Effects Of Rotor-stator Interaction Research Articles

An Analysis of the Effect of Cavitation on Rotor–Stator Interaction in a Bidirectional Bulb Tubular Pump

This study delves into rotor–stator interaction within a bidirectional bulb tubular pump under cavitation conditions. Using pressure pulsation tests on a model pump and numerical simulations performed with ANSYS CFX software, we analyzed pressure pulsation and flow field data across three distinct flow rates and multiple cavitation numbers. Both time-domain and frequency-domain analyses were conducted to examine the patterns of pressure pulsation influenced by flow rates and cavitation numbers at various monitoring locations. A numerical flow field analysis further validated the findings. The results reveal that rotor–stator interaction manifests in the vaneless spaces of the pump during cavitation. The onset of cavitation alters the amplitudes of dominant frequencies at different flow rates. Near the guide vane and impeller, the dominant frequencies shift toward the impeller frequency and guide vane frequency, respectively. Under low-flow conditions, the rotor–stator interaction effect is more conspicuous due to the deteriorated flow pattern. Pressure pulsations are more strongly influenced in the front vaneless space (FVP) than in the rear vaneless space (RVP). This difference arises because the front guide vane destabilizes rather than stabilizes the flow pattern, worsening the rotor–stator interaction. Additionally, the FVP is less affected by the impeller than the RVP, further amplifying the influence of rotor–stator interaction on pressure pulsation. These findings provide a theoretical foundation for mitigating the effects of rotor–stator interaction on the operational stability and efficiency of bidirectional bulb tubular pumps.

Comparison of Two Fourier-Based Methods for Simulating Inlet Distortion Unsteady Flows in Transonic Compressors

The aerodynamic performance of transonic compressors, particularly the stall margin, is significantly influenced by inlet distortion. While time-marching methods accurately simulate such unsteady flows, they can be time-consuming. To enhance the computational efficiency, two Fourier-based methods are proposed in this paper: the time-accurate method with interface filtering and the time–space collocation (TSC) method. The time-accurate method with interface filtering ignores the rotor–stator interaction effects, enabling a larger time step and faster convergence. In contrast, the TSC method accounts for harmonics of conservative variables and transforms the unsteady simulation into multiple steady-state calculations, thereby reducing computational costs. The two Fourier-based methods are validated using NASA Stage 67 and a two-stage transonic fan. Near the peak efficiency point, the results from both methods closely match that of URANS simulation and experimental data. The time-accurate method with interface filtering demonstrates a speed enhancement of 4 to 5 times as a result of a reduction in the iteration steps. In contrast, the TSC method exhibits a speed improvement of at least 20 times in two specific cases, attributable to the significantly smaller mesh size and iteration steps employed in the TSC method compared to the URANS method. Near the stall point, more harmonics for inlet distortion are necessary in TSC simulation to accurately capture flow separation. In the two-stage transonic fan simulations, the strong rotor–stator interaction effects lead to deviations from the URANS simulation; nevertheless, the Fourier-based simulations accurately reflect the trend of the stall margin under total pressure distortion. Overall, the Fourier-based methods show promising potential for engineering applications in estimating the performance degradation of compressors subjected to inlet distortion.

Numerical investigation on vortex characteristics in a low-head Francis turbine operating of adjustable-speed at part load conditions

In this paper, the vortex characteristics in a low-head Francis turbine operating of adjustable-speed at part load conditions are numerically investigated. First, the rules of fixed-speed and adjustable-speed operations are introduced in detail, aiming at operating limits extension. Second, comparative analysis on vortex rope is conducted, with emphasis on vortex rope volume, tail water excitation and spontaneous power swing. Finally, inter-blade vortex has been analyzed and successfully demonstrated, and its induced high amplitude pressure fluctuation characteristic is explored. It is found that at deep part load, vortex rope volume and power swing coefficient of adjustable-speed operation decreased by 69 % and 61 % respectively. The amplitude of Rheingans frequency decreased by 17 %, while the amplitude of blade passing frequency increased by 83 %. After decreasing runner speed, inter-blade vortex is stranded at blade suction surface leading-edge. In addition to low-frequency disturbance, pressure fluctuation shows high-frequency wide-band characteristics. It is concluded that adjustable-speed operation has beneficial effects on improvement of cavity cavitation and energy stability. As for hydraulic stability, the Rotor-Stator Interaction effect cannot be ignored. After changing runner speed, the inter-blade vortex becomes more serious, which could provoke low-cycle and high-cycle fatigue of the blades.

