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Deep learning (DL) models have achieved great success in fault diagnosis (FD). However, most existing DL models are memory-intensive and computationally expensive. These DL-based FD methods suffer from three drawbacks when deploying them on edge devices with limited resources in real industrial fields: large model sizes, high computational demands, and long inference times. To address these drawbacks, a sparse convolutional neural network (CNN) framework is proposed for efficient FD where models have to run on edge devices. First, a standard CNN is built and trained until convergence on the target FD task. Then, a Taylor expansion-based criterion is designed to evaluate the importance of convolutional filters. As a result, the unimportant and redundant filters of the trained CNN can be iteratively pruned. Its remaining filters constitute a sparse CNN (SCNN) which is smaller and faster to run. Finally, the SCNN is applied to efficiently diagnose faults. The effectiveness of the proposed framework is demonstrated on two public disassembling part datasets and a real industrial oxygen compressor dataset. Experimental results indicate that the proposed SCNN framework significantly improves memory and computational performance on edge devices compared to standard CNNs, while still achieving superior accuracy relative to state-of-the-art methods. [ABSTRACT FROM AUTHOR]

Dual-source heat pumps have the potential to improve heating efficiency and / or the space required for heat sources. Parallel operation of two heat sources using two compressors can increase these benefits but poses technological challenges – specifically in the increased refrigerant cycle interconnection complexity, refrigerant and compressor oil management. These benefits and challenges have yet to be thoroughly investigated which is the primary objective of this research paper. An experimental analysis was conducted on a dual-source heat pump that utilized both an air heat source and a ground heat source. It included both individual and parallel operation modes of the heat sources. A prototype with a novel two-compressor interconnection was designed, manufactured, and tested in laboratory conditions. Analysis of the energetic benefit included efficiency evaluation at different ambient conditions and the corresponding loads on the ground source heat exchanger. Energetically, the single source operation showed comparable results in the coefficient of performance to conventional heat pumps despite the increased interconnection complexity. Parallel operation could efficiently cover heating loads at reduced load on the individual heat sources (at -7 °C, a reduction to 41 % on the ground-source and 58 % on the air-source heat exchanger). Technological challenges were highlighted in refrigerant and compressor oil shifts. While a control-based solution for the refrigerant shift was demonstrated, the oil shift requires further analysis of oil conditions in failing compressors. [ABSTRACT FROM AUTHOR]

Shock is the main characteristic of supersonic compressors. There are relatively few studies of the control of shock structure and secondary flow in supersonic compressors by nonaxisymmetric endwall optimization. The lack of understanding of the mechanism of flow structure changes in supersonic compressors by the nonaxisymmetric endwall limits the application of this technique in supersonic compressor interiors. In this paper, the effects of nonaxisymmetric endwall on the supersonic compressor and flow mechanism were studied using the numerical simulation method and verified by experiment. The results showed that the optimized nonaxisymmetric endwall design increased the peak isentropic efficiency of the supersonic compressor by 0.6%, verifying the effectiveness of the nonaxisymmetric endwall in improving the supersonic compressor. By comparing the flow fields at the peak efficiency points before and after optimization, it was found that the shock loss in the rotor was reduced by the change of shock structure induced by the nonaxisymmetric endwall, and the secondary flow loss was controlled by the change of shock structure in the rotor. Moreover, the rotor's nonaxisymmetric endwall changed the downstream stator's inlet conditions, reducing the stator's total pressure loss. Therefore, the nonaxisymmetric endwall has a wide range of applications for regulating the internal shock structure of supersonic compressors. [ABSTRACT FROM AUTHOR]

Surge phenomenon is investigated for an axial compressor through a set of experiments. In addition, the full-annulus numerical simulation method is used to numerically simulate the surge phenomenon and analyze the flow field details during the surge process. The results identified four distinct stages in the surge: forward deceleration, reverse flow, forward recovery, and chamber recovery. The forward recovery stage, the flow field experiences stall with the occurrence of unevenly distributed stall regions. In contrast, the chamber recovery stage at the same flow rate exhibits a more uniform flow field without stall regions. These findings highlight the capability of the capability of the full-annulus calculation method to provide insights into the flow field details during the surge process. The information can serve as a reference for the development of accurate surge models and the study of the influence of surge on the internal flow of the compressor passage. [ABSTRACT FROM AUTHOR]

Today, conventional controllers are commonly used in most refrigerators and freezers. They adjust the compressor speed to maintain the desired air temperature, irrespective of users’ usage profiles. In this study, a fuzzy logic-based smart control concept that incorporates occupant door-opening profiles was integrated into a free-standing commercial freezer. The intelligent controller adjusts air temperature setpoint, maximum compressor speed, and defrost periods according to the door opening patterns of users. The selected freezer was tested under two different usage profiles with both fixed-speed and variable-speed compressors. Test results showed that the intelligent controller can achieve more homogeneous pack temperature profiles by precooling before active usage and desynchronizing defrosting events with active usage periods. For the active user profile, the intelligent controller achieved around 7% improved energy efficiency compared to the standard controller for both fixed-speed and variable-speed compressors while keeping the maximum pack temperature at the same level. For inactive usage profile tests, the smart controller decreased the temperature rise of the packages by 0.5 °C with fixed-speed and by 1 °C for the unit with variable-speed compressor. Additionally, the intelligent controller demonstrated approximately 5% higher energy efficiency than the standard controller for units with fixed-speed and variable-speed compressors. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to overcome the inherent lack of precision in commonly used interpolation procedures when solving the mathematical model of turbofan engines, as well as to address the issue that the theoretical variogram model in traditional Kriging models is prone to subjective selection bias, which makes it impossible to accurately capture the inherent fluctuation patterns in compressor data. Design/methodology/approach: To mitigate this challenge, based on the spatial distribution characteristics of the compressor characteristic data of a certain type of turbofan engine, the input and output dimensions of the model are defined. By determining the stable operating region from the original component data, the authors use the proposed Kriging method improved with a support vector machine model to reconstruct the characteristics at unknown speeds within this region. The effectiveness of the proposed method is evaluated using the established assessment metrics. Findings: Experimental results demonstrate that the proposed method exhibits significant advantages over the conventional Kriging approach. Specifically, it leads to a substantial reduction in root mean square error and mean absolute error by 0.0153/0.0118 (low speed), 0.1306/0.0362 (medium speed) and −0.0066/0.2366 (high speed). Originality/value: This refined approach not only offers notable engineering applicability but also contributes significantly to the enhancement of aerospace engine model solutions' precision. [ABSTRACT FROM AUTHOR]

