Stall In Compressors Research Articles

A Compressor Stall Warning System for Aeroengines Based on the Continuous Wavelet Transform and a Vision Transformer

A Compressor Stall Warning System for Aeroengines Based on the Continuous Wavelet Transform and a Vision Transformer

Measurement of unsteady force on rotor blade surfaces in axial flow compressor

To assess the aerodynamic performance and vibration characteristics of rotor blades during rotation, a study of unsteady blade surface forces is conducted in a low-speed axial flow compressor under a rotating coordinate system. The capture, modulation, and acquisition of unsteady blade surface forces are achieved by using pressure sensors and strain gauges attached to the rotor blades, in conjunction with a wireless telemetry system. Based on the measurement reliability verification, this approach allows for the determination of the static pressure distribution on rotor blade surfaces, enabling the quantitative description of loadability at different spanwise positions along the blade chord. Effects caused by the factors such as Tip Leakage Flow (TLF) and flow separation can be perceived and reflected in the trends of static pressure on the blade surfaces. Simultaneously, the dynamic characteristics of unsteady pressure and stress on the blade surfaces are analyzed. The results indicate that only the pressure signals measured at the mid-chord of the blade tip can distinctly detect the unsteady frequency of TLF due to the oscillation of the low-pressure spot on the pressure surface. Subsequently, with the help of one-dimensional continuous wavelet analysis method, it can be inferred that as the compressor enters stall, the sensors are capable of capturing stall cell frequency under a rotating coordinate system. Furthermore, the stress at the blade root is higher than that at the blade tip, and the frequency band of the vibration can also be measured by the pressure sensors fixed on the casing wall in a stationary frame. While the compressor stalls, the stress at the blade root can be higher, which can provide valuable guidance for monitoring the lifecycle of compressor blades.

A Review of Numerical Methodologies for Predicting Rotating Stall and Surge in High-Speed Centrifugal Compressors

Abstract High-speed supersonic radial compressors are a critical enabling technology for meeting the requirements of future aviation- propulsion and thermal-management systems. These turbomachines must be designed to be both efficient and robust on the widest possible operating range. Flow instabilities in the form of rotating stall and surge are therefore phenomena that must be accurately predicted early in the design process. Unsteady full-annulus computational fluid dynamics can be used to get accurate information about the onset of instabilities, but at the expense of costly simulations. As a result, the design of new compressors continues to rely on existing correlations for the prediction of the critical mass flow rate. This approach, however, leads to sub-optimal compressor designs. This article provides a review of the numerical methodologies that can be used for the accurate prediction of the critical mass flow rate in high-speed centrifugal compressors. Methods of different fidelity level and computational cost are described. Two particularly promising models, namely those proposed by Spakovszky and Sun, are subsequently examined in more detail. Exemplary applications of these two models are finally discussed.

Rapid identification and early warning of axial compressor stall based on multiscale CNN-SVM-FC model

Early prewarning of compressor stall and surge is crucial to avoid aircraft engine instability, yet it is challenging due to the complex and unstable flow field characterized by multiple modes and multiscale features. To enhance the multi-scale feature representation capability of Convolutional Neural Network-Support Vector Machine (CNN-SVM) algorithm, a novel classifier modelling method combined multiscale windows with CNN-SVM is introduced for stall prewarning in this paper, named Multiscale CNN-SVM-FC. Multiscale detection windows are utilized to adaptively identify various pressure features during the stall process. Additionally, to reduce the false alarm rate, a fuzzy control algorithm is integrated with the temporal accumulation of prediction results from the multi-branch network for joint analysis. A series of test data from a five-stage axial compressor at different operating speeds is used to verify this method. The results indicate that the proposed Multiscale CNN-SVM-FC method enhances the accuracy of classification and reduces the false alarm rate compared to the standard CNN-SVM model, achieving over 99% accuracy in identifying unstable states under various speeds. Compared to three traditional stall prewarning methods, the Multiscale CNN-SVM-FC model provides an average warning signal 164 milliseconds ahead of stall, and reduces the uncertainty associated with threshold selection, which typically relies on engineering experience.

