Compressor Characteristic Curves Research Articles

Surge and stall instabilities finite-time control of nonlinear uncertain-disturbed compression system by using a novel robust approach

This paper describes a new approach to control stall and surge instabilities in the compressor system by using of finite time backstepping-based adaptive sliding mode method. The most important innovation of this study is to provide a finite time adaptive control method to simultaneously prevent the stall and surge instabilities in a compressor system in the presence of disturbance and uncertainty in the compressor characteristic curve as well as the throttle valve. The disturbance and uncertainty issues are covered by a robust sliding mode control and the gain coefficients of this controller as well as the estimation of uncertain terms are obtained by using the adaptive method. The Lyapunov stability criterion is used to evaluate the finite-time stability of the closed-loop system. The performance of the proposed method is compared with other literature methods through simulation in Matlab. The simulation results show that the proposed controller is better than the existing methods in terms of surge preventing and robustness against uncertainty and disturbance.

Development of Automated Processes for Three-Dimensional Numerical Simulation of Compressor Performance Characteristics

Compressor characteristic evaluation is a critical step in design and optimization. Corrected characteristic curves are typically derived via experimental testing or CFD computation which is typically executed through manual manipulation. For compressors necessitating extensive characteristic computation across multiple speeds and operational conditions, the involved process is inherently complex. This paper introduces an automation approach, employing dichotomy and optimization algorithms aligned with a 3D numerical solver, to streamline the derivation of compressor characteristic curves. Initially, the paper delineated the procedural frameworks for two methodologies and validated them using a single-stage transonic compressor. Both methods achieved the automated resolution of the characteristic lines. The result indicates that the volume of the iterative computations hinges on the granularity of the space searching step and the precision in identifying the stall boundary point. Pertaining to the subject investigated herein, the dichotomy method entailed fewer iterations relative to the optimization algorithm. Subsequent adjustments to the optimization algorithmic process revealed that direct optimization mitigated computational demands substantially by reducing a cycle, thereby attesting to its superior efficacy. In summary, when simulating compressor characteristic curves, the dichotomy method proves more efficient when the interval value of the stall boundary range can be approximated. Conversely, direct optimization is preferable when the estimation of the compressor’s stall boundary is imprecise. The proposed methodologies contribute to compressor research and expedite the progression of compressor development and performance advancement.

Research on the Methods of Predicting Compressor Characteristic Curve

Compressors are one of the three major components of gas turbines, and their characteristic curves are used to analyze off-design performance. How to infer the characteristic curve based on different data is an important research topic. In this paper, PG9351FA gas turbine is taken as the research object. Two methods, artificial neural network and parameter estimation, are used to predict its characteristic curve, and the prediction accuracy and application conditions of the two methods are discussed. This article compares the two methods from the perspectives of known speed characteristic curve regression and unknown speed characteristic curve inference, analyzes the impact of sample size and sample error on their inference results, and quantitatively analyzes the error through statistical methods such as calculating the mean square deviation of the data. The application scope and conditions of different methods are provided. The research results show that the method based on neural network to infer the characteristic curve has high accuracy and is suitable for the prediction of known and unknown speed characteristic curves under sufficient data, but not for the prediction of unknown side curves. The elliptic equation fitting method based on parameter estimation has a slightly lower accuracy in processing the nearly vertical compressor characteristic curve, but it can be used as an effective and reliable method to infer the compressor characteristic curve in the case of a small amount of data. The modulization method based on parameter estimation has high accuracy and is applicable to the estimation of complete characteristic curve from partial data of known characteristic curve. In this paper, the application scope and conditions of these two methods are determined, which can provide reference for engineering practice.

Compressor Stability at Pulsating Condition Via Gas Dynamics Responses Analysis

Abstract The compressor is operated at unsteady exit conditions in many scenarios such as the instability of combustion in gas turbine and denotation engine. The aerodynamic stability of the compressor is inevitably influenced by the unsteady operating environment. In this paper, a one-dimensional (1D) model that combines pulsation and unsteady responses of the compressor is developed to investigate the stability of the compressor system. The results show that the onset of surge and the transient responses of the compressor during surge are well predicted by the method. The amplitude of the component at surge frequency obtained by fast Fourier transformation (FFT) method is applied as a criterion to quantitively evaluate the onset and the strength of the surge. Compressor stability is enhanced at pulsating conditions due to the interaction between forced oscillation of pulsation and self-sustained oscillation of surge. An analytical model is established to understand the mechanism of the enhancement of compressor stability under pulsation. The change of total energy of the compressing system is proposed to evaluate the influence of pulsating conditions. Specifically, the energy change is reduced for pulsation conditions due to two aspects: the lower slope of compressor characteristic curve due to the lag-effect of compressor responses and the higher energy dissipation due to the nonlinear throttling effect.

