A Theoretical Analysis of Unsteady Fluid Forces and Pressure Distributions on a Blade of Cavitating Cascades. 1st Report, The Flow with Flow Rate Fluctuation and Inlet Pressure Fluctuation.

Abstract Affected by rotor–stator interaction and unstable inner flow, asymmetric pressure distributions and pressure fluctuations cannot be avoided in centrifugal pumps. To study the pressure distributions on volute and front casing walls, dynamic pressure tests are carried out on a centrifugal pump. Frequency spectrum analysis of pressure fluctuation is presented based on Fast Fourier transform and steady pressure distribution is obtained based on time-average method. The results show that amplitudes of pressure fluctuation and blade-passing frequency are sensitive to the flow rate. At low flow rates, high-pressure region and large pressure gradients near the volute tongue are observed, and the main factors contributing to the pressure fluctuation are fluctuations in blade-passing frequency and high-frequency fluctuations. By contrast, at high flow rates, fluctuations of rotating-frequency and low frequencies are the main contributors to pressure fluctuation. Moreover, at low flow rates, pressure near volute tongue increases rapidly at first and thereafter increases slowly, whereas at high flow rates, pressure decreases sharply. Asymmetries are observed in the pressure distributions on both volute and front casing walls. With increasing of flow rate, both asymmetries in the pressure distributions and magnitude of the pressure decrease.

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Analysis of Unsteady Pressure Fluctuation in a Semi-Open Cutting Pump

Energies ◽

10.3390/en13143657 ◽

2020 ◽

Vol 13 (14) ◽

pp. 3657

Author(s):

Weidong Cao ◽

Jiayu Mao ◽

Wei Li

Keyword(s):

Flow Rate ◽

Pressure Fluctuation ◽

Pressure Fluctuations ◽

Three Dimensional ◽

Flow Characteristics ◽

Internal Flow ◽

Lower Plate ◽

Pressure Distributions ◽

Axial Forces ◽

Blade Frequency

In order to understand the pressure fluctuation characteristics of a semi-open cutting pump, the three-dimensional unsteady flow fields were calculated. External and internal flow characteristics of four schemes with different relative angles between the rotary cutter and the impeller were studied. The pressure fluctuations in the lower plate, the upper plate, the clearance between the rotary cutter and the fixed cutter, the first section in volute and nearby parts of the tongue were all analyzed, which are all the places that pressure distributions are greatly affected by the static and dynamic interaction, and at the same time, the force on the impeller was also analyzed. The results show that the fluctuations at different positions change periodically; the main frequency is blade frequency. The amplitude of pressure fluctuation decreases from near the rotating part to far away, from near the tongue to far from the tongue. Due to the influence of both impeller and rotary cutter, the pressure fluctuation on the lower plate is the largest. The pressure fluctuation is affected by flow rate, the larger the flow rate, the greater the pressure fluctuation. The radial and axial forces of the impeller change periodically with time, and the number of wave peaks and wave valleys is the same as the number of blades.

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Effect of incidence angle on cavity blockage and flow stability in the net positive suction head drop of mixed-flow pumps

Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science ◽

10.1177/0954406220973055 ◽

2020 ◽

pp. 095440622097305

Author(s):

Yong-In Kim ◽

Sung Kim ◽

Kyoung-Yong Lee ◽

Young-Seok Choi

Keyword(s):

Flow Pattern ◽

Flow Rate ◽

Pressure Fluctuation ◽

Incidence Angle ◽

Experimental Tests ◽

Design Flow ◽

Inlet Pressure ◽

Stable Flow ◽

Fft Analysis ◽

Design Flow Rate

The cavitation is an inevitable factor in pumps used in the whole industry, which is a major cause of energy loss and mechanical breakdown. In this study, the cavitation phenomena at the design flow rate were numerically analyzed for two pumps with different incidence angles. The design flow rate for both models was located near the best efficiency point (BEP). The incidence angle was determined with the impeller inlet diameter and the blade angle. A pump with a smaller incidence angle consistently showed a stable flow pattern as the inlet pressure decreased, whereas a pump with a larger incidence angle contained non-uniform flow streamlines despite a very small amount of the generated cavities. The flow pattern at the impeller inlet was handled by the shape and thickness of the generated cavities which could act as an additional blockage in the pumps. The inception and growth of the cavity with a decrease of inlet pressure were also inferred, which was specifically quantified as the blockage ratio. A pump with a larger incidence angle performed poor cavitation characteristics and obtained the pressure fluctuation and cavity oscillation. The magnitude of pressure fluctuation was indicated using the fast Fourier transform (FFT) analysis. The experimental tests were performed on both pumps to validate the numerical results.

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Theoretical Analysis of Unsteady Fluid Forces Working on Inducer Blades Under Rotating Cavitation.

TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series B ◽

10.1299/kikaib.67.688 ◽

2001 ◽

Vol 67 (655) ◽

pp. 688-695

Author(s):

Satoshi WATANABE ◽

Hironori HOROGUCHI ◽

Akinori FURUKAWA ◽

Junichiro FUKUTOMI ◽

Yoshinobu TSUJIMOTO

Keyword(s):

Theoretical Analysis ◽

Fluid Forces ◽

Unsteady Fluid

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Theoretical Analysis of Fluid Forces on an Open-Type Centrifugal Impeller in Whirling Motion

Journal of Fluids Engineering ◽

10.1115/1.1458582 ◽

2002 ◽

Vol 124 (2) ◽

pp. 342-347 ◽

Cited By ~ 8

Author(s):

Akira Hiwata ◽

Yoshinobu Tsujimoto

Keyword(s):

Theoretical Analysis ◽

Temporal Change ◽

Centrifugal Impeller ◽

Shaft Speed ◽

Open Type ◽

Tip Leakage ◽

Fluid Forces ◽

Whirling Motion ◽

Minor Contribution ◽

Unsteady Fluid

For turbomachines operating at supercritical shaft speed, it is important to understand the characteristics of unsteady fluid forces on the impeller that occur due to shaft vibration. The present paper treats the forces on an open-type centrifugal impeller in whirling motion using unsteady potential flow theory. The whirling forces obtained agree reasonably with experimental results and show a destabilizing region at small positive whirl. It was found that the destabilizing force is due to the forces on the hub caused by temporal change in the thickness of the flow channel, with minor contribution of tip leakage on the destabilization.

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The Effect of Fuel Staging on the Structure and Instability Characteristics of Swirl-Stabilized Flames in a Lean Premixed Multi-Nozzle Can Combustor

Volume 4A: Combustion, Fuels and Emissions ◽

10.1115/gt2017-63688 ◽

2017 ◽

Cited By ~ 1

Author(s):

Janith Samarasinghe ◽

Wyatt Culler ◽

Bryan D. Quay ◽

Domenic A. Santavicca ◽

Jacqueline O’Connor

Keyword(s):

Heat Release ◽

Flow Rate ◽

Heat Release Rate ◽

Release Rate ◽

Pressure Fluctuation ◽

Fuel Flow Rate ◽

Fuel Flow ◽

Rate Fluctuation ◽

Fuel Staging ◽

Fluctuation Amplitude

Fuel staging, or fuel splitting, is a commonly used strategy for the suppression of combustion instabilities in gas turbine engines. In multi-nozzle combustor configurations, this is achieved by varying the fuel flow rate to the different nozzles. The effect of fuel staging on flame stabilization and heat release rate distribution (referred to as flame structure), and self-excited instability characteristics is investigated in a research can combustor employing five small-scale lean-premixed industrial nozzles. The nozzles are arranged in a “four-around-one” configuration and fuel staging is achieved by injecting additional fuel to the middle nozzle. An operating condition was identified where all five nozzles were fueled equally and the combustor was subject to a self-excited instability. At the operating condition considered, the self-excited instabilities are suppressed with fuel staging: this is true for cases where overall equivalence ratio is increased by staging (by only increasing the fuel flow rate to the middle nozzle) as well as cases where overall equivalence ratio is kept constant while staging (by simultaneously decreasing the fuel flow rate of the outer nozzles while increasing the fuel flow rate to the middle nozzle). Fuel staging causes variations in the distribution of time-averaged heat release rate in the regions where adjacent flames interact. The locations of highest heat release rate fluctuation are not altered with increased fuel staging but the fluctuation amplitude is reduced. A breakup in the monotonic phase behavior that is characteristic of convective disturbances is observed with increased fuel staging, resulting in a lower pressure fluctuation amplitude. In particular, the monotonic variation in phase in the middle flame and the region where adjacent flames interact is out-of-phase with that of the outer flames, resulting in a cancellation of the global heat release rate oscillations. The distribution of local Rayleigh integral within the combustor shows that during a self-excited instability, the regions of highest heat release rate fluctuation are in phase-with the pressure fluctuation. When staging fuel is introduced, these regions fluctuate out-of-phase with the pressure fluctuation, further illustrating that fuel staging suppresses instabilities by altering the phase relationship of convective disturbances that travel along the flame front.

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Stabilization of the Speed of the Hydraulic Motor Through Throttle Compensation for Volume Losses

International conference KNOWLEDGE-BASED ORGANIZATION ◽

10.2478/kbo-2020-0126 ◽

2020 ◽

Vol 26 (3) ◽

pp. 126-130

Author(s):

Krasimir Kalev

Keyword(s):

Flow Rate ◽

Hydraulic Drive ◽

Pressure Change ◽

Operating Conditions ◽

Drive System ◽

Inlet Pressure ◽

Schematic Diagram ◽

Hydraulic Characteristics ◽

Hydraulic Motor ◽

Flow Through

AbstractA schematic diagram of a hydraulic drive system is provided to stabilize the speed of the working body by compensating for volumetric losses in the hydraulic motor. The diagram shows the inclusion of an originally developed self-adjusting choke whose flow rate in the inlet pressure change range tends to reverse - with increasing pressure the flow through it decreases. Dependent on the hydraulic characteristics of the hydraulic motor and the specific operating conditions.

