ОСОБЕННОСТИ РЕГУЛИРОВАНИЯ ЦЕНТРОБЕЖНОГО КОМПРЕССОРА ПРИ РАБОТЕ НА ПОТРЕБИТЕЛЯ С ЖЕСТКО ЗАДАННЫМИ ПАРАМЕТРАМИ

A holistic design framework of centrifugal compressors for high temperature heat pumps considering wet compression prevention and global optimization

Integrally geared multistage centrifugal compressors have been widely used in many industries. The design of the new compressor is very complicated and needs a reliable design process. This paper discussed the development of a high efficiency integrally geared driven centrifugal compressor for industrial applications. An inhouse program was used to design the centrifugal compressor through aerodynamic and structural optimization. CFD (Computational Fluid Dynamics) is a very important tool for centrifugal compressor design. CFD can help compressor design and perform three-dimensional optimization to further optimize the compressor. The compressor stage matching is also impact the overall compressor performance. The good stage match is very important to make the design success. The Finite Element Analysis (FEA) was used to verify the structure integrity. The CFD and FEA (Finite Element Analysis) analysis are performed to obtain a final compressor performance and to make sure to have a robust operation. The centrifugal compressor has the characteristics of high efficiency, no resonance, and low noise. The designed compressor prototype was built and performance tests were conducted. The performance test results demonstrated that the analytical are fairly agreed with experimental results. The development process and tools are successfully used in the compressor design. The design process can be used for future compressor development.

An air compressor is the core component of the air supply system of a hydrogen fuel cell, which demands high efficiency and reliable stability in a wide operation region. In this work, a centrifugal air compressor for a hydrogen fuel cell is first designed and then measured experimentally. Furthermore, a test rig for assessing the aerodynamic performance of the centrifugal air compressor is established, which includes a pipeline, gas flowmeter, flow regulating valve, pressure transmitter, centrifugal compressor, controller, DC power supply and computer. Then, the orthogonal method is employed to conduct the aerodynamic performance optimization. Four optimization parameters—including blade number, blade angle at the inlet, blade angle at the outlet and wrap angle—are set with three levels. Nine compressor individuals are designed according to the orthogonal method, and then numerical simulation is implemented to confirm the aerodynamic performance and flow pattern. Results show that the blade number has the greatest influence on the compressor’s performance, and the blade angle at inlet is also very important. The optimal performance of the compressor improves compared to that of the baseline compressor; the efficiencies of the baseline compressor and optimal compressor are 81.3% and 83.8%, respectively, improving by 2.5%. The frequency domain of pressure fluctuation in the centrifugal compressor is related to the stator-rotor interaction. The peak value of pressure fluctuation amplitude occurs at the rotation frequency of 833 Hz and its harmonic frequency. In comparison with the baseline compressor, the pressure fluctuation amplitude of the optimal compressor is obviously reduced, especially near the volute tongue.

Regarding the issue of changes in the aerodynamic force of the bridge main beam under the action of wind-driven rain, this article explores the changes in air density caused by rainfall, the calculation theory of raindrop impact force and its simplified mass-weighted equivalent method (MWEM), and the calculation method of water accumulation thickness on the surface of the main beam. The calculation shows that the changes in air density caused by rainfall can be ignored, and the error of the MWEM increases with the increase in rainfall intensity; however, even at a rainfall intensity of 709 mm/h, the deviations in the MWEM value of the horizontal and vertical raindrop impact force is only about +5% and −4%, respectively. Then, based on the above analysis, a calculation model for the aerodynamic three-component forces of the main beam caused by rainfall under the action of wind-driven rain is provided. Finally, taking two typical main beam sections as an example, static three-component force tests are carried out on the main beam model under different rainfall intensities. The experimental results show that the drag coefficient variations obtained through the MWEM are in good agreement with experimental data, which proves the correctness of the theoretical model of the raindrop impact force. But for the lift and torque coefficient, the differences between theoretical and experimental values are much more significant than the drag coefficient, and it increases with the increase in rain intensity. It can be seen that the surface ponding model and influence of rainfall intensity need to be further explored. In summary, the theoretical calculation method for the additional aerodynamic force of wind-driven rain on the main beam proposed in this article is convenient and practical, and it can provide a certain reference for the rapid safety assessment of bridges under extreme meteorological conditions.

