirl angle of more than the requirement of the acceptance criteria.Thus, to meet the acceptance criteria of HIS (1980) and IIHR(Nakato 1990) a vortex breaker of suitable shape and size shouldbe used. This study recommends a conical vortex breaker witheight fins of base diameter equal to 0.75 times the bell mouth diam-eter; and breaker height that is 0.75 times the distance between thebell mouth and the floor.

Tests were also conducted at different discharges, water levels,and combinations of pumps with the vortex breaker. The resultsare listed in Tables 4–8, where Fm and F p = Froude numbers inthe model and the prototype, respectively; and V m and V p = veloc-ities in the suction line in the model and the prototype, respectively.In these tests, the swirl angle was not greater than 3°. The operationof CW 1, 2, 3, and 4 and ACW 1 and 2 were found to be

Table 3. Swirl Angle (θ) for Design Discharge and Minimum Water LevelWithout and With Vortex Breaker

Run number Pumps Swirl angle

Without vortexbreaker

With vortexbreaker

1 CW 1 5.3 0.1

CW 2 5.2 0.9

CW 4 5:2 0.0

CW 5 1:5 0:72 CW 1 8.9 0.1

CW 2 8.0 0.7

CW 3 1:5 0:1

CW 4 6.8 0.7

3 CW 2 0.9 1:8

CW 3 0.5 0.1

4 CW 3 3:2 0.0

CW 4 2.0 0.1

5 CW 1 4.4 0.1

CW 5 1:5 0:3

Fig. 3. Proposed vortex breaker fitted in model




most stringent among other combinations of CW and ACW pumps

operated in the model. In addition to the Fm ¼ F p condition, the

model tests were also conducted in Fm ≅ 1:5F p condition, as rec-

ommended by ANSI (1998). The variation of swirl angle with

Fm=F p is depicted in Fig. 4, clearly indicating that the maximum

swirl is not more than 2°, which is much lower than the recom-

mended values.Tests were also conducted for other combinations of pump at a

higher Froude number, i.e., Fm of up to 2:3F p. The results of all

such tests for variation of swirl angle with Froude number are plot-

ted in Fig. 5. The trend line shows that even up to Fm=F p ¼ 2:3, the

swirl angle is within 2°. This finding is also supported by the varia-

tion of swirl angle with velocity ratio for all the tests shown

in Fig. 6.The subsurface vortices increase with discharge because of

high-velocity shear near the bottom floor and the side walls near

Table 4. Maximum Discharge and Minimum Water Level

RunNo. Pumps

Q

(L=s)