Unsteady numerical investigations of the effect of guide vane openings on the hydrodynamic characteristics under stall conditions in a pump-turbine pump mode

The stall is extremely prone to surge of hydraulic loss, excessive pressure fluctuation and radial force of the pump-turbine in pump mode. These can pose a great threat to the safety operation of the unit. Current research focuses more on the manifestations and propagation mechanisms of the stall, which has limitations and effective methods for passive stall suppression cannot be directly identified. In this paper, unsteady simulations based on the SST-SAS turbulence model are conducted to discuss the effects of guide vane openings on the hydrodynamic characteristics under stall conditions of the pump-turbine from the perspectives of flow pattern, energy loss, pressure fluctuation and radial force. Firstly, the performance test results show that the positive slope of the flow-head curves is the largest at small guide vane openings and smallest at optimal guide vane openings. Then, energy loss analysis based on the energy balance equation indicates that the energy loss in the stay vane is most influenced by guide vane openings, with maximum turbulent kinetic energy production at large guide vane openings. Furthermore, the analysis of the stall characteristics in the impeller illustrates that at large guide vane openings, the axial meridional velocity in the impeller is negative under deep stall conditions, and the flow separation and vortex induce a great local pressure drop in the suction surface of impeller blades near the shroud. Subsequently, the stall characteristics analysis in the diffuser reveals that large-scale vortices in the vaneless regions and stay vane channels result in more severe flow blockage and higher energy loss at large guide vane openings. As the increased guide vane openings, the Rotor-stator interaction effect is weakened by the unstable flow pattern in the diffuser, and the low frequency and near blade frequency signals gradually become the dominant frequencies in the diffuser. Finally, the simulation results in the volute show that the unstable flow pattern in the diffuser provides poor inlet conditions for the volute, which significantly increases the energy loss and pressure fluctuations in the volute. The increase of guide vane openings can also make the flow inhomogeneity in the volute worse. The radial forces on the impeller and diffuser under deep stall conditions both increase with increasing guide vane openings due to the unstable flow patterns.

Experimental Investigation on Velocity Fluctuation in a Vaned Diffuser Centrifugal Pump Measured by Laser Doppler Anemometry

Turbulent flow, mainly originating from the rotor-stator interaction (RSI), is closely associated with the normal and safe operation of the centrifugal pump. In the current research, to clarify turbulent flow in the centrifugal pump with a vaned diffuser, the non-intrusive LDA (Laser Doppler Anemometry) system is applied to measure velocity pulsation signals at different regions when the pump operates at various flow rates. Time and frequency domain analysis methods are combined to investigate the velocity signals, and the velocity distribution around the volute tongue region is reconstructed from twenty measuring points. Results show that the velocity spectrum is characterized by the discrete components at the blade passing frequency and its higher harmonics, and it is caused by the RSI between the impeller and the diffuser. For the points in the volute spiral and diffusion sections, due to the significantly reduced RSI effect, the velocity spectrum shows an evident difference from comparison with the points between the impeller and diffuser, and the blade passing frequency is not always the dominant frequency. The comparison of velocity amplitudes and RMS* (root mean square of velocity) values at different points proves that the measuring position and flow rate affect velocity pulsations. As observed from velocity distribution reconstructed by LDA signals, high velocity regions are developed downstream of the diffuser channel for all the measured flow rates.