The compressor in the heat pump is crucial for efficient geothermal energy utilization, but faces challenges in optimizing energy efficiency, especially under variable working conditions. This paper investigates the complex energy characteristics of the R134a refrigerant in centrifugal compressors using CFD, combining entropy generation and relative energy rotor enthalpy to analyze energy conversion theory. Key factors such as temperature and pressure are fully considered. The results indicate that energy loss in centrifugal compressors mainly occurs in the gap between the blade top and near the tongue, with a vortex tendency at the impeller's tail edge. As the flow rate increases from 1.2 kg/s to 1.45 kg/s, the maximum total entropy generation in the impeller decreases by 161%, and the rotor enthalpy minimum value increases by about 90%. This energy conversion analysis method can identify changes in the location and extent of energy loss, offering a new perspective for optimizing the structure and energy-saving design of centrifugal impellers. [ABSTRACT FROM AUTHOR]

Tandem blades have been recognized for their potential to enhance the loading capacity of compressors. However, tandem stators currently do not exhibit advantages due to insufficient understanding of the complex end-wall flow mechanisms. To address this, an extensive study was conducted on tandem stators using experimental and numerical methods. The analysis focused on loss development, three-dimensional flow structures, and interaction mechanisms between front and rear blades. The results indicated the following: (1) The rear blade's influence on the front blade has contrasting effects in mid-span and end-wall regions. The stagnation action of the rear blade increases front blade load, leading to greater corner separation losses. (2) Mid-span flow losses account for over 60% of total losses near stalls, primarily due to increased mixing losses from the migration of front blade corner separations towards the mid-span region in the rear blade channel. (3) At higher mass flow rates, corner separations occur in the rear blade, driven by significant circumferential pressure differences at the front section of the rear blade, causing end-wall fluid migration towards suction surfaces. (4) Corner stalls predominantly occur in the front blade, with associated losses exceeding those in conventional blades. [ABSTRACT FROM AUTHOR]

The reversible use of a volumetric machine as a compressor and expander shows potential for micro-scale compressed air energy storage systems because of lower investment costs and higher operational flexibility. This paper investigates experimentally the reversible use of a 3 kW oil-flooded twin-screw compressor as an expander for a micro-scale compressed air energy storage system to assess its operation while minimizing operating costs and the need for adjustments. As a result, the oil injection was only implemented in the compressor operation since the oil takes part in the compression process, while its use appears optional in expander operation. The results indicate that the compressor exhibited an efficiency in the range of 0.57–0.80 and required an input power from 1 kW up to 3 kW. These values decreased for the expander, whose efficiency was in the range of 0.24–0.38 and the delivered power between 300 and 1600 W. The experimental data allow assessing the operation of such machine in a hypothetical micro-scale compressed air energy storage. The calculation revealed that this machine may operate in this energy storage asset and deliver up to 90% of the power recovered in the charging process when the temperature of the stored air is 80 °C. [ABSTRACT FROM AUTHOR]

In this paper, an unsteady Reynolds-averaged N–S equations (URANS) method is developed to calculate the surge dynamic process of compressor. Using this method, the surge dynamic process of a four-stage high-speed axial compressor at 70% design speed under different B parameters is numerically simulated. The simulation results show that the classical surge is induced when the B parameter is 0.35 and 0.4, and the deep surge is induced when the B parameter is 1.0 and 1.44. The surge frequency decreases with the increase in the B parameter, and the surge frequency obtained when the B parameter is 1.44 is very close to the experimental results. The body-force model (BFM) is another numerical simulation method with low computational cost and can capture the details of the flow field to a certain extent. For the same high-speed four-stage compressor, under the condition that the surge frequency is almost the same as that in the experiment, the calculation results of the surge dynamic process by the URANS method and the previously developed BFM are compared. The results show that the prediction of the dynamic pressure of the wall by the two methods is in good agreement with the experimental data, and the two methods have also achieved similar results in the prediction of the blade force. The meaningful comparison results show that the URANS method can be used as a supplement to the experiment in many aspects and provide more abundant calibration data for the further development of BFM. [ABSTRACT FROM AUTHOR]

In order to improve the compressor efficiency, a wavy leading edge design method is introduced. A single objective optimization method is adopted to find the optimal wavy leading edge design and the effect of the wavy leading edge on the suction surface separation of a subsonic compressor stator is investigated by means of numerical simulations and controlling the sinusoidal function. The optimization results indicate that the amplitude has a significant impact on the compressor efficiency. Three amplitude schemes were studied, and the results show that as the amplitude increases, the efficiency of the compressor first increases and then decreases. The optimal schemes can reduce flow loss by 21.8% and increase the peak efficiency of the compressor by 1.46%. The wavy leading edge blades could change the static pressure distribution and induce the formation of leading edge vortex pairs behind the valley to improve the ability of resisting the separation for the flow. [ABSTRACT FROM AUTHOR]

