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.

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 Transient Behavior of a Prototype Centrifugal Pump with Abrupt Decreasing Flow Rate

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Yan-Juan Zhao ◽  
Yu-Liang Zhang
Keyword(s):  
Flow Field ◽  
Centrifugal Pump ◽  
Flow Rate ◽  
Transient Flow ◽  
Three Dimensional ◽  
Transient Behavior ◽  
Sliding Mesh ◽  
Engineering Requirement ◽  
Low Specific Speed ◽  
Volume Method

Centrifugal pump often operates at different working flow rates to meet engineering requirement. To better reveal the transient behavior of centrifugal pump in the process of decreasing flow rate, the finite volume method (FVM), RNG k-ε turbulence model, sliding mesh technology, and user-defined functions (UDF) were employed to simulate the three-dimensional unsteady viscous incompressible flow in a low-specific-speed centrifugal pump during the abrupt valve-off period. The results show that the differences are very obvious between transient and quasi-steady calculations. The velocity is maximum on the wall of hub and shroud, while the velocity is minimum and uniform distribution at middle positions. The transient flow field lags behind the quasi-steady flow field, which may be related to the reasons; namely, kinetic energy cannot convert pressure energy in time.

scholarly journals Experimental Study of a Cavitating Centrifugal Pump During Fast Startups

2010 ◽  
Vol 132 (2) ◽  
Author(s):  
S. Duplaa ◽  
O. Coutier-Delgosha ◽  
A. Dazin ◽  
O. Roussette ◽  
G. Bois ◽  
...  
Keyword(s):  
Centrifugal Pump ◽  
Flow Rate ◽  
Transient Flow ◽  
Flow Behavior ◽  
Rocket Engine ◽  
Rotation Velocity ◽  
Transient Behavior ◽  
Operating Conditions ◽  
Physical Analysis ◽  
Different Types

The startup of rocket engine turbopumps is generally performed only in a few seconds. It implies that these pumps reach their nominal operating conditions after only a few rotations. During these first rotations of the blades, the flow evolution in the pump is governed by transient phenomena, based mainly on the flow rate and rotation speed evolution. These phenomena progressively become negligible when the steady behavior is reached. The pump transient behavior induces significant pressure fluctuations, which may result in partial flow vaporization, i.e., cavitation. An existing experimental test rig has been updated in the LML Laboratory (Lille, France) for the startups of a centrifugal pump. The study focuses on the cavitation induced during the pump startup. Instantaneous measurement of torque, flow rate, inlet and outlet unsteady pressures, and pump rotation velocity enable to characterize the pump behavior during rapid starting periods. Three different types of fast startup behaviors have been identified. According to the final operating point, the startup is characterized either by a single drop of the delivery static pressure, by several low-frequency drops, or by a water hammer phenomenon that can be observed in both the inlet and outlet of the pump. A physical analysis is proposed to explain these three different types of transient flow behavior.

Numerical Simulation of the Transient Flow in a Centrifugal Pump During Starting Period

2010 ◽  
Vol 132 (8) ◽  
Author(s):  
Zhifeng Li ◽  
Dazhuan Wu ◽  
Leqin Wang ◽  
Bin Huang
Keyword(s):  
Centrifugal Pump ◽  
Transient Flow ◽  
Three Dimensional ◽  
Internal Flow ◽  
Published Data ◽  
Pipe System ◽  
Mesh Method ◽  
Slip Region ◽  
Transient Operations ◽  
Dynamic Slip

Computational fluid dynamics were used to study the three-dimensional unsteady incompressible viscous flows in a centrifugal pump during rapid starting period (≈0.12 s). The rotational speed variation of the field around the impeller was realized by a dynamic slip region method, which combines the dynamic mesh method with nonconformal grid boundaries. In order to avoid introducing errors brought by the externally specified unsteady inlet and outlet boundary conditions, a physical model composed of a pipe system and pump was developed for numerical self-coupling computation. The proposed method makes the computation processes more close to the real conditions. Relations between the instantaneous flow evolutions and the corresponding transient flow-rate, head, efficiency and power were analyzed. Relative velocity comparisons between the transient and the corresponding quasisteady results were discussed. Observations of the formations and evolutions of the primary vortices filled between the startup blades illustrate the features of the transient internal flow. The computational transient performances qualitatively agree with published data, indicating that the present method is capable of solving unsteady flow in a centrifugal pump under transient operations.

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.