θ

(degree) Fm=F p V m=V p

1 CW 1 23.95 0.0 1.4 0.4

CW 2 23.33 1.3 1.4 0.4

CW 4 23.30 0:2 1.4 0.4

CW 5 21.50 0:4 1.3 0.4

2 CW 1 24.60 0.1 1.5 0.5

CW 2 24.15 1.5 1.4 0.4

CW 3 23.85 1.3 1.4 0.4CW 4 25.03 1.0 1.5 0.5

3 CW 2 26.05 0.9 1.5 0.5

CW 3 26.01 0.6 1.5 0.5

CW 4 23.30 0.0 1.4 0.4

CW 5 20.21 0:3 1.2 0.4

4 CW 1 24.60 0.0 1.5 0.5

CW 3 26.51 0.4 1.6 0.5

CW 4 23.30 0:1 1.4 0.4

CW 5 20.21 0:6 1.2 0.4

5 CW 1 22.74 0.1 1.3 0.4

CW 2 26.76 1.1 1.6 0.5

CW 3 23.47 1.8 1.4 0.4

CW 5 18.95 0:4 1.1 0.3

6 CW 1 31.50 0.0 1.9 0.6

CW 2 36.37 1.2 2.1 0.7

7 CW 2 35.07 1.2 2.1 0.6

CW 3 39.21 1.2 2.3 0.7

8 CW 3 39.21 0.5 2.3 0.7

CW 4 37.66 0.4 2.2 0.7

9 CW 2 28.90 0.6 1.7 0.5

CW 3 30.08 1.2 1.8 0.6

CW 4 31.63 0.7 1.9 0.6

10 CW 1 30.85 0.1 1.8 0.6

CW 4 32.28 0.1 1.9 0.6

CW 5 22.18

0:5 1.3 0.4

Table 5. Maximum Discharge and Normal Water Level

Runnumber Pumps Q (L=s) θ (degree) Fm=F p V m=V p

1 CW 1 25.27 0.0 1.5 0.5

CW 2 25.69 1.1 1.5 0.5

CW 4 25.84 0.1 1.5 0.5

CW 5 18.88 0:7 1.1 0.3

2 CW 1 23.10 0.0 1.4 0.4

CW 2 23.52 0.7 1.4 0.4

CW 3 27.24 0.7 1.6 0.5

CW 4 27.37 1.6 1.6 0.5

3 CW 2 38.46 0.8 2.3 0.7

CW 3 44.01 0.1 2.6 0.8

Table 6. Design Discharge and Normal Water Level


1 CW 1 17.50 0.0 1 1

CW 2 17.50 1.2 1 1

CW 4 17.50 0.0 1 1

CW 5 17.50 0:1 1 1

2 CW 1 17.50 0.1 1 1

CW 2 17.50 1.0 1 1

CW 3 17.50 0.6 1 1CW 4 17.50 1.0 1 1

3 CW 2 17.50 0.1 1 1

CW 3 17.50 1.7 1 1

Table 7. Maximum Discharge and Maximum Water Level


1 CW 1 24.6 0.0 1.4 0.5

CW 2 24.8 0.4 1.5 0.5

CW 4 25.3 0.2 1.5 0.5

CW 5 18.6 0:9 1.1 0.3

2 CW 1 22.12 0.1 1.3 0.4

CW 2 22.74 0.9 1.3 0.4

CW 3 26.59 0.9 1.6 0.5

CW 4 26.54 0.7 1.6 0.5

3 CW 2 38.71 0.9 2.3 0.7

CW 3 43.82 0.1 2.6 0.8

Table 8. Design Discharge and Maximum Water Level

Run

number Pumps Q (L=s) θ (degree) Fm=F p V m=V p

1 CW 1 17.50 0.1 1 1

CW 2 17.50 0.5 1 1

CW 4 17.50 0.0 1 1

CW 5 17.50 0:4 1 1

2 CW 1 17.50 0.1 1 1

CW 2 17.50 1.1 1 1

CW 3 17.50 1.1 1 1

CW 4 17.50 0.3 1 1

3 CW 2 17.50 0.5 1 1

CW 3 17.50 1.4 1 1

7




the bell mouth, which results in higher swirl angle. However, therate of increase of the swirl angle at discharges more than the Frou-dian discharge is not significant. The minor increase in the swirlangle at higher discharges, i.e, at higher Froude number and veloc-ity, is mainly attributed to high turbulence rather than the presenceof swirl in the flow. Thus, the results in Figs. 4 and 6 show that thestudy model should be conducted at Froudian similarity and at higher Froude numbers. This finding resolved the issue of not con-ducting the pump-sump study model at higher Froude numbers, assuggested by other previous investigators.

Velocity Distribution in Bays

To study the spatial and temporal velocity distribution in bays,

3D velocities were measured at nine points on a section, located

at 900 mm upstream of the center line of the suction line. For this

purpose, pump combinations CW 1, 2, 4, and 5 and ACW 1 and 2were undertaken. The location of the nine points on a section is

shown in Fig. 7. The model was run for the design discharge

and minimum water level, i.e., 1:7 m. Because of low velocities

(6 mm =s) in the bays, the use of miniature-type propeller current

meter and conventional pitot tube was not practically feasible.

Thus, the Nortek 10-MHz ADV meter was used for this purpose.

Velocity measurement near the bed of bays was not possible

because of the limited length of the ADV probe. At a point, 3D

velocities were measured for 60 s. Temporal variations of 3D point

velocities at all the nine points in two bays are shown in Figs. 8 and

9. In these figures u, v, and w = velocities in the direction of flow x ,

transverse direction y, and vertical direction z, respectively.

Longitudinal velocity distributions over the flow area in the baysof CW 4 and 5 were almost uniform, with an average velocity of

6 mm =s. However, the velocity in the right vertical at the upper

layer of the CW 1 bay was 3 mm =s, which was lower than the aver-

aged velocity. Longitudinal velocity in the right vertical of the

CW 2 bay was low—this was also visually observed during the

model run. The CW 3 was not operational, and this had resulted

in a slight nonuniformity in the flow in CW 1 and 2. Such low

velocities in the right vertical of the CW 1 and 2 bays resulted

in approximately 5° swirl angle in the clockwise direction. Thus,

vortex breakers are required to limit the swirl angle within a per-

missible value.