Based on unsteady numerical simulation, the feasibility of utilizing a fluid oscillator to generate oscillating jets for relieving the compressor cascade's corner separation was investigated. First, at design incidence angle, the optimal jet position is located where corner separation is not fully developed (74% axial chord length). Jets at more upstream and downstream positions are less effective due to premature dissipation of jet effects and the occurrence of high corner losses, respectively. The effectiveness of separation control through jet injection increases with higher jet mass flow rates, and the scheme with 0.66% relative jet flow rate exhibits a wide effective jet position range. However, excessively low jet flow rates are sensitive to jet position selection, while excessively high jet flow rates lead to significant mixing losses, resulting in high overall field losses and reduced engineering applicability. Second, the optimal jet scheme remains consistent at both design and high incidence angles and exhibits effective control at other off-design incidence angles. Finally, the oscillating jet suppresses the spanwise development of wall vortex and passage vortex within the blade passage by injecting high-momentum flow. Moreover, proper orthogonal decomposition analysis indicates that the oscillating jet redistributes the modal energy of the original flow field, exciting the vortex structures into high-frequency, small-scale oscillations at the jet frequency. Meanwhile, the oscillating jet primarily facilitates momentum exchange through strong mixing with passage vortex, wall vortex, and concentrated separation vortex, ultimately mitigating corner separation and reducing corner loss. [ABSTRACT FROM AUTHOR]

This paper explores the secondary surge during compressor surge recovery. Utilizing the test rig at Northwestern Polytechnical University, the surge is induced by tail cone adjustment. A secondary surge follows tail cone retraction post-initial surge. Signal changes are analyzed, and causes are expounded from energy and fluid dynamics. Experimental outcomes confirm the secondary surge is repeatable and observable under set conditions. Its frequency stabilizes at 4.83 Hz across consecutive events and rotor axes, being system-inherent. From energy, with enthalpy as a proxy, potential energy amasses as the compressor interacts with cavity potential shifts from tail cone changes. Exceeding kinetic supply instigates violent airflow oscillations. Peak pressure trends and simulations suggest surge likelihood at ∼3.33 × 105 J enthalpy. In fluid dynamics, post-initial surge, a stall state ensues. Tip clearance vortices from spillage and backflow expand, merge, and fill the passage. Their pre-secondary surge breakdown elevates pipeline pressure, causing gas reflux and surge recurrence. Conclusively, this research enhances compressor secondary surge comprehension, offering support for design optimization and anti-surge strategies. [ABSTRACT FROM AUTHOR]

Centrifugal compressors play a crucial role in energy and power systems, and compressor surge significantly impact their safe operation. Monitoring typical surge inception characteristics in a compressor can effectively serve as an early warning indicator, thereby enhancing safety. This paper presents the results of an acoustic experiment conducted on a centrifugal compressor setup. Four microphones were positioned in front of the compressor inlet to record the noise emitted as the compressor entered its surge region from a near-surge state. An entropy-based method is proposed to extract surge inception from acoustic signals by evaluating the informational complexity. Four types of entropy, including approximate entropy, sampling entropy, fuzzy entropy, and information entropy, were calculated from the acoustic signals. Their time-domain curves exhibit a clear increasing trend prior to surge inception. Further analysis reveals differing growth rates of the entropy curves among the four microphones, confirming the impact of microphone position on the capture of flow information and, consequently, on surge warning accuracy. Eventually, an entropy-weight method is proposed to eliminate the effects of positions and enhance surge warning capabilities by accounting for multiple acoustic signals. [ABSTRACT FROM AUTHOR]

In order to clarify the influence of circumferential non-uniform tip clearance (CNTC) on the flow, this paper studies the tip clearance structures with different minimum clearance sizes and distribution forms while ensuring the consistency of the average tip clearance size. The results indicate that CNTC can directly affect the tip flow structure, and the effective structure can significantly expand the stall margin (SM). The flow structure analysis shows that CNTC mainly influences the tip leakage flow rate (TLF) and tip leakage angle (TLA). The smaller the minimum clearance size is, the smaller the TLF. The distribution of CNTC primarily affects the TLA, and a larger tip clearance size on the suction surface will result in a better flow trend. When the minimum tip clearance size is 0.5 τ and the suction surface tip clearance size is 1.5 τ , the CNTC structure achieves a SM improvement of 5.72% and a peak efficiency improvement of 0.22%. The partial CNTC results show that the modifications of each region are independent, and the direct superimposition can approximately obtain the distribution trend of the overall modification. It is more effective for the front modification, while the effect of the rear modification is weak. It is worth noting that an enlargement of the clearance on the suction surface will cause the internal flow within the clearance to be directly influenced by the shock wave, which will directly affect the modification effect. [ABSTRACT FROM AUTHOR]

With the advancement of aerodynamic design techniques for turbomachinery, the high-loss flow in the end wall region has emerged as a bottleneck, limiting further improvements in the aerodynamic performance of fans and compressors. In this study, the end wall region of a linear cascade is flexibly parameterized using the advanced extended free-form deformation method and subsequently optimized through adjoint optimization, enabling an integrated design of the entire end wall region. A refined design featuring flexible hub deformation and a smoothly corner region is achieved. The results demonstrated that the finely integrated design significantly reduced the loss coefficient by 16.81% and effectively controlled corner separation. [ABSTRACT FROM AUTHOR]

