Compressor Characteristics Research Articles

Design features of CNG stations of block-complete design

The classification, standard-size range and technical characteristics of small and medium-capacity CNG units of block-complete design (BC CNG units) are given. The basic technological scheme of the automobile gas-filling compressor station of modular block-complete design (CNG BC) is presented. A general view and a schematic diagram of the functional block-complete system of the station are given. The features of the compressed natural gas production technology of the BC CNG are summarized. The structural and technological scheme of a typical automated process control system of CNG BC is presented. The system of accumulation and distribution of compressed gas is given. Keywords compressed natural gas, classification and characteristics of BC CNG stations, station frame, multi-stage compressor, compressor drive, technological and functional equipment, gas filling station, gas storage and distribution

Design features of CNG stations of block-complete design. Part 1

The classification, standard-size range and technical characteristics of small and medium-capacity CNG units of block-complete design (BC CNG units) are given. The basic technological scheme of the automobile gas-filling compressor station of modular block-complete design (CNG BC) is presented. A general view and a schematic diagram of the functional block-complete system of the station are given. The features of the compressed natural gas production technology of the BC CNG are summarized. The structural and technological scheme of a typical automated process control system of CNG BC is presented. The system of accumulation and distribution of compressed gas is given. Keywords: compressed natural gas, classification and characteristics of BC CNG stations, station frame, multi-stage compressor, compressor drive, technological and functional equipment, gas filling station, gas storage and distribution

Flow-noise characteristics of turbocharger compressors with rotational balance cuttings

To correct the balance of the rotating assembly of a turbocharger, some parts of the compressor wheel are removed by cutting. A numerical investigation of the turbulent flows and flow noises produced by compressor wheels modified with such cutting parts was performed by a turbulence model and detached-eddy simulations. For the 6-cutting case, 0, 2, 4, and 6 circular cuttings and two additional—rectangular and triangular—shapes were used. To investigate the effects of the balance cuttings in a compressor wheel, the evaluation process using computational fluid dynamics was tried. It was found that the fluid forces due to the various wheel shapes have the potential to restore the eccentricity by approximately 50%. Severe variations of velocity, pressure, and turbulent kinetic energy in the interspace between the wheel and volute were observed. In particular, the wavelike patterns of pressure and turbulent kinetic energy were intensified for the modified wheels. The turbulent kinetic energy of the 6-cutting case had a dominant frequency at approximately 3000 Hz. The spectrum of the sound-pressure level of the modified compressor wheels exhibited the features of buzz-saw noise. The flow fields suggested that this feature of the sound pressure is related to the tip-clearance flow affected by the balance cuttings. In addition, the acoustic pressure and flow characteristics of the different types of modified compressor wheels were discussed and the resulting acoustic power was evaluated.

Optimal design of full order state observer for active surge control in centrifugal compressors using genetic algorithm

This paper presents the design of a genetic algorithm (GA) based full order state observer for a compressor system. The observer measures the compressor system parameters and computes the difference between the measured output and the setpoint, which is used as feedback to the active surge controller. The proposed control structure with a GA tuned compressor characteristic is required to minimize system oscillations and energy losses induced by the piston actuation gas recycling technique. The design method for GA based full order observer begins with a state observer modelling, observer error estimation based on the magnitude of fluid friction and mechanical effects on measured parameters. The aim of the controller is to regulate the compressor driver speed such that the measured output achieves its required set point. In order to achieve a maximum compressor operating capacity, the compressor characteristics were optimized using GA, where the mass flow was maximized to improve the compressor efficiency. Simulations were carried out, and results showed the viability of GA based full order state observer compared with the piston actuation recycle method to control active surge in centrifugal compressor systems

Combined cold supply system for ship application based on low GWP refrigerants - Thermo-economic and ecological analyses

The withdrawal of popular high-GWP refrigerants will significantly affect maritime industry. Refrigeration and air conditioning systems currently used on ships are not ready to fulfil future limitations. Therefore, there is a need for system, which will operate with low-GWP refrigerants and at the same time will be efficient and reliable in difficult environmental conditions. This paper explains the concept of a cold supply system, in which refrigeration/freezing plant rejects heat not to a seawater but to a chilled water, produced by the air conditioning unit. Configuration of single stage compression with internal heat exchanger and HFO refrigerant was used in the air conditioning system, while in the refrigeration/freezing plant, two-stage compression trans-critical booster with R744 as refrigerant. Comparative thermodynamic analyses of presented concept with other configurations of thermodynamic cycles and refrigerants were performed. They were carried out in wide range of seawater temperature values and incorporated efficiency characteristics of compressors produced by a well-known manufacturers. Results confirmed ability of described system to improve energy efficiency in comparison with separated and currently used on ships cold supply systems, especially in hot climate. Economic and ecological analyses of proposed concept exhibited an additional benefit - positive environmental impact.