As an important device for water chillers, the centrifugal refrigeration compressor with gas bearings has new features compared with traditional oil and magnetic bearings. It is an important development direction for water chillers and needs to be studied. To research the performance of compressors for water chillers, the R134a centrifugal refrigeration compressor with gas bearings is researched by the computation fluid dynamics (CFD) method. The prototype of the two-stage centrifugal compressor was tested in the water chiller. The test bench of the centrifugal chiller has two kinds of gas supply systems for gas bearings. The axial force of impellers is simulated under different working conditions by the CFD method. Compared with the two-stage impeller in the same direction arrangement, the opposite direction arrangement can reduce the total axial force of the rotor by up to 98.3%. The simulation performance of gas bearings and test results show that the gas bearings can bear the axial force caused by the gas force of two impellers. The results from the simulation and experiment are compared with the average error of 4.3% when the rotating speed is 21000 r⋅ min−1.

Second law analysis on performance of double stage reciprocating air compressor with inter cooler

Effect of internal heat leakage on the performance of a high pressure ratio centrifugal compressor

A method for calculating pressure losses during pneumatic transport is considered with the aim of choosing the most favorable operating mode, which allows to reduce the consumption of compressed air. It has been established that the generally accepted formulas for calculating pressure losses along the path, calculated as the sum of the pressure losses for pure gas and material, do not explain the fact of the initial decrease in pressure losses with increasing air flow rate, and then their growth. The importance of accounting for changes in air density and air flow velocity along the length of the pipe, as well as the need to take into account the overlap of part of the pipeline section with material in the case of high concentrations, is shown. It is proposed to determine the pressure loss using the Bernoulli equation in integral form, for example, the Gauss method using eight nodes. The applicability of the method for calculating both straight and inclined sections of pipelines is established. The experimental results of studying and analyzing the proposed isothermal model in a vacuum pneumatic transport laboratory installation are presented. An example of calculating the pressure loss for an industrial pneumatic conveying system with a pipe length of 450 m and an inner diameter of 147 mm at various flow rates of the material is shown. Ill. 4. Ref. 21. Tab. 1.

As inlet bent-pipes are often used in vehicle turbocharger compressors, understanding of the inlet bent-pipe’s effect on centrifugal compressor and the mechanism of flow loss is important to improve the turbocharger compressor performance. Experiment and numerical simulation were carried out on a centrifugal compressor with straight pipe and bent-pipe. Numerical simulated compressor performance was compared with test data obtained from compressor flow bench test and to validate the numerical method. The analysis is mainly based on numerical results and it indicated that the inlet bent pipe induces a serious distortion at impeller inlet and increases the risk of blade high-cycle fatigue. The level of distortion changes to be more serious as the operation point of compressor varies from design point to high load. When an impeller channel enters distortion, the larger pressure difference between inlet and outlet makes this channel get clogged and the flow rate through this channel is reduced. At design point the bent pipe mainly influences the flow loss in the inlet pipe and impeller while at high load more serious flow distortion induced by bent-pipe is able to extend its stronger effect to the downstream diffuser and volute.