This study investigates the efficiency evaluation of a compressor rotor designed for drive units requiring compressors with a power demand of less than 30 kW. The primary aim of the research presented in this article is to assess the feasibility of utilizing axial compressors to maintain high efficiency across a broad range of rotor speeds. A critical challenge in the considered power range is the occurrence of low Reynolds numbers, specifically those below 250,000. This research seeks to identify the underlying causes of efficiency degradation at low Reynolds numbers and determine the rotor's geometric parameters which most significantly influence the localized efficiency drop. Compressor efficiency was evaluated through numerical simulations. The numerical model was validated using experimental data and subjected to a grid independence study. Simulations were conducted for nine geometric configurations of the axial compressor rotor, with modifications to parameters such as the blade angle, blade thickness, blade solidity, and hub-to-tip ratio. For each configuration, a series of simulations was performed at rotor speeds ranging from 400 RPM to 2400 RPM. The simulation results indicated that the blade angle solidity was the most influential parameter affecting efficiency. A reduction in the blade angle led to approximately a 20% decrease in efficiency, primarily due to localized flow separation near the blade tip. Additionally, altering the number of blades caused a 20% efficiency reduction attributed to hub corner separation. The findings enabled the identification of optimal parameters, which will serve as a foundation for efficiency testing in the multistage configuration. [ABSTRACT FROM AUTHOR]

Our present investigation mainly focus on to identify the most appropriate refrigerants from various groups for replacing HFC-134a in a household refrigerator. The study involved conducting experiments using refrigerants from three different groups: Hydrofluoroolefin (HFO), Hydrofluorocarbon (HFC), and Hydrocarbon (HC). Among the tested refrigerants, R152a from the HFC group and HFC 1234yf from the HFO group showed the most potential. Compared to HFC-134a, both R152a and HFC 1234yf shows a reduction in refrigerating effect by approximately 4-7% and less power consumption in the compressor by around 5-7%.In conclusion, for replacing HFC-134a in a domestic refrigerator without needing alterations to the existing refrigeration system, two recommendable refrigerants are R152a and HFC 1234yf. These refrigerants are considered eco-friendly with zero ozone depletion potential (ODP) and low global warming potential (GWP) values. [ABSTRACT FROM AUTHOR]

In regions characterized by high temperature gradients, vapor compression systems often necessitate operation at very high pressure ratios resulting in a reduction in system capacity. Economized vapor injection compressors are used to avoid these issues, yet a precise predictive map for various compressor technologies with minimal data and relatively better performance remains unclear. This paper establishes a black-box compressor model to accurately predict compressor power, injection mass ratio, and evaporator mass flow rate in compressors with a single vapor injection port. This model is compared against three legacy models from literature and the ANN model, for reference. All five models are evaluated based on their ability to predict the aforementioned metrics. The proposed black-box model can predict the relevant metrics all within 5 % Mean Absolute Percentage Error (MAPE). Additionally, a refrigerant sensitivity analysis is performed with the black-box models. The model is trained using data from R410A and then used the coefficients to predict the performance of the same compressor when using R454B, and vice versa. It can estimate the evaporator mass flow rate with an accuracy within 3 %, the power within 2 %, and the injection mass ratio with MAPE less than 3 %. [ABSTRACT FROM AUTHOR]

• The dynamic model of the combined algebraic spiral scroll compressor was developed. • Discrete green's theorem method can accurately calculate the working chamber volume. • The influence of various parameters on the dynamic characteristics was analyzed. The combined algebraic spiral (CAS) effectively maximizes the geometric performance of a scroll compressor; however, its dynamic behavior remains inadequately explored. Utilizing the geometric model of the CAS scroll compressor, this study derived the functional relationship between the meshing point and the rotation angle, and calculated the working chamber volume using the discrete Green's theorem method. A dynamic model of the CAS scroll compressor was developed, and the influence of various parameters on its dynamic characteristics was analyzed. The findings indicate that when the polar angle interval is <0.01π, the discrete Green's theorem method accurately computes the working chamber volume. Among the gas forces acting on the CAS scroll compressor, the axial gas force is the most significant, followed by the tangential gas force, while the radial gas force is considerably smaller. The tangential gas force predominantly influences the overturning and rotational moments. Notably, when the polar angles of the connection points between the higher-order curve and the starting and ending algebraic spirals are set at 1.5π and 3π, the gas force remains low while maintaining geometric performance. This configuration results in reduced variation in gas force and enhanced dynamic performance. The spiral coefficient and spiral index of the starting algebraic spiral should be set as intermediate values to ensure optimal geometric and dynamic performance of the CAS scroll compressor. [ABSTRACT FROM AUTHOR]

The self-lubricating linear compressor with aerostatic bearings has good prospect for the scenario which has difficulties of oil returning. This study presents a novel oil-free linear compressor and establishes a frictional damping model by using equivalent circuit approach to evaluate the mechanical performance of the compressor. The changes in friction damping characteristics of VISLLC under different piston strokes and injection pressure are analyzed. The flow resistance coefficients within the porous medium and gas gap are obtained by experimental tests and modeling analysis. Simulation results indicate that the equivalent frictional damping coefficient can be reduced by 36.1 % comparing with that of the non-injection and the efficiency can improved the by 17.2 %. The frictional damping coefficient in the porous bearing thickness of 0.9 mm at 600 kPa injection pressure is 3.64 N·s·m−1. [ABSTRACT FROM AUTHOR]