Numerical and experimental study of bleed impact in multistage axial compressors

In this study, the influence of inter-stage bleeding on the compressor performance and inter-stage flow field of a multistage axial compressor is investigated by both experimental and numerical methods. The experiment is conducted on a four-stage low-speed axial compressor, and a specific computational model is built to simulate the experiment environment accurately. To illuminate the fluid mechanisms of bleeding effect in detail, both the experiment and the simulation are carried out twice, i.e., in the first time, the mass flow rate upstream the bleed location is constant under different bleed rate conditions; while in the second time, the mass flow rate downstream the bleed location is constant under different bleed rate conditions. The results demonstrate that inter-stage bleeding has little influence on upstream compressor characteristics, and affects the upstream flow field only in the rear half of the stator. The bleed effect on the downstream flow field is embodied in the variation of an incoming flow profile, an increase as the compressor inlet flow coefficient decreases. Therefore, such an effect is only significant on compressor characteristics at small flow coefficient conditions. In multistage compressors, the variation of compressor characteristics and flow field caused by inter-stage bleeding is the comprehensive result of the bleeding and the variation of the upstream working condition. In addition, the comparison between numerical and experimental results shows that the flow moves towards top half of span through the downstream rotor passage in the numerical simulation, whereas the trend of flow field variation with different bleed rates at the outlet of the downstream rotor and stator is the same with that at the inlet of the downstream rotor in the experiment, which means that the numerical method has overestimated the radial mixing intensity of the flow.

Evaluation of non-uniform water film behavior on the performance of an axial aeroengine compressor

Abstract Two-phase flow CFD simulations are conducted to investigate the performance characteristics of an axial flow compressor operating under an excessive amount of water intrusion exposed to a rainy atmosphere. In order to obtain a certain compressor behavior under the water film irregularities, the blade surfaces are divided into a small number of regions depending on the film thickness. In addition, to examine the droplets interaction with rotating blades and splashing process, a self-compiled FORTRAN code has been used. The results showed that uneven roughening of blade surfaces is the effective technique to identify the deterioration in performance with irregular wall film thickness. The overall adiabatic efficiency and pressure ratio are decreased by 6% and 0.88 at a 5% water injection rate using an irregular rough wall model. Moreover, the increased wall film has adversely influenced the internal flow mechanism, which resulted the increase of passage shock intensity, entropy level within the main flow zone as well as the blade surface temperature.

Математическая модель метода универсального моделирования девятой версии для расчета и проектирования центробежных компрессоров: идентификация и верификация по экспериментальным данным

Identification and verification of a new version of mathematical model for universal modeling method for calculation of centrifugal compressors gas dynamic characteristics are carried out. To identify the loss model, the results of 70 tests of 20SE family model stages at LPI-SPbPU Compressor Engineering Problem Laboratory were used. A total of 420 efficiency values were compared. At the first stage, identification was carried out only for stages without a vane diffuser; the average error of efficiency calculation was 0.513 %, and, on the whole, for the characteristic is 1 %. When identifying vane diffuser stages, the search objects were coefficients influencing losses in the vane diffuser only, the average error of efficiency calculation was 0.525 %, for the whole characteristic is 1.12 %. To verify the empirical coefficients affecting losses in the axial separation impeller, test results of TKR-175E and TKR-140E compressors for turbocharger units were used. In the IDENT database we gave characteristics of TKR-140E compressor at conditional Mach numbers 0.437, 0.5836, 0.728, 0.8739; average error of efficiency calculation was 0.889 %, for the whole characteristic is 1.55 %. To verify the mathematical model, the results of the tests of Clark (USA) low-flow model stages were used. Ten tests of low-flow stages were considered; the average error of efficiency calculation was 1.08 %, for the whole characteristic is 1.31 %

Numerical Investigation of Negative Flow Characteristics in a Centrifugal Compressor With Vaned Diffuser and Internal Volute