Investigation on Rotor-Stator Interaction in a Low Specific Speed Centrifugal Pump

2015 ◽  
Author(s):  
Ning Zhang ◽  
Minguan Yang ◽  
Bo Gao ◽  
Zhong Li ◽  
Dan Ni
Keyword(s):  
Centrifugal Pump ◽  
Flow Rate ◽  
Pressure Pulsation ◽  
Vortical Structure ◽  
Fluid Dynamic ◽  
High Amplitude ◽  
Operating Conditions ◽  
Rotor Stator Interaction ◽  
Low Specific Speed ◽  
Specific Speed

In centrifugal pump, due to intense rotor-stator interaction, high amplitude pressure pulsating would be induced, and it has a crucial influence on the stable operating of the pump. In this paper, a low specific speed centrifugal pump is investigated to illustrate unsteady flow within the centrifugal pump. Pressure pulsation signals are attained by mounting 20 monitoring points along the spiral volute, covering all the interested region of the model pump. FFT (Fast Fourier Transform algorithm) is applied to analyze the time-domain pressure signals. Results show that in pressure spectra, evident peaks at blade passing frequency fBPF together with its high harmonics can be identified, and the amplitudes are closely associated with operating conditions of the model pump and the positions of the monitoring points. At nominal flow rate, four vortical regions with high amplitude are captured inside the model pump. And the unsteady vortical structure at the near tongue region is related to the relative position of the impeller with respect to the tongue, and the upstream effect of the volute tongue significantly affects the vorticity distribution on the blade pressure side. At off-design conditions, the interaction pattern between the vortical structure and the volute tongue is significantly affected compared with that at the rated condition, as to the upstream effect of the tongue. At high flow rate, partial vortex would separate from the main vortex, but at low flow rate, the cutting and impingement effects of the tongue are much weaker due to almost all the vortex moving to the narrow side of the tongue. Based on the analysis of rotor-stator interaction in the model pump, some conclusions could be obtained. Pressure amplitudes at fBPF are associated with the positions of monitoring points and operating conditions of the model pump. Vorticity magnitude at blade exit increases as the impeller passes the volute tongue. And the fluid-dynamic blade-volute interaction is dominated by the vorticity shedding from blade trailing edge and their impingement on the volute tongue with subsequent cutting and distortion. And high pressure amplitude is generated with the corresponding high vorticity magnitude observed. So the intense interaction between flow structures (jet-wake pattern) and volute tongue is crucial to unsteady pressure pulsation. Thus, to lower pressure pulsation amplitude and fluid dynamic forces, controlling the vortical structure at blade trailing edge is an effective method.

Optimization of Curved Spacer Prototype Design for Flow Improvement in Centrifugal Pump Impeller

2018 ◽  
Author(s):  
Munther Y. Hermez ◽  
Badih Jawad ◽  
Liping Liu ◽  
Sabah Abro
Keyword(s):  
Flow Field ◽  
Centrifugal Pump ◽  
Water Flow ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Stable Operation ◽  
Inlet Section ◽  
Computational Domain ◽  
Centrifugal Pumps ◽  
Flow Recirculation

An optimization of modified shrouded impeller with a curved spacer to suppress the unsteady flow recirculation was pursed. Centrifugal pumps are required to sustain a stable operation of the system they support under all operating conditions. Effect of minor geometrical modifications on the flow inside the three dimensional impeller passages are yet not fully understood, leading to costly trial and error approaches in the solution of instability problems. The idea of using a curved spacer to enhance the specified centrifugal impeller characteristics was validated. This modification with positioning the successful curved spacer prototype model at the impeller inlet section provided a wider pressure operation range at both low and high flow rates in a high-speed centrifugal pump type. Seven curved spacer models were numerically analyzed in combination with the same original closed type impeller. The research investigated the effects of each inlet curved spacer model on the impeller’s performance improvement. The flow field inside a centrifugal pump is known to be fully turbulent, three-dimensional, and unsteady associated with secondary flow recirculation and separation at the impeller’s inlet and exit section. The rotor-stator interaction mechanisms or other unsteady effects often influence the water flow. The present research addresses the problem of Net Positive Suction Head Required (NPSHR) increase due to flow recirculation at the impeller suction side. The three dimensional unsteady water flow inside different models were analyzed by using a 3-D Navier-Stokes code with a standard k-ε turbulence model. The computational domain consists of four main zones: inlet, impeller hub, vanes, and outlet. The measurements with test rig were conducted for the pump hydraulic performances and flow field in the impeller passages. The numerical simulation and experimental tests of prototype performance concluded: (1) Positioning a 3-D curved spacer at the impeller inlet section has a great impact on the centrifugal pump performance. (2) Favorite effects were achieved on impeller performance by separating the inlet flow region into two lanes. (3) The curved spacer resulted in improvement of closed impeller inlet static and total pressure values. (4) Q-ΔP-η data and flow structures in the impeller passages were analyzed.