Under off-design conditions, scroll compressors can lead to reduced efficiency, motor damage, and even cause safety problems such as leaks or explosions. To solve the above problems, this paper analyzes the influence mechanism of different voltages on the spectrum of pressure pulsation signal and modulation signal and provides theoretical support for fault diagnosis and enhances the interpretability of the model. A voltage fault diagnosis method of scroll compressor based on Time-frequency Principal component Convolutional Network (TPCN) model is proposed. By demodulation analysis of the pressure pulsation signal of the low-pressure inlet and high-pressure outlet of the refrigerant in the scroll compressor, the spectrum information of the principal component modulation signal under different voltages is obtained. The pooling strategy is used to accurately identify and extract the fault information in the modulated signal spectrum as the input data of the model. The input data is divided into the training set and the test set according to the ratio of 8:2 to complete the training and testing of the fault diagnosis model. The experimental results show that the accuracy of TPCN model for the diagnosis of 5 types of faults reaches 100 %. The average accuracy of the model is 100 %, which indicates that the model has good stability. [ABSTRACT FROM AUTHOR]

Copyright of Fluid Machinery is the property of Fluid Machinery Editoral Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Fluid Machinery is the property of Fluid Machinery Editoral Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Fluid Machinery is the property of Fluid Machinery Editoral Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Fluid Machinery is the property of Fluid Machinery Editoral Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Approximate Computing (AC) have widely adopted in designing large-scale logic circuits. In particular, approximate adder and multiplier circuits have been considerably targeted in the realm of image processing due to their high energy-saving while preserving proper level of computing accuracy. Nevertheless, intensive research and development are maintained in the means of seeking more matured designs that effectively prioritize design overheads over error resilience. In this paper, low error-distance approximate 4:2 compressor circuits are proposed to construct high-speed approximate adders. The developed compressors realize high logic computing and incur competitive area and power consumption, and therefore, they were leveraged to configure an approximate 8×8 multiplier designs. To achieve a favorable trade-off between computational accuracy and hardware resource usage, we develop a simulation framework that evaluates the accuracy of the proposed multiplier designs at the gate-level (measuring error distance) and at the application-level (evaluating SNR and SSIM) of an image. The framework truncates specific propagated carry bits, i.e., least significant bits (LSBs), to realize profitable area- and power-saving. Furthermore, two main high-speed multiplier designs are proposed herein, namely High Computing Performance Approximate Multiplier (HCP-AMUL) and HCP Low Error Approximate Multiplier (HCPLE-AMUL). Matlab R2022b along with VS Code are used for running simulations and accuracy evaluation, while Vivado 2018.2 is utilized for HDL reconfigurable logic design and implementation and evaluation of area, power, and speed, configured on an FPGA Xilinx Nexys 4 Artix-7 (XC7A100T1CSG324) trainer board. The experimental results demonstrate the efficacy of the developed multipliers as the developed HCPLE-AMUL delivers 54.26%, 11.72%, and 449.85 of speedup, power saving, and Power-Delay-AreaError-Product (PDAEP) improvement, respectively. On the other hand, the presented HCP-AMUL realizes an improved saving of area and power at the expense of an acceptable lowering of computation accuracy. It achieves 9.66%, 505.40, and 53.73% of power saving, PDAEP, and speedup respectively, Thus, the proposed compressor and multiplier circuits potentially can be promising approximate computing modules for image processing applications to provide improved trade-off between computation accuracy and logic utilization complexity. [ABSTRACT FROM AUTHOR]

In line fiber Mach–Zehnder inferometer (MZI) pulse compression was designed three different lengths of single mode-polarization maintaining fiber with (8, 16, 24) cm after splicing them between two single mode fibers (SMF-28e) with (23 and 13) cm and applying different weights on splicing region and the cross sectional area of SM-PM fiber, the designed performance of the in line fiber compressor system was studies in terms of compressor factor. Two minima pulse compression factor were obtained, one is 1.13 with FWHM 251.584 pm, centered wavelength 1547.394 nm, 52 cm interferometer length and 5 g was applied on the micro-cavity splicing region, and the second is equal 1.10 with FWHM 259.730 pm, centered wavelength 1547.120 pm and, 68 cm interferometer length and 10 g was applied on the cross sectional area of the second PMFs, in the case of single and cascaded interferometers, respectively. The input of the all interferometers was pulsed laser source with peak power 1.2297 mW, 286 pm spatial FWHM, 10 ns temporal FWHM, 3 kHz repetition rate and centered at 1546.7 nm. [ABSTRACT FROM AUTHOR]

In the experimental study of a compressor's cascade under the near-stall condition, the test bench has the disadvantages of high risk and high maintenance cost. This paper explores a method of using the inlet guide vane to imitate near-stall conditions instead of the rotor. The suction groove is set in the sectorial cascade so as to explore the aerodynamic performance of the fluid and the change in the flow field structure. Three different schemes are proposed along the suction surface, and the results indicate that the EW2 scheme, which is located behind the separation starting point and near the vortex core of the separation vortex, has the best performance. The suction groove weakens the downwash caused by the boundary layer on the upper endwall, reducing the radial dimension of the corner and suppressing separation. Suction on the upper endwall also increases the pressure difference in the radial direction of the flow passage, resulting in a slight increase in the suction-side horseshoe vortex (HSV) at the hub. An overall loss reduction of 9.4% is achieved when the suction coefficient is 46%, and the corner separation is most effectively suppressed while ensuring that the HSV at the hub only slightly increases. [ABSTRACT FROM AUTHOR]

