Surge Margin Research Articles

Effect of Tip Gap Size on the Performance of an Axial Compressor Stage with and without Active Flow Control

The tip gap region of an axial compressor rotor is a source of complex flows, inducing losses and stability issues. Recent works have proven the ability of blowing high-speed jets in the tip region to improve the surge margin of an axial compressor stage with a narrow tip gap configuration. However, the tip gap size can evolve during the compressor lifetime, possibly affecting its performance and operability. The objective is to evaluate the performance of an active flow control system on a compressor with different tip gap sizes. The present work is based on the single-stage compressor CME2 located at the Laboratory of Fluid Mechanics of Lille and equipped with actuators blowing at the rotor tip leading edge. Configurations with two different values of the tip gap to chord ratio (0.6% and 2.4%) are experimentally tested. RANS simulations are also performed. The effect of tip gap sizes and tip blowing on the flow topology and compressor performance is evaluated (surge margin improvement of the order of 200% for the larger tip gap size).

Multidimensional analysis and performance prediction of heavy-duty gas turbine based on actual operational data

This study aims to analyze and predict the degradation, safety and operational performance of a heavy-duty gas turbine based on actual operational data after running for a long time. The dataset consists of 288,039 operational records from the Ban Shan Power Plant. The data is screened using Pearson correlation coefficients and 2-means clustering. Then, efficiency degradation of compressor and gas turbine is conducted by decoupling operation state from degradation. Next, Long short-term memory(LSTM) is employed to build data-driven T-model based on algorithm structure similarity. Meanwhile, the safety requirements containing the compressor surge and turbine inlet temperature boundary are determined, which are considered in operational performance analysis. Results show that abnormal operation data is identified during operational times 37, 38, 39, 40, 41, 42, and 248. After 254,341 minutes, the compressor efficiency degrades nearly 1%. The surge margin of a compressor is a binary function of the corrected air mass flow and inlet guide vane (IGV). The pressure ratio of the working margin moves downward by 0.11 for each 1° increase in IGV. What’s more, the T-model demonstrates high accuracy and can predict operational performance at high environmental temperatures, with the accuracy of turbine outlet temperature within 0.995. The unit is particularly sensitive to IGV, natural gas flow mass, compressor inlet temperature, and turbine outlet gauge pressure. When the relative humidity is 68%, the electrical power is the highest and overall efficiency is the best. Overall, this study's approach has significant potential for multidimensional analysis and performance prediction.

Statistical evaluation of stability margin of a multi-stage compressor with geometric variability using adaptive polynomial chaos-Kriging model

Compressed air energy storage systems must promptly adapt to power network demand fluctuations, necessitating a high surge margin in the compression system to ensure safety. It is challenging to completely eliminate blade geometric variations caused by limited machining precision, the important effects of which should be considered during aerodynamic shape design and production inspection. The present paper explores the uncertainty impact of geometric deviations on the stability margin of a multi-stage axial compressor at a low rotational speed. Initially, an adaptive polynomial chaos expansion-based universal Kriging model is introduced, and its superior response performance in addressing high-dimensional uncertainty quantification problems is validated through rigorous analytical and engineering tests. Then, this model is used to statistically evaluate the stability margin improvement (SMI) of the compressor due to the Gaussian and realistic geometric variabilities separately. The results show that the mean and standard deviation of SMI are −0.11% and 0.5% under the Gaussian geometric variability, while those are 0.33% and 0.39% under the realistic variability. For both the geometric variabilities, the stagger angle and maximum thickness deviations of the first-stage rotor are the most influential parameters controlling the uncertainty variations in the stability margin. Finally, the underlying impact mechanism of the influential geometric deviations is investigated. The variation in the stability margin caused by the geometric deviations primarily results from the alteration of inlet incidences, affecting the size of the tip leakage vortex blockage and boundary-layer separation regions near the blade tip of the first-stage rotor.