Low-pressure exhaust gas recirculation (LP-EGR) is an EGR configuration in which clean exhaust gas is taken downstream of the turbine and aftertreatment, and then reintroduced upstream of the compressor (1). Employing LP-EGR on Diesel engines can improve fuel economy by reducing pumping losses, lowering intake manifold temperature and facilitating advanced combustion phasing (2, 3). The LP-EGR can also improve compressor and turbine performance by moving their operating points towards higher flow rate and higher efficiency points, which is reflected as a net reduction in pumping losses of the engine. In this study, we focus on effects of introducing LP-EGR on the compressor pressure ratio, and isentropic total-to-total efficiency. The flow field of LP-EGR and air mixing upstream of the compressor as well as the entire compressor stage were studied using a CFD RANS model. The model was validated against turbocharger gas stand measurements. A T-junction mixer was chosen as the design baseline, and various configurations of this mixer were evaluated. The impact of the geometric configuration of the mixer was studied by varying mixing length, EGR jet introduction angle, and EGR-to-air cross section area ratio over a wide range of relevant engine operating conditions. The flow field upstream of the compressor is strongly affected by the dimensionless quantity EGR-to-air momentum ratio. At intermediate momentum ratios, stream-wise counter-rotating vortex pairs (4) are induced in the flow. These vortices can reach the impeller inlet, and depending on vorticity and length scale, perturb the local velocity triangle. At low and high momentum ratios, creeping or impinging jets respectively are formed. In addition prewhirl can be induced by eccentric introduction of EGR. The EGR-induced prewhirl acts similar to an inlet guide vane and can alter the incidence angle at the impeller inlet. The performance of the compressor is altered by the EGR-induced flow field. Compressor pressure ratio is either increased or decreased depending on the direction of EGR-induced prewhirl with eccentric EGR introduction. The compressor efficiency decreases at low flow rates by introduction of concentric EGR due to perturbation of the velocity triangle at the impeller inlet. On the other hand, at low flow rates compressor efficiency can be improved by eccentric EGR introduction, which generates prewhirl in the direction of rotation of the impeller leading to improved incidence angle. The extent to which the compressor is influenced by the EGR-induced flow field is generally reduced by increasing the EGR mixing length, due to viscous damping and breakdown of large-scale EGR-induced vortices. The LP-EGR configuration provides a potential pathway towards improvement of compressor performance, not only by increasing compressor flow rate, but also by manipulation of the flow field. Given that the engine pumping losses are strongly dependent on compressor performance, specifically the compressor efficiency, this study indicates that LP-EGR provides an important path towards reducing pumping loss and improving fuel conversion efficiency.

Roles of recirculating bubble on the performance of centrifugal compressors

The performance of the centrifugal compressor, which is the main component of the electric supercharger, significantly impacts the engine’s dynamics, economy, emissions, and responsiveness. The purpose of this paper is to enhance the aerodynamic performance of the centrifugal compressor of the electric supercharger for the two-stroke engine by optimizing the design of its impeller and diffuser parameters. The paper employs the numerical simulation method and applies the Spalart–Allmaras turbulence model to solve the RANS equations to analyze the impact of impeller-related parameters on the centrifugal compressor’s performance. Subsequently, the paper optimizes the initial model parameters based on the simulation results and confirms its performance through an experiment. The findings indicate that enhancing the isentropic efficiency and pressure ratio of the compressor can be achieved by increasing the number of blades on the impeller, selecting an appropriate blade backward angle, and increasing the relative outlet width. After optimization, the compressor’s efficiency can achieve 0.842, the pressure ratio can reach 1.49 with a working margin of 22%, and the efficiency is enhanced by 1.4%, while the pressure ratio is increased by 1.8% compared to the pre-optimization state. Moreover, the optimized model is experimentally validated to meet the design requirements.

