Computational Fluid Dynamics- Based Pump Redesign to Improve Efficiency and Decrease Unsteady Radial Forces

In this study, a double volute centrifugal pump with relative low efficiency and high vibration is redesigned to improve the efficiency and reduce the unsteady radial forces with the aid of unsteady computational fluid dynamics (CFD) analysis. The concept of entropy generation rate is applied to evaluate the magnitude and distribution of the loss generation in pumps and it is proved to be a useful technique for loss identification and subsequent redesign process. The local Euler head distribution (LEHD) can represent the energy growth from the blade leading edge (LE) to its trailing edge (TE) on constant span stream surface in a viscous flow field, and the LEHD is proposed to evaluate the flow field on constant span stream surfaces from hub to shroud. To investigate the unsteady internal flow of the centrifugal pump, the unsteady Reynolds-Averaged Navier-Stokes equations (URANS) are solved with realizable k-e turbulence model using the CFD code FLUENT. The impeller is redesigned with the same outlet diameter as the baseline pump. A two-step-form LEHD is recommended to suppress flow separation and secondary flow encountered in the baseline impeller in order to improve the efficiency. The splitter blades are added to improve the hydraulic performance and to reduce unsteady radial forces. The original double volute is substituted by a newly designed single volute one. The hydraulic efficiency of the centrifugal pump based on redesigned impeller with splitter blades and newly designed single volute is about 89.2%, a 3.2% higher than the baseline pump. The pressure fluctuation in the volute is significantly reduced, and the mean and maximum values of unsteady radial force are only 30% and 26.5% of the values for the baseline pump

Upward air–water bubbly flow characteristics in a vertical square duct

In nuclear engineering fields, gas–liquid bubbly flows exist in channels with various shape and size cross-sections. Although many experiments have been carried out especially in circular pipes, those in a noncircular duct are very limited. To contribute to the development of gas–liquid bubbly flow model for a noncircular duct, detail measurements for the air–water bubbly flow in a square duct (side length: 0.136 m) were carried out by an X-type hot-film anemometry and a multi-sensor optical probe. Local flow parameters of the void fraction, bubble diameter, bubble frequency, axial liquid velocity and turbulent kinetic energy were measured in 11 two-phase flow conditions. These flow conditions covered bubbly flow with the area-averaged void fraction ranging from 0.069 to 0.172. A pronounced corner peak of the void fraction was observed in a quarter square area of a measuring cross-section. Due to a high bubble concentration in the corner, the maximum values of both axial liquid velocity and turbulent kinetic energy intensity were located in the corner region. It was pointed out that an effect of the corner on accumulating bubble in the corner region changed the distributions of axial liquid velocity and turbulent kinetic energy intensity significantly

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

Computational fluid dynamics were used to study the three-dimensional unsteady incompressible viscou

The Enkurgram: A characteristic frequency extraction method for fluid machinery based on multi-band demodulation strategy

International audienc

A Control Method to Balance the Efficiency and Reliability of a Time-Delayed Pump-Valve System

The efficiency and reliability of pumps are highly related to their operation conditions. The concept of the optimization pump operation conditions is to adjust the operation point of the pump to obtain higher reliability at the cost of lower system efficiency using a joint regulation of valve and frequency convertor. This paper realizes the control of the fluid conveying system based on the optimization results. The system is a nonlinear Multi-Input Multioutput (MIMO) system with time delays. In this paper, the time delays are separated from the system. The delay-free system is linearized using input-output linearization and controlled using a sliding mode method. A modified Smith predictor is used to compensate time delays of the system. The control strategy is validated to be effective on the test bench. The comparison of energy consumption and operation point deviation between conventional speed regulation and the new method is presented

Improvement of Fast Kurtogram Combined with PCA for Multiple Weak Fault Features Extraction

Demodulation plays an important role in fault feature extraction for rotating machinery. The fast kurtogram method was proved to be effective for rotating machinery demodulation. However, the demodulation effectiveness of fast kurtogram was poor for multiple fault features extraction under low signal-to-noise ratio. In this paper, an improved method of fast kurtogram, called P-kurtogram, is presented. The proposed method extracted the multiple weak fault features from multiple envelope signals-based principal component analysis. Compared with extracting features from one envelope signal of fast kurtogram, P-kurtogram showed a better demodulation performance for multiple faults. Combined with principal component analysis method, the proposed method also showed a good performance under low signal-to-noise ratio(SNR). By simulation analysis, the P-kurtogram method showed good performance for multiple modulation features extraction and robust performance in demodulation under low SNR. Then, the proposed method was demonstrated by applications of bearing faults detection and propeller detection. The results verified that the P-kurtogram has a better demodulation performance than fast kurtogram for multiple weak fault features extraction, especially under low signal-to-noise ratio. The proposed method provides a reliable basis for multiple weak fault features extraction of rotating machinery

