Centrifugal Compressor Research Articles

Centrifugal Compressor Surge in Innovative Heat Pump: Fluid Dynamic and Vibrational Analysis

Abstract In the current energy scenario, it is necessary to reduce fossil fuel consumption to achieve the far-sighted and stringent decarbonization goals. To date, heat is mainly produced through fossil fuels. Alternatively, electrically driven heat pumps can exploit renewable power to recover environmental and waste heat, offering energy efficient and environmentally friendly heating and cooling for applications ranging from domestic and commercial buildings to process industries. For this reason, they are expected to play a primary role in complementing or displacing natural gas boilers in the residential and industrial sectors in the near future. Centrifugal compressors are already used as prime movers of the working fluid in heat pumps, thanks to their industrial replicability, compact size, affordable costs, and good performance in terms of efficiency and low noise. However, they are subject to instabilities such as surge and stall like any other dynamic compressor and these phenomena develop quite differently than in classic open-loop systems such as gas turbines. In fact, such peculiarity is mainly due to the closed-loop configuration with real gases in two-phase conditions, occurring in typical heat pump cycles. In addition, heat exchangers also contribute to make these phenomena different from what is commonly studied. Compressor surge in closed-loop heat pump systems has received lower attention than other applications by the engineering community, lacking dedicated experimental characterization, and clear exposition of the phenomenon. The aim of this paper is to experimentally investigate the behavior of a centrifugal compressor installed into an innovative close loop heat pump system under stable and unstable conditions from both vibrational and fluid-dynamic points of view. The impact of the main process parameters on the evolution of the instability is shown, highlighting how surge cycles change by varying system operating conditions. The energy contents of surge cycles and pressure fluctuations are highlighted, using data postprocessing techniques such as fast Fourier transform and phase locked average. The vibro-acoustic analysis enrich the comprehension of the phenomena. The experimental results shown in this paper can be a basis for the future development of validated mathematical models of closed-loop heat pumps systems equipped with dynamic compressors operating under stable and unstable operating conditions.

Machine learning techniques for the smart faults detection and diagnosis of centrifugal compressor

In this work, we have conducted a comparative study among several machine learning techniques with the aim of selecting the best one for classifying faults affecting the compressor system to enable smart monitoring. This study encompasses various machine learning techniques, including Support Vector Machine, k-nearest neighbor, Decision Tree, Naive Bayes, AdaBoost, and Bag ensembles. To determine the optimal classification technique, we applied three distinct criteria: the confusion matrix, error histogram, and mean square error through cross-validation. Based on these criteria, the results indicate a tie for the top position between two classification models: Decision Tree and Bag ensemble. To solidify our choice of a single model, we employed the new AutoML technique to automatically identify the most suitable machine learning classification model for our case study. We evaluated this approach using process data obtained from an operational industrial centrifugal compressor. Consequently, the results presented in this work affirm that Decision Tree is the superior technique for classifying faults in the 3MCL compressor.

A Coupling Optimisation Strategy for Improving Flow Stability and Aerodynamic Performances of Turbocharger Centrifugal Compressors

A Coupling Optimisation Strategy for Improving Flow Stability and Aerodynamic Performances of Turbocharger Centrifugal Compressors

Study of unsteady shear flow near stall in a shrouded supercritical carbon dioxide centrifugal compressor

This study investigates the unsteady shear flow patterns and their relation with the aerodynamic instability of a shrouded supercritical carbon dioxide (SCO2) centrifugal compressor impeller using the dynamic mode decomposition method combined with detached eddy simulation. The results demonstrate that discrete shedding vortex array in the blade tip region is the dominant mode of the SCO2 shrouded centrifugal compressor impeller, with a frequency of 0.5 times the blade passing frequency. In contrast, the main flow structures in the identical impeller using ideal air consist of small-scale shedding vortices near the suction surface and the separated secondary flow. Further analysis of flow field details indicates that the shedding vortex structure inside the shrouded centrifugal impeller originates from the Kelvin–Helmholtz instability generated on the shear interface between the mainstream and the recirculation flow. The greater shear intensity within the SCO2 centrifugal impeller is the reason for the evident occurrence of vortex shedding phenomena in its flow field. Additionally, during the transition from near-stall to stall, vortex pairing phenomena happens at the throat of the centrifugal impeller due to evolutional behaviors of the vortexes. The occurrence of vortex pairing leads to faster blockage of the blade tip region and then the secondary flow spillage over to adjacent passage, ultimately resulting in reverse flow in the blade tip region and extensive blockage at the impeller inlet. The unsteady shear flow evolution clearly demonstrates the processes of stall in SCO2 shrouded impellers.

