Transient Characteristics of a Closed-Loop Pipe System During Pump Stopping Periods

2014 ◽  
Vol 136 (2) ◽  
Author(s):  
Dazhuan Wu ◽  
Peng Wu ◽  
Shuai Yang ◽  
Leqin Wang
Keyword(s):  
Kinetic Energy ◽  
Flow Rate ◽  
Rotational Speed ◽  
Closed Loop ◽  
Transient Flow ◽  
Operating Conditions ◽  
Rotational Inertia ◽  
Transient Characteristics ◽  
Pipe System ◽  
The Impact

In order to study the transient characteristics of a closed-loop pipe system with room temperature water, experiments were carried out based on different pump stopping periods from rate rotational speed to zero. Various stopping periods were realized by changing the rotational inertia of the rotors, controlling the frequency of the motor and braking the shaft. Experimental results of different operating schemes were compared, and transient flow rate of the pipe system and transient characteristics of the pump were analyzed. The influences of the kinetic energy of the loop fluid and pump rotors to the stopping periods were summarized. Results show that rapid change of the pump operating conditions occurs during the stopping period and transient flow rate of the pipe system and characteristics of the pump depend largely on the way of stopping. The kinetic energy stored in the pump can drive the impeller keeping rotating for more time after the motor is shutdown. Due to the kinetic energy stored in the loop pipe, the flow rate does not reach zero immediately after the rotational speed reaches zero. The inertia of pump rotor and fluid inertia affect the impact of fluid flow and the duration of the loop during pump stopping period.

Experimental and Numerical Studies of Pump Transient Characteristics During Stopping Period

2014 ◽  
Author(s):  
Peng Wu ◽  
Dazhuan Wu ◽  
Leqin Wang
Keyword(s):  
Centrifugal Pump ◽  
Flow Rate ◽  
Rotational Speed ◽  
Pressure Rise ◽  
Operating Conditions ◽  
Hydrodynamic Characteristics ◽  
Rotational Inertia ◽  
Operating Characteristics ◽  
Transient Characteristics ◽  
Numerical Studies

Experimental and numerical studies were carried out to study the transient characteristics of the centrifugal pump during stopping periods. Different stopping schemes were realized by changing the rotational inertia of the flywheels. Transient revolution rotational speed, flow-rate, total pressure rise and torque were measured under different rotational inertia. Experimental results of different operating conditions were compared, and transient hydrodynamics performances of the centrifugal pump model were analyzed. In order to provide boundary conditions for numerical simulations, the revolution curves of the flow-rate and the rotational speed were polynomial fitted. Three dimensional unsteady incompressible viscous flows during stopping periods were studied by using DES model in FLUENT. Results show that the hydrodynamic characteristics of numeric and experiment agree well. The transient effect is not so evident, and the quasi-steady assumption is acceptable during most part of coastdown process. The pump characteristics are further explained by analyzing the relative velocity on the middle stream surfaces. At the end of the stopping period, the transient vortex evolution between blades is the main reason why the transient curves deviates the steady curve. The studies can help understand the operating characteristics of centrifugal pump when power failure accident occurs.

Numerical Investigation of Transient Flow in a Prototype Centrifugal Pump during Startup Period

2017 ◽  
Vol 34 (2) ◽  
Author(s):  
Yu-Liang Zhang ◽  
Zu-Chao Zhu ◽  
Hua-Shu Dou ◽  
Bao-Ling Cui ◽  
Yi Li ◽  
...  
Keyword(s):  
Centrifugal Pump ◽  
Flow Rate ◽  
Transient Flow ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Transient Performance ◽  
Pipe System ◽  
Incompressible Viscous Flow ◽  
Rotor Stator Interaction ◽  
Startup Period

AbstractTransient performance of pumps during transient operating periods, such as startup and stopping, has drawn more and more attentions recently due to the growing engineering needs. During the startup period of a pump, the performance parameters such as the flow rate and head would vary significantly in a broad range. Therefore, it is very difficult to accurately specify the unsteady boundary conditions for a pump alone to solve the transient flow in the absence of experimental results. The closed-loop pipe system including a centrifugal pump is built to accomplish the self-coupling calculation. The three-dimensional unsteady incompressible viscous flow inside the passage of the pump during startup period is numerically simulated using the dynamic mesh method. Simulation results show that there are tiny fluctuations in the flow rate even under stable operating conditions and this can be attributed to influence of the rotor–stator interaction. At the very beginning of the startup, the rising speed of the flow rate is lower than that of the rotational speed. It is also found that it is not suitable to predict the transient performance of pumps using the calculation method of quasi-steady flow, especially at the earlier period of the startup.

