Centrifugal Compressor Research Articles

Load sharing strategy for parallel-operated variable speed centrifugal compressors in chillers

The building space cooling is accounting for a significant portion of global energy use, and it is essential to enhance chiller efficiency for energy reduction and climate change mitigation. Chiller systems with multiple compressors provide the flexibility to meet varying cooling demands. The load-sharing strategy controls how the cooling load is distributed among the compressors. The load-sharing strategy optimization can significantly affect the chiller overall power consumption. This paper presents a mathematical analysis of the power consumption of centrifugal compressors under specific ambient temperatures. The influence of the inlet guide vane and the variable frequency drive efficiency on the compressor power consumption are considered and discussed briefly. An optimal load-sharing strategy for commonly used systems with identical compressors is proposed. Additionally, the scenarios involving a mix of different compressors are investigated. To validate the proposed strategies, a case study using the established performance data of a commercial centrifugal compressor is conducted. The case study results align with the mathematical analysis and the proposed strategy. This study provides valuable insights for designing and managing efficient chiller systems.

Objective sound quality evaluation of the electric two-stage centrifugal compressor for fuel cell vehicles-experimental investigations

Sound quality is one of the most challenging studies in the field of automotive NVH. The most important noise source in fuel cell vehicles (FCVs) is the air compressor, and its noise seriously affects the sound quality of FCVs. The centrifugal compressor is now the mainstream choice for commercial FCVs, but there are few studies on its sound quality evaluation using objective psychoacoustic parameters. Therefore, a comprehensive vibration-noise experiment is conducted on an electric two-stage centrifugal compressor (ETCC) for FCVs to evaluate the sound quality accurately, including all operating conditions. The sound quality is evaluated by four objective psychoacoustic parameters: loudness, sharpness, fluctuation strength and roughness, which are the most widely used indicators. The reasons for the variation of these acoustic parameters under dynamic operating conditions are accordingly explained. It can be concluded that the loudness and sharpness show a strong and positive correlation with the rotational speed, while the fluctuation strength and roughness just reflect the sound quality of the ETCC for the low-frequency band and high-frequency band, respectively. So, taking loudness and sharpness as the core indicators under accelerating conditions is recommended. Then, the sound quality of the ETCC under unstable conditions at variable speeds is investigated. It is found that the sound quality of the ETCC deteriorates under surge conditions. When entering into the deep surge, the loudness and sharpness both fluctuate drastically, which is caused by the periodic impulse noise. The fluctuation strength rises sharply and keeps a high level in the process of deep surge because of the obvious low-frequency characteristics of the surge. The above three parameters have a clear correlation with the rotational speed, while roughness is the only parameter that is not significantly connected with the rotational speed, which can be explained by the existence of a high-frequency fluctuation under the entire surge process. Finally, the causes of sound quality deterioration are explored using secondary signal processing. The results show that the outlet pressure pulsations of the ETCC under surge conditions lead to the increases and fluctuations of these acoustic parameters, and compressor surge is the main cause of deterioration in sound quality for FCVs. Based on the results, the objective sound quality evaluation of the ETCC is accomplished, and four psychoacoustic parameters can be modified to improve the sound quality. This study provides a theoretical basis for proposing methods to accurately evaluate and improve the sound quality of FCVs.

Viability assessment of large-scale Claude cycle hydrogen liquefaction: A study on technical and economic perspective

The competitiveness of hydrogen as a sustainable energy carrier depends greatly on its transportation and storage costs. Liquefying hydrogen offers advantages such as enhanced purity, versatility, and higher density, yet current industrial liquefaction processes face efficiency and cost challenges. Although various large-scale and efficient liquefaction concepts exist in the literature, they often overlook the economic and technical viability of such plants. Here, we addresses this issue by establishing a framework for modeling a large-scale hydrogen liquefaction concept and conducting both technical and economic assessments, with a specific focus on 125 tonnes per day (TPD) high-pressure hydrogen Claude-cycle concept. The technical analysis involves preliminary designs of key process components, while the economic assessment utilizes Aspen Process Economic Analyzer. Our findings indicate that at an electricity price of €0.1/kWh, the Claude-cycle liquefier concept yields a specific liquefaction cost (SLC) of €1.55/kgLH2. A sensitivity analysis was performed, which shows that electricity price has a significant influence on the economics. Further investigation on the compressors design shows that incorporating high-speed centrifugal compressors could reduce the SLC by 5.42% and potentially more. Scaling up to 250 and 500 TPD reveals further cost improvements, while cost projections indicate substantial declines as the technology matures. Ultimately, this paper presents novel cost-scaling and experience curves of hydrogen liquefaction technology, demonstrating the compelling economic viability of integrating large-scale hydrogen liquefaction into sustainable energy infrastructure.