Modulation effect on rotor-stator interaction subjected to fluctuating rotation speed in a centrifugal pump

In the paper, the modulation effect of rotor-stator interaction subjected to fluctuating rotation speed is investigated numerically. A quasi-bivariate variable mode decomposition method for analyzing non-stationary flow fields is proposed for the first time. Different from the previous studies, this paper emphasizes the local features of the transient flow field at fluctuating rotation speed. The results show that the impact of fluctuating rotation speed on the impeller force is limited, but it significantly impacts the pressure pulsation at fluctuating frequency. The correlation between amplitude and fluctuation ratio is positive. Meanwhile, the fluctuating rotation speed also induces sidebands centered on the blade passing frequency and its harmonics. The periodic changes in rotational speed lead to frequency and amplitude modulation of pressure pulsations. The magnitude of the instantaneous frequency and amplitude increases as the fluctuation ratio grows. The change in pressure field is well synchronized with the rotational speed, while the change in velocity field lags behind the rotational speed. The variation of pressure field with rotational speed is mainly attributed to two aspects. One is the flow structure at the fluctuating frequency, and the other is the instantaneous component of the flow structure at blade passing frequency.

Investigation on Stall Characteristics of Centrifugal Pump with Guide Vanes

Stall usually occurs in the hump area of the head curve, which will block the channel and aggravate the pump vibration. For centrifugal pumps with guide vanes usually have a clocking effect, the stall characteristic at different clocking positions should be focused. In this paper, the flow field of the centrifugal pump under stall conditions is numerically simulated, and the rotor–stator interaction effects of the centrifugal pump under stall conditions are studied. The double-hump characteristic is found in the head curve by using SAS (Scale Adaptive Simulation) model. The hump area close to the optimal working condition is caused by hydraulic loss, while the hump area far away from the optimal working condition point is caused by the combined action of Euler’s head and hydraulic loss. The SAS model can accurately calculate the wall friction loss, thus predicting the double-hump phenomenon. The pressure fluctuation and head characteristics at different clocking positions under stall conditions are obtained. It is found that when the guide vanes outlet in line with the volute tongue, the corresponding head is the highest, and the pressure fluctuation is the lowest. The mechanism of the clocking effect in the centrifugal pump with guide vanes is obtained by simplifying the hydrofoil. It is found that when the downstream hydrofoil leading edge is always interfered with by the upstream hydrofoil wake, the wake with low energy mixes the boundary layer with low energy, which causes small-pressure pulsation. The results could be used for the operation of centrifugal pumps with guide vanes.

Mechanism of the rotor−stator interaction in a centrifugal pump with guided vanes based on dynamic mode decomposition

In this paper, the mechanism of the rotor–stator interaction in a centrifugal pump with guide vanes is studied numerically and theoretically. The dynamic mode decomposition method is employed to decouple and reconstruct the unsteady flow. A diametrical mode theory suitable for centrifugal pumps with guided vanes is proposed to determine the source of harmonics with higher amplitudes quickly. The results show that the dominant frequencies of the pressure pulsation in the volute and guide vanes are the blade passing frequency and its harmonic frequencies, and the corresponding flow structure is stable and has higher modal energy. The rotor–stator interaction effect around the impeller outlet is most pronounced. The potential flow effect works on the impeller and guide vanes but decays rapidly. The pressure pulsation caused by the wake effect propagates downstream and persists for long distances, which is the main reason for forming the modal pressure field in the volute. The modal reconstruction can reproduce the dynamic evolution process of the pressure field at the characteristic frequencies. The propagation characteristics of the modal pressure field in the volute can be accurately predicted by theoretical analysis. This research can provide an essential reference for fault diagnosis and vibration control of the centrifugal pump.

Flow unsteadiness and rotor-stator interaction in a two-stage axial turbine

This paper presents an in-depth investigation of the unsteady flows through two-stage high-pressure (hp) axial turbine with analyses of the rotor-stator interaction effects on the aerothermodynamic performance. The unsteady flow structures are characterized by the formation and convection of the tip leakage vortex and the hub corner vortices from the first stage blade-row through the second stage nozzle guide vanes (NGV) and blade-row. The modal decomposition of the circumferential distributions of static pressure depicts the modulation of the potential effect in the form of lobed structure propagating in both sides. Moreover, the blade pressure field shows that the first blade-row is exposed to a periodic overpressure induced by the first NGV while in the second blade-row the linear combination of both potential effects is dominant and results in a complex unsteady blade loading. FFT analyses of unsteady turbine performance for two-stage and part stages reveal that the total-to-total isentropic efficiency, torque-based efficiency and pressure ratio of the first stage depend strongly on the first blade-row passing frequency (BPF), whereas the total-to-total isentropic efficiency in second stage and two-stage turbine is related to the second blade-row BPF while the pressure ratio and the torque-based efficiency depend on the two rotors BPFs. Finally, the torque oscillations are mainly associated with the combination of frequencies of first stage NGV with that of second stage NGV. Furthermore, the obtained results show that Unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations are essential in analyzing the complex wakes and vortical structures through the two-stage turbine components and may produce better estimation of the performance.