Research on identification and quantification methods for loss sources of compressors

Abstract A deep understanding of the internal loss mechanisms and specific values of turbomachinery is crucial for its design and analysis. In this paper, based on the theory of entropy production, the loss sources in the NASA Rotor67 transonic fan and Radiver centrifugal compressor were quantified by using numerical simulation methods and physical flow characteristic description methods. The proportion of losses in various regions was presented. The results show that in the transonic fan, boundary layer losses and wake losses account for more than 70%, while direct shock losses account for less than 2%. Additionally, as the mass flow increases, the losses gradually move downstream, with the proportion of wake losses increasing. Within the wake losses, the influence of tip leakage flow and corner separation flow exceeds 70%. In the centrifugal compressor, as the mass flow decreases, the proportion of impeller losses to the total stage losses increases significantly, from 21.7% at the choking condition to 63.5% near the design condition. Most of the losses within the impeller occur near the casing area, accounting for about 47% of the impeller losses. The areas near the blades and the main flow area are the other two major sources of impeller losses, with both contributing to 36% of the losses.

Effect of non-equilibrium phase transition on the aero-thermodynamic performance of supercritical carbon dioxide compressors

Phase transition is a prominent issue for the supercritical CO2 compressors operating near the critical region. The non-equilibrium behavior of phase transition makes it difficult to accurately predict performance under these conditions. A non-equilibrium phase transition model is proposed to analyze the aero-thermodynamic performance of supercritical CO2 centrifugal compressors with different inlet conditions. The model examines phase change characteristics and compressor performance under variable operating conditions. The results indicate that this model can effectively predict the aero-thermodynamic performance of compressor near critical conditions, with an average error of less than 2% in the performance curves. The inconsistency between low-temperature and low-pressure regions, along with the increase in liquid phase volume, are typical characteristics of non-equilibrium phase transition in supercritical CO2 compressors. The non-equilibrium effect of phase transition can reduce the leakage loss at high flow rates, but also increases the likelihood of stall at low flow rates. Furthermore, the concept of “non-equilibrium degree” (NED) is introduced to quantify these effects. When NED exceeds 0.2, the isentropic efficiency of the compressor decreases by 15.1% compared to its maximum efficiency. Designing inlet conditions for supercritical CO2 compressors with NED below 0.1 is more suitable because it has a larger inlet flowrate and higher efficiency.

Dynamic Unbalance Identification in Steady-State Rotating Machinery: A Hybrid Methodology Integrating Physical and Data-Driven Techniques

Rotating machinery plays a strategic role in key industrial sectors, making its analysis a subject of great interest for both academia and industry. Effective maintenance planning for this equipment is essential for asset management and for meeting current industrial requirements. To address this demand, this work presents a novel unbalance identification approach based on a digital representation of a rotating machine's dynamic behavior in relation to the development of specific faults. A hybrid methodology is proposed, integrating Finite Element Modeling, a Kalman Filter for parameter estimation, and Referenced Moving Window Principal Component Analysis. This Principal Component Analysis extension enhances vibration pattern recognition, enabling accurate fault quantification directly from slight changes in the system's steady-state behavior. The methodology uniquely eliminates the need for phase angle measurements, facilitating continuous monitoring of unbalance progression in steady-state conditions. Two case studies demonstrate the methodology's potential: one utilizing synthetic data from a Floating Production Storage and Offloading centrifugal compressor unit, and the other based on real data from a hydroelectric turbine-generator. These studies illustrate the integration of computational modeling, data-driven analysis, and monitored vibration data, achieving robust and accurate unbalance identification. This approach provides valuable insights into current capabilities and opens promising pathways for future applications, particularly in the digital twin domain for rotating machinery.