Effects of Cavity Purge Flow on Intermediate Turbine Duct Flowfield

2018 ◽  
Author(s):  
Jun Liu ◽  
Qiang Du ◽  
Guang Liu ◽  
Pei Wang ◽  
Hongrui Liu ◽  
...  
Keyword(s):  
Flow Field ◽  
Flow Rate ◽  
Design Criterion ◽  
Operating Conditions ◽  
Duct Flow ◽  
Intermediate Turbine Duct ◽  
Low Pressure Turbine ◽  
Cavity Structure ◽  
Flow Mechanisms ◽  
Purge Flow

To increase the power output without adding additional stages, ultra-high bypass ratio engine, which has larger diameter low pressure turbine, attracts more and more attention because of its huge advantage. This tendency will lead to aggressive (high diffusion) intermediate turbine duct design. Much work has been done to investigate flow mechanisms in this kind of duct as well as its design criterion with numerical and experimental methods. Usually intermediate turbine duct simplified from real engine structure was adopted with upstream and downstream blades. However, cavity purge mass flow exists to disturb the duct flow field in real engine to change its performance. Naturally, the wall vortex pairs would develop in different ways. In addition to that, purge flow rate changes at different engine representative operating conditions. This paper deals with the influence of turbine purge flow on the aerodynamic performance of an aggressive intermediate turbine duct. The objective is to reveal the physical mechanism of purge flow ejected from the wheel-space and its effects on the duct flow field. Ten cases with and without cavity are simulated simultaneously. On one hand, the influence of cavity structure without purge flow on the flow field inside duct could be discussed. On the other hand, the effect of purge flow rate on flow field could be analyzed to investigate the mechanisms at different engine operating conditions. According to this paper, cavity structure is beneficial for pressure loss. And the influence concentrates near hub and duct inlet.

Experimental and Numerical Investigation of Centrifugal Pump Performance When Handling Viscous Fluids

2005 ◽  
Author(s):  
M. H. Shojaee Fard ◽  
M. B. Ehghaghi ◽  
F. A. Boyaghchi
Keyword(s):  
Soviet Union ◽  
Centrifugal Pump ◽  
Turbulent Flows ◽  
Characteristic Curve ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Viscous Fluids ◽  
Test Bed ◽  
Flow Process ◽  
Pump Performance

On the test bed of centrifugal pump, the centrifugal pump performance has been investigated using water and viscous oil as Newtonian fluids, whose kinematic viscosities are 1 × 10−6, 43 × 10−6 and 62 × 10−6 m2/s, respectively. Also, the finite volume method is used to model the three dimensional viscous fluids for different operating conditions. For these numerical simulations the SIMPLEC algorithm is used for solving governing equations of incompressible viscous/turbulent flows through the pump. The κ-ε turbulence model is adopted to describe the turbulent flow process. These simulations have been made with a steady calculation and using the multiple reference frame (MRF) technique to take into account the impeller-volute interaction. Numerical results are compared with the experimental characteristic curve for each viscous fluid. The data obtained allow the analysis of the main phenomena existent in this pump, such as: head, efficiency, power and pressure field changes for different operating conditions. Also, the correction factors for oils are obtained from the experimental for part loading (PL), best efficiency point (BEP) and over loading (OL) and the results are compared with proposed factors by American Hydraulic Institute (HIS) and Soviet Union (USSR). The comparisons between the numerical and experimental results show a good agreement.

scholarly journals Improvement of Pump Performance at Off-Design Conditions

1985 ◽  
Author(s):  
J. Paulon ◽  
C. Fradin ◽  
J. Poulain
Keyword(s):  
Experimental Study ◽  
Flow Field ◽  
Mass Flow ◽  
Flow Characteristic ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Pump Performance ◽  
Wide Range ◽  
Mass Flows ◽  
Design Value

Industrial pumps are generally used in a wide range of operating conditions from almost zero mass flow to mass flows larger than the design value. It has been often noted that the head-mass flow characteristic, at constant speed, presents a negative bump as the mass flow is somewhat smaller than the design mass flows. Flow and mechanical instabilities appear, which are unsafe for the facility. An experimental study has been undertaken in order to analyze and if possible to palliate these difficulties. A detailed flow analyzis has shown strong three dimensional effects and flow separations. From this better knowledge of the flow field, a particular device was designed and a strong attenuation of the negative bump was obtained.

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