Fluctuation of the unsteady force on the rotor blade surface under circumferential distortion in axial flow compressor

To deeply understand the negative impact of circumferential inlet distortion on the internal flow of the compressor, by using the unsteady force testing technique of a rotor blade surface under a rotating coordinate system, the pressure fluctuations on the rotor blade surface are successfully captured when the rotor blade rotates through the distortion region. Results show that the pressure on the suction surface increases and the inlet angle of attack decreases before the rotor blade enters the distorted region. The pressure difference between the pressure and suction surface is obviously enhanced, thereby sharply increasing the blade load and intensifying the flow separation, which is easy to induce instability. When the rotor blade rotates out of the distortion region, the pressure on the suction surface is still low; thus, the inlet angle of attack in this position is larger than before entering the distorted region. It also shows that the outlet of the distorted region is prone to trigger stall. In addition, the dynamic spectrum characteristics of unsteady forces on the blade surface demonstrate that the energy of the rotor frequency and its harmonics increases significantly and the energy of low frequency disturbance is enhanced when the rotor blade rotates through the distorted region. As a result, the vibration is more obvious in the distorted region, especially the energy of natural vibration frequency of the rotor blade is enhanced. When the compressor stalls, the vibration at the rotor blade root is intensified, which is significantly stronger than at the rotor blade tip. It provides support for evaluating the influence of stall and surge on the lifecycle of rotor blade when suffering from circumferential inlet distortion.

AI-Based Detection of Surge and Rotating Stall in Axial Compressors via Dynamic Model Parameter Estimation

Compressors are an essential component of aircraft engines. Their design and operation must be extremely reliable as engine safety and performance depend greatly on these elements. Axial compressors exhibit instabilities, such as surge or rotating stall, in a region close to the peak of their performance curves. These fluid dynamic instabilities can cause drops in efficiency, stress on the blades, fatigue, and even failures. Compressors are handled therefore by operating with a safety margin far from the surge line. Moreover, models able to predict onset instabilities and to reproduce them are of great interest. A dynamic system able to describe successfully both surge and rotating stall is the model presented by Moore and Greitzer That model has also been used for developing control laws of the compressor dynamics. The present work aims at developing an artificial neural network (ANN) approach able to predict either the permanence of the system in stable working condition or the onset instabilities from a time sequence of the compressor dynamics. Different solutions were tried to find the most suitable model for identifying the system, as well as the effects of the duration of the time sequence on the accuracy of the predicted compressor working conditions. The network was further tried for sequences with different initial values in order to perform a system analysis that included multiple variations from the initial database. The results show how it is possible to identify with high accuracy both rotating stall and surge with the ANN approach. Moreover, the presence of an underlying fluid dynamic model shares some similarities with physically informed AI procedures.

Stall and stability enhancement mechanisms of transonic compressor with inlet total temperature distortion

Inlet total temperature distortion refers to the nonuniform distribution of the total temperature at the inlet of the aero-engine, which is one of the external destabilizing factors that have the most remarkable impact on the stability of an aero-engine. In this study, the stalling process of the Darmstadt transonic compressor is investigated under the total temperature distortion of 180 deg circumferential extent and 500 K intensity by full-annulus unsteady numerical simulation. The analysis shows the addition of inlet total temperature distortion deteriorates the compressor stall margin from 22.7% to 17.0% with a considerable decrease in the pressure ratio. The type of compressor stall inception under temperature distortion conditions remains spike. Pressure perturbations and radial vortex formation are first clearly detected when the rotor rotates into the high temperature distortion region. The circumferential propagation of the stall cells under the total temperature distortion is 66% of the rotor speed, which is faster than that under uniform condition whose value is 44% of the rotor speed. The optimized casing treatment (CT) has extended the stall margin of the rotor without producing efficiency loss under uniform condition. The anti-distortion ability of CT is first verified despite its negative impact on efficiency under total temperature distortion. The adoption of CT could obviously push the shock wave into the blade passage under total temperature distortion condition. In addition, it can reduce the tip blade loading, thus removing the low Mach number area in the tip region, while increasing the blade loading below 80% span.

