Measurement of the flow around the submerged vortex cavitation in a pump intake by means of piv
01 Jan 2003-
TL;DR: In this article, the authors used particle image velocimetry to measure the flow around the vortex in a pump suction intake sump and evaluated the accuracy of CFD calculation predicting vortex cavitation.
Abstract: The flow structure of the vortex occurring in a pump suction intake sump has been investigated and the accuracy of CFD calculation predicting vortex cavitation evaluated experimentally by using particle image velocimetry to measure the flow around the vortex. The test apparatus consisting of the model suction intake and the pressure tank could control the mean inlet velocity, the circulation, and the pressure at the pump intake bell mouth. Vortices of various strengths were generated using this apparatus, and velocity fields around them were measured and compared — with respect to the velocity distribution, the circulation, and the core radius — with the corresponding fields obtained by CFD calculation. The results of those comparisons and the difference between the instantaneous and time-averaged velocity profiles are described and discussed.
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01 Oct 2007
TL;DR: In this article, the velocity and vorticity distribution in the sump were measured by using a PIV method and the calculated results were compared with experimental ones for flow patterns, locations of vortices, and their vortivity.
Abstract: The sump size is being reduced in order to lower the construction costs of urban drainage pump stations in Japan. As a result of such size reductions, undesirable vortices such as air-entrained and submerged vortices are apt to appear in sumps because of the higher flow velocities. The Turbomachinery Society of Japan (TSJ) Standard S002:2005 states that the appearance of such visible vortices is not permissible for conventional sumps, and experiments with scale models usually have been done to assess the performance of sumps. Such tests, however, are expensive and time-consuming, and therefore, alternative computational fluid dynamics (CFD) methods for evaluating sump performance are desirable. The Research Committee on Pump Sump Model Testing, which is an organization in the TSJ, carried out a benchmark for flows in model sumps. They contributed commercial CFD codes such as “Virtual Fluid System 3D”, “Star-CD 3.22”, “Star-CD 3.26”, and “ANSYS CFX 10.0”. Some of the benchmark results were reported by Matsui, J. at the 23 rd IAHR Symposium in Yokohama, Oct 2006. The remaining results comprise this second paper. The calculated results were compared with experimental ones for flow patterns, locations of vortices, and their vorticity. In the experiments, the critical submergences for flow rates were minutely examined through visual observation with a video camera. The locations of the vortices were obtained by using the laser light sheet visualization method. The velocity and vorticity distribution in the sump were measured by using a PIV method. The following results were obtained. 1) The critical submergence for the air-entrained vortex is almost proportional to the flow rate in the sump. The vortex behavior is unsteady and the duration of the vortex varies greatly. 2) The submerged vortex appears accompanying the air-entrained vortex in the region of low submergences and high flow rates. The critical submergence for the submerged vortex is also proportional to the flow rate. 3) Some CFD codes can predict the visible vortex occurrence and its location for submergence and flow rate conditions with enough accuracy for industrial use. 4) The calculated velocity distribution at the bell entrance qualitatively agrees with the experimental results. However, the agreement is poor in terms of the magnitude and distribution patterns of the vorticity. This difference is caused by the lack of accuracy of the experiment and CFD computation. 5) Predicting the critical submergence for the visible vortices was not imposed in the benchmark. The calculated stream lines and vortex core lines are not able to be used to predict the visible vortices with much accuracy. An additional post-processing such as obtaining the vortex core static pressure and comparing it with ambient pressure for an air-entrained vortex or with the saturated vapor pressure of the water for a submerged vortex would be necessary to predict the visible vortices.
49 citations
Cites background from "Measurement of the flow around the ..."
...As mentioned above, this is caused by that the experimental vorticity is calculated from the average velocity but the instantaneous velocity should be used instead (Nagahara 2003)....
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...Nagahara (2003) already pointed out this phenomenon....
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TL;DR: Effectiveness of anti-submerged vortex device (AVD) for the suppression of the vortex occurrence in a single pump intake, as well as in a multi-intake pump sump model has been examined by the methods of experiment and numerical analysis.