Performance analysis of NH3/CO2 cascade refrigeration system using CO2 centrifugal compressor with gas bearing

Performance analysis of NH3/CO2 cascade refrigeration system using CO2 centrifugal compressor with gas bearing

Impact of Part-Speed Geometry Changes on Centrifugal Compressor Performance

The effects of part-speed geometry changes on the performance of an aeroengine centrifugal compressor are evaluated. In many applications, impellers are often of a high-flow-coefficient, high-specific-speed design. When coupled with the high rotational speeds and high temperature ratios of modern impellers, significant deformation occurs as the compressor moves across its operating range from low speeds to high speeds. At each operating speed studied, the impeller geometry was deformed to achieve the running, warm geometry at that speed. Typically, a single hot-to-cold analysis is performed to generate the cold geometry needed for fabricating the hardware. The hot as-designed geometry is used to predict performance at all operating speeds. The present study shows that this approach tends to overpredict part-speed performance. The variation between the hot geometry and the warm geometry at part speeds below 80% of design speed was nearly one point in efficiency and more than 1.2% in total pressure ratio. The assumption of constant geometry is made due to the time-consuming and computationally expensive iterative procedure required to compute the warm part-speed geometries. To address this, a scaling is presented that allows for part-speed geometries to be determined using only the as-manufactured and as-designed geometries.

Performance improvement of a centrifugal compressor for cogeneration

This work presents the performance improvement of a centrifugal compressor designed for cogeneration applications. The study involves modifications to geometric parameters, including impeller and diffuser configurations, to enhance pressure ratio, temperature ratio, and overall efficiency using computational fluid dynamics to verify the improvement of those parameters. The study has examined the compressor’s behaviour under surge, design, and choke conditions, showcasing improved homogeneity, reduced low-velocity zones, and an extended operating range. The compressor maps are presented to graphically observe the impact of each proposed modification, facilitating the analysis of each of these and evaluating the performance under various operating conditions. The final compressor configuration exhibits notable improvements in key performance metrics, with pressure ratio, temperature ratio, and efficiency showing increases of 1.753%, 1.640%, and 1.760%, respectively.

Research on aerodynamic performance of centrifugal compressors for hydrogen-mixed natural gas.

Natural gas-doped hydrogen transportation has been widely used in industrial engineering. The change of the physical parameters of the conveying medium affects the working performance of the centrifugal compressor. This study aims to explore the aerodynamic performance of centrifugal compressors for hydrogen mixed natural gas, including the effects of hydrogen blending ratio (HBR) and inlet temperature on the pressure ratio and isentropic efficiency of compressors. The numerical simulation method is used and the results are compared with the experimental results to determine the reliability of the numerical simulation method. The results show that the pressure ratio decreases with the increase of HBR where the inlet temperature and rotation speed are constant. The pressure ratio and efficiency of the compressor are the highest when the conveying medium is pure natural gas (HBR = 0). The maximum pressure ratio reduction is 4.8% when the HBR is 5% and the inlet temperature is increased by 20 K. In summary, when the conveying medium of the compressor changes from pure natural gas to hydrogen-mixed natural gas, the working range and efficiency of the compressor will be reduced. Therefore, it is necessary to increase the rotation speed of the compressor or redesign the centrifugal compressor for hydrogen-mixed natural gas in order to achieve a constant flow rate at the outlet of the compressor.

Numerical Prediction of Inlet Geometry Influence on the In-Duct Acoustics of Small Centrifugal Compressors

Abstract Small centrifugal compressors are employed to boost automotive internal combustion engines or hydrogen fuel cells, amongst other applications. In many scopes, the overall intensity and quality of noise emission is a major concern, so many researchers develop and assess numerical models to predict acoustic spectra. In this work, detached Eddy simulations (DES) of a vaneless centrifugal compressor are conducted to assess the impact of intake geometries on its aeroacoustic performance. Experimental measurements are employed as a means of validation. Flow field analysis and Dynamic Mode Decomposition allow us to analyze the underlying mechanisms of the most relevant acoustic features. This work provides insight into the implications for noise generation of employing tight elbows due to packaging constraints.