Numerical and experimental study of variable speed automobile engine cooling water pump.

To investigate the performance of engine cooling water pump in automobile with variable rotating speed, experimental tests and numerical simulation are carried out on an engine cooling water pump under the rotating speed of 2650, 2960, 3700, and 4300 r/min. The hydraulic performance under 3700 r/min rotating speed and the cavitation performance under 340 L/min flow rate are tested and analyzed. The predicted results agree well with the experimental results, indicating that the simulation has high accuracy. The results show that the head of engine cooling water pump increases gradually and the best-effective region moves toward high flow rate condition with the increase in rotating speed. The augment of rotating speed would deteriorate the internal flow fields and causes more energy losses, which is due to the increase in tip leakage flow and enhancement of rotor-stator interaction effects. And, the rotor-stator interaction effect is sensitive to the temperature under various rotating speeds. Furthermore, the required net positive suction head increases with the increase in rotational speed and anti-cavitation performance is weakened during cavitation conditions.

The Action Mechanism of Rotor–Stator Interaction on Hydraulic and Hydroacoustic Characteristics of a Jet Centrifugal Pump Impeller and Performance Improvement

The aim of this study was to investigate the action mechanism of the rotor–stator interaction (RSI) on the transient flow field and hydrodynamic noise field inside the impeller of jet centrifugal pumps (JCPs) and optimize effects of the guide vane on the hydraulic and hydroacoustic characteristics of the impeller. The numerical method of CFD (computational fluid dynamics) coupled with CFA (computational fluid acoustics) was used to analyze the correlation between the guide vane and the flow/sound performances of the impeller. The orthogonal test method, with the hydroacoustic performance of the impeller taken as the objective, was used to optimize the structural parameters of the guide vane for the stability of the hydraulic performance of the JCP. The results show that the RSI leads to a significant increase in the hydroacoustic level of the impeller, but it is indispensable for improving the hydraulic performance of the pump. The RSI effect on the fluctuation intensity of the transient flow field inside the impeller is much more sensitive than the time-average, and the fluctuation intensity of the flow field is positively correlated with the vortex intensity inside the impeller. When the impeller geometry is constant, the evolution processes of the flow field inside the impeller are mainly related to the blade number of the guide vane; when the number of guide vanes is given, the RSI effect on the hydroacoustic characteristic of the impeller is characterized by a positive correlation between the total sound pressure level (SPL) and the fluctuation intensity of the flow field. The frequency spectrum characteristics of the hydroacoustic SPL of the impeller are not consistent with the pressure fluctuation characteristics inside the impeller. The pressure fluctuation characteristics are related not only to the blade number and speed of the impeller but also to its wake characteristics determined by the guide vane. The optimization scheme for the stable hydraulic performance of the JCP significantly reduced the total SPL of the impeller compared with the original scheme, which verifies the feasibility of using the weight matrix optimization method to obtain the global optimization scheme.

Flutter analysis of a one-and-a-half-stage fan at low speed using nonlinear harmonic method

Multirow effects on flutter stability of a 1.5-stage fan at low speed are investigated using nonlinear harmonic method in a one-way coupled fashion. In the first part, the mesh-independence verification and validation of nonlinear harmonic method to simulate multirow effects are performed. In the second part, multirow effects are separated into two parts including acoustic reflection and rotor–stator interaction induced by relative motion between rotor and stators with each part investigated individually. Effect of acoustic reflection from upstream and downstream blade rows is investigated separately using a harmonic truncation method to avoid the change of time-mean flow. The results show that acoustic reflection can have a large effect on flutter stability of rotor blade. The simulation of the rotor–stator interaction effect indicates that the rotor–stator interaction does not significantly affect the flutter stability of rotor blade in this case. Lastly, the variation of aerodynamic modal damping ratio with the size of gap between inlet guide vane and rotor is investigated. Aerodynamic modal damping ratio at a nodal diameter whose fundamental mode is cut-on varies periodically with gap size. Wave splitting method is employed to further investigate the relation between the phase difference between incoming and outgoing wave and aero damping, which can be used to improve the flutter stability at the design stage.