Exergy and dynamics analyses in centrifugal turbomachinery pressurized long-distance natural gas pipelines based on Hamiltonian model

Natural gas pipelines represent intricate systems comprising diverse components, which is crucial to industry, yet demanding substantial energy consumption. However, the nuanced energy and exergy transfer dynamics within these pipelines, particularly during dynamic processes, remain relatively unexplored. Given the distributed nature and complicated component coupling among pipeline elements, coolers, and compressors, traditional energy analysis tools face challenges in their application. In this study, we introduce a novel approach utilizing Hamiltonian formalism to establish an energy and exergy analysis framework for natural gas pipelines. Specifically, we develop Hamiltonian energy functions for various components, including pipes, centrifugal compressors, and coolers, accounting for dynamic mechanisms. Through comprehensive simulations covering static and dynamic scenarios, we elucidate energy and exergy transfer processes, leveraging Hamiltonian energy function terms. Our findings validate the efficacy of the proposed analysis framework in accurately characterizing energy transfer and dissipation processes. Furthermore, validation with field data demonstrates the capability of our method to online exhibit energy transfer features effectively.

Upgrading the Compressor Stage of the CAT250TJ Micro Gas Turbine Engine

AbstractDue to their simplicity and relative ease of manufacture, single-stage centrifugal and mixed flow micro gas turbine (MGT) engines are preferred in thrust-based remotely piloted aerial vehicles. A single-stage mixed-flow compressor upgrade for the 200 N CAT250TJ MGT engine is numerically evaluated and presented. An in-house developed mean line application and commercial CFD software is used for the design and performance evaluation of the proposed upgrade configurations. The CAT250TJ – Gen1 engine features a single-stage centrifugal compressor, annular combustor, and single stage axial turbine. Apart from an upgraded impeller, a new crossover diffuser configuration is introduced to replace the wedge-type, straight outlet diffuser configuration of the Gen1 engine. The new single vane crossover diffuser configuration provides a design point total-to-total efficiency and pressure ratio increase of 8.3% and 12.1%, respectively. A disadvantage of a single-vaned crossover diffuser compared to legacy diffusers is a narrower operating range. To alleviate this issue, various combinations of tandem and splitter vane crossover diffuser configurations are proposed. These provide an enhanced operating range, comparable with the operating range displayed by the Gen1 configuration. A turbine power matching analysis is additionally completed to ensure proper compressor integration. Gas turbine cycle software is used to evaluate the on-engine performance of the upgraded compressor configurations. It is shown that the new baseline, single vane crossover diffuser configuration provides a 10.74% increase in design point static thrust.

The Hybrid Concept of Turboshaft Engine Enhanced by Steam Cycle Using Waste Heat Recovery—Combined Analytical and Numerical Calculation of Its Efficiency

<div>The article presents a hybrid concept of a turboshaft engine that fits into the area of PGE (pressure-gained combustion). It combines the advantages and elements of a piston engine and a turbine engine. The combustion takes place in isochoric chambers. The proposed timing system of the engine efficiently realizes the Humphrey cycle. Additionally, the main gas cycle engine was enhanced by the Clausius–Rankine steam cycle to achieve effective power of engine equal to 1231.3 kW. It was supplied by waste heat recovery from the exhaust gas. The enhancement of the engine by the secondary steam cycle significantly improved engine effective efficiency with a final value reaching 0.446. The effective efficiency and specific fuel consumption of the engine were calculated using merged analytical–numerical CFD (computational fluid dynamics) analysis. The centrifugal compressor, gas turbine, and steam turbine can work on the common shaft whose rotational velocity is 35,000 rpm. Because of additional weight, it could have potential applications for stationary use or heavy military units.</div>