scholarly journals Numerical Investigation on a Prototype Centrifugal Pump Subjected to Fluctuating Rotational Speed

2014 ◽  
Vol 2014 ◽  
pp. 1-8
Author(s):  
Yu-Liang Zhang ◽  
Jun-Jian Xiao ◽  
Yan-Jun Zhao ◽  
Ying-Yu Ji
Keyword(s):  
Centrifugal Pump ◽  
Rotational Speed ◽  
Closed Loop ◽  
Static Pressure ◽  
Transient Flow ◽  
Response Characteristic ◽  
Turbulence Energy ◽  
Pipe System ◽  
Performance Results ◽  
Variation Tendency

The rotational speed of pumps often encounters fluctuation in engineering for some reasons. In this paper, in order to study the transient response characteristic of a prototype centrifugal pump subjected to fluctuating rotational speed, a closed-loop pipe system including the pump is built to accomplish unsteady flow calculations in which the boundary conditions at the inlet and the outlet of the pump are not required to be set. The external performance results show that the head’s responsiveness to the fluctuating rotational speed is very good, while the flow rate’s responsiveness is slightly delayed. The variation tendencies of the static pressures at the inlet and the outlet of the pump are almost completely opposite, wherein the variation tendency of the static pressure at the outlet is identical with that of the rotational speed. The intensity of the turbulence energy in each impeller channel is relatively uniform in the transient flow calculations, while, in the quasi-steady flow calculation, it becomes weaker in a channel closed to the volute tongue. The nondimensional flow rate and head coefficients are dependent on the rotational speed, and their variation tendencies are opposite to that of the fluctuating rotational speed as a whole.

Study of Transient Behavior in Centrifugal Pump During Startup Period

2012 ◽  
Author(s):  
Yu-liang Zhang ◽  
Zu-chao Zhu ◽  
Bao-ling Cui ◽  
Yi Li
Keyword(s):  
Flow Field ◽  
Centrifugal Pump ◽  
Flow Rate ◽  
Transient Flow ◽  
Three Dimensional ◽  
Transient Behavior ◽  
Operating Conditions ◽  
Pipe System ◽  
Rotor Stator Interaction ◽  
Startup Period

To explore the transient characteristic of a centrifugal pump with the specific speed of 90 during startup period, the internal three-dimensional unsteady flow was solved by using CFD. Wherein to overcome the difficulty in implement of boundary conditions in numerical simulation, a closed-loop pipe system that includes a centrifugal pump was built to accomplish self-coupling calculation. The results show that at the very beginning of startup, flow rate rises slowly and non-dimensional head coefficient is much higher than quasi-steady value, the quasi-assumption can not be competent for predicting transient effect well. Moreover, the insufficient of energy conversion makes the evolvement of transient flow field lags behind that of quasi-steady flow field, i.e., kinetic energy can’t convert pressure energy in time during acceleration flow period. Rotor-stator interaction makes flow rate present slight fluctuation characteristic under stable operating conditions.

scholarly journals A New Method to Determine the Impact of Individual Field Quantities on Cycle-to-Cycle Variations in a Spark-Ignited Gas Engine

Energies ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 4136
Author(s):  
Clemens Gößnitzer ◽  
Shawn Givler
Keyword(s):  
Kinetic Energy ◽  
Flow Field ◽  
Turbulent Kinetic Energy ◽  
Negative Impact ◽  
Operating Conditions ◽  
Engine Operation ◽  
Gas Engine ◽  
Cycle Simulation ◽  
Simulation Results ◽  
The Impact

Cycle-to-cycle variations (CCV) in spark-ignited (SI) engines impose performance limitations and in the extreme limit can lead to very strong, potentially damaging cycles. Thus, CCV force sub-optimal engine operating conditions. A deeper understanding of CCV is key to enabling control strategies, improving engine design and reducing the negative impact of CCV on engine operation. This paper presents a new simulation strategy which allows investigation of the impact of individual physical quantities (e.g., flow field or turbulence quantities) on CCV separately. As a first step, multi-cycle unsteady Reynolds-averaged Navier–Stokes (uRANS) computational fluid dynamics (CFD) simulations of a spark-ignited natural gas engine are performed. For each cycle, simulation results just prior to each spark timing are taken. Next, simulation results from different cycles are combined: one quantity, e.g., the flow field, is extracted from a snapshot of one given cycle, and all other quantities are taken from a snapshot from a different cycle. Such a combination yields a new snapshot. With the combined snapshot, the simulation is continued until the end of combustion. The results obtained with combined snapshots show that the velocity field seems to have the highest impact on CCV. Turbulence intensity, quantified by the turbulent kinetic energy and turbulent kinetic energy dissipation rate, has a similar value for all snapshots. Thus, their impact on CCV is small compared to the flow field. This novel methodology is very flexible and allows investigation of the sources of CCV which have been difficult to investigate in the past.