Fm /F

p

0.8 1.0 1.2 1.4 1.6 1.8 2.0

S w i r l A n g l e

-1

0

1

2

3

4

5

Design Discharge

Higher Discharges

Trend line

Fig. 4. Variation of swirl angle with ratio of Froude number Fm=F p for

operation of pump combinations CW 1, 2, 3, and 4 and ACW 1 and 2

Fm /F

p

0.9 1.1 1.3 1.5 1.7 1.9 2.1 2.3 2.5

S

w i r l A n g l e

-2

-1

0

1

2

3

4

5

Design Discharge

Higher Discharges

Trend line

Fig. 5. Variation of swirl angle with ratio of Froude number Fm=F p for

operation of all combination of pumps

Vm /V

p

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

S w i r l A n g l e

-2

-1

0

1

2

3

4

5

Design Discharge

Higher Discharges

Trend line

Fig. 6. Variation of swirl angle with velocity ratios for operation of all

combination of pumps

Fig. 7. Location of points in bay where velocities were measured




Time [s]

V e l o c i t y [ m / s ]

-10

-5

0

5

10

u

v

w

Point:P1

Point:P2 Point:P

3

(a) Upper Layer

Time [s]


-10

-5

0

5

10

u

v

w

Point:P4

Point:P5 Point:P

6

(b) Middle Layer

Time [s]

0 20 40 60 80 100 120 140 160 180

0 20 40 60 80 100 120 140 160 180

0 20 40 60 80 100 120 140 160 180


-10

-5

0

5

10

u

vw

Point:P7

Point:P8 Point:P

9

(c) Lower Layer

Fig. 8. Temporal variation of 3D velocities at various points in CW 1




Axial Velocity Distribution at Throat of Bell Mouth

Axial velocities at five points at throat of bell mouth as shown in

Fig. 10 were measured using 3 mm Pitot tube. These velocities

were taken for one of the stringent combinations of four CW pumps

i.e, CW-1, CW-2, CW-3, CW-4 at design discharge and minimum

water level with vortex breakers. The measured velocities are

depicted in Fig. 11, which indicates that the point velocities were

almost uniform over the throat and were well within the 10% of the

average velocity. Thus, the same is acceptable as per HIS accep-

tance criteria. The velocity at point 3, located near the front wall

was more in all the throats due to convergence of streamline toward

this point.

Time [s]


-10

-5

0

5

10

u

v

w

Point:P1

Point:P2 Point:P

3

(a) Upper Layer

Time [s]


-10

-5

0

5

10

u

v

w

Point:P4

Point:P5 Point:P

6

(b) Middle Layer

Time [s]

0 20 40 60 80 100 120 140 160 180

0 20 40 60 80 100 120 140 160 180

0 20 40 60 80 100 120 140 160 180

V e l o c i t y

[ m / s ]

-10

-5

0

5

10

u

v

w

Point:P7

Point:P8 Point:P

9

(c) Lower Layer

Fig. 9. Temporal variation of 3D velocities at various points in CW 2

12

3

5

4

4 4 m m

Flow direction

Throat of bell m

Fig. 10. Location of points for measurement of axial velocity




Conclusions

The present model study of a pump-sump yields the following ob-servations. No separation of flow and dead zones were found in theforebay. Furthermore, no separation of flow was observed once thedye was injected on the bed of the forebay. This confirms that a 20°diversion of side walls and a 9° downward slope are sufficient for negligible flow separation in the forebay. No surface vortices wereobserved in any of the tests; however, Type-2 subsurface vortices