Abstract Negative flow from the outlet through the volute, diffuser, and impeller to the inlet of the centrifugal compressor can occur continuously as a result of system accidents. A physical comprehension of negative flow dynamics is crucial in evaluating the compressor characteristics under abnormal working conditions and is also important in exploring the compressor aerodynamics over the entire flow range. However, limited research on the negative flow dynamics in centrifugal compressors, particularly with the consideration of vaned diffusers and volutes, can be found. This study aims to determine the compressor characteristics, including the negative flow rates of a centrifugal compressor, and to clarify the negative flow mechanism under the interaction of the volute, diffuser, and impeller. The last stage of a four-stage centrifugal compressor, including an internal volute, a vaned diffuser, and a closed impeller, was simulated under both positive and negative flow conditions using a computational fluid dynamics (CFD) model. The results show that the pressure ratio–negative flow characteristic is almost matched with a parabolic curve. At negative flow rates, the backflow generated on the hub and shroud sides in the impeller expands upstream and causes flow separation in the diffuser. The negative flow enters the impeller at a large incidence angle and results in jet-wall impingement on the pressure surface, flow spillage over the trailing edge, and flow separation near the suction surface. The impeller partially acts as a turbine impeller and performs negative work on the fluid. This work is of scientific significance to enrich the compressor aerodynamics in accident scenarios and of engineering value to improve the advanced design of compressor protection systems.

Flow characteristics of impeller backside cavity and its effects on the centrifugal compressor for compressed air energy storage

In order to improve the accuracy of numerical simulation for compressor aerodynamic performance, and to understand the interaction and internal flow characteristics of each compressor component, this paper numerically calculates all mainstream channels coupled impeller backside cavity (IBC) in a centrifugal compressor for compressed air energy storage (CAES). The internal flow field in IBC and the coupling characteristics of the compressor are analyzed under variable operating conditions. Furthermore, the influences of variable rotating speeds of the upstream coupled impeller and variable angles of the downstream coupled adjustable vaned diffusers (AVDs) are studied. The results show that IBC has a unique airflow field structure and vortex flow characteristics. The velocity field, pressure field, temperature field, and other aerodynamic parameters in IBC are different from the mainstream. Due to its coupling relationships with upstream and downstream, variable rotating speeds or AVDs’ angles will affect the overall performance of the compressor and internal flow field characteristics in IBC.

Effect of circumferential non-uniform tip clearance on the dynamic stall process of a single-stage axial compressor with total pressure distortion

In this paper, the single-stage compressor with circumferential non-uniform tip clearance is experimentally investigated under 180° total pressure distortion for the compressor characteristics and the dynamic stall process. In the special structure of the circumferential non-uniform tip clearance, different circumferential distortion areas are adopted to actively induce the stall. The maximum or minimum flow coefficient near the stall point occurs when the location where the rotor departs the distortion area is at the average tip clearance rather than the maximum or minimum tip clearance. Based on the time-frequency analysis regarding the dynamic stall process at different correspondences between the inlet distortion and the tip clearance, it is found that the rotating frequency of the stall cell that is independent of the location of the distortion area is slightly less than 50% rotor rotating frequency and the large-scale stall inception whose frequency is 4–8 times the rotor rotating frequency occurs. Besides the circumferential phase difference from 90° to 180° between the location where the disturbance occurs and the location where the rotor departs, the distortion area exists. According to the dynamic stall process, the stall interpretation model of circumferential total pressure distortion under the circumferential non-uniform tip clearance is established.

Refrigerant migration and oil sump viscosity change of R290 high-pressure rotary compressor during shutdown process

Propane (R290) has excellent thermophysical properties and development potential. The dynamic characteristics of R290 rotary compressors and room air conditioners have been studied mainly on the start-up and defrost processes. There is little research on the shutdown process. Unlike hydrofluorocarbons (HFCs), the density of liquid propane is lower than that of lubricant. It is difficult for propane to dissolve into the oil sump and downward after the refrigerant separation after shutdown. The shutdown state affects the distribution of refrigerant in the oil sump and the mixture viscosity of the restart-up, which is related to the compressor reliability. In this paper, an R290 room air conditioner system was built and the variations of system pressures, temperatures, and oil sump parameters of an R290 high-pressure rotary compressor with three different lubricants were measured after shutdown in two conditions. As the experiments indicated, driven by the refrigerant supersaturation (the difference between the actual refrigerant solubility and saturation solubility) resulting from the rapid pressure drop after shutdown, a large amount of refrigerant separated from the oil sump, and the refrigerant solubility dropped fast. As the compressor temperature decreased, the bottom viscosity reached a peak. For the low-temperature heating condition, the peak was about 120.4∼160.1mPa•s. However, when the degree of supersaturation decreased to a certain value, the refrigerant no longer separated out. There is always a solubility gradient of refrigerant in the oil sump of R290 high-pressure compressor after shutdown. Its size was related to the pressure drop and the miscibility of lubricants and refrigerants.