Comparative Analysis of Diagonal and Centrifugal Compressors with Synergy Theory in Compressed Air Energy Storage System

Comparative Analysis of Diagonal and Centrifugal Compressors with Synergy Theory in Compressed Air Energy Storage System

Design and Analysis of an Axial Hybrid Magnetic Bearing With the Slice Stator for the Magnetically Suspended Centrifugal Compressor

Design and Analysis of an Axial Hybrid Magnetic Bearing With the Slice Stator for the Magnetically Suspended Centrifugal Compressor

Investigation of the mild surge in an axial–centrifugal compressor

The performance and structural integrity of compressors are critically impacted by aerodynamic instability. This study examines an unstable phenomenon, known as high-frequency mild surge (HFMS), in axial–centrifugal compressors through an experimental investigation and a low-order model. The results reveal that the pressure signal during HFMS is synchronized along the circumferential and streamwise directions. To elucidate the HFMS mechanism and further explore its influential law, a multi-actuator model is developed, successfully capturing the dynamic instability behavior. As the mass flow decreases, the front axial stage becomes unstable first, while the latter centrifugal stage remains stable with a negative slope near the operating point on the performance curve. The strong pressurization of the centrifugal stage maintains the stability of the entire compression system, increasing the mass flow rate. Subsequently, the pressure ratio of the latter centrifugal stage decreases with increasing mass flow, causing the front axial stage to become unstable again. The axial stage's Helmholtz frequency is consistent with the test HFMS frequency, further proving that it is a local systematic instability dominated by the axial stage. This matching feature is particularly common in combined compressors, making HFMS a typical instability phenomenon in such systems.

Reduced-dimensional prediction method for the axial aerodynamic forces in the off-design operation of near-critical CO2 centrifugal compressors

In the high-load centrifugal compressor of near-critical CO2 (NcCO2) power-generation cycle, the overload of axial aerodynamic force causes significant harms to the structural safety and operational stability of turbomachinery components. Based on a transcritical CO2 compressor of a MWt-class simple recuperated cycle, we numerically studied the aero-thermodynamic characteristics of back-cavity leakage, and discussed the physical model of the axial aerodynamic forces in off-design operation of NcCO2 compressors. Finally, reduced-dimensional prediction method for the axial aerodynamic forces in the near-critical CO2 compressor was developed. Wherein, the Japikse's method was used to estimate the primary aerodynamic loads of centrifugal impeller, and a 1-D radial equilibrium equation with angular velocity ratio was derived to predict the thrust force acting on the impeller back disk. Furtherly, based on the near-wall distribution pattern of angular velocities and physical property of Rankine vortex, a semi-empirical model of angular velocity ratio was introduced and completed the model of back-disk force. In validation, the reduced-dimensional prediction method exhibited satisfactory accuracy with perfectly acceptable errors compared to the refined CFD simulations. Thereby, a reduced-dimensional prediction method for the axial aerodynamic forces was developed for the economical and agile analysis of NcCO2 compressors in engineering practices.

Investigation of the Map Width Improvement in a Radially Reduced Diffuser Design Concept for a Centrifugal Compressor

Abstract Often, an improvement in performance at one operating point in a compressor/turbine operating map will lead to a reduction in performance at another area. For example, improving the efficiency of a compressor at design point (DP) may result in a reduction of efficiency at other operating points or it may result in a reduced stable operating range. In order to reduce the compressor cost and weight, a 15% radial reduction was applied to the diffuser passage length of a high pressure ratio centrifugal compressor. The diffuser endwall was diverged to achieve an appropriate area ratio from diffuser inlet to outlet. Two different vane shapes were considered with the radially reduced diffuser passage. The first diffuser vane was a scaled version of the baseline airfoil vane shape and this was used to develop an understanding of the impact of the passage length reduction and diverging endwall. The second vane geometry was parameterized using an unconventional method derived from published literature and optimized to improve performance at DP. Increased losses were generated through the diffuser passages of the radially reduced designs, but this was compensated for by lower losses through the volute due to more desirable flow at volute inlet. As a result, the radially reduced designs not only matched the performance of the baseline configuration, but also succeeded in achieving a marginal efficiency improvement. Furthermore, despite not being one of the goals of the optimization procedure, an extension of the stable operating range of 36% and 20% at the highest speed condition was achieved for the scaled and optimized designs, respectively. The current study focuses on understanding the physical reasons that generated this significant enhancement to the compressor operating range. In order to acquire the desired understanding, experimental data is presented to validate the Computational Fluid Dynamics (CFD) model and a detailed numerical investigation is presented to explain the changes in the flow field within the radially reduced designs. The study focuses on low flow rate operating points, necessitating the use of an Unsteady Reynolds Averaged Navier-Stokes (URANS) approach to analyse the flow. Detailed scrutiny of the flow field revealed a secondary flow feature in the diffuser passage which resulted in higher diffuser passage losses at DP but stabilised the flow as it developed for lower mass flow rate operating points.