were noticed in most of the tests without vortex breaker. Swirl an-gle was high in most of the tests without vortex breakers. A conicalvortex breaker with eight fins was very effective in reducing theswirl angle. Tests conducted at higher Froude number and velocityratios for different combinations of pumps and water levels indicatea minor increase in the swirl, which can be mainly attributed to a higher level of turbulence rather than the swirl in the flow. The mea-sured velocity distribution in bays for pump combination CW 1, 2,4, and 5 indicates a fairly uniform velocity distribution in the baysof CW 4 and 5 and minor nonuniformity in the bays of CW 1 and 2.The measured axial velocities at five points at the throat of the bellmouth of four CW pumps (i.e, CW 1, 2, 3, and 4) indicate that thepoint velocities are almost uniform over the throat and are wellwithin the 10% of the average velocity in all the throats. It is con-cluded from this study that fixing the dimensions of a pump-sumpas recommended by various standards is merely a guideline. Tomeet the acceptance criteria of standards, a vortex breaker of suit-able shape and size should used. A conical vortex breaker witheight fins of base diameter equal to 0.75 times the bell mouth diam-eter and a breaker height that is 0.75 times the distance between thebell mouth and the floor is recommended. It is also concluded that the model study should be conducted at Froudian similarity and not at higher Froude numbers. This finding resolved the issue of not conducting the pump-sump model study at a Froude number greater than the prototype Froude number, as suggested by other previous investigators.

Acknowledgments

The writers wish to sincerely thank the reviewers whose commentsgreatly improved the quality of this paper. The writers would alsolike to thank the laboratory staff of the hydraulics laboratory of theDepartment of Civil Engineering, IIT Roorkee for their help in con-ducting the model tests.

Notation

The following symbols are used in this paper:

d = diameter of suction pipe;F = Froude number;

Fm = Froude number in model;F p = Froude number in prototype; L r = length scale;Qr = discharge scale;S c = critical submergence.T r = time scale;

V m = velocity in suction line in the model;V p = velocity in suction line in the prototype;

V r = velocity scale;V z = axial velocity in suction pipe;V θ = tangential velocity at radial distance;θ = swirl angle; andω = angular velocity of vortimeter.

References

Ahmad, Z., Rao, K. V., and Mittal, M. K. (2008). “Critical submergence for horizontal intakes in open channel flows.” J. Dam Eng., 19(2), 71–90.

American National Standards Institute (ANSI). 1998). “Pump intake de-sign.” ANSI/HI 9.8, New York.

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

V e l o c i t y ( m / s )




0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

(a) CW-1(b) CW-2

(c) CW-3 (d) CW-4

1

2

3

4

51

2

2

2

1

1

3

3

3

4

4

4

5

5

5

Fig. 11. Axial velocity at different points at throat of bell mouth




Queries

1. Please check that ASCE Membership Grade Marks (M.ASCE, etc.) are provided for all authors that are members.

2. Please check if changes in sentence “This could be controlled...,” are appropriate.

3. Please check if changes in sentence “The various dimensions of the model...,” are appropriate.

4. We have defined rpm as revolutions per minute. Is this correct?

5. HIS 1980 is not in your reference list. Please provide full reference information or remove this citation.

6. Table parts (Tables 4a to 4e) were converted into separate tables (Tables 4 to 8). Please check.

7. Please check if changes in sentence “In addition to the Fm ¼ F p condition...,” are appropriate.

8. Please check if changes in sentence “This finding is also supported by the variation...,” are appropriate.

9. Please confirm the changes to American National Standards Institute 1998. Hydraulic Institute Standard 9.8 was changed toAmerican National Standards Institute and the standard was assumed as ANSI/HI 9.8. New York was supplied as location.

10. Please confirm the changes to American National Standards Institute 2001.

11. In Anwar 1965, please indicate the volume and page numbers.

12. In Anwar 1966, please indicate the volume and page numbers and make sure that the journal title is correct.

13. In Anwar et al. 1978, please indicate the volume and page numbers and make sure that the journal title is correct.

14. Please confirm the changes to Bureau of Indian Standards (BIS) 2003.

15. In Chang 1979, please indicate the location (city, state, country) of British Hydromechanics Research Association (BHRA).

16. In Daggett and Keulegan 1974, please indicate the page range.

17. Please confirm the suplied page range to Denny 1956.

18. In Denny and Young 1957, please indicate the location (city, state/country) of IAHR.

19. Please insert a location for McGraw-Hill (city, state/country)

20. In Prosser 1977, please indicate the location (city, state/country) of Construction Industry Research and Information Association.

21. In Rohan 1966, please indicate the location (city, state/country) of CWPRS. For proceedings, ASCE requires the location of thepublisher/sponsor, not the location of the event.

22. Do you have an update regarding the publication of Singh and Adachi 2010?


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