The Design and Performance Analysis of a 15 g/mol Helium–Xenon Mixture Centrifugal Compressor

One of the primary parts of a closed Brayton cycle that uses a helium–xenon mixture as the working medium is a centrifugal compressor. Nowadays, there has been minimal research on the theoretical underpinnings and design procedures of a helium–xenon mixture centrifugal compressors, and the internal flow mechanisms remain poorly understood. In this study, we present a redesign of the 15 g/mol helium–xenon centrifugal compressor originally developed by Bruno M, utilizing a helium–xenon mixture as the working fluid to enhance compressor performance and facilitate an in-depth analysis of the internal flow dynamics. The findings indicate a significant expansion of the stable operating range of the redesigned compressor under identical outlet conditions, with a 33.27% increase in flow margin and substantial improvements in the pressure ratio. Furthermore, under consistent inlet conditions, at an operational flow rate of 0.8657 kg/s, the redesigned compressor exhibits a pressure ratio that is 2.11% greater than that of the original design, along with a variable efficiency increase of 1.1%.

Analysis of The Flow-Field Distorsions Induced by Pneumatic Pressure Probes In Test Bench Experiments On Centrifugal Compressors: Are We Testing Right?

Abstract Experimental testing at the test rig still plays a key role in the development of new centrifugal compressor designs for industrial applications. Although a wide set of different probes is used as per common practice, the overall impact of the probes? dimensions on the stage performance and rangeability is often assumed to be negligible. In this study, we aimed at quantifying the intrusiveness effects of pneumatic pressure probes on the flow-field inside a vaned diffuser using a model stage of an industrial centrifugal compressor, for which different experimental setups were tested at the University of Florence test rig. Performance and rangeability were initially assessed using a conventional set of pneumatic probes inserted in the flow path. Then, comparative analyses were realized through dedicated tests by either removing all probes at the diffuser inlet or introducing only a single pressure probe in the upstream section and varying its angular position in the measuring section. Experiments revealed an impact of upstream probes much higher than expected, with a decrease in efficiency and a substantial reduction of stall margin. Moving from this experimental evidence, accurate 3D CFD simulations of the entire stage were carried out including the actual geometry of the probes for two probes configurations and three operating points. Simulations highlighted the effect probes? wakes on downstream vanes and the induced blockage effect, which both appear in line with experimental evidence. As a handout, a recommendation on the optimal probe positioning is suggested.

Transient Analysis of Flow Unsteadiness And Machine Instabilities In a Centrifugal Compressor at Surge and Second Quadrant Operation

Abstract Instabilities in turbomachinery operation originate from intrinsic flow unsteadiness, sudden variations of operating conditions, and interactions with the surrounding system, affecting both system stability and machine reliability. The flow unsteadiness, presenting a characteristic behaviour, requires a deep understanding of the underlying flow fundamentals, a careful analysis using advanced experimental methods and a clear distinction on how the system might lead to instabilities. The identified approach addresses deep surge and second quadrant characterization. The analysis presented here benefits from the responsiveness and flexibility of the experimental test rig, fine tuning of the system layout, the instrumentation installation, and the transient tests procedure. The main focus area is the time-frequency analysis of flow and pressure signals at transients, thus providing a proper reconstruction of flow mechanisms and instability evolution. Valuable techniques include: short-time fast Fourier transform, wavelet analysis, and Wigner-Ville distribution; coherence between flow and pressure, to trace waves propagation, is considered too. These, presented outlining their strengths and weaknesses, are evaluated considering real time field applicability with regards to computational resources too. The experimental campaigns and data processing are presented, with a test matrix covering a wide range of parameters, including system layout and surge volume size, rotational speeds, flow rates ranging from nominal point to full second quadrant operation. These data are vital for system modeling validation for a full compressor-system digital twin. Results indicate the importance of ensuring reliable data acquisition and analysis, with adequate instrumentation range, accuracy, synchronization, responsiveness and positioning.

