Inducer Blade Research Articles

Fast predesign methodology of centrifugal compressor for PEMFCs combining a physics-based loss model and an interpretable machine learning method

For boosted hydrogen fuel cells, the centrifugal compressor greatly affects the system's efficiency, stack power and costs. However, the design of the centrifugal compressor is a lengthy and high-cost process. To tackle this issue, a new method combining a physics-based loss model and a machine learning method was proposed to achieve a fast and more accurate preliminary design step. A high-precision physics-based loss model was developed and validated for data generation. Furthermore, two gradient boosting decision tree (GBDT) models with Bayesian hyperparameter turning were established to construct mapping relationships between geometric parameters and aerodynamic performance. Then, the Sobol sensitivity analysis and Shapley Additive Explanations (SHAP)-based interpretability were used to explore the impact of the geometric parameters on the aerodynamic performances. Results showed that the outlet blade angle, impeller outlet diameter, impeller outlet width, inducer shroud diameter, and inducer blade angle (at the shroud) were the five most sensitive parameters. Additionally, some practical design recommendations were extracted using SHAP-based interpretability. The isentropic efficiencies of two redesign cases with optimal geometric parameters were increased by 2.59% and 1.85% compared with the baseline impellers. The performance prediction was completed within a time of 6 s using the proposed new predesign method. This study represents a significant new attempt to advance the preliminary design methodology of centrifugal compressors.

The effect of fan-type inducer blade tip geometry on cavitation behavior and noise in an industrial centrifugal pump

Cavitation is one of the biggest problems in industrial centrifugal pumps because it causes serious vibration and noise. Therefore, there is a demand for pump manufacturers to prevent problems due to the cavitation before delivering products to the site. Noise is considered to increase due to the development of cavitation at the tip of the inducer blades. In this study, the location of cavitation development was controlled by changing the inducer blade tip geometry to reduce noise. A centrifugal pump with a fan-type inducer was operated to measure noise at various cavitation numbers and flow rates with a microphone set up on the outer wall near the inducer. A visualization experiment using an acrylic casing around the inducer, a high-speed camera, and strobe light was also conducted to observe the behavior of cavitation development. The relationship between cavitation form and noise was investigated in detail.

New type of cavitation instability with peculiar frequency characteristic in liquid rocket inducer

In a liquid rocket turbopump with low pressure and thin wall tanks, cavitation inevitably occurs at the inducer which is installed at the inlet of the turbopump. The cavities at each blade oscillate periodically, and the turbopump sometimes becomes unstable, called cavitation instability. Rotating cavitation is one of the common types of cavitation instability, in which the cavities at each inducer blade oscillate respectively and appear to propagate from blade to blade. However, the new type of cavitation instability which does not follow the conventional principle has been observed in our experiment with an inducer. Converting the frequency in the inertial frame to that in the rotational frame and organizing it in the cavitation number, it was found that the frequency of unsteady cavitation increases as the cavitation number decreases, and this is the peculiar point of this instability. Additionally, during the cavitation instability, a few numbers of backflow vortex cavities were observed and moved sub-synchronously from blade to blade. In addition, the tip leakage vortex cavitation on each blade also propagates like sub-synchronous rotating cavitation but in different propagation speed from that of the backflow vortex cavities. As a result, it was supposed that the new instability is one of the types of sub-synchronous rotating cavitation related to backflow vortex cavitation, tip leakage vortex cavitation, and interaction between cavity propagation and inducer blade.

Relationship between noise and cavitation at various cavitation numbers in fan type inducer blades of a centrifugal pump

Cavitation is one of the biggest problems in the industrial centrifugal pumps because it causes serious vibration and noise. So, it is demanded for the pump manufacturers to solve such problems due to cavitation before delivering products to the site. Hence, the experiments were conducted to establish a practical technique for predicting the occurrence, form, and erosion risk of cavitation by sound measurements outside of pipes. A centrifugal pump with a fan type inducer was operated to measure noise at various cavitation numbers and flow rate. The visualization test of the inducer was also conducted to identify the cavitation form. In addition, the paint erosion test was also conducted to estimate the risk of cavitation erosion occurring for the inducer. The relationship among noise, cavitation form, and erosion risk was investigated in detail.