Modeling, performance enhancement, and the NOx emission reductions of the triple-pressure reheat water-recuperated air-cooled gas turbine combined cycle power plant using interstage compressor water injection and optimization

Interstage compressor water injection (ICWI) reduces the work of an air compressor, air temperature at its outlet, adiabatic flame temperature, and NOx emissions. When ICWI is introduced to combined cycles, it decreases the surge margin for the air compressor and increases the mass flow rates of the gas through the gas turbine (GT) and generated steam for the heat recovery steam generator and, therefore, power output. For the combined cycle with ICWI, air with two distinct characteristics (before and after ICWI) is used to cool the GT and mix with the expanded gas. In this paper, ICWI was introduced to the triple-pressure reheat air-cooled GT combined cycle. Detailed modeling was carried out for the processes of compression, ICWI, combustion, and GT expansion. Constraints were imposed on the amount of injected water and its temperature and pressure leading to a practical application of ICWI and a safe surge margin for the air compressor. The efficiency of the combined cycle with ICWI was optimized relative to the pressure of ICWI, injected water temperature, and relative humidity of air at the outlet of the water injector at different values of turbine inlet temperatures and air compression ratios. The results indicated that ICWI and optimization could reduce the initial NOx emissions by more than 90% (the NOx emissions that are produced at the adiabatic flame temperature) and enhance cycle efficiency by 1.9 to 2.7 percentage points and power output by 27 to 34 percent. The water recovery system could produce a significant amount of water that exceeds twice the injected amount at no fuel cost and could be integrated into the cycle at no additional equipment costs if CO2 capture or exhaust gas recirculation was implemented.

Experimental and numerical study on aerodynamic stability of compressor L-inlet duct

Total pressure loss and vortex pair are the two independent flow phenomena that affect the flow quality at the compressor L-inlet duct (CLID). Both flow phenomena do affect the compressor efficiency, aerodynamic stability and surge margin. However, no general report on the control of the two flow phenomena is found in the open literature. Therefore, in this study, a wind tunnel test bench is independently built to undertake the optical diagnostic test research of the CLID internal flow. Then, the internal flow in CLID is investigated with both the Particle Image Velocimetry (PIV) test and the numerical simulation. Furthermore, the effects of typical parameters on the CLID aerodynamic stability are investigated. Finally, based on the parametric sensitivity analysis, an orthogonal design method with array L16(45) is adopted to achieve the optimized CLID aerodynamic design. Results show that the designed wind tunnel test bench can successfully carry out the PIV test, and the test error is controlled below 1.5%. PIV test results show that two counter rotating vortex pairs are generated at compressor inlet case annular section P-a4 (φ=180°) and P-a5 (φ=225°). They are believed to affect the compressor surge margin. SC60 is validated to capture the vortex pairs, DC60 is validated to capture the total pressure loss. The larger the width (a/D4), depth (b/D4) and cone diameter (D0/D4), the better the CLID aerodynamic stability. The optimized CLID aerodynamic design is achieved by the L16(45) orthogonal design.

Surge margin monitoring of one turboshaft engine with inlet distortion

In order to explore the engine surge when inlet distortion index and engine surge margin, the relationship between the parameter characteristics of research engine surge, strengthen safety monitoring assessment engine, this paper designed a kind of a certain type of engine bench test surge monitoring system, and unstable flow field of a certain type of vortex axis engine working parameters for monitoring and analysis. In this paper, a plug-plate distortion generator is used to induce a surge engine, and the circumferential static pressure changes of the inlet and outlet of the engine, the axial compressor and the centrifugal compressor under different working conditions are obtained. The changes of circumferential unevenness and mean turbulence, the pressure ratio at working point and the converted air flow rate at working point are analyzed with the increase of the height of the plug-plate under different working conditions. The results show that the distortion index of the working point increases and the surge margin decreases with the increase of the height of the plug-plate at the same rotating speed. When the height of the plug-plate is similar, the higher the speed is, the greater the distortion index of the working point is, and the smaller the surge margin is.