A Method of Stall and Surge Prediction in Axial Compressors Based on Three-Dimensional Body-Force Model

Abstract The occurrence of stall and surge in axial compressors has a great impact on the performance and reliability of aero-engines. Accurate and efficient prediction of the key features during these events has long been the focus of engine design processes. In this paper, a new body-force model that can capture the three-dimensional and unsteady features of stall and surge in compressors at a fraction of time required for URANS computations is proposed. To predict the rotating stall characteristics, the deviation of local airflow angle from the blade surface is calculated locally during the simulation. According to this local deviation, the computational domain is divided into stalled and forward flow regions, and the body-force field is updated accordingly; to predict the surge characteristics, the local airflow direction is used to divide the computational domain into reverse flow regions and forward flow regions. A single-stage axial compressor and a three-stage axial compressor are used to verify the proposed model. The results show that the method is capable of capturing stall and surge characteristics correctly. Compared to the traditional fully three-dimensional URANS method (fRANS), the simulation time for multistage axial compressors is reduced by 1–2 orders of magnitude.

Centrifugal Compressor Stall Control by the Application of Engineered Surface Roughness on Diffuser Shroud Using Numerical Simulations.

Downsizing in engine size is pushing the automotive industry to operate compressors at low mass flow rate. However, the operation of turbocharger centrifugal compressor at low mass flow rate leads to fluid flow instabilities such as stall. To reduce flow instability, surface roughness is employed as a passive flow control method. This paper evaluates the effect of surface roughness on a turbocharger centrifugal compressor performance. A realistic validation of SRV2-O compressor stage designed and developed by German Aerospace Center (DLR) is achieved from comparison with the experimental data. In the first part, numerical simulations have been performed from stall to choke to study the overall performance variation at design conditions: 2.55 kg/s mass flow rate and rotational speed of 50,000 rpm. In second part, surface roughness of magnitude range 0–200 μm has been applied on the diffuser shroud to control flow instability. It was found that completely rough regime showed effective quantitative results in controlling stall phenomena, which results in increases of operating range from 16% to 18% and stall margin from 5.62% to 7.98%. Surface roughness as a passive flow control method to reduce flow instability in the diffuser section is the novelty of this research. Keeping in view the effects of surface roughness, it will help the turbocharger manufacturers to reduce the flow instabilities in the compressor with ease and improve the overall performance.

Failure mechanism of casing treatment in improving stability of a highly loaded two-stage axial compressor

Casing treatment is a powerful method for enhancing stability of certain aircraft compressors in which tip leakage vortex (TLV) triggers stall. An optimized slot-type casing treatment was installed on the first rotor of a highly loaded two-stage compressor. The experimental result showed that the casing treatment could not increase the compressor stability at three tested speeds. This study aims to understand the failure mechanism of the casing treatment for developing an effective method to depress stall. A “three-step method” is proposed to determine the stall-limiting location and understand the underlying stall mechanism. At 90% speed, there is a spike in the aerodynamic flow parameters in the tip region of the first rotor under the near stall condition compared with that under the design condition. The spike is induced by an interaction among the TLV, boundary layer at the blade suction surface, and passage shockwave. Both the TLV and the shockwave–boundary layer interaction contribute to the accumulation of tip blockage which triggers compressor stall. The TLV does not break down under the near stall condition, but unsteady forward spillage of the TLV at the blade tip leading edge can be detected, resulting in unsteady tip flow. When the casing treatment is installed on the first rotor, a typical flow circulation is established in the slots. The intensity of the TLV and the flow unsteadiness are greatly depressed, and the discharge capability in the tip region is remarkably improved. However, the flow circulation cannot manipulate the fierce boundary layer separation induced by the shockwave, which causes increased tip blockage and reduced compressor stability. A coupled casing treatment, which can bleed the shockwave induced blockage, is proposed and found to be very effective in improving compressor stability. Therefore, the technology for damping the compressor stall should be capable of manipulating both the TLV and the shockwave induced boundary layer separation. At 100% speed, a shedding vortex is initiated at the hub of the second stator. This vortex expands sharply in the stalling process and triggers compressor stall. Variation of the location at which the compressor stalls is the reason for the failure of the casing treatment at 100% speed.