Research on Real-Time Model of Turboshaft Engine with Surge Process

The main data source for the verification of surge detection methods still rely on test rigs of the compressor or the whole engine, which makes the development of models of the whole engine surge process an urgent need to replace the high-cost and high-risk surge test. In this paper, a novel real-time surge model based on the surge mechanism is proposed. Firstly, the turboshaft engine component level model (CLM) and the classic surge dynamic model, Moore-Greitzer (MG) model is established. Then the stability of the MG model is analyzed and the compressor characteristics in the classical MG model are extended to establish the extended MG model. Finally, this paper considers the coupling relationship of the compressor’s rotor speed, mass flow and pressure between CLM and the extended MG model to establish the real-time model of the turboshaft engine with surge process. The simulation results show that this model can realize the whole surge process of the turboshaft engine under multiple operating states. The change characteristics of the rotor speed, compressor outlet pressure, mass flow, exhaust gas temperature and other parameters are consistent with the test data, which means that the model proposed can be further applied to the research of surge detection and anti-surge control.

A new first-principles model to predict mild and deep surge for a centrifugal compressor

Centrifugal compressors are used in many applications, including automotive turbochargers. Surge is an instability that occurs at low mass flow rates that is often damaging. Even mild surge produces noise characteristics that cause problems with customer acceptance. It is therefore important to be able to predict both mild and deep surge onset.In existing literature, models resulting in cubic-shaped compressor characteristics have been developed from first principles. This paper extends these to include diffuser recirculation and show a new quintic-like shape for compressor characteristics which, for the first time, can differentiate between mild and deep surge.These characteristics are incorporated into a model for an experimental facility and resulting simulations show remarkable fit to experimental data. The model allows for variations in both space and time, so simulations can capture wave dynamics in the pipework. The model captures: stable operation, mild surge, transition from mild to deep surge, deep surge, and the potential for a stable quiet period beyond the surge limit.Furthermore, the model can provide physical explanations for the surge dynamics observed. This combined with the model's predictive ability will be of help to turbocharger manufacturers during early design stages, prior to experimental tests or detailed CFD studies.

Internal Flow Field Analysis of Twin-Screw Compressor Based on Three-Dimensional Numerical Simulation

Twin-screw compressor is a kind of rotary positive displacement pump with excellent performance. Due to its advantages of reliable operation, high efficiency, low noise and multiphase mixed transportation, it has been widely used in the fields of energy power, biomedicine, refrigeration and air conditioning, petrochemical industry, industrial construction and other rudder fields. In recent decades, although the study of screw compressor is more in-depth, but the three-dimensional flow field simulation design of twin screw compressor still needs breakthrough. In this paper, 3d flow characteristics of twin screw compressor are studied based on CFD numerical simulation. In this paper, CFD software is used for numerical simulation of twin screw compressor, and the distribution of pressure cloud, temperature cloud and velocity cloud of internal flow field is obtained.

극저온 냉각시스템용 스크롤 압축기 성능실험

This paper describes the performance test of a helium scroll compressor originally used for Gifford-McMahon (GM) cryocooler. This compressor can also be used for the reverse Brayton cryogenic refrigeration system. In this paper, the performance characteristics of a scroll compressor is experimentally investigated with helium and neon gas to obtain reference data for designing thermodynamic cycle of cryogenic refrigeration system. To maintain constant suction pressure during experiments, an experimental setup contains pressure regulation system which consists of three control valves and gas buffer. Pressures, mass flow rate and power consumption are measured for 400, 450, 500, 550 kPa of suction pressure condition. With experimental measurements, performance characteristics of a helium scroll compressor is investigated. The tested scroll compressor shows the higher isentropic efficiency with helium as a working gas than neon.

마이크로 가스터빈 엔진에 적용된 압축기 공력성능 특징

A centrifugal compressor is essentially applicable to a micro gas turbine because it can produce a high-pressure ratio over than 3.0 within a limited geometrical allowance. In this paper, aerodynamic design and internal flow characteristics of the centrifugal compressor were described in detail by comparing them with those of turbocharger compressors. Then a centrifugal compressor design procedure with a pressure ratio of 5.0 at the design point for a 1,000 N thrust micro gas turbine has been introduced and the internal flow field at the design point has been further investigated with CFD methods. High impeller pressure ratio led to high absolute Mach number at the impeller outlet, however, small gap between the impeller outlet and diffuser inlet did not sufficiently recover static pressure and it caused large flow separation region and corresponding total pressure at the diffuser hub. For this reason, it requires sophisticated matching between impeller and diffuser stages in micro gas turbines. Based on the internal flow analysis, ideas for further performance improvements have been proposed while maintaining essential compressor performances.