Reduced-Order Modelling of Rotating Stall

2020 ◽  
Author(s):  
Dominik Schlüter ◽  
Robert P. Grewe ◽  
Fabian Wartzek ◽  
Alexander Liefke ◽  
Jan Werner ◽  
...  
Keyword(s):  
Single Cell ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Rotational Speed ◽  
Stability Limit ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Transonic Compressor ◽  
Experimental Findings

Abstract Rotating stall is a non-axisymmetric disturbance in axial compressors arising at operating conditions beyond the stability limit of a stage. Although well-known, its driving mechanisms determining the number of stall cells and their rotational speed are still marginally understood. Numerical studies applying full-wheel 3D unsteady RANS calculations require weeks per operating point. This paper quantifies the capability of a more feasible quasi-2D approach to reproduce 3D rotating stall and related sensitivities. The first part of the paper deals with the validation of a numerical baseline the simplified model is compared to in detail. Therefore, 3D computations of a state-of-the-art transonic compressor are conducted. At steady conditions the single-passage RANS CFD matches the experimental results within an error of 1% in total pressure ratio and mass flow rate. At stalled conditions, the full-wheel URANS computation shows the same spiketype disturbance as the experiment. However, the CFD underpredicts the stalling point by approximately 7% in mass flow rate. In deep stall, the computational model correctly forecasts a single-cell rotating stall. The stall cell differs by approximately 21% in rotational speed and 18% in circumferential size from the experimental findings. As the 3D model reflects the compressor behaviour sufficiently accurate, it is considered valid for physical investigations. In the second part of the paper, the validated baseline is reduced in radial direction to a quasi-2D domain only resembling the compressor tip area. Four model variations regarding span-wise location and extent are numerically investigated. As the most promising model matches the 3D flow conditions in the rotor tip region, it correctly yields a single-cell rotating stall. The cell differs by only 7% in circumferential size from the 3D results. Due to the impeded radial migration in the quasi-2D slice, however, the cell exhibits an increased axial extent. It is assumed, that the axial expansion into the adjacent rows causes the difference in cell speed by approximately 24%. Further validation of the reduced model against experimental findings reveals, that it correctly reflects the sensitivity of circumferential cell size to flow coefficient and individual cell speed to compressor shaft speed. As the approach reduced the wall clock time by 92%, it can be used to increase the physical understanding of rotating stall at much lower costs.

scholarly journals Computational Analysis on Numerical Simulation of Internal Flow Physics for Pump as Turbine in Renewable Small Hydro Energy Generation

Complexity ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Du Jianguo ◽  
Daniel Adu ◽  
Emmanuel Acheaw ◽  
Shakir Hafeez ◽  
Eric Ofosu Antw
Keyword(s):  
Flow Rate ◽  
Rotational Speed ◽  
Human Life ◽  
Three Dimensional ◽  
Internal Flow ◽  
Hydroelectric Power ◽  
Small Hydropower ◽  
Speed Increase ◽  
Blade Thickness ◽  
The Impact

Energy contributes significantly in almost all aspects of human life as well as economic activities and plays a crucial role in the infrastructural development of a county to alleviate poverty. Generating energy from a renewable source such as small hydropower through the application of pump operating as a turbine mode called Pump as Turbine is one of the best alternatives to provide clean and inexpensive energy. Using Pump as Turbine helps in generating reasonably priced hydroelectric power for communities in underdeveloped counties. This study investigates the effects of internal flow behaviour and performance of Pump as Turbine under different rotational speed and flow rate. The rotational speed is an essential physical parameter as it affects the Pump as Turbine operation. A model-specific speed centrifugal pump model with head 32 (m), flow rate of 12.5 (m3/h) and the rotational speed of 2900 rpm, has been selected for the study. Numerical simulations have been conducted using the k-ω turbulence model to solve three-dimensional (3D) equations. The pump mode experimental data were used to confirm the results for better analysis. The results predicted that vortex and turbulent kinetic energy increase per rotational speed increase. Also, at the higher rotational speed, very high recirculation of flow is detected at the blade suction chamber, although the pressure side has a smooth flow. This study provides beneficial information which will serve as a reference to help improve PAT performance along with selecting PAT for a small hydropower site. Future works will consider the impact of blade thickness and cavitation in Pump as Turbine.

scholarly journals A Simulation and Optimization Study of the Swirling Nozzle for Eccentric Flow Fields of Round Molds