Design and Optimization of Synchronous Motor Using PM Halbach Arrays for Rim-Driven Counter-Rotating Pump

This document deals with the design of a Permanent Magnet Synchronous Motor (PMSM) to peripherally drive a counter-rotating pump inducer. The motor/pump is associated using a rim-driven principle where the motor’s active parts are located at the periphery of the inducer blades. It proposes using a Halbach array of permanent magnets for the active rotor of the motor. This solution allows the generation of a Sinusoidal Electromotive Force (EMF). Therefore, a more stable electromagnetic torque is reached. An optimum geometry suitable for the inducer specifications while respecting operational constraints is determined. The obtained geometry is then simulated using the Finite Element Method. The results are satisfactory in terms of average torque and EMF waveform. Use of the Halbach array allows a significant improvement of the flux density in the air gap compared to a designed surface-mounted machine. The experimental validation will be performed once the prototype is realized in the Laboratory of Fluid Engineering and Energy systems (LISFE).

Collaborative Robust Design Optimization of Blade Geometry and Manufacturing Tolerance for a Transonic Centrifugal Impeller

Abstract Turbomachinery components are inevitably subjected to various sources of manufacturing errors. The resultant variations in blade geometry eventually lead to performance degradation. This is especially true for transonic centrifugal compressor impellers where the complex interaction between the geometric variations and shock waves may amplify such degradation. However, relevant studies on uncertainty quantification or robust design optimization of centrifugal impellers are quite rare. The mechanisms of how the realistic manufacturing errors influence the impeller aerodynamic performance are not clear. In addition, most existing studies have considered a fixed level of manufacturing tolerance applied to the impeller blade surface, which neglects the combined effect of blade geometry and manufacturing tolerance on impeller performance. In this study, a collaborative robust design optimization was performed for a transonic centrifugal impeller considering realistic manufacturing errors. The realistic manufacturing error field was first modeled based on the measurements of 92 centrifugal impellers. With a combination of computational fluid dynamics simulation and the non-intrusive polynomial chaos method, the influence of manufacturing errors on impeller performance and flow field variations was quantified. To save computational costs for the uncertainty quantification, a dual dimensionality reduction method was proposed to reduce the dimensionality of uncertainties. Finally, blade angles and the manufacturing tolerance of the impeller were collaboratively optimized to enhance the impeller performance robustness against manufacturing errors. The results show that the impeller aerodynamic performance exhibited a downward trend in the presence of manufacturing errors. The flow mechanisms responsible for this trend were mainly associated with increased intensity of the shock waves near the inducer blade tip. Such shock waves were significantly alleviated by reducing impeller inlet blade angles without the loss of pressure rise capability. Consequently, the impeller performance robustness against manufacturing errors was enhanced with the standard deviation of polytropic efficiency being reduced by 35% at a lower anticipated manufacturing cost due to increased tolerance allowance.

Influence of Tip Clearance on Cavitation Characteristics of an Inducer of Turbopump: CFD Study

The tip clearance, a compact gap between the inducer blade tip and casing wall, is critical to both the liquid leakage and cavitation-induced forces of a turbopump. In this study, we numerically investigate the effect of tip clearance on the cavitation characteristics of an inducer. Six different tip clearances, 0.1, 0.3, 0.5, 1.0, 1.5, and 2 mm, namely Models A–F, were designed to evaluate the cavitation performance, cavity structure, blade loading, radial force, etc. Model D (1.0 mm) had the relatively highest head coefficient and smallest cavity area on each blade as compared to all other models. The pressure coefficient distribution and blade loading further confirmed that Model D can maintain a higher pressure head and better suppress the cavitation onset than the other models. The radial force signals in the time and frequency domains show that Model D has an intermediate force magnitude with slightly higher noises at the rotating frequency and its harmonic frequencies. Model D also has a relatively smaller vortex region and smaller vortex strength (λ2 criterion). In short, all results show that Model D is the best alternative to balance the complex interactions of the bulk flow and tip leakage flow, compromising the hydraulic head and rotating cavitation.