Abstract: The head-capacity curves for pumps developed by the pump manufacturer are based on tests of a single pump operation in a semi-infinite basin with no close walls or floors and with no stray currents. Therefore, flow into the pump intake is with no vortices or swirling. However, pump station designers relying on these curves to define the operating conditions for the pump selected sometimes experience reductions of capacity and efficiency, as well as the increase of vibration and additional noise, which are caused by free air mixed with the pump inlet flow. Therefore, sump model test is necessary in order to examine the flow structure around pump intake. In this study, flow uniformity according to the flow distribution in the pump intake channel is examined to find out the cause of vortex occurrence in detail. A multi-intake pump sump model with 7 pump intakes and a single-intake pump sump model are adopted for the investigation. Furthermore, effectiveness of anti-submerged vortex device (AVD) for the suppression of the vortex occurrence in a single pump intake, as well as in a multi-intake pump sump model has been examined by the methods of experiment and numerical analysis. The results show that most high value of flow uniformity is found at the inlet of pump intakes #3 and 5 in the multi-intake pump sump with 7 pump intakes. Therefore, when the pump station is designed, the flow patterns at the upstream region of pump intake inlet in the forebay diffusing area should be to consider in detail because the unbalanced flow at the channel inlet region gives considerable influence on the vortex occurrence around bell-mouth. Strong submerged vortex can be successfully suppressed by AVD installation on the bottom of pump intake channel just below the bell mouth.
46 citations
26 Nov 2012
TL;DR: In this paper, the authors examined the cause of vortex occurrence in detail by experiment and CFD, and the effectiveness of an anti vortex device for the suppression of the vortex occurrence has been examined by AVD type.
Abstract: The head-capacity curves of pumps developed by the pump manufacturer are based on tests of a single pump operation in a semi-infinite basin with no closed walls of floors and with no stray currents. Therefore, the flow into the pump intake has no vortices of swirling. However, pump station designers relying on these curves to define the operating conditions for the selected pump sometimes experience reductions in capacity and efficiency, as well as an increase of vibration and additional noise. Therefore, sump model testing is necessary in order to examine the flow structure around intake. In this study, flow uniformity according to the flow distribution in the pump intake channel is examined to find out the cause of vortex occurrence in detail by experiment and CFD. Furthermore, the effectiveness of an anti vortex device for the suppression of the vortex occurrence in a single intake pump sump model has been examined by AVD type. The AVDs used for experimental testing, one of which has the shape of a rectangular bar and the other was a trident shape, are attached at the bottom of pump intake channel just below the bell-mouth. The AVD type for CFD test is in the shape of a trident. The experimental sump model was scaled down by a ratio of 1:8 whereas the CFD sump model was scaled to the actual size.
24 citations
TL;DR: In this paper, an experimental investigation on the effective shape of a floor splitter to reduce sub-surface vortices and cavitation which arise in the vicinity of the pump bells in pump sump is performed.
Abstract: An experimental investigation on the effective shape of a floor splitter to reduce sub-surface vortices and cavitation which arise in the vicinity of the pump bells in pump sump is performed. A test model sump was designed based on the Froude number similitude for the recommended structure layout by HI-9.8 standard for pump intake design. To obtain an effective shape of the splitter as an anti-vortex device (AVD), three types of quadrilateral submerged bar with different shape and dimension in sectional area are considered. From the experimental results with and without the splitter attached on the floor under the bell mouth, it was confirmed that the installation of the AVD is very effective to reduce abnormal vortices including sub-surface vortices, pre-swirls and other undesirable hydraulic phenomena. Because of the splitter, sub-surface vortices under the bell mouth did not appear anymore and the swirl was dramatically weakened. The evaluation of AVD was made by the measurement of swirl angles indicating the strength of the vortices and pre-swirls. Splitters with square sections showed partly large swirl angles beyond the acceptable criteria of HI standard though a large square was more effective than a small one. Meanwhile, the splitter with trapezoidal section was showed swirl angle values of less than 5 degrees in all cases of pump operation. Among the three types of AVD, the trapezoidal splitter is the most effective one to suppress the vortices. It is very useful to reduce the occurrence of submerged vortices and to obtain stable inflow condition for designing a high performance pump sump.
17 citations
TL;DR: In this article, a new configuration was proposed for reservoir bottom outlet to increase the pressurized flushing efficiency, where a projecting semi-circular structure was connected to the upstream edge of bottom outlet.
Abstract: Sediment flushing in many reservoirs of the world is accomplished with low efficiency. In this study, a new configuration was proposed for reservoir bottom outlet to increase the pressurized flushing efficiency. In the new configuration, a projecting semi-circular structure was connected to the upstream edge of bottom outlet. It was observed that by employing the projecting bottom outlet, the sediment removal efficiency increased significantly compared to the flushing via typical bottom outlet. In the case of new-configuration bottom outlet with L
sc
/D
outlet
= 5.26 and D
sc
/D
outlet
= 1.32, the dimensionless length, width and depth of flushing cone increased 280%, 45% and 14%, respectively, compared to the reference test. The proposed structure can ensure the sustainable use of reservoirs.