Robust active finite-time control of gas compressor system surge in the presence of unmatched disturbance and uncertainty

Active and robust control of surge instability is a special necessity for optimal and safe operation of centrifugal compressors, and for the purpose, this article presents a new hybrid scheme based on fuzzy and terminal sliding mode methods. The Greitzer model is used to design a novel controller when the disturbance instability in the flow and pressure alike the uncertainity in the compressor characteristic curve and throttle valve are embedded in it. The fuzzy approximator is used to estimate the effects of parametric uncertainty and the nonlinear terms, and the robustness of the proposed method is guaranteed using the terminal sliding mode control method. The Lyapunov criterion is utilized to verify the finite-time stability of the closed-loop system. The performance of the presented method is compared with other methods in the literature through simulations in MATLAB software. The results suggest that our designed controller outperforms the existing ones in terms of surge prevention and robustness against unmatched uncertainties and disturbances.

Dynamic performance simulation analysis method of split shaft gas turbine based on RBF neural network

In the operation of gas turbine unit, it often come across condition changes such as acceleration, deceleration and external drag effects. This will cause transient process of gas turbine system, which is of great significance to the dynamic performance simulation. This paper established dynamic simulation model of different components in gas turbine unit, introduced several process methods of compressor characteristic curves, and finally the RBF neural network method is used. Through simulation test, the variation rule of each parameter can be obtained so as to improve the operation efficiency of the whole unit, which lay a foundation for further optimization study.

Influence of pressure pulsation on the performance of compression system and turbocharged engine

Pressure pulsation widely exists in power machinery combining compression components and pipelines. It has substantial effects on the performance of compressor as part of the compression system, as well as the engine. In this paper, the pressure pulsations under different excitation frequencies are measured and analyzed in the intake system of a turbo-charged and inter-cooled internal combustion engine. It is pointed out that the amplification of the pressure pulsation at the compressor inlet and outlet is caused by the coupling effects within the compression system, which consequently lead to the formation of a stable standing wave. Further research indicates that the pulsation at the compressor boundary will cause its pressure ratio to fluctuate. Additionally, because the compressor characteristic curve resembles a concave function, the fluctuation of transient pressure ratio will further cause the time-averaged pressure ratio to decline. Finally, the impact on engine performance is evaluated based on a well-validated simulation model.

A Model for Predicting Post-Stall Behavior of Axial Compressors

The current paper reports on a new theory developed by modifying the basic Moore-Greitzer model, which can predict the performance of a compression system during the instabilities in more details. The general assumptions such as the compression system layout, the lags in the entrance and exit ducts, the compressor axisymmetric characteristic and the small disturbances are similar to those of Moore-Gereitzer model. However, a second order hysteresis is used in the current work for the pressure rise of the rotor and stator rows. As a result, some new parameters are added to the governing equations, such as the stall cell acceleration ( ), second derivative of the mean axial flow coefficient ( ), second derivative of the disturbance amplitude ( ) and slope of the compressor characteristic curve. This gives the modified model new capabilities, like investigating the transient speed of the stall cell or the effect of the throttling rate on the instabilities, which are discussed in details in the current paper.

Investigation on the unsteadiness of centrifugal compressor exposed to pulsating backpressure

Centrifugal compressor is exposed to pulsating backpressure due to the movement of intake valves in internal combustion engine. The performance of compressor deviates from the steady performance map, which affects the matching between turbocharger and engine. The behavior of compressor system at pulsation conditions are investigated via an in-house developed 1D unsteady code validated by experimental results. The influence of pulse frequency, magnitude and compressor characteristic curve on the compressor transient responses, including filling-emptying effect and wave dynamics, are analyzed. Results show that the strength of wave dynamics grows stronger with the increasing of pulse frequency, while the strength of filling-emptying effect increases first then decreases. The rise of pulse magnitude results in an almost linearly increasing of filling-emptying effect, while it can hardly affect the wave dynamics. Furthermore, the influence of pulsation magnitude and frequency represents the influence of local pressure gradient, and a correlation as quadratic curve can be evaluated between the pressure gradient and compressor unsteadiness. On the other hand, the influence of operating point, including the average mass flow rate and the slope of characteristic curve, is confirmed to be evidently smaller, comparing to the influence of pulsation frequency and magnitude. This study is helpful to estimate the behavior of compressor and the discrepancy of performance when operating at unsteady environment or matched with engine.

Compressor surge control using a new robust adaptive method in the presence of uncertainty and unmatched disturbance

The surge is the most common and important instability associated with compressors and its control is very important due to its damaging effects on the compressor system. This paper presents a new method of surge control using a robust adaptive method in which the stability of the system is guaranteed according to the Lyapunov method. In the used model, the unmatched disturbance is introduced into the compressor system, and the compressor characteristic curve is assumed to be unknown. The characteristic curve of the throttle valve is also considered unknown. The comparative results in the simulation section illustrate the capabilities of the proposed method.

A new method for correcting characteristic curves for centrifugal compressors

In gas pipeline industry, a centrifugal compressor's performance is often tested in the factory under specified condition and formulated as performance map before it is offered to its buyer. Concerned performances include head, efficiency and so on. A compressor's original head or efficiency characteristic curve may deviate from its actual one because of various reasons after it runs in field for a period of time. So correction is needed before these characteristic curves are used for simulation, optimisation or other applications. A compressor's actual head and efficiency are extracted from its operating records and used for correction. The correction method is designed according to the idea to move a compressor's characteristic curves to best fit its actual performance. Two different types of compressors operated on Central Asia – China gas pipeline are utilised to test the proposed method and satisfactory results are got.