Investigation of off-design performance of supercritical carbon dioxide recompression cycle using a deep learning-based turbine with variable inlet guide vanes

Many control strategies have been proposed to improve the off-design performance of supercritical carbon dioxide (sCO2) cycles caused by changes in cycle parameters. However, the component-level control scheme solely utilizes the compressor with variable inlet guide vanes (VIGV) and not the VIGV-equipped turbine for the sCO2 cycle. In this study, we examine the potential of using a VIGV-equipped turbine in a supercritical carbon dioxide recompression cycle (sCO2-RC) heated by molten salt to enhance the system's off-design thermal efficiency under low-load conditions. To accurately model the system's behavior, one-dimensional design and off-design models of the sCO2-RC are developed, as simplified component models are inadequate. Following the completion of the preliminary design, we present the optimal off-design performance of the inventory-controlled system as the load changes. We then analyse the impact of the VIGV-equipped turbine on the system's performance at low load. The results show that when the load is decreased from 100% to 10%, both the system and turbine efficiencies decrease from 41.55% and 90% to 24.31% and 66.62%, respectively, and the surge margin of the compressor is significantly reduced. While the VIGV-equipped turbine improves the efficiencies of both the system and turbine at 10% load, the nozzle opening is constrained by the surge margin of the compressor. We propose a hybrid control strategy, comprising of inventory and turbine bypass, to facilitate the utilization of the VIGV-equipped turbine and enhance its efficiency while maintaining the system's performance no lower than the initial value.

Machine learning for optimal flow control in an axial compressor.

Air jets for active flow control have proved effective in postponing the onset of stall phenomenon in axial compressors. In this paper, we use a combination of machine learning and genetic algorithm to explore the optimal parameters of air jets to control rotating stall in the axial compressor CME2. Three control parameters are investigated: the absolute injection angle, the number of injector pairs and the injection velocity. Given an experimental dataset, the influence of the air jet parameters on the surge margin improvement and power balance is modeled using two shallow neural networks. Parameters of the air jets are then optimized using a genetic algorithm for three rotational velocities, i.e., [Formula: see text]. First, surge margin improvement and power balance are being maximized independently. Then, a bi-objective optimization problem is posed to explore the trade-off between the two competing objectives. Based on the Pareto front, results suggest that a globally optimal set of parameters is obtained for a velocity ratio (defined as the ratio of the injection velocity to the rotor tip speed) ranging from 1.1 to 1.6 and an injection angle attack varying from [Formula: see text]. These outcomes point out a potential generalization of the control strategy applicable to other compressors.

Improved Thrust Performance Optimization Method for UAVs Based on the Adaptive Margin Control Approach

This study proposes a strategy for improving the thrust performance of fixed-wing UAV turbine engines from the perspective of aircraft/engine integration. In the UAV engine control process, the inlet distortion caused by the angle of attack change is taken into account, the inlet distortion index is calculated in real time by predicting the angle of attack, and the influence of the inlet distortion on the engine model is analyzed mechanically. Then, the pressure ratio command is adjusted according to the new compressor surge margin requirement caused by the inlet distortion to finally improve the engine thrust performance. To verify the effectiveness of the algorithm, an adaptive disturbance rejection controller is designed for the flight control of a fixed-wing UAV to complete the simulation of horizontal acceleration. The simulation results show that, with this strategy, the UAV turbofan engine can improve the turbofan engine thrust performance by more than 8% under the safety conditions.

On the Effect of Side Clearance in the Vaned Diffuser of a Centrifugal Compressor