ABSTRACT To address the discrepancy between the steam parameters extracted by pure condensing units/combined heat and power units and those required by users, this paper introduces the design of a steam screw pressure matcher(SSPM) and determines its optimal steam supply scheme. The SSPM primarily comprises a twin‐screw expander (TSE), twin‐screw compressor(TSC), electric motor, and generator. Initially, models were developed for a 300‐MW subcritical intermediate reheat condensing steam turbine unit, an SSPM, and a desuperheater and pressure reducer(DPR). Subsequently, these models are incorporated into the Ebsilon Professional software to simulate the operational characteristics of the SSPM. The performance parameters of the two options are then compared and analyzed. Simulation results reveal that the operational characteristics of the SSPM closely correlate with the mass flow rate of the TSE. As the TSE mass flow rate varies from 47 to 91 t/h, the efficiency of the TSE declines from 66.3% to 65.3%, while the power performed by the SSPM increases from −2457.978 to 1558.469 kW. Under identical operating conditions, the SSPM scheme exhibits a 6.2%–12.4% improvement in efficiency compared to the DPR scheme. Building upon the aforementioned analysis, the SSPM demonstrates effective cascade utilization of heat steam energy and exhibits favorable regulation characteristics under variable operating conditions. Contrasted with traditional DPR, the SSPM notably mitigates constraints on steam extraction by boilers and enhances the maximum generation efficiency of a single unit. [ABSTRACT FROM AUTHOR]

Aerodynamic optimization is an effective technology to improve the performance of turbomachinery. Traditional aerodynamic optimizations often focus on blade profiles and neglect the interactions between the blade and end wall, which may lead to suboptimal optimization result. To address this challenge, this study introduces an integrated optimization framework to simultaneously optimize both the blade and hub end wall aerodynamic shape. A hierarchical free form deformation (FFD) technique is employed to achieve integrated parameterization of the blade and hub, with a total of 580 design variables. To ensure efficient optimization with such a high-dimensional problem, the discrete adjoint method is used, which makes the optimization cycle less than one day. Under the framework, the blade optimization and integrated optimization of a typical compressor fan, rotor37, are conducted. With strict constraints on flow rate and total pressure ratio, the integrated optimization achieves a 2.85% improvement in isentropic efficiency—about 0.6% higher than blade optimization. The flow control mechanisms of two optimization approaches are compared, revealing that both blade optimization and integrated optimization effectively modify the blade profile to weaken the shock wave. Furthermore, by modifying the hub aerodynamic shape to improves the flow structure near the end wall, integrated optimization it is more efficient in turbomachinery aerodynamic optimization. [ABSTRACT FROM AUTHOR]

As a critical component of the variable cycle engine (VCE), the variable cycle core compression system (VCCCS) necessitates exceptional performance stability across a wide range of operating conditions. This research delves into the effects of varying the angles of variable inlet guide vanes (VIGV) on the thermodynamic characteristics and internal flow structure of the VCCCS under wide-range operational adjustments. The results reveal that modulating the VIGV significantly broadens the operating envelope of the VCCCS, extending the range of stable and efficient operation from a single curve to a surface. Moreover, adjusting the VIGV reconfigures the load distribution among VCCCS components, consequently altering the internal flow structure. The relationship between aerodynamic losses and entropy distribution in VCCCS components at different VIGV angles has been clarified. Closing the VIGV reduces the secondary flow losses and the extent of high-entropy regions within the core driven fan stage (CDFS) passage, while having a relatively minor impact on the losses in the high-pressure compressor (HPC). The evolution of the feasible domain of the bypass ratio and the mechanisms of adjustment limitation are uncovered. Notably, when the VIGV is adjusted from −20° to 50°, the sources of flow instability within the VCCCS under extreme boundary conditions exhibit three distinct changes. Additionally, a correlation has been established between the VIGV configurations and the thermodynamic characteristics of the VCCCS, thereby providing valuable insights for the design of efficient operation across a wide range of operating conditions. [ABSTRACT FROM AUTHOR]

Parameterized optimization methods are effective approaches for achieving high aerodynamic performance in compressors. Traditional parameterized optimization methods rely on a designer's preselected control parameter layout (including control frame orientation, point density distribution, control point displacement direction, number of variables, and variable ranges), which are purely based on empirical knowledge without sufficient theoretical basis. This paper selects the free-form deformation (FFD) method and Bayesian algorithm as the parameterization method and optimization algorithm for compressor airfoil optimization and studies the influence of FFD control parameter layouts on aerodynamic optimization performance. Additionally, an adaptive optimization method for control parameters based on FFD is proposed, where the orientation and density of the control framework can be incorporated as variables into the control parameters. During the optimization process, the range of design variables is adaptively expanded. A comparison between FFD optimization results based on B-spline and Bernstein basis functions shows that the former achieves an average performance improvement of 4% relative to the latter. Furthermore, an optimization method with an infinitely expandable boundary based on Bernstein basis FFD is proposed, which improves the performance by 12% compared to general adaptive boundary expansion methods. [ABSTRACT FROM AUTHOR]

We conduct experimental investigations of the effect of the tip air injection as a stability control method on a low-speed axial-flow compressor experiencing severe circumferential total pressure distortion. Eight Coanda-shaped injectors, uniformly distributed upstream of the rotor blade leading edge, were employed to counteract stall margin degradation caused by a flat-baffle circumferential distortion. Unsteady pressure data from the tip clearance and rotor wake regions were captured using time-resolved sensors and probes and analyzed through time-frequency transformation and proper orthogonal decomposition (POD) techniques. POD investigation under distorted inflow conditions reveals that the third-order POD mode, which characterizes unsteady tip leakage flow (TLF), plays a dominant role in triggering stall. Based on this insight, tip air injection with varying momentum ratios was applied to enhance the stall margin. The positive correlation between the injected momentum ratio and stall margin improvement was established, demonstrating the stabilizing effect of tip air injection under the circumferential distortion. The results indicate that tip air injection primarily acts on the rotor blade tip region to suppress the unsteady TLF at the center and downstream areas of the distortion, leading to an increase in tip blade load and a reduction in both the scale and number of pre-stall disturbances. However, the injection has a minimal impact on the unsteady TLF frequency band in the rotor wake region. Additionally, the POD analysis confirms that as the injection rate is increased, the energy percentage, flow field intensity, and power spectral density amplitude of the third-order POD mode are decreased, further reflecting the mitigation of unsteady TLF. The present work provides important insight into the stability control mechanisms of a tip air injection under circumferential distortion, offering design guidance for the implementation of active stability control strategies in axial-flow compressors. [ABSTRACT FROM AUTHOR]