Axial thrust instability analysis and estimation theory of high speed centrifugal pump

High-speed centrifugal pumps are widely used in the aerospace and chemical industries. However, the large axial thrust of a rotor due to high rotating speeds exacerbates the device operation instability. Herein, the axial thrust characteristics of a high-speed centrifugal pump under variable speed conditions are analyzed via numerical simulations and experiments. Results show that at high rotating speeds, although the dynamic reaction of the impeller and axial force on the inducer blade only account for a small proportion of the axial thrust, they are the main sources of axial thrust instability. Moreover, axial thrust exhibits a linear relation with the axial force acting on the front and back surfaces of the impeller, and the values of these parameters are very close. However, huge errors are afforded when these two parameters are interchanged, and many axial thrust estimation models ignore this. Therefore, considering the influence of the impeller dynamic reaction and the axial force of the inducer blade on axial thrust, this study proposes an estimation theory for predicting axial thrust. Comparison of the prediction results of the estimation theory and the numerical simulation results reveals that the maximum and minimum relative errors of these two parameters are 11.1% and 2.6%, respectively, under different rotational speeds, thereby suggesting that the prediction results of the estimation theory are sufficiently accurate. The estimation theory can greatly reduce the calculation cost, shorten the design cycle of the centrifugal pump, and provide certain reference for engineering practice.

Impact of the inducer meridional length on the tandem impeller performance within a transonic centrifugal compressor

Tandem impeller configuration has the potential to improve the performance of highly loaded transonic centrifugal compressors, while the related research is still in the early stages and general design guidelines, such as the selection of inducer meridional length, are limited so far. In this paper, a highly loaded transonic centrifugal compressor with various tandem impeller configurations is numerically investigated. The objective is to evaluate the impact of inducer meridional length [Formula: see text] on the tandem impeller flow structure and performance, and further to look into the underlying flow mechanisms and design principles of the tandem impeller. The results indicate that the inducer meridional length [Formula: see text] has significant effect on the tandem impeller and compressor stage performance. There exits an optimized tandem impeller [Formula: see text] value of Appr. 38% that achieves a compressor stage pressure ratio and efficiency gain (at the P.E. points) of 2.6% and 1.8%, respectively, and deviating from the optimized [Formula: see text] value will lead to deteriorated compressor performance. In terms of the impeller performance, the inducer trailing edge determined by the inducer meridional length [Formula: see text] should be located downstream of the passage shock to reduce the shock and inducer wake losses. However, the inducer blade should also be placed in the impeller axial part to avoid the exudcer incidence angle deviation. In terms of the diffuser performance which is partly determined by the impeller discharge flow uniformity, the inducer meridional length [Formula: see text] directly affects the tandem impeller discharge flow uniformity by rearranging and controlling the secondary flow patterns, and the flow uniformity is prone to be insensitive to the [Formula: see text] variation when the [Formula: see text] value is large enough (i.e. ≥30%). Additionally, the [Formula: see text] value should be large enough (i.e. ≥20%) to generate intense inducer shedding vortexes, which can suppress the development of Coriolis vortex and finally improve the impeller flow uniformity.

Influence of Geometric Variations of an Inlet Cover Bleed System on Inducer Performance for an Axial Pump Operating Under Cavitating Conditions

AbstractA stability control device (SCD) is a passive inlet cover treatment that can be applied to high suction performance inducers. Significant improvements in stability have been observed when an inducer operates with an SCD, including suppression of backflow at the leading edge of the inducer at low off-design flow coefficients. This is possible because of a local increase in mass flow at the leading edge of the pump, which allows an inducer to operate with an incidence near the design point value over a wide range of flow coefficients. In this paper, the suction performance of several inducers was explored with several different SCD geometries and at different flow coefficients. Specifically, five different SCD geometries were considered to explore the influence that SCD bleed slot width and resistance to flow through the SCD channel have on inducer performance. Further, removal of tangential velocity of the energized fluid transporting through the SCD channel was considered for some scenarios to highlight the impact of swirl on inducer performance. The results reveal that for all inducers and SCD combinations considered, the most important factor affecting the mass flow through the SCD, and subsequent mass flow gain, is the inlet diffusion of the inducer. This holds for both single-phase and multiphase scenarios. Further, the cavitation number where cavitation first starts to develop in the blade throat passage of the inducer is primarily dependent on the inlet blade angle and not the SCD geometry. Consequently, the shape of the cavitation breakdown curve is largely determined by the inducer blade angle.