AbstractEnvironmental and regulatory pressures have prompted original equipment manufacturers (OEMs) to explore highly boosted internal combustion (IC) engines as a means to minimize toxic air pollutants and meet strict legislative targets. The exhaust gas turbocharger is a key technology used to achieve the boost pressures necessary for advanced engines of the future. Centrifugal compressors with vaneless diffusers have been widely implemented in turbochargers for IC engines, particularly passenger vehicles, primarily due to their compact size and ability to deliver high-pressure ratios over a wide range of flowrates. Methods to improve compressor efficiency near surge without reducing the surge margin have received considerable interest in the past. In many situations, changes to the impeller blade design and/or diffuser are limited by the need to meet the strict engine-rated power target. Such competing demands have encouraged designers to develop variable geometry compressors with the aim of improving near surge performance without sacrificing rated power performance. The on/off-type vaned diffuser is a variable geometry compressor capable of delivering a pressure ratio benefit near surge by utilizing a vaned diffuser rather than a vaneless diffuser. The vanes are retracted prior to the diffuser choking to form a vaneless diffuser in order to reach the engine-rated power condition. Diffuser vane-shaped clearances in the hub or the shroud end wall, termed side clearances, enable axial sliding variability of the vanes into and out of the diffuser passage. Unfortunately, the clearances manifest themselves as a discontinuity in the flow field which gives rise to an efficiency penalty. It is not yet clear how the side clearance geometry and position affect the compressor performance i.e., efficiency and stability. Hence, a numerical and experimental investigation was carried out to determine the impact of side clearance geometry and end wall position on compressor performance. It was found that a side clearance positioned at the shroud end wall reduced the surge margin of the investigated compressor for both types of clearance geometry considered. In contrast to this, a clearance positioned at the hub end wall improved the compressor surge margin but had the lowest efficiency benefit near surge. An experimentally validated Computational Fluid Dynamics (CFD) model was used to inspect the flow field and to elucidate the reasons behind the changes in compressor performance.

Development of a mathematical model to simulate a natural gas compression system and its anti-surge control to improve performance: A case study to reduce the energy consumption, and the environmental impact

Compression systems are extensively used in the petrochemical industry. They are very intensive energy consumers, and simulation and analysis of this process are vital for their better maintenance and limiting their energy consumption. Here we follow an industrial case study to model and simulate a compression loop of the petrochemical industry and show potentials for energy savings and environmental improvements In this paper we introduce a modular quasi-one-dimensional model to simulate a two-step seven-stage compressor and all components of the compression loop, including the surge control system. For each component, including pipes, separation drums, heat exchangers, and compressors, a thermodynamic model based on the mass, momentum, and energy conservation laws is obtained, then each component of the system can be presented as an independent module. By stacking all modules together, the entire compression system is modeled. Finally, a numerical simulation is performed for many different scenarios to study the behavior of the surge phenomenon, the surge control system, and especially the effects of the intentional anti-surge valve openness for extra surge margin, which results in huge energy loss and environmental impacts. This simulation shows that removing the intentional openness of the anti-surge valves will reduce about 15.8% of the CO2 emissions, and the power consumption required to run the turbine may be reduced up to 1.8 MW.

Simulation of Sequential Turbocharging Switching Control System for Low Speed Diesel Engines

In order to study the sequential turbocharging switching process of low-speed diesel engine, this paper uses GT-power software to establish a simulation model of sequential turbocharging low-speed diesel engine. It is enhanced and improved into a model of a sequential supercharged diesel engine. Modules such as load, governor, valve control, and surge margin are set up in the simulation model. Then parameters such as switching speed, valve opening time and response time are set in the model. Through the above preparations, the thesis has carried out the simulation calculation of the sequential supercharging transient switching process and verified the rationality of the setting parameters and the accuracy of the module setting. This provides a certain reference for the valve control strategy of the sequential supercharging switching system of low-speed diesel engines.

Research of Comprehensive Modeling of Two-Dimensional Vector Nozzle/Actuator Load/Turbofan Engine

To investigate the effect of the dynamic deflection process of a two-dimensional vector nozzle on its actuator load and engine performance, a comprehensive modeling method of two-dimensional vector nozzle/actuator load/turbofan engine is proposed. Firstly, based on the two-dimensional vector nozzle spatial motion model, combined with force and moment analysis, the mechanical model of vector nozzle actuation system is established; The load spectrum of the actuating system under different working conditions and deflection angles is obtained by CFD numerical simulation results; Using AMESim, the hydraulic actuation system model of two-dimensional vector nozzle is established. Finally, a two-dimensional vector nozzle/actuator/turbofan engine comprehensive model is established based on the component-level model of turbofan engine. The comprehensive model can accurately calculate the changes of main performance parameters such as engine rotor speed, thrust and pre-turbine temperature when the nozzle vector deflects. The simulation results show that the load on the nozzle actuator is positively correlated with the deflection angle, and the load change will lead to the fluctuation of the output displacement of the hydraulic actuation system. During vector deflection, due to the change of engine circulation capacity and thrust coefficient, the performance parameters such as engine low-pressure rotor speed and surge margin fluctuate greatly.