Influence of blade vibrations on aerodynamic performance of axial compressor in gas turbine: Direct numerical simulation

Flutter instability because of the blade vibrations is a major problem in axial compressor cascades. This paper investigates the effects of blade oscillations on aerodynamic performance and turbulent flow characteristics of modern gas-turbine compressors. Highly accurate direct numerical simulations (DNS) are performed based on the spectral-hp element method to predict the flow instabilities, pressure fluctuations and vortex generation on the surface of the compressor blades by considering all complex physical parameters at different vibration frequencies (0 < f < 8.28 Hz). The main novelty of this study is to consider the aeroelastic vibrations of the compressor blades in DNS analysis. The novel proposed method enables the detailed analysis of complex structure fluid interactions, which cannot be obtained using other methods such as RANS models. The simulations revealed that the blade oscillations have a huge impact on the vortex generation and laminar separation bubble on the suction side of the blade. Moreover, the amplitude of unsteady pressure distribution is greater at 90% span, with the phage angle deviating between 100° and 350°. Strong fluctuations are observed at the centre of the wake region of the vibrating blade cascade. These fluctuations are activated by the flow disturbances resulting from the blade oscillation. Moreover, intense pressure fluctuations happen in the wake region of the oscillating compressor blade compared with the stationary one. The separating point occurred 8.28% sooner on the suction surface of the vibrating blade with k = 0.4 (Xsep/C = 0.288) compared to the stationary blade with Xsep/C = 0.314.

Centrifugal Compressor and Bell mouth Air Intake Preliminary Design for Micro Turbojet Engine

This paper presents a design of centrifugal compressor and air intake for micro turbojet engine of 200 N thrust. Because of the small size of the micro turbine engines the air intake is designed in the form of bellmouth air intake in order to capture the needed amount of mass flow rate (0.45 kg/s). The function of the air intake is to deliver the air to the entry of the centrifugal compressor. The air intake has been drawn with start-up motor to take in the consideration the effect. The centrifugal compressor was designed to deliver 3.8 pressure ratio with efficiency about 77%. The compressor impeller was built with 7 main blades and 7 splitters in order to reduce the effect of slip at the exit of the impeller due to pressure difference between pressure and suction side of the main blade. Diffuser of 13 vanes also was designed to increase the static pressure, direct the flow to the combustion chamber and decrease the flow velocity before to enhance the combustion process. The structural integrity for impeller was validated using ANSYS software for aluminum alloy 7075-T6; 7075651. In addition, the aerodynamic analysis was investigated using NUMECA software. The most important findings of the extensive analysis were; the impact of air intake on compressor performance is very crucial. It add an increment in efficiency and pressure ratio, it should be taken in consideration in early design stage of the compressor. The highest performance characteristics of compressor were achieved by accurate design optimization of impeller-diffuser interaction.

Experimental investigation on stall characteristics of contra-rotating compressor with variable speed ratios

By experiment at a low-speed large-scale axial contra-rotating compressor, the near stall points of 19 speed configurations were captured and the stall characteristics under different speed ratios were obtained successfully. The results show that the compressor with speed ratio greater than 1 are more likely to stall than the compressor with speed ratio less than 1 and the flow rate at the starting point of stall is at least 18% earlier, the pressurization capacity is at least 5.5% higher when speed values of the front and rear rotors are interchanged. At the same speed ratio, the dimensionless characteristic lines of pressure rise coefficient-flow coefficient almost coincide. With the decrease of speed ratio, the dimensionless characteristic line of contra-compressor moves upward. Through summing up all speed configurations' stall types and stall initial disturbance frequency, it can be found that: there is a critical speed ratio between 1.125 and 1.167 in the contra-rotating compressor studied in this paper. When the speed ratio is less than the critical value, the stall disturbance has the characteristic like spike stall. At this time, the initial stall disturbance frequency is higher with the speed ratio is smaller. And at the same speed ratio, the initial stall disturbance frequency increases with the increase of the average speed of the front and rear rotors. When the speed ratio is greater than the critical value, the stall disturbance doesn't rotate circumferentially.