Effect of Suction and Discharge Conditions on the Unsteady Flow Phenomena of Axial-Flow Reactor Coolant Pump

In order to study the effects of the suction and discharge conditions on the hydraulic performance and unsteady flow phenomena of an axial-flow reactor coolant pump (RCP), three RCP models with different suction and discharge configurations are analyzed by computational fluid dynamics (CFD) method. The CFD results are validated by experimental data. The hydraulic performance of the three RCP models shows little difference. However, the unsteady flow phenomena of RCP are significantly affected by the variation of suction and discharge conditions. Compared with that of Model E-S (baseline, elbow-single nozzle), the pressure pulsation in rotating frame of Model S-S (straight pipe-single nozzle) and Model E-D (elbow-double nozzles) is weakened in different degrees and forms, due to the more uniform flow fields upstream and downstream of the impeller, respectively. It indicates that the generalized rotor-stator interaction (RSI) actually exists between the rotating impeller and all stationary components causing the circumferentially non-uniform flow. Furthermore, improving the circumferential uniformity of the flow upstream and downstream of impeller (suction and discharge flow) also contributes to reducing the radial dynamic fluid force acting on the impeller. Compared with those of Model E-S, the dynamic FX and FY of Model S-S are severely weakened, and those of Model E-D also gain a minor amplitude decrease at fBPF. In contrast, the general pressure pulsation in fixed frame is mainly related to the rotating impeller and barely affected by the suction and discharge conditions

Computational Fluid Dynamics-Based Pump Redesign to Improve Efficiency and Decrease Unsteady Radial Forces

In this study, a double volute centrifugal pump with relative low efficiency and high vibration is redesigned to improve the efficiency and reduce the unsteady radial forces with the aid of unsteady computational fluid dynamics (CFD) analysis. The concept of entropy generation rate is applied to evaluate the magnitude and distribution of the loss generation in pumps and it is proved to be a useful technique for loss identification and subsequent redesign process. The local Euler head distribution (LEHD) can represent the energy growth from the blade leading edge (LE) to its trailing edge (TE) on constant span stream surface in a viscous flow field, and the LEHD is proposed to evaluate the flow field on constant span stream surfaces from hub to shroud. To investigate the unsteady internal flow of the centrifugal pump, the unsteady Reynolds-Averaged Navier-Stokes equations (URANS) are solved with realizable k-epsilon turbulence model using the CFD code FLUENT. The impeller is redesigned with the same outlet diameter as the baseline pump. A two-step-form LEHD is recommended to suppress flow separation and secondary flow encountered in the baseline impeller in order to improve the efficiency. The splitter blades are added to improve the hydraulic performance and to reduce unsteady radial forces. The original double volute is substituted by a newly designed single volute one. The hydraulic efficiency of the centrifugal pump based on redesigned impeller with splitter blades and newly designed single volute is about 89.2%, a 3.2% higher than the baseline pump. The pressure fluctuation in the volute is significantly reduced, and the mean and maximum values of unsteady radial force are only 30% and 26.5% of the values for the baseline pump

A Review of Fluid-Induced Excitations in Centrifugal Pumps

This paper describes the related research work in the field of fluid-induced vibration of centrifugal pumps conducted by many researchers. In recent years, all walks of life have put forward higher demands for the vibration performance of pumps which drives the investigation on the root cause of pump vibration and the development of guidelines for the design of low-vibration pumps. Fluid-induced excitation is the most important and significant source of pump vibration. Understanding its generation mechanism and dominant characteristics is important for developing low-vibration pump design methodology. This paper starts with the analysis of unsteady flow in the centrifugal pump and summarizes unsteady flow characteristics such as jet–wake structure, secondary flow, and rotational stall in the operating pump. Based on the understanding of the unsteady flow structure in the pump, the fluid-induced excitation mechanism and its characteristics based on the investigation of unsteady pressure pulsation and excitation forces in the pump are summarized. For the pump operating at nominal flow rate, the excitation at blade passing frequency (BPF) dominates and related suppression methods are classified and summarized to provide reference for the design of a low-vibration pump

Fluid-Structure Interaction Analysis on Turbulent Annular Seals of Centrifugal Pumps during Transient Process

The current paper studies the influence of annular seal flow on the transient response of centrifugal pump rotors during the start-up period. A single rotor system and three states of annular seal flow were modeled. These models were solved using numerical integration and finite difference methods. A fluid-structure interaction method was developed. In each time step one of the three annular seal models was chosen to simulate the annular seal flow according to the state of rotor systems. The objective was to obtain a transient response of rotor systems under the influence of fluid-induced forces generated by annular seal flow. This method overcomes some shortcomings of the traditional FSI method by improving the data transfer process between two domains. Calculated results were in good agreement with the experimental results. The annular seal was shown to have a supportive effect on rotor systems. Furthermore, decreasing the seal clearance would enhance this supportive effect. In the transient process, vibration amplitude and critical speed largely changed when the acceleration of the rotor system increased