Analysis of the Effect of Fan-Type Inducer Blade Angle on Pump Suction Performance

Industrial centrifugal pumps that require low NPSHR over a wide flow range, such as when pumping liquefied natural gas from storage tanks, are equipped with low solidity fan type inducers. Further improvement of pump suction performance is industrially expected because the lowest liquid level height that can be pumped directly affects the economic efficiency. In this study, several inducers made by a 3D printer were attached to an industrial centrifugal pump and investigated experimentally and using computational fluid dynamics to analyze the effect of the blade angle of the fan-type inducer on pump suction performance. The experimental results showed that the blade angle has no significant effect on the pump performance curve but has a clear influence on the pump suction performance, and CFD was used to investigate the cause of this for a flow rate with φ = 0.099, the design flow coefficient of the attached centrifugal pump. From the calculation results, the vapor volume was visualized and flow blockage due to cavitation in the internal flow path of the pump was analyzed. It was confirmed that the tendency of cavitation generation differs depending on the inducer vane angle even at the same cavitation number. Further analysis of the CFD results revealed that the influence of the swirling flow generated by the inducer on the flow field at the impeller inlet changed the occurrence of cavitation at the impeller inlet, leading to the occurrence of cavitation at the impeller inlet. As a result, the authors considered that there is a clear influence on the breakdown performance of the centrifugal pump.

Identification of inducer cavitation instabilities using high-speed visualization

This paper presents a new inducer cavitation instability detection method based directly on quantitative high-speed visualization. The new method uses the grayscale values of pixels, representing fluctuations in the cavity structure, to identify cavitation instability. The method is validated against unsteady pressure measurements in two- and three-bladed inducers. Both unsteady pressure measurements and grayscale fluctuations have been analyzed in the frequency domain via Fourier transformation and traveling wave energy analysis to establish the correspondence between the two types of data. Finally, the new method is applied to demonstrate its capability to detect alternate blade cavitation in a 2-bladed inducer and super-synchronous rotating cavitation in a 3-bladed inducer.

Development of pumps with improved anti-cavitation characteristics

When considering the creation of pumps with improved anti-cavitation characteristics, the results of an in-depth analysis of the problem of pumping viscous liquids at high temperatures are presented. On the example of the technological process of evaporation of sugar syrup on a film evaporator of the latest type, the problem of the occurrence of cavitation when pumping viscous liquids at high temperatures was revealed. After analyzing the existing machines used for the specified operating conditions, critical design and operating parameters were identified that affect the appearance of cavitation. Namely, the appearance of cavitation is influenced by the reduced diameter of the impeller inlet, the diameter of the impeller inlet, the number of blades, the width of the blades and the rotor speed. To study the level of influence of these parameters, a method of physical modeling was chosen, an experimental stand was designed and manufactured. Studies have been carried out on the operation of the pump with and without a reducer. The work with a two- and three-blade inducer is analyzed, the work with an open and closed impeller, with one and two-level blade system is investigated. As a result of the analysis of experimental data, the optimal design of the hydraulic part with a three-blade reducer and a semi-open impeller with a two-level blade system was chosen. In turn, this made it possible to reduce the compression of the flow at the inlet to the impeller without loss of energy efficiency; the angles of inclination of the inducer and impeller blades were synchronized. The experience gained made it possible to design and manufacture an industrial sample of a cantilever pump with an inducer and a semi-open impeller. Thus, allowing to solve the problem of pumping thick syrup on a film evaporating unit of the Teofipol sugar plant (Khmelnytskyi region, Ukraine), with a cavitation reserve of 1.5 m.