Research of transient rotor–stator interaction effect in a mixed-flow pump under part-load conditions

In order to analyze the unsteady flow characteristic and the pressure fluctuation features of mixed-flow pump caused by the interaction between the impeller and guide vanes under part-load conditions, the unsteady flow field in the mixed-flow pump was numerically simulated based on the standard k–e turbulence model. The pressure distribution and the velocity distribution in the rotor–stator interaction (RSI) zones were acquired, and the time domain and frequency domain of the pressure fluctuation were emphatically analyzed. The results showed that the velocity within the rotor–stator interaction zones is mainly affected by the relative position of impeller and guide vane. With the decrease in flow rate condition, the flow fields become more violent and more vortexes generate in the RSI zone, which causes much energy losses. With the rotation of impeller, the vortexes generating from RSI zones move into the guide vane and dissipate in the guide vane passage in the end. The pressure pulsations at various monitoring points fluctuate periodically, and there appear four peak and four trough values with the same number of leaves. The dominant frequency of pressure pulsation was approximate to the impeller blade passing frequency (BPF). Within the rotor–stator interaction zones, the pressure pulsation coefficient in the rotor–stator interaction zone of the mixed-flow pump changes most obviously. The BPF and double and triple frequency of the pressure pulsation are dominant frequencies, and the frequency distribution range is relatively concentrated.

Correlation research of rotor–stator interaction and shafting vibration in a mixed-flow pump

In order to study the shaft system vibration of mixed-flow pump under rotor–stator interaction, the unsteady pressure fluctuation characteristics are measured and the rotor axis orbit obtained based on the Bentley 408 data acquisition system. The relationship between pressure fluctuation and vibration characteristics of shaft system at the blade passing frequency is analyzed. The results show that the pressure fluctuation amplitude is the largest and the rotor–stator interaction effect is the most obvious in the middle of the impeller. Along the direction of the main stream, the velocity energy is converted into pressure energy, the rotor–stator interaction effect is gradually weakened, and the main frequency of the pressure pulsation gradually turns from the 4 X frequency to the 1 X frequency of the impeller rotation frequency. The hydraulic stirring vibration and other factors lead to jagged sharp corners on the original axis orbit. The axis orbit of 1 X frequency is an ellipse with little difference between long and short axis while the 2 X frequency is the opposite, from which the existence of arcuate rotary whirl and misalignment phenomenon of the rotor can be judged. Combined with time–frequency characteristics of pressure pulsation, it can be found that the hydraulic imbalance has a great influence on the vibration of the shafting, while the rotor–stator interaction at the blade passing frequency takes the second place, which is the main factor of inducing the 4 X frequency vibration of the axis orbit. This study targets is that providing practical guidance for improving operation stability and preventing the vibration failure of the mixed-flow pump.

On the Rotor Stator Interaction Effects of Low Specific Speed Francis Turbines

The rotor stator interaction in a low specific speed Francis model turbine and a pump-turbine is analyzed utilizing pressure sensors in the vaneless space and in the guide vane cascade. The measurements are analyzed relative to the runner angular position by utilizing an absolute encoder mounted on the shaft end. From the literature, the pressure in the analyzed area is known to be a combination of two effects: the rotating runner pressure and the throttling of the guide vane channels. The measured pressure is fitted to a mathematical pressure model to separate the two effects for two different runners. One turbine with 15+15 splitter blades and full-length blades and one pump-turbine with six blades are investigated. The blade loading on the two runners is different, giving different input for the pressure model. The main findings show that the pressure fluctuations in the guide vane cascade are mainly controlled by throttling for the low blade loading case and the rotating runner pressure for the higher blade loading case.