Casing treatments are extensively utilized in engineering to significantly enhance stability. The impedance boundary-controlled casing treatment (IBCCT), based on a three-dimensional compressible stability model, is one of the examples and has demonstrated a notable stall margin improvement in a series of extensive experiments. However, the impedance model employed to characterize the perforated plates in IBCCT falls short in considering complex geometric parameters, such as dimensionless thickness and perforation edge angle. With an aim to optimize geometric parameters, the impedance of perforated plates with different vena contracta is determined by appropriate boundary conditions within an acoustic resistance model in this study. These impedance values are integrated with previous models to perform sensitivity analysis. The appropriate cross-sectional profiles for perforation are designed to achieve the desired adjustment of different vena contracta. IBCCTs with different vena contracta are subjected to experimental validation to substantiate the predictions. The results of both the experiments and the sensitivity analysis indicate that the stall margin improvement of IBCCTs increases as the vena contracta decreases. In addition, single-passage numerical simulations are performed under casing treatment conditions to determine whether the IBCCT with varying vena contracta intensifies the impact on the steady flow field. By integrating sensitivity analysis, experimental data, and numerical simulations, the impact of vena contracta on the stability enhancement performance of IBCCTs can be elucidated. [ABSTRACT FROM AUTHOR]

Precise information about the oil discharge rate (ODR) of a compressor and the oil retention rate (ORR) in the oil sump is essential for compressor design, development, and operation. An extended two-fluid model (E–TFM) is developed to study the complicated refrigerant vapor–lubricating oil two-phase flow inside a compressor. Gas–liquid bubbly, droplet, and well-mixed flows are defined on the local cell scale in the E–TFM. Numerical simulations are conducted to investigate the oil–vapor flow field and predict the ODR and ORR of a scroll compressor. The ODR predictions given by the volume-of-fluid method, the conventional Euler–Euler model, and the E–TFM are compared and validated against available measured data. The results confirm the reliability and applicability of the E–TFM. Most oil droplets escaping from the discharge pipe are found to originate from the newly generated droplets via stripping and breakage of the down-flowing thin oil film in the middle cavity. The droplet diameter significantly influences the predicted ODR, whereas the termination criterion for gas–liquid bubbly flow has little effect on the predicted ODR or flow field over the range considered in this study. To improve the ODR prediction performance of E–TFM, efforts should be made to implement a population balance equation to capture the droplet size. [ABSTRACT FROM AUTHOR]

Transient gas network simulations can significantly assist in design and operational aspects of gas networks. Models used in these simulations require a detailed framework integrating various models of the network constituents ‐ pipes and compressor stations among others. In this context, the port‐Hamiltonian modelling framework provides an energy‐based modelling approach with a port‐based coupling mechanism. This study investigates developing compressor models in an integrated isothermal port‐Hamiltonian model for gas networks. Four different models of compressors are considered and their inclusion in a larger network model is detailed. A numerical implementation for a simple test case is provided to confirm the validity of the proposed model and to highlight their differences. [ABSTRACT FROM AUTHOR]

In this study, a fish scale structure with low viscous drag was proposed and applied to the suction surface of a compressor cascade to reduce total pressure loss and suppress corner separation, a key source of compressor inefficiency. By using CFD simulations, the biomimetic structure was identified and integrated into the cascade design. To evaluate its effects, we analyzed secondary flow structures using 2D projected streamlines, axial velocity density (AVD), and vortex visualization techniques. The results show that the fish scale structure effectively reduces the volume of low-energy fluid by 18.36% and decreases total pressure loss at the outlet by 3.5%. Additionally, the AVD iso-surface proved instrumental in identifying low-energy fluid regions, which correlate closely with total pressure loss distribution. These findings highlight the potential of biomimetic-inspired designs to improve compressor performance by mitigating corner separation and reducing flow losses. [ABSTRACT FROM AUTHOR]

Over-compression of scroll compressor in variable refrigerant flow (VRF) system is a common problem in improving system efficiency because it operates in part load conditions for most of the year. By introducing intermediate discharge valves (IDVs) to allow gas bypass from compression chamber to discharge side during compression process, the over-compression loss can be eliminated. In this study, the characteristics of compression process in IDV compressor are analysed and the effects of IDV port location and port size on compressor efficiency are discussed based on the validated high fidelity scroll compressor model. It is found that the IDVs could be able to adjust gas bypass process in different compression ratio conditions and maintain high efficiency over wider compression ratio range than that of non-IDV compressor. In addition, the VRF system model is integrated to verify the system performance improvement by IDV compressor. It is found that VRF system performance is significantly improved in cooling conditions with the IEER enhanced by 23.9 %, while limited improvement is obtained in heating conditions as the operating compression ratios are relatively higher. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation of the effects of a decreasing refrigerant charge on the performance and operating conditions of an R513A water-to-water heat pump equipped with a large liquid receiver, an electronic expansion valve, and a vapor accumulator at the compressor inlet. The mass of the refrigerant inside the machine is progressively extracted to simulate refrigerant leakages occurring during the normal operation or in case of failures. The results show that the subcooling is the parameter mostly affected by a refrigerant charge variation since it rapidly collapses to 0 K with the charge reduction. Furthermore, it is possible to identify three different zones in which almost all the properties analyzed (COP, heating capacity, operating pressures and expansion valve opening) exhibit peculiar trends with the charge decrease: subcooling sensitivity zone, constant parameters zone, and compressor failure risk zone. The extension of these zones is determined by the size of the liquid receiver which is installed in the system and, for the heat pump under consideration, is between 100% and 95% of the initial charge for the first zone, between 95% and 40% for the second zone, and below 40% for the third zone. [ABSTRACT FROM AUTHOR]