Design of a transonic centrifugal compressor for High-speed turbomachinery

The paper presents a design of a small-scale centrifugal compressor to match the performance of up to 20% larger diameter compressor in order to meet the demands for a higher mass flow rate and wide operating range for turbocharging applications. This development considers the 44 mm diameter impeller design involving transonic blading and state-of-the-art blade features. In the course of design, the investigation on the inducer blade angle [Formula: see text] and blade inducer-to-outlet radius ratio has shown to have a dominant influence on the magnitude of inlet relative Mach number. Diffuser width and volute A/R ratio are also observed to be parameters affecting the overall performance of the compressor stage. Based on the diffuser parametric study, the most efficient diffuser width equal to 70% of the blade exducer width is observed. The performance of the present compressor stage is analyzed with computational fluid dynamics simulations and experimental tests. The comparison of the predicted and measured results of the 44 mm compressor stage shows a good agreement for overall performance. Besides, the 44 mm compressor stage having the most efficient diffuser width and enlarged volute A/R ratio shows a good overlap of performance with approximately 20% larger diameter (52 mm) compressor stage performance. This development demonstrates that the impeller with state-of-the-art design features are likely to contribute to enhancement of the compressor performance.

Conjugate heat transfer study of backdisc cooling of a radial turbine

Radial turbines used in turbochargers and micro-turbines are subjected to high inlet temperature. This creates high thermal stress in the turbines, and possible creep of turbine inducer blades, and can reduce turbines’ reliability. With the ever-stringent engine emission regulations and the continuous drive for engine power density, turbine inlet temperature is significantly increased recently and the risk of thermo-mechanical failure of turbine rotor is heightened. To solve this problem, an innovative turbine cooling method is proposed by injecting a small amount of compressor or intercooler discharge air onto the upper backdisc region of turbine rotor to cool the disc and the inducer blades. A conjugate heat transfer simulation was carried out to investigate the effects of this cooling method with a turbocharger turbine. Flow conditions and geometric configurations were investigated for their influences on the cooling effectiveness of the method. The results show that using the compressor discharger air after intercooler with only 0.5–2.0% of turbine mass flow, the averaged cooling efficiency of the turbine backdisc is promoted by 23–43%; only four to six jets may be needed to cool the entire backdisc; and turbine efficiency is reduced by less than 1% point.

Effect of meridian plane dip angle of the variable pitch inducer blade on cavitation performance of high-speed centrifugal pump

To study the effect of the dip angle of the inducer blade section in the meridian plane on the cavitation performance of the high-speed centrifugal pump, four schemes of the inducer have been considered only by changing the dip angle of the blade section in the meridian plane while keeping the other geometrical parameters unchanged. Based on the RNG k–ɛ turbulence model and Zwart-Gerber-Belamri cavitation model, three-dimensional numerical simulation of a high-speed centrifugal pump is carried out. The results show that the cavitation performance of high-speed centrifugal pump will be improved when the dip angle of the blade section in the meridian plane increases within a certain range, but the cavitation performance will deteriorate when the dip angle exceeds a certain extent. A moderate raise of the blade section dip angle will change the blade inlet angle and blade outlet angle of the shroud and hub of the inducer, improve the matching of the liquid flow angle with the blade inlet angle and restrain the cavitation at the blade leading edge. The change in the dip angle has a weak influence on the external performance of the high-speed centrifugal pump, indicating that there is almost no effect on the capacity of the inducer.

Inducer/Exducer Matching Characteristics inside Tandem Impellers of a Highly Loaded Centrifugal Compressor

A centrifugal compressor usually operates with low isentropic efficiency and a terrible stable operating range, resulting from the complex impeller flow structure companied with the intense interaction among the impeller and the diffuser downstream. In many studies, the potential of centrifugal compressor tandem-impeller configurations for improving the compressor has been demonstrated. Whereas, compared with the convincing results on the tandem-designed axial compressors, the results on tandem impellers are limited and contradictory. Very little insight has been provided into the flow mechanisms inside tandem impellers, which is considered to be the primary reason for the confusion in tandem impeller design and application. Tandem impellers are expected to exhibit a totally different behavior due to the intense aerodynamic interaction between the inducer and the exducer, which substantially contributes to the flow structure and the compressor performance change. In the present study, a numerical study of a highly-loaded centrifugal compressor with various tandem designs was conducted to explore the inducer/exducer matching characteristics and the underlying flow mechanism inside tandem impellers. Two tandem impeller design parameters, namely, the inducer/exducer clocking fraction and the axial gap (overlap), were considered in the tandem impeller design process. The tandem impeller was also compared to the existing conventional impeller which the tandem impeller was redesigned for. The results demonstrated that the tandem-designed impeller can improve the centrifugal compressor stage performance and intense inducer/exducer interaction can be observed with changes in the clocking fraction and the axial gap (overlap). The tandem impeller performance is sensitive to changes in axial gap (overlap) when the suction side of the exducer blade is circumferentially close to the inducer blade. The fundamental reason for the performance variation in the inducer and the exducer lies in the inducer pressure change in the blade trailing edge that is determined by the Kutta condition. Additionally, the correlation between the tandem impeller slip effect and the discharge flow quality should be emphasized in the inducer/exducer gap jet analysis, in which the jet injection angle and the Coanda effect of the exducer suction surface critically affect the discharge flow characteristics.