A nonlinear disturbance observer for sliding mode control of surge in centrifugal compressors via TCV actuator

Surge is a form of dynamic instability created as an unstable pattern in the flow of fluid and can severely affect centrifugal compressor performance by causing fluctuations in flow and pressure parameters. Due to the heavy and costly damage that the surge may cause in various industrial processes such as petrochemical plants, it is necessary to design an appropriate control system to reduce the effect of this phenomenon. The problem of active surge control of a centrifugal compressor using the throttle control valve (TCV) in the presence of compressor parametric uncertainties as well as large demands on upstream and downstream loads is investigated in this work. The control objective was to design a robust control system that can stabilize the compressor over a wide operating range without knowing the upper bound for the uncertainties and load demand. The controller should also react quickly by generating a smooth control signal without saturating the control input. These objectives are achieved by designing a sliding mode controller along with a nonlinear disturbance observer. The performance of the proposed disturbance observer-based controller is evaluated under various operational and load conditions and the results are compared against fuzzy type 1, conventional sliding mode, and wavelet-based neural network robust adaptive controllers. The results show that the proposed method can tolerate large disturbances without any knowledge on the upper bound of the incident disturbance, both on the downstream pressure and upstream mass flow which is highly desirable in practice. The comparative study proves the efficacy of the proposed method using various performance measures. The study also confirms the superior robust performance and stability of the proposed method in front of matched and mismatched disturbances as well as model uncertainties especially close to the instability boundary. Although choosing a TCV actuator has made the control system design easier, the sensitivity of the control valve to flow coefficient and zero calibration under different operating ranges of the compression system is studied carefully and some recommendations for the users are provided.

On the elastic–plastic behaviors of centrifugal steam compressor impeller under cyclic thermomechanical loading

AbstractIn this paper, the cyclic elastic–plastic behaviors of the centrifugal steam compressor impeller (CSCI) structure under practical operating conditions are discussed employing the linear matching method (LMM). The three‐stage strategy of the LMM is employed to determine the shakedown and ratchet boundaries by conducting a series of iterative direct steady cyclic analysis, and based on this, the load regions corresponding to different types of damage behavior that may occur during the operation are identified. Computational results reveal slight contraction in the structural response diagram when considering actual material constitutive relationships, compared to ideal elastic–plastic models. Meanwhile, by integrating the unified ratchet and fatigue program with fatigue experimental data, a series of constant low‐cycle fatigue life curves has been presented for different service conditions. Furthermore, a comparison with detailed step‐by‐step inelastic analyses confirms the applicability and great efficiency of the LMM in practical engineering problems.

Development of Curved Shape Diffuser Duct for Aero Engines With a Backend Centrifugal Compressor

In the present study, a design of the curved shape diffuser-duct is proposed to apply to the compressor stage for aero-engines with a backend centrifugal compressor. For these configurations, the flow exiting radially from the centrifugal impeller needs to be changed from radial-to-axial direction to meet downstream combustion chamber requirements. Hence, the specially designed exit duct with a curved shape to manage the flow from the radial-to-axial direction was later diffused using the diffuser-shaped exit duct. This study aims to design and develop an efficient diffuser-duct for the adequate deceleration of flow in the exhaust diffuser and, as a result, a uniform and low-velocity flow at the exit. This configuration comprises a radial-to-axial turning annular passage at the centrifugal impeller exit. Then, the passage is directed to either a purely axial direction or is inclined to the axial direction by a slight angle. The results indicate a uniform total pressure at the stage exit with marginal variation along the span. It shows equivalent end wall effects near both the shroud and hub surfaces. This endwall effect may be occurring mainly due to the growth of the boundary layer across the diffuser passage.