A new method for correcting characteristic curves for centrifugal compressors

In gas pipeline industry, a centrifugal compressor's performance is often tested in the factory under specified condition and formulated as performance map before it is offered to its buyer. Concerned performances include head, efficiency and so on. A compressor's original head or efficiency characteristic curve may deviate from its actual one because of various reasons after it runs in field for a period of time. So correction is needed before these characteristic curves are used for simulation, optimisation or other applications. A compressor's actual head and efficiency are extracted from its operating records and used for correction. The correction method is designed according to the idea to move a compressor's characteristic curves to best fit its actual performance. Two different types of compressors operated on Central Asia – China gas pipeline are utilised to test the proposed method and satisfactory results are got.

Effect of Circuit Geometry on Steady Flow Performance of an Automotive Turbocharger Compressor

Downsizing and turbocharging are today considered an effective way to reduce CO2 emissions in automotive gasoline engines. To this aim, a deep knowledge of turbocharger behavior could be a key solution to improve the engine-turbocharger matching calculation. The influence of the intake system geometry on the surge line position is an important aspect to guide the project of the intake manifold, enlarging the compressor stable zone. This aspect has a considerable impact on engine performance, especially during transient operation. A wide experimental investigation was carried out at the turbocharger test facility of the University of Genoa on a small turbocharger compressor. Compressor characteristic curves measured considering an automotive intake circuit are compared with standard maps provided by turbocharger's manufacturer. This information allows the optimization of 1D model implementing more realistic maps of compressor. The influence of three different layouts has been investigated varying overall circuit volume and length, keeping values in a range compatible with passenger cars packaging constraints. In the paper, the main results of the experimental campaign are presented taking into account the influence of geometry variations on compressor map and surge line position.

서지 마진 증가를 고려한 원심 압축기 설계 최적화

This study presents a numerical procedure to optimize the compressor design to increase the surge margin of compressor with response surface method (RSM). The Box-Behnken design method is used to reduce the number of calculation for fitting the second-order response surface. In order to consider the increase of surge margin during numerical optimization without any calculation at the surge point, the slope of compressor characteristic curve at the design point is suggested as an objective function in the present optimization problem. Mean line performance analysis method is used to get the design and off-design characteristic curves of centrifugal compressor. The impeller exit angle, impeller exit height and impeller radius are chosen as design variables. The optimum shapes show the increase of surge margin for the surge margin optimization and increase of efficiency for the efficiency optimization in comparison with an initial shape.

Development of a One-Dimensional Modular Dynamic Model for the Simulation of Surge in Compression Systems

The paper deals with the development of a nonlinear one-dimensional modular dynamic model for the simulation of transient behavior of compression systems. The model is based on balance equations of mass, momentum, and energy, which are derived through a general approach and are written by using the finite difference method. The model also takes rotating mass dynamics into account through a lumped parameter approach. Moreover, it reproduces the behavior of the system in the presence of the surge phenomenon through steady-state performance maps, which represent the compressor operation in the inverse flow region by means of a third degree polynomial curve. The model is implemented through the Matlab Simulink tool, where the system of ordinary differential equations is solved by using a fourth- and fifth-order Runge–Kutta method. A sensitivity analysis is carried out to evaluate the influence on compressor outlet pressure oscillations of the model parameters, of the supplied torque, of ambient conditions and of the shape of the compressor characteristic curves. The results show that the model proves effective in capturing the physical essence of surge phenomenon without being computationally too heavy.

Aerothermodynamic Considerations Involved in Turbocharging Four and Two-Cycle Diesel Engines

Abstract The turbocharged engine is, in effect, a compound engine in which the engine itself handles the high-pressure end of both compression and expansion, while the exhaust-turbine-driven compressor takes care of the low-pressure end. The turbocharger pressure ratio determines the division of work between high-pressure and low-pressure components, and the value of this pressure ratio governs, to a large extent, the values of all engine performance variables. In this paper the interrelationships between all of these variables are discussed, and curves are presented giving, numerically, the interdependence, one on the other, of turbocharger pressure ratio, thermal loading, specific fuel consumption, and turbocharger combined efficiency, with and without intercooling. The aerothermodynamic situation of the two-cycle engine is treated separately, with emphasis on the all-important flow-handling ability of the engine. This ability is defined by the concept of the “gas change process merit ratio,” and, by means of a series of curves, the specific engine air flow is given for different merit ratios and different turbocharger combined efficiencies for a range of turbocharger pressure ratios. Finally, for both two-cycle and four-cycle engines, the importance of good matching between engine air consumption characteristics and turbocharger air delivery characteristics is discussed, and as a criterion for this matching the engine operating line, as it appears superimposed on the compressor characteristic curves, is used.