Study on Dynamic Characteristics of Single-Span Rotor Under Cross-Coupling Stiffness Control on Non-drive End

Abstract The sealing-induced cross-coupling stiffness (CCS) often decreases the rotordynamic stability of turbomachinery. In our previous study, an active negative CCS control strategy applied between two bearings in the middle of the rotor was validated to enhance the stability of the rotor system. In this paper, a different approach was taken by applying both positive and negative CCS control strategies to the non-drive end, aiming to investigate their effects on rotordynamic stability using a rotordynamic model. The model represented a single-span centrifugal compressor rotor with CCS at the seal node. The logarithmic decrements and unbalance response of the rotor system were compared under different CCS applications at the non-drive end and in the span. The results demonstrate that applying both positive and negative CCS at the non-drive end can improve system stability, but the positive CCS strategy has limitations, and its applicability is not as extensive as Negative CCS. A “critical stiffness” phenomenon emerges when the rotor system is actively stabilized at the non-drive end, resembling critical resonance. Furthermore, when components like seals introduce cross-coupling stiffness out of the span, they contribute to system stabilization. These findings provide valuable insights into actively enhancing the stability of rotor systems.

State monitoring and fault prediction of centrifugal compressors based on long short–term memory and principal component analysis (LSTM-PCA)

Centrifugal compressors are widely used in the petroleum and natural gas industry for gas compression, reinjection, and transportation. Early fault identification and fault evolution prediction for centrifugal compressors can improve equipment safety and reduce maintenance and operating costs. This article proposes a dynamic process monitoring method for centrifugal compressors based on long short-term memory (LSTM) and principal component analysis (PCA). This method constructs a sliding window for monitoring at each sampling point, which contains 100 data from the past and current time points, and uses LSTM to predict 30 future data points. At the same time, this method is also combined with the PCA threshold process monitoring method to construct a new LSTM-PCA monitoring algorithm. And the method was validated using centrifugal compressor process data. The results show that this method can effectively detect process anomalies, The improvements significantly reduced the false positive rate of detected anomalies, and can make multi-step advance predictions of system behavior after faults occur.

Development of an Additively Manufactured Stationary Diffusion System for a Research Aeroengine Centrifugal Compressor

Abstract This paper introduces the next generation of the Centrifugal Stage for Aerodynamic Research (CSTAR) facility at the Purdue University Compressor Research Lab. The research centrifugal compressor is designed with an additively manufactured stationary diffusion system which comprises a vaned diffuser, a turn-to-axial bend, and deswirler vanes. The dimensional accuracy and surface finish of the diffusion system has allowed for rapid prototyping of several iterative diffusion system designs and has allowed for configuration of in situ pressure and temperature measurements to experimentally evaluate the aerodynamics and performance of centrifugal compressor diffusion systems. The diffusion system is manufactured from a commercially available stereolithography (SLA) resin, and the design of the parts is adapted to the constraints imposed by current technological and material limits of resin 3D printing. The implementation of additive manufacturing in the prototyping of the diffusion system has allowed for decreased cost and lead time while allowing rapid turnaround to generate experimental data. Performance data have verified the repeatability and temperature independence of the additively manufactured diffusion system through several design iterations. A survey of candidate materials for additively manufacturing these parts is also presented, and the tradeoffs of their material properties are discussed.

Analysis of single shaft turbojet engines structures and evaluation their safety with the use of FDM-A and FAM-C diagnostic methods

The article reviews the main stages of development of single-shaft turbojet engines. Selected construction of these engines are presented divided into three periods (before, during and after World War II) and two main jet engine schemes were discussed (with a centrifugal compressor and an axial compressor). The SO-3 jet engine installed on the TS-11 “Spark” aircraft was chosen to present the method of assessing the safety of structures. The FDM-A diagnostic methods developed in AFIT were used to experimentally verify the technical condition of the engine and FAM-C, based on the analysis of disturbances in the instantaneous rotational speed of the engine shaft. The results of tests related to the assessment of engine shaft misalignment, the assessment of the degree of wear of the engine shaft bearings and the assessment of the shaft clamping force in the bearings are presented. The summary lists the main advantages of single-shaft turbojet engines (simplicity of design for a solution with a centrifugal compressor and high thrust enabling breaking the sound barrier) and their disadvantages (complex design for a solution with an axial compressor and high failure rate of shaft bearing supports as the most loaded engine component).

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.