Aerodynamic performance enhancement of centrifugal compressor using numerical techniques

Background Centrifugal compressors are dynamic machines utilizing a rotating impeller, efficiently accelerate incoming gases, transforming kinetic energy into pressure energy for compression. They serve a wide range of industries, including air conditioning, refrigeration, gas turbines, industrial processes, and applications such as air compression, gas transportation, and petrochemicals, demonstrating their versatility. Designing a centrifugal compressor poses challenges related to achieving high aerodynamic efficiency, surge and choke control, material selection, rotor dynamics, cavitation, erosion, and addressing environmental considerations while balancing costs. Optimizing maintenance, reliability, and energy efficiency are essential aspects of the design process. Methods The primary objective of this research is to comprehensively investigate and improve the aerodynamic performance of centrifugal compressors. To accomplish this, a comprehensive investigation of variables such as blade number and hub diameter, along with various turbulence models will be conducted. This approach will leverage numerical techniques to fill the significant gaps in the current literature regarding centrifugal compressor design and optimization. The study encompasses the evaluation of two turbulence models, namely Shear Stress Transport and K-epsilon. Furthermore, it delves into the fine-tuning of blade geometry, including variations in blade number and hub diameter, aiming to refine the design for optimal performance. Extensive analyses using Ansys CFX encompass key variables such as Pressure, Mach Number, Density, Velocity, Turbulence Kinetic Energy, and Temperature. Results Notably, the optimized pressure profile yielded remarkable results, achieving a substantial 36% improvement, demonstrating the tangible benefits of these design enhancements. Conclusion The outcomes of this research hold significant utility for engineers, manufacturers, and regulatory bodies, offering invaluable insights and guidance to enhance compressor performance and efficiency.

Analysis and Optimization of the Performances of the Tandem Blade Radial Compressor Using the CFD

Centrifugal compressors are frequently used in both military and commercial areas because they can be easily manufactured and reach high-pressure compression ratios. The factor that limits the performance and operating range of compressors is flow instability. Many ideas have been put forward for performance improvement, but tandem blade radial compressors, which do not require an extra air system, have attracted the most interest. In this study, computational fluid dynamics (CFD) analyses were carried out on various parameters of the tandem blade (TB) radial compressor, and an optimization study was carried out to find the best design using a genetic algorithm on a whole operating curve. It was investigated how these parameters affected the efficiency and total pressure ratio between the determined lower and upper limits. The numerical analyses of the optimum design obtained as a result of the iterations were carried out. As a result of the iterations, three optimum designs were obtained and numerical analysis was carried out according to one of them, and then they were compared with the results in the literature. The general agreement of computational fluid dynamics and the literature data served as a validation for the computational approach. The error rates between the numerical analysis results and the experimental results in the literature were calculated for different flow rates and were found to be 1.98% as the highest and 0.35 as the lowest. The work carried out in this article will provide a valuable reference for future advanced tandem blade compressor designs.

Investigation of dual-ported shroud casing in a centrifugal compressor: Aerodynamic performance and aeroacoustics

The dual-ported shroud casing has two ports over the impeller section in a centrifugal compressor, different from the traditional ported shroud casing. This paper uses numerical simulations and experiments to investigate the effects of the dual-ported shroud on the centrifugal compressor, including aerodynamic performance and aeroacoustics. According to the experimentally measured compressor performance map, the novel finding is that the dual-port casing treatment extends the compressor operating range by improving the instability margin and increasing the compressor choke flow capacity. The mechanism contributing to the choke flow capacity increase is the bypass function. The dual-ported shroud casing bypasses a part of the air to enter the impeller channels at the blade tips without going through the impeller geometry throat. Besides the benefits, the efficiency and aero-acoustic measurements identify the disadvantages of the dual-ports casing treatment: the peak efficiency deterioration at high rotational speeds and louder noise emission at the compressor inlet.