Using Machine Learning Tools to Predict Compressor Stall

Abstract Clean energy has become an increasingly important consideration in today’s power systems. As the push for clean energy continues, many coal-fired power plants are being decommissioned in favor of renewable power sources such as wind and solar. However, the intermittent nature of renewables means that dynamic load following traditional power systems is crucial to grid stability. With high flexibility and fast response at a wide range of operating conditions, gas turbine systems are poised to become the main load following component in the power grid. Yet, rapid changes in load can lead to fluid flow instabilities in gas turbine power systems. These instabilities often lead to compressor surge and stall, which are some of the most critical problems facing the safe and efficient operation of compressors in turbomachinery today. Although the topic of compressor surge and stall has been extensively researched, no methods for early prediction have been proven effective. This study explores the utilization of machine learning tools to predict compressor stall. The long short-term memory (LSTM) model, a form of recurrent neural network (RNN), was trained using real compressor stall datasets from a 100 kW recuperated gas turbine power system designed for hybrid configuration. Two variations of the LSTM model, classification and regression, were tested to determine optimal performance. The regression scheme was determined to be the most accurate approach, and a tool for predicting compressor stall was developed using this configuration. Results show that the tool is capable of predicting stalls 5–20 ms before they occur. With a high-speed controller capable of 5 ms time-steps, mitigating action could be taken to prevent compressor stall before it occurs.

Impact of compressed air energy storage demands on gas turbine performance

Industrial gas turbines are now required to operate more flexibly as a result of incentives and priorities given to renewable forms of energy. This study considers the extraction of compressed air from the gas turbine; it is implemented to store heat energy at periods of a surplus power supply and the reinjection at peak demand. Using an in-house engine performance simulation code, extractions and injections are investigated for a range of flows and for varied rear stage bleeding locations. Inter-stage bleeding is seen to unload the stage of extraction towards choke, while loading the subsequent stages, pushing them towards stall. Extracting after the last stage is shown to be appropriate for a wider range of flows: up to 15% of the compressor inlet flow. Injecting in this location at high flows pushes the closest stage towards stall. The same effect is observed in all the stages but to a lesser magnitude. Up to 17.5% injection seems allowable before compressor stalls; however, a more conservative estimate is expected with higher fidelity models. The study also shows an increase in performance with a rise in flow injection. Varying the design stage pressure ratio distribution brought about an improvement in the stall margin utilized, only for high extraction.

On Initiation of Stall in Axial Flow Compressors

This Technical Note calls attention to the fact that observed initiation of stall in an axial flow compressor can be explained by the pressure pulses reflecting between the stator and rotor blades. The phenomenon of reflection of pressure pulses between the rotor and stator blades of turbines was first observed in in 1965 and reported in 1966. It can occur in turbines and axial- flow compressors. Subsequently the reflecting pressure pulses were able to explain turbine and axial- flow compressor blade vibrations.

Observations of the Growth and Decay of Stall Cells during Stall and Surge in an Axial Compressor

This research investigated unsteady events such as stall inception, stall-cell development, and surge. Stall is characterized by a decrease in overall pressure rise and nonaxisymmetric throughflow. Compressor stall can lead to surge which is characterized by quasi-axisymmetric fluctuations in mass flow and pressure. Unsteady measurements of the flow field around the compressor rotor are examined. During the stall inception process, initial disturbances were found within the rotor passage near the tip region. As the stall cell develops, blade lift and pressure ratio decrease within the stall cell and increase ahead of the stall cell. The stall inception event, stall-cell development, and stall recovery event were found to be nearly identical for stable rotating stall and surge cases. As the stall cell grows, the leading edge of the cell will rotate at a higher rate than the trailing edge in the rotor frame. The opposite occurs during stall recovery. The trailing edge of the stall cell will rotate at the approximate speed as the fully developed stall cell, while the leading edge decreases in rotational speed in the rotor frame.