Due to long lifetime, low level vibration and negligible electromagnetic interference, the Joule-Thomson (JT) cryocooler working at liquid helium temperature has been used in space. However, its cooling capacity and thermodynamic efficiency still need to be further improved under a certain mass limit, which is an essential improvement for space-efficient application of the JT cryocooler. Therefore, in this study, optimization design is carried out for a JT cryocooler working at liquid helium temperature. Based on the modification of Stirling cryocooler, pulse tube cryocooler and JT compressor, the developed JT cryocooler can provide a cooling capacity of 0.36 W at 4.18 K while the total input power and the total mass (without cryostat) are 1157 W and 26.8 kg, respectively. Compared with the literature research, it can be found that the developed JT cryocooler is suitable for space applications. [ABSTRACT FROM AUTHOR]

This article focuses on a 300MPa ultra-high pressure liquid driven piston compressor, redesigning it with a liquid sealing structure that utilizes glycerol (C3H8O3) as the sealing liquid. A grate structure is employed to depressurize the sealing liquid in the middle, enhancing the piston sealing life and the sealing effectiveness. CFD simulations were conducted to analyze the flow field of the circulating sealing liquid and to determine the pressure distribution and circulating flow rate. The pressure reduction effect of the grate teeth was numerically simulated, considering parameters such as tooth width, tooth height, spacing, and tooth number. The pressure reduction effect of the grate teeth was numerically simulated, considering parameters such as tooth width, tooth height, spacing, and tooth number. The optimized geometric parameters of the grate teeth, as indicated by the CFD simulation, ensure that the seal design meets the design requirements, offering theoretical guidance for selecting seals in ultra-high pressure liquid driven piston compressors. [ABSTRACT FROM AUTHOR]

The micro-refrigeration system can be utilized in various fields, including personal cooling, medical applications, and other specialized fields. Compressors represent a crucial component of vapor compression refrigeration systems. A simulation model of the micro scroll compressor has been developed. The operating characteristics and leakage of scroll compressors with different capacities (10, 50, 100 cm3/rev) are compared. The effects of rotational speeds, condensing temperature, volume ratios, and clearance on the characteristics of micro scroll compressors have been analyzed. For the scroll compressor that has a suction capacity of 10 cm3/rev, the volumetric and isentropic efficiencies tend to initially rise and subsequently decrease as the rotational speed is raised. The volumetric efficiency reaches a maximum value of 86.26% at 5000 rpm, while the isentropic efficiency reaches a maximum value of 72.93% at 6000 rpm. As the volume ratio increases from 0.79 to 1.0 of the theoretical volume ratios, the volumetric efficiency remains stable, while The isentropic efficiency demonstrates a pattern of initially rising and then falling, reaching a peak of 71.63% at a volume ratio of 0.91 compared to the theoretical volume ratios. [ABSTRACT FROM AUTHOR]

Vaned diffusers are widely used in centrifugal compressors due to their higher pressure-recovery coefficients compared to vaneless diffusers. In this study, the effects of the diffuser vanes' wrap angle and number of vanes on the aerodynamic performance of an industrial Methane centrifugal compressor with a pressure-ratio of 1.288 are studied using high fidelity steady-RANS numerical simulations. Three wrap angles (WA = 19.3o, 22.3o and 25.3°) and three number of vanes (NDiff. = 16, 20 and 24) are examined, while all the other geometrical and operational parameters are kept constant. Results showed that decreasing the wrap angle can enhance the choke flow rate of the compressor, with slight reduction in pressure ratio at low flow rates. However, increasing the diffuser wrap angle, intensifies the flow separation over the diffuser vanes. On average, the best aerodynamic performance of the compressor occurred at WA=22.3°. Results also showed that reducing the number of diffuser vanes enlarges the operating range of the compressor, however, the pressure ratio will be lower at the flow rates less than the design point. Conversely, higher pressure ratios will be achieved at the flow rates greater than the design flow rate. The optimal aerodynamic efficiency of the diffuser, considering both the pressure ratio and the total-to-total efficiency, was achieved when the NDiff value was set to 20. [ABSTRACT FROM AUTHOR]

The accurate prediction of the aeroelastic behavior of turbomachinery for aircraft propulsion poses a difficult yet fundamental challenge, since modern aircraft engines tend to adopt increasingly slender blades to achieve a higher aerodynamic efficiency, incurring an increased aeroelastic interaction as a drawback. In the present work, we present a reduced order model for flutter prediction in axial compressors. The model exploits the aerodynamic influence coefficients technique with the adoption of a broadband frequency signal to compute the aerodynamic damping for multiple reduced frequencies using a single training simulation. The normalized aerodynamic work is computed for a single oscillation mode at three different vibration frequencies, comparing the outputs of aerodynamic input/output models trained with a chirp signal to those from single-frequency harmonic simulations. The results demonstrate the ability of the adopted model to accurately and efficiently reproduce the aerodynamic damping at multiple frequencies and arbitrary nodal diameters with a single simulation. [ABSTRACT FROM AUTHOR]