Aerodynamic Stability Enhancement of a Sco2 Centrifugal Compressor by Riblets of the Shroud

Abstract This paper investigates the mechanism of aerodynamic instability of shrouded SCO2 compressors and accordingly proposes a new method for stability enhancement via the casing treatment in terms of shroud riblets. Firstly, the experimentally validated CFD method is employed to investigate the flow mechanism of the compressor under near-surge condition. The significant backflow phenomena within the impeller were revealed. Further analysis indicated that the imbalance of the Coriolis force and pressure gradient in blade-to-blade direction pushed the low-momentum fluid toward the shroud suction side. Additionally, higher Reynolds number resulted in thinner SCO2 boundary layer at the inlet near end-wall, increasing passage vorticity and further intensifying the aggregation of low-energy fluid on the shroud suction side. Based on the flow mechanisms, the streamwise riblets on shroud were designed to impede the migration of low-energy fluid. The CFD results revealed that under low-flow condition, riblets inhibit the formation of inducer vortices and backflow, enhancing impeller aerodynamic stability and reducing the surge mass-flow rate. Further research indicated that riblets obstruct the migration of low-energy fluid towards shroud suction side, reducing the accumulation of low-energy fluid and blockage, thereby increasing the flow area and aerodynamic stability. Moreover, additional riblets wake and friction losses contributed to the deterioration of compressor performance at middle/large mass-flow-rate conditions. Specifically, riblets reduced the flow area between blades at near choke mass-flow rate, leading to more pronounced shock structures and compressor earlier choke.

PROSPECTS FOR THE USE OF GAS TURBINE CENTRIFUGAL COMPRESSOR UNITS AT OIL AND GAS FACILITIES

The article is devoted to the study of gas turbine compressor units and, on the basis of this, the determination of technological, parametric and specific criteria and features of the use of gas turbine centrifugal compressor units in gas transmission systems and underground gas reservoirs. For this purpose, the advantages and disadvantages of gas turbine compressor units are analyzed. Comparative information is provided on the use of centrifugal, piston and screw compressors, which are often used in the oil and gas industry. The influence of the supply limit and supply volume, production time, and maintenance procedures on the choice of compressor type is shown. shown. A number of gas turbine compressor stations currently operating in Azerbaijan have been reported. The problems of gas lift operation of wells and the use of gas turbine centrifugal compressor devices in gas transmission systems and underground gas storage facilities have been studied from the point of view of technological, parametric and specific criteria, the unique characteristics of each system have been determined, and the unique characteristics of each system have been determined. Recommendations for pre-design studies have been developed for the purpose of using gas turbine centrifugal compressor devices in various systems. Keywords: gas turbine, compressor, gas lift system, gas transport, underground gas storage.

Study on the influence of variable inlet guide vane slot on the aerodynamic performance in air storage centrifugal compressor

The influence of variable inlet guide vanes with slots (SVIGVs) on the aerodynamic performance of an air-storage centrifugal compressor was studied using numerical simulations. The inlet position of the slot was set to 4 % of the chord length of the variable inlet guide vanes (VIGVs), and the outlet position was set to 14 %. The results show that the high-loss area near the VIGVs suction surface increases owing to the secondary flow generated by the slot jet, and the change in the inlet flow angle of the impeller results in a decrease in the compressor efficiency under the 30° pre-swirling angle condition. In contrast, the slot can effectively reduce the loss caused by the VIGVs at 40° and 50° pre-swirling angles and optimise the impeller inlet flow angle, thereby improving the efficiency and pressure ratio of the centrifugal compressor. At a pre-swirling angle of 50°, the efficiency and pressure ratio of the compressor increased by 8.3 % and 0.2, respectively. Furthermore, the influence of the SVIGVs on the impeller aerodynamic loads of a centrifugal compressor was revealed through an unsteady numerical simulation. The results showed that the SVIGVs effectively improved the aerodynamic load distribution on the impeller, reduced the aerodynamic load by three, four, and five times the frequency of rotation, and reduced the frequency amplitude by up to 2/3.