Investigation of Flow Field at the Inlet of a Turbocharger Compressor Using Digital Particle Image Velocimetry

Abstract The flow field at the inlet of a turbocharger compressor has been studied through stereoscopic particle image velocimetry (SPIV) experiments under different operating conditions. It is found that the flow field is quite uniform at high mass flow rates; but as the mass flow rate is reduced, flow reversal from the impeller is observed as an annular ring at the periphery of the inlet duct. The inception of flow reversal is observed to occur in the mid-flow operating region, near peak efficiency, and corresponds to an incidence angle of about 15.5 deg at the inducer blade tips at all tested speeds. This reversed flow region is marked with high tangential velocity and rapid fluctuations. It grows in strength with reducing mass flow rate and imparts some of its angular momentum to the forward flow due to mixing. The penetration depth of the reversed flow upstream from the inducer plane is found to increase quadratically with decreasing flow rate.

Entropy production analysis for the clocking effect between inducer and impeller in a high-speed centrifugal pump

The clocking effect between the inducer and the impeller has a certain impact on the performance of the high-speed centrifugal pump, which however, is often ignored by designers. In the present study, three-dimensional numerical simulation based on Reynolds-averaged Navier–Stokes method is adopted to evaluate the influence of this clocking effect on the performance of a full-scale liquid rocket engine oxygen turbopump. A novel entropy production method with the correction of wall effects was introduced to evaluate the energy loss generated in the pump and to clarify the formation mechanism of this clocking effect from the perspective of the second law of thermodynamics. Results show that the best performance is captured when the relative circumferential angle between the inducer blade trailing edge and the impeller blade leading edge was set as 0° and the maximum difference in pump efficiency is approximately 1.5% at different clocking positions. The entropy production analysis of each component of the pump reveals that the clocking effect on the pump performance mainly originates from the turbulent dissipation in the impeller and the diffuser. The study of the local entropy production rate and the streamline distributions shows that the formation of this clocking effect is owing to the different extent of the separation vortices in the impeller passage near the shroud and the impeller blade wake in the diffuser inlet as well as the backflow vortices in the diffuser blade passage near the volute tongue.

Visualization of Rotating Cavitation Oscillation Mechanism in a Turbopump Inducer

An experimental investigation has been conducted on rotating cavitation in a turbopump inducer. Previous research suggested that incidence angle variation leads to rotating cavitation. This study, using particle image velocimetry (PIV) method, provides the first measurement of the incidence angle distribution near the tip region of an inducer blade's leading edge with and without rotating cavitation. Without rotating cavitation, the incidence angle near the leading edge of the following blade is positive. Under rotating cavitation, the tip leakage vortex cavitation regions on the blades become uneven, forming large and small tip leakage vortex cavitation regions. A large tip leakage vortex cavitation on the leading blade increases the axial and absolute tangential velocities near the following blade's leading edge. Thus, the incidence angle on the following blade becomes negative, suppressing tip leakage vortex cavitation. Conversely, a small tip leakage vortex cavitation on the leading blade increases the incidence angle and promotes tip leakage vortex cavitation on the following blade. Due to such suppression and promotion mechanisms, the tip leakage vortex cavitation region on each blade oscillates in sequence, seemingly but not actually propagating in the forward direction. High-speed camera flow visualization has been used to confirm the same oscillation mechanism of rotating cavitation.