An Investigation of Non-Linear Surge Characteristic in a High-Speed Centrifugal Compressor

Abstract In centrifugal compressors, it is common to observe a rapid reduction in surge margin toward high rotational speed, which shows a non-linear surge characteristic against the change of rotational speed. This paper presents a comprehensive experimental and numerical study to understand the flow mechanisms leading to the non-linear surge behavior in a high-speed centrifugal compressor. It shows that for the studied compressor, there are two critical flow coefficients (ϕ = 0.255 and 0.136) where the stability of the compressor stage is significantly weakened. At a higher speed, the impeller rotating stall happens at the first critical point where the diffuser instability is also enhanced. This is caused by the increase of the flow non-uniformity at the impeller exit as well as increased diffuser inflow angle due to the impeller compressibility effect. Therefore, both the impeller and diffuser’s instability are matched and trigger the surge at a high flow coefficient. In contrast, at a lower speed, the diffuser instability is not enhanced by the impeller rotating stall, this mismatch of the two component’s instability allows the compressor to pass through the first critical point and extend the surge limit to the second critical point where the diffuser reaches the stability limit and causes the rotating stall spontaneously. By these different behaviors at each speed, the non-linearity of the surge characteristic is established.

Experimental investigations on effects of the self-circulation casing treatment on acoustic and surge characteristics in a centrifugal compressor

Self-recirculation casing treatment is an effective technique to improve centrifugal compressor surge margin. This paper experimentally investigates the impacts of casing treatment on a centrifugal compressor using experimental methods and focuses on aerodynamic performance, surge trigger, surge cycles, and inlet acoustic characteristics. The measuring data were obtained from fast dynamic pressure transducer and microphones, and temporarily and spectrally analyzed to show surge inception and noise variation. The experimental results lead to the conclusions that (1) two separate phenomena trigger compressor to surge with different surge frequencies in the compressor with and without the casing treatment, and (2) the casing treatment suppresses the broadband noise sources but enhances the discrete frequency noise sources during surge cycles.

A multi-input based full envelope acceleration schedule design method for gas turbine engine based on multilayer perceptron network

Acceleration schedule design is a crucial task in gas turbine engine (GTE) control system design as it dramatically influences the acceleration performance of GTE. The corrected parameter based (CPB) method is the traditional solution for acceleration schedule design, which is simple to implement but could not fully exploit GTE acceleration performance in full envelope. It even fails to prevent the GTE from exceeding its surge margin boundary in some envelope points. In this paper, aiming to improve full envelope acceleration performance of GTE, a novel multi-input based (MIB) method for high-precision acceleration schedule design is proposed. Firstly, the full envelope acceleration schedule (FEAS) design problem is represented, and the CPB method is realized as a baseline. Then, the proposed MIB method is formulated, which integrates a combined input selection (CIS) strategy and a multilayer perceptron (MLP) network. With a weighted integration loss function to evaluate sensors of GTE, the CIS strategy determines appropriate inputs to design a high-precision and robust FEAS. The MLP network is employed to further enhance the FEAS precision. Finally, effectiveness of the proposed method is verified through a series of simulations and flight data verification. Compared with the CPB, the simulation results of acceleration processes under random envelope points indicate that the high-precision MIB method significantly improves acceleration performance of GTE and reduces its possibility of violating the surge margin boundary. Acceleration performances of the two methods are further compared under 1000 random envelope points, and similar results show the effectiveness of the MIB. Moreover, the CIS strategy performs better than other input selection strategies and contributes to enhancing the FEAS design precision and robustness. The MLP network is more qualified to improve FEAS precision than other classical machine learning models.

Optimization of ACE mode transition control schedule considering geometric adjustment speed

Abstract Aiming to optimize the mode transition control schedule of the adaptive cycle engine (ACE), an optimization method based on a gradient algorithm was proposed. During the mode transition, the compressor surge margin, the total turbine inlet temperature and the combustion chamber fuel-air ratio are not exceeded. The integration of thrust by time was selected as the optimization objective. The geometric parameters were updated via the optimization target derivative. The speed limit of the geometric adjustment mechanism was also considered in the optimization process. The control schedules of two mode transition processes, from triple to double bypass mode and from double to triple-bypass mode were optimized. The optimization method presented in this paper can be applied to various mode transitions and the geometric adjustment speed meets all the constraints.