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Large Eddy Simulation of Periodic Transient Pressure Fluctuation in a Centrifugal Pump Impeller at Low Flow Rate

Symmetry ◽

10.3390/sym13020311 ◽

2021 ◽

Vol 13 (2) ◽

pp. 311

Author(s):

Renfei Kuang ◽

Xiaoping Chen ◽

Zhiming Zhang ◽

Zuchao Zhu ◽

Yu Li

Keyword(s):

Large Eddy Simulation ◽

Centrifugal Pump ◽

Flow Rate ◽

Pressure Fluctuation ◽

Low Frequency ◽

Pump Impeller ◽

Eddy Simulation ◽

Inlet Flow Rate ◽

Large Eddy ◽

Centrifugal Pump Impeller

This paper presents a large eddy simulation of a centrifugal pump impeller during a transient condition. The flow rate is sinusoidal and oscillates between 0.25Qd (Qd indicates design load) and 0.75Qd when the rotating speed is maintained. Research shows that in one period, the inlet flow rate will twice reach 0.5Qd, and among the impeller of one moment is a stall state, but the other is a non-stall state. In the process of flow development, the evolution of low-frequency pressure fluctuation shows an obviously sinusoidal form, whose frequency is insensitive to the monitoring position and equals to that of the flow rate. However, inside the impeller, the phase and amplitude in the stall passages lag behind more and are stronger than that in the non-stall passages. Meanwhile, the strongest region of the high-frequency pressure fluctuation appears in the stall passages at the transient rising stage. The second dominant frequency in stall passages is 2.5 times to that in non-stall passages. In addition, similar to the pressure fluctuation, the evolution of the low-frequency head shows a sinusoidal form, whose phase is lagging behind that by one-third of a period in the inlet flow rate.

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Numerical and Experimental Analysis of Flow and Pulsation in Hump Section of Siphon Outlet Conduit of Axial Flow Pump Device

Applied Sciences ◽

10.3390/app11114941 ◽

2021 ◽

Vol 11 (11) ◽

pp. 4941

Author(s):

Fan Yang ◽

Yiqi Zhang ◽

Yao Yuan ◽

Chao Liu ◽

Zhongbin Li ◽

...

Keyword(s):

Flow Field ◽

Flow Rate ◽

Vortex Structure ◽

Pressure Fluctuation ◽

Axial Flow ◽

Mean Value ◽

Hydraulic Loss ◽

Pressure Amplitude ◽

Measuring Point ◽

Outlet Conduit

In order to study the variation law of the flow field and pressure fluctuation in the hump section of the siphon outlet conduit, the flow field characteristics and frequency spectrum characteristics of the flow field were analyzed by combining a physical model test and numerical simulation under the conditions of the interaction between the axial flow pump and siphon outlet conduit, and the influence of the residual circulation at the outlet of the guide vane on the siphon outlet flow was investigated. Based on the influence of the flow field and hydraulic loss in the conduit, the equivalent surface method based on the Q criterion was used to analyze the vortex structure in the siphon outlet conduit and to analyze the internal vortex state. The results showed that with the increase of the flow rate, the intensity of the vortices in the cross-section of the hump section of the siphon outlet conduit decreased gradually, the average velocity circulation decreased gradually and the axial velocity distribution uniformity increased and tended to be stable; water flow stratification existed under three characteristic conditions with no circulation, and the hydraulic loss was greater with the circulation flow while it had a circulation under the small flow condition. Under the low flow rate conditions, the hydraulic loss was 6.6 times higher under the condition of circulation than without. Under a high flow condition, it was 1.3 times. Under the condition of a small flow rate, the vortex structure was distributed centrally at the inlet of the flow conduit, and under the other two characteristic conditions, the vortex structure mostly appeared as a strip; the pressure fluctuation in the hump section had obvious periodicity, and with the increase of the flow rate, the maximum pressure fluctuation amplitude in the hump section decreased gradually; with the decrease of the rotational speed, the pressure amplitude at the same measuring point in the hump section decreased gradually and at the optimum condition. Under the following conditions, the mean value of the pressure amplitude at the top of the hump section was reduced by 69.63%, and the mean value of the pressure amplitude at the bottom of the hump section was reduced by 63.5%. Under all the calculation conditions, the main frequency of pulsation at each measuring point of the hump section was twice the frequency of the rotation.

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