Effect of Exit Pressure Pulsation on the Performance and Stability Limit of a Turbocharger Centrifugal Compressor

It is well known that compressor surge imposes a significant limit on the flow range of a turbocharged internal combustion engine. The centrifugal compressor is commonly placed upstream of the inlet manifold, and hence, it is exposed to the intermittent flow regime of the inlet valves. Surge phenomena have been well studied over the past decades, and there still remains limited information with regard to the unsteady impact caused by the inlet valves. This study presents an experimental evaluation of such a situation. Engine representative pulses are created by a downstream system comprising a large volume, two rotating valves, a throttle valve, and the corresponding pipe network. Different pulsation levels are characterized by means of their frequency and the corresponding amplitude at the compressor inlet. The stability limit of the system under study is evaluated with reference to the parameter B proposed by Greitzer (1976, “Surge and Rotating Stall in Axial Flow Compressors—Part II: Experimental Results and Comparison With Theory,” ASME J. Eng. Power, 98(2), pp. 199–211; 1976, “Surge and Rotating Stall in Axial Flow Compressors—Part I: Theoretical Compression System Model,” ASME J. Eng. Power, 98(2), pp. 190–198). B describes the dynamics of the compression system in terms of volume, area, equivalent length, and compressor tip speed as well as the Helmholtz frequency of the system. For a given compressor, as B goes beyond a critical value, the system will exhibit surge as the result of the flow instability progression. The reduced frequency analysis shows that the scroll diffuser operates in an unsteady regime, while the impeller is nearly quasi-steady. In the vicinity of the surge point, under a pulsating flow, the instantaneous operation of the compressor showed significant excursions into the unstable side of the surge line. Furthermore, it has been found that the presence of a volume in the system has the greatest effect on the surge margin of the compressor under the unsteady conditions.

Output Feedback Control of Surge and Rotating Stall in Axial Compressors

AbstractActive control has been widely studied to expand the stable operating range of axial flow compressors in aero‐engines.In this paper, a nonlinear active state feedback controller is proposed first based on bifurcation analysis results of MG model.Then by taking pressure ratio as output parameter, a state observer is designed to estimate the compressor's flow coefficient. An output feedback controller is thus established by combining the observer with the state feedback controller.Finally, digital simulation shows that the proposed output feedback controller not only eliminates the hysteresis loop associated with rotating stall and emergence of surge, but also extends the stable operating range of axial flow compressors effectively.Furthermore, being flexible in using pressure transducer and throttle valve as sensor and actuator respectively, which have been equipped in common engines, the proposed controller has good applicability.

Delay of Rotating Stall in Compressors Using Plasma Actuators

Rotating stall is a well-known aerodynamic instability in compressors that limits the operating envelope of aircraft gas turbine engines. An innovative method for delaying the most common form of rotating stall inception using an annular dielectric barrier discharge (DBD) plasma actuator had been proposed. A DBD plasma actuator is a simple solid-state device that converts electricity directly into flow acceleration through partial air ionization. However, the proposed concept had only been preliminarily evaluated with numerical simulations on an isolated axial rotor using a relatively basic CFD code. This paper provides both an experimental and a numerical assessment of this concept for an axial compressor stage as well as a centrifugal compressor stage, with both stages being part of a low-speed two-stage axial-centrifugal compressor test rig. The two configurations studied are the two-stage configuration with a 100 mN/m annular casing plasma actuator placed just upstream of the axial rotor leading edge (LE) and the single-stage centrifugal compressor with the same actuator placed upstream of the impeller LE. The tested configurations were simulated with a commercial RANS CFD code (ansys cfx) in which was implemented the latest engineering DBD plasma model and dynamic throttle boundary condition, using single-passage multiple blade row computational domains. The computational fluid dynamics (CFD) simulations indicate that in both types of compressors, the actuator delays the stall inception by pushing the incoming/tip clearance flow interface downstream into the blade passage. In each case, the predicted reduction in stalling mass flow matches the experimental value reasonably well.