Optimization of ACE mode transition control schedule considering geometric adjustment speed

Abstract Aiming to optimize the mode transition control schedule of the adaptive cycle engine (ACE), an optimization method based on a gradient algorithm was proposed. During the mode transition, the compressor surge margin, the total turbine inlet temperature and the combustion chamber fuel-air ratio are not exceeded. The integration of thrust by time was selected as the optimization objective. The geometric parameters were updated via the optimization target derivative. The speed limit of the geometric adjustment mechanism was also considered in the optimization process. The control schedules of two mode transition processes, from triple to double bypass mode and from double to triple-bypass mode were optimized. The optimization method presented in this paper can be applied to various mode transitions and the geometric adjustment speed meets all the constraints.

Aerodynamic Optimization of Transonic Rotor Using Radial Basis Function Based Deformation and Data-Driven Differential Evolution Optimizer

The complicated flow conditions and massive design parameters bring two main difficulties to the aerodynamic optimization of axial compressors: expensive evaluations and numerous optimization variables. To address these challenges, this paper establishes a novel fast aerodynamic optimization platform for axial compressors, consisting of a radial basic function (RBF)-based blade parameterization method, a data-driven differential evolution optimizer, and a computational fluid dynamic (CFD) solver. As a versatile interpolation method, RBF is used as the shape parameterization and deformation technique to reduce optimization variables. Aiming to acquire competitive solutions in limited steps, a data-driven evolution optimizer is developed, named the pre-screen surrogate model assistant differential evolution (pre-SADE) optimizer. Different from most surrogate model-assisted evolutionary algorithms, surrogate models in pre-SADE are used to screen the samples, rather than directly estimate them, in each generation to reduce expensive evaluations. The polynomial regression model, Kriging model, and RBF model are integrated in the surrogate model to improve the accuracy. To further save optimization time, the optimizer also integrates parallel task management programs. The aerodynamic optimization of a transonic rotor (NASA Rotor 37) is performed as the validation of the platform. A differential evolution (DE) optimizer and another surrogate model-assisted algorithm, committee-based active learning for surrogate model assisted particle swarm optimization (CAL-SAPSO), are introduced for the comparison runs. After optimization, the adiabatic efficiency, total pressure ratio, and surge margin are, respectively, increased by 1.47%, 1.0%, and 0.79% compared to the initial rotor. In the same limited steps, pre-SADE gets a 0.57% and 0.51% higher rotor adiabatic efficiency than DE and CAL-SAPSO, respectively. With the help of parallel techniques, pre-SADE and DE save half the optimization time compared to CAL-SAPSO. The results verify the effectiveness and the rapidity of the fast aerodynamic optimization platform.

A novel control strategy with an anode variable geometry ejector for a SOFC-GT hybrid system

A novel control strategy was developed with an anode variable geometry ejector for a solid oxide fuel cell-gas turbine (SOFC-GT) system. The anode inlet temperature was controlled by combining two modes to achieve a greater controllable range: anode variable geometry ejector adjusting and after-burner fuel valve adjusting. Two tests were carried out under small-scale and large-scale load steps. The results indicate that all controlled variables can be effectively kept around set-point. Moreover, the critical parameters are kept within safe ranges, including steam-to-carbon ratio higher than 2.0, peak temperature gradient below 10 K/cm, peak time-dependent temperature gradient below 3 K/min, and surge margin higher than 15%. The developed novel control strategy can maintain almost constant SOFC spatial temperature. The spatial temperature variation is within 2.50 K under 5% load step, and within 14.30 K under 30% load step. Besides, the novel control strategy can keep the system efficiency at a high level (more than 63.21%) during the load tracking. Compared with the conventional control strategy with a fixed geometry ejector, the results demonstrated that the novel control strategy can significantly improve the system performance, especially the transient behaviors of after-burner fuel rate, turbine inlet temperature, and system efficiency.