Metals ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 691
Author(s):  
Peng Lin ◽  
Yan Jin ◽  
Fu Yang ◽  
Ziyu Liu ◽  
Rundong Jing ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Rotation Angle ◽  
Steel Slag ◽  
Submerged Entry Nozzle ◽  
Operating Conditions ◽  
Gas Absorption ◽  
Simulation And Optimization ◽  
Bias Flow ◽  
The Impact

In continuous casting, the nozzle position may deviate from the center under actual operating conditions, which may cause periodic fluctuation of the steel-slag interface and easily lead to slag entrapment and gas absorption. Swirling nozzles can reduce these negative effects. A mathematical simulation method based on a round mold of steel components with a 600 mm diameter is applied to study the flow field of molten steel in a mold. The swirling nozzle is optimized through the establishment of a fluid dynamics model. Meanwhile, a 1:2 hydraulic model is established for validation experiments. The results show that, when the submerged entry nozzle (SEN) is eccentric in the mold, it results in serious bias flow, increasing the drift index in the mold up to 0.46 at the eccentric distance of 50 mm. The impact depth of liquid steel and turbulent kinetic energy can be decreased by increasing the rotation angle of the nozzle. The nozzle with one bottom hole, which significantly decreases the bottom pressure and turbulent kinetic energy, greatly weakens the scour on nozzle and surface fluctuation. In the eccentric casting condition, using the optimized swirling nozzle that employs a 5-fractional structure, in which the rotation angle of 4 side holes is 30° and there is one bottom outlet, can effectively restrain bias flow and reduce the drift index to 0.28, a decline of more than 39%.

scholarly journals 1D-3D coupling investigation of hydraulic transient for power-supply failure of centrifugal pump-pipe system

2019 ◽  
Vol 21 (5) ◽  
pp. 708-726 ◽  
Author(s):  
Xiaoqin Li ◽  
Xuelin Tang ◽  
Min Zhu ◽  
Xiaoyan Shi
Keyword(s):  
Turbulent Flows ◽  
Flow Rate ◽  
Power Supply ◽  
Nuclear Power ◽  
Transient Flow ◽  
Internal Flow ◽  
Transition Process ◽  
Pipeline System ◽  
Pipe System ◽  
Rotating Speed

Abstract In the pumping station, the main feedwater system and the reactor system of nuclear power plant, power-supply failure causes strong hydraulic transients. One-dimensional method of characteristics (1D-MOC) is used to calculate the transient process in the pipeline system while three-dimensional (3D) computational fluid dynamics is employed to analyze the turbulent flows inside the pump and to obtain the performance parameters of the pump, and the data exchanges on the boundary conditions of the shared interface between 1D and 3D domains are updated based on the MpCCI platform. Based on the equation of motion of the pump motion parts, the relationship between the external characteristics and the internal flow field in the pump is further investigated because the dynamic behavior of the pump and the detailed fluid field evolutions inside the pump are captured during the transition process, and the transient flow rate, rotating speed, and pressure inside the impeller are comprehensively investigated. Meanwhile, compared with the data gained by experiment and traditional 1D-MOC, the relative errors of rotating speed and the flow rate obtained by 1D-3D coupling method are smaller than those by 1D-MOC. Furthermore, the influences of the main coupling parameters and coupling modes on the calculation results are analyzed, and the cause of the deviation is further explained.

Experimental Investigation of Oil Flowrate in a Hermetic Reciprocating Compressor

2014 ◽  
Author(s):  
Sibel Tas ◽  
Sertac Cadirci ◽  
Hasan Gunes ◽  
Kemal Sarioglu ◽  
Husnu Kerpicci
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Rotational Speed ◽  
High Speed ◽  
Operating Conditions ◽  
Lubricating Oil ◽  
Reciprocating Compressor ◽  
Oil Flow ◽  
Oil Flow Visualization

The aim of this experimental study is to investigate the mass flow rate of the lubricating oil in a hermetic reciprocating compressor. Essential parameters affecting the performance of the lubrication are the rotational speed of the crankshaft, the viscosity of the oil, the operating temperature and the submersion depth of the crankshaft. An experimental setup was built as to measure the oil mass flow rate with respect to the oil temperature variation during different operating conditions. The influence of the governing parameters such as the rotational speed, temperature (viscosity) and the submersion depth on the mass flow rate from crankshaft outlet are studied in detail. In addition, the oil flow visualization from the upper hole of the crankshaft is performed using a high-speed camera in order to observe the effectiveness of the lubrication of the various parts of the compressor. This study reveals that with increasing rotational speed, the submersion depth of the crankshaft and with decreasing viscosity of the lubricant, the mass flow rate from the crankshaft increases.

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