16 citations
Cites background from "Measurement of the flow around the ..."
...Nagahara et al. (2003) claimed that the velocity and pressure distribution of these submerged vortices is such a way that, at the center of the vortex the velocity is maximum and the pressure is minimum, so that, by increasing the distance from the center, the velocity decreases and the pressure increases....
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...Nagahara et al. (2003) claimed that the velocity and pressure distribution of these submerged vortices is such a way that, at the center of the vortex the velocity is maximum and the pressure is minimum, so that, by increasing the distance from the center, the velocity decreases and the pressure…...
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References
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TL;DR: In this paper, the authors used LDV measurements of the tangential velocity component in the tip vortex to determine that the minimum pressure in the vortex varies with lift coefficient squared, i.e., that the incipient cavitation number σi should follow a Cl 2 relation (σi ≈ Cl 2 ).
Abstract: Tip vortex cavitation studies were made with a hydrofoil that was elliptical in planform, with an aspect ratio of 3, and having a modified NACA 662 -415 profile. LDV measurements of the tangential velocity component in the vortex were used to determine that the minimum pressure in the vortex varies with lift coefficient squared, i.e., that the incipient cavitation number σi should follow a Cl 2 relation (σi ≈ Cl 2 ). This is in contradiction to previous observations (Arndt et al. 1991) that the tip vortex cavitation index varied approximately with lift coefficient to the power 1.4. By carefully monitoring the tensile strength of the water, i.e., its susceptibility to cavitation, the discrepancy was traced to the capability of the test water to sustain a tensile stress. Cavitation in “weak” water (no tensile strength) does follow the Cl 2 relationship, whereas observations in “strong” water (rupture considerably below vapor pressure) more closely followed the previously observed variation, i.e., σi ≈ Cl 1.4 . Since the structure of the vortex cannot be affected by changes in the water quality, the discrepancy can be explained only by the amount of tension that can be sustained by the test water before inception occurs. Apparently a relatively larger value of tension can be sustained in the vortex is the strength of the vortex is increased (i.e., increasing Cl ). This would explain the observed deviation from the expected Cl 2 law for water with measurable tensile strength.
106 citations
"Measurement of the flow around the ..." refers background in this paper
...Thus, it appears that the velocity profile around the cavitating cores in the vicinity of the vortex center slightly increase compared with the velocity profile of vortices having noncavitating cores in order to compensate the lack of the total angular momentum per unit length in the vortex core because of the cavitation [8]....
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TL;DR: In this paper, experiments aimed at improving the understanding of vortices that form in water-pump intake bays were conducted in a laboratory model of a simple intake bay compri...
Abstract: This paper describes experiments aimed at improving the understanding of vortices that form in water-pump intake bays. Experiments were conducted in a laboratory model of a simple intake bay compri...
71 citations
"Measurement of the flow around the ..." refers result in this paper
...[2,3] reported that the numerically simulated flow field around the intake sump of a model pump was in good agreement with the one measured by particle imaging velocimetry (PIV)....
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01 Jan 2001
TL;DR: In this article, the effect of submerged vortices on the hydraulic forces of a mixed-flow pump impeller was studied using a model pump with an intake sump, and the relationship between the strength of the submerged vortex and its effect on the fluctuation of hydraulic forces was described.
Abstract: The effect of submerged vortices on the hydraulic forces of a mixed flow pump impeller was studied using a model pump with an intake sump. The experiments comprise observation of submerged vortices reaching the impeller with a high-speed video camera and measurement of the velocity distribution around the submerged vortex by PTV (particle tracking velocimetry) to obtain the strength of the vortex. Measurement results are compared with CFD (computational fluid dynamics) calculation to evaluate their accuracy. Hydraulic forces on the model pump when the submerged vortex reached the pump impeller was measured with load cells. The relationship between the strength of the submerged vortex and the effect of the vortex on the fluctuation of the hydraulic forces are described
19 citations
"Measurement of the flow around the ..." refers background in this paper
...On the other hand, we previously investigated the effect of the occurrence of submerged vortices on the hydraulic forces of the pump impeller [7]....
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