Numerical and experimental study on the pressure fluctuation, vibration, and noise of multistage pump with radial diffuser

Multistage pump can provide high-pressure liquid, which is widely used in various areas of national economy. In order to improve the stability and reduce the noise of multistage pump, the relationships among the pressure fluctuation, vibration, and noise were studied deeply by using computational fluid dynamics and experimental measurement. Based on the unsteady numerical calculation, the phase of the pressure fluctuation wave in the middle section of the impeller and the diffuser was obtained, and the unsteady velocity distribution was acquired in the rotor–stator interaction (RSI) region between the rotational impeller and the stationary diffuser. Moreover, the vibration and noise tests of a five-stage pump with radial diffuser were performed. The results show that the phase distribution of the pressure fluctuation wave in the impeller and diffuser can be divided into four regions: the impeller flow channel region, the impeller transition region, the diffuser transition region, and the diffuser flow channel region. In addition, the pressure fluctuation, vibration and noise of the multistage pump are strongly related to each other, that is, RSI induces strong unsteady flow and pressure fluctuation in the pump, which makes the pump produce serious vibration and cause the corresponding noise. The key to controlling the vibration and noise is to reduce the effect of RSI between the impeller and the diffuser.

Experimental and numerical investigation on the pressure pulsation and instantaneous flow structure in a nuclear reactor coolant pump

Abstract The instantaneous vortical flow structure is one of the typical flow structures inside the nuclear reactor coolant pump (RCP), which would cause the unsteady pressure pulsations, vibrations of the unit and fatigue of components. Due to high safety requirement of the RCP during the actual operation of the nuclear power plants (NPPs), revealing instantaneous nature of vortical flow structure and its pressure pulsation becomes a crucial issue for studying the internal flow mechanism of the RCP. The purpose of this study is to shed comprehensive light on the pressure pulsation and instantaneous vortical flow structure in the RCP by using the experimental method and the numerical simulation method. Based on the result of comparison with the experiment and numerical simulation, it can be considered that the LES method can better identify instantaneous nature of vortical flow structures in the low frequency band. The instantaneous vortical flow structure is attached to the impeller RBPS (rotor blade pressure surface) and transient jet wake vortex flow structures between the impeller and diffuser under the rotor-stator interaction effect are fairly obvious by Q-criterion. On the other hand, in the axial-vorticity component distribution, the rotor-stator interaction effect between the impeller and diffuser cannot be clearly revealed. From the three-dimensional structures, the main vortex structures are in the front and back cavity of the right-hand side near the discharge nozzle and the right-hand side below the discharge nozzle in the spherical casing. Meanwhile, combined with pressure spectrum, it is convinced that their unsteady characteristic is the main reason that causes complex excitation frequencies in the low frequency band of the right-hand side near the discharge nozzle.

Erratum to: Simulation of the joint effect of rotor-stator interaction and circumferential temperature unevenness on losses in the turbine stage

Erratum to: Simulation of the joint effect of rotor-stator interaction and circumferential temperature unevenness on losses in the turbine stage

Simulation of the joint effect of rotor-stator interaction and circumferential temperature unevenness on losses in the turbine stage

The article devotes to problems of unsteady interaction of the hot streams downstream of the combustion chamber with the rotating blades of the rotor wheel. The hot streams downstream of the combustion chamber are caused by discrete circumferentially located fuel nozzles and openings for air supply to the combustion chamber mixing zone. Unsteady interaction of the hot streams with the rotating blades of the rotor wheel leads to local redistribution of the time average gas flow temperature which has effect on the blade – “temperature segregation”.

Simulation of the joint effect of rotor-stator interaction and circumferential temperature unevenness on losses in the turbine stage

The article devotes to problems of unsteady interaction of the hot streams downstream of the combustion chamber with the rotating blades of the rotor wheel. The hot streams downstream of the combustion chamber are caused by discrete circumferentially located fuel nozzles and openings for air supply to the combustion chamber mixing zone. Unsteady interaction of the hot streams with the rotating blades of the rotor wheel leads to local redistribution of the time average gas flow temperature which has effect on the blade – “temperature segregation”.