Pressure pulsations into a centrifugal compressor can move its operating point into surge. This is concerning in pipeline stations where centrifugal compressors operate in series/parallel with reciprocating compressors. Sparks (1983, “On the Transient Interaction of Centrifugal Compressors and Their Piping Systems,” ASME Paper No. 83-GT-236); Kurz et al. (2006, “Pulsations in Centrifugal Compressor Installations,” ASME Paper No. GT2006-90700); and Brun et al. (2014, “Impact of the Piping Impedance and Acoustic Characteristics on Centrifugal Compressor Surge and Operating Range,” ASME J. Eng. Turbines Power, 137(3), p. 032603) provided predictions on the impact of periodic pressure pulsation on the behavior of a centrifugal compressor. This interaction is known as the “compressor dynamic response” (CDR) theory. Although the CDR describes the impact of the nearby piping system on the compressor surge and pulsation amplification, it has limited usefulness as a quantitative analysis tool, due to the lack of prediction tools and test data for comparison. Testing of compressor mixed operation was performed in an air loop to quantify the impact of periodic pressure pulsation from a reciprocating compressor on the surge margin (SM) of a centrifugal compressor. This data was utilized to validate predictions from Sparks’ CDR theory and Brun’s numerical approach. A 50 hp single-stage, double-acting reciprocating compressor provided inlet pulsations into a two-stage 700 hp centrifugal compressor. Tests were performed over a range of pulsation excitation amplitudes, frequencies, and pipe geometry variations to determine the impact of piping impedance and resonance responses. Results provided clear evidence that pulsations can reduce the surge margin of centrifugal compressors and that geometry of the piping system immediately upstream and downstream of a centrifugal compressor will have an impact on the surge margin reduction. Surge margin reductions of over 30% were observed for high centrifugal compressor inlet suction pulsation.

Centrifugal compressors are crucial components in several industrial applications, making it fundamental to understand their behavior, particularly under incipient surge conditions, to optimize their operating region. This study examines surge transitions in centrifugal compressors by utilizing a comprehensive approach that combines dynamic mass flow rate and pressure measurements, obtained through anemometric fiber film probes and high-frequency piezoresistive pressure transducers, along with vibroacoustic data collected from micro mono-axial accelerometers and microphones. To better understand the transition from stable to unstable compressor operation, an extensive experimental campaign was conducted on a centrifugal compressor at the test bench for components of propulsion systems of the University of Genoa. These tests involved both steady-state and transient measurements to characterize the compressor’s behavior in the stable region, during incipient surge, and under deep surge condition. The acquired experimental data on the compressor’s fluid dynamics and mechanical response were analyzed using frequency and time-frequency techniques to define the compressor operation as stable or unstable. Time-domain synchronous average was found to be effective in the identification of incipient surge conditions. Additionally, statistical methods such as Skewness and Kurtosis were also employed proving their reliability in surge detection. Finally, coherence functions calculated using multiple sensors in both stable and unstable conditions demonstrated strong potential as a tool for surge detection. The main goal of this study is to provide insights that support the development of advanced control strategies and predictive protocols, helping to mitigate surge-related problems and enhance the overall performance and reliability of systems where centrifugal compressors are installed.

Up to now, the design methods for centrifugal compressors have been based on results of physical experiments. The possibility of correct CFD calculation of centrifugal compressors gas-dynamic characteristics could fundamentally change the situation. Gas-dynamic projects will become more reliable, cheaper, and the performance of compressors will be improved. However, the problem has not been solved yet. The experience of various authors shows that CFD calculations in many cases do not align well with experimentally obtained data. The aim of this paper is to check whether the commercial CFD software is capable of simulating centrifugal compressor characteristics using a 16 MW pipeline two-stage compressor as an example. The calculated characteristics of pressure ratio, efficiency and head coefficient are compared with characteristics measured using the manufacturer test bench on air. The calculations are performed in two ways: in the first case the flow in the impeller-stator gaps is taken into consideration, and in the second one it is not. In the first case, we do not take into account friction losses of the outer surfaces of impeller shrouds and leakage through labyrinth seals. The interface “STAGE” averages the parameters of flow at the impeller outlet and vaneless diffuser inlet. The flow leaving the impeller is averaged in tangential direction. This way of calculation excludes the mixing process of high and low-energy flow zones at the exit of the impeller. The calculated characteristic configurations are similar to the experimental ones, but they are shifted to the area of higher flow rates, and the difference in pressure ratio is out of the limits acceptable for engineering and research. Calculations that take into consideration gap losses underestimate the maximum efficiency by up to 2.5%. The characteristics calculated without gap losses are closer to the experimental characteristics. However, it is hardly possible to use this circumstance as a recommendation for the simulation methodology. The problem needs further investigation.