Identify the Rotating Stall in Centrifugal Compressors by Fractal Dimension in Reconstructed Phase Space

Based on phase space reconstruction and fractal dynamics in nonlinear dynamics, a method is proposed to extract and analyze the dynamics of the rotating stall in the impeller of centrifugal compressor, and some numerical examples are given to verify the results as well. First, the rotating stall of an existing low speed centrifugal compressor (LSCC) is numerically simulated, and the time series of pressure in the rotating stall is obtained at various locations near the impeller outlet. Then, the phase space reconstruction is applied to these pressure time series, and a low-dimensional dynamical system, which the dynamics properties are included in, is reconstructed. In phase space reconstruction, C–C method is used to obtain the key parameters, such as time delay and the embedding dimension of the reconstructed phase space. Further, the fractal characteristics of the rotating stall are analyzed in detail, and the fractal dimensions are given for some examples to measure the complexity of the flow in the post-rotating stall. The results show that the fractal structures could reveal the intrinsic dynamics of the rotating stall flow and could be considered as a characteristic to identify the rotating stall.

An improved wavelet adaptive logarithmic threshold denoising method for analysing pressure signals in a transonic compressor

This paper proposes an improved wavelet threshold denoising algorithm based on orthogonal wavelet transform. The algorithm, called adaptive logarithmic threshold denoising algorithm based on wavelet (ALTDAW), processes the dynamic pressure signals generated by a transonic axial compressor. Combined with an adaptive logarithmic threshold function, it sets the optimal threshold for each decomposition level. In this way, noise is effectively identified and eliminated. Since ALTDAW is adaptable, it reduces the maximum decomposition level, thereby decreasing the processing time and improving the computational efficiency. In numerical experiments, the performance of ALTDAW was compared with that of the classical soft and hard threshold algorithms. Relative to the classical algorithms, ALTDAW increased the signal-to-noise ratio (SNR) by 27.9% and 44.2%, and reduced the processing time by 38.5% and 37.6%, respectively. The practicality of the algorithm was validated on the complex dynamic pressure signals of a transonic axial compressor. When processing these signals, the algorithm depicted that disturbance passes through the tips and the spike three revolutions before the compressor stalls, consistent with the physical properties of transonic axial compressors.

Aeromechanical Control of High-Speed Axial Compressor Stall and Engine Performance—Part II: Assessments of Methodology

A theoretical assessment was made explaining how aeromechanical feedback control can be implemented to stabilize rotating stall inception in high-speed axial compression systems. Ten aeromechanical control strategies were quantitatively evaluated based on the control-theoretic formulations and dimensionless performance analysis outlined in the Part I companion paper (McGee and Coleman, 2013, “Aeromechanical Control of High-Speed Axial Compressor Stall and Engine Performance—Part I: Control-Theoretic Models,” ASME J. Fluids Eng., 135(3), p. 031101). The maximum operating range for each aeromechanical control scheme was predicted for optimized structural parameters. Predictability and changeability in the hydrodynamic pressure, temperature, density, operability, and aeromechanical performance of dynamically-compensated, high-speed compressor maps of corrected pressure, corrected mass flow, corrected speeds, temperature ratios, and optimum efficiency were compared for the various aeromechanical control strategies. Compared with dynamically-compensated, low-speed compressor maps of pressure rise and flow coefficient (Gysling and Greitzer, 1995, “Dynamic Control of Rotating Stall in Axial Flow Compressors Using Aeromechanical Feedback,” ASME J. Turbomach., 117(3), pp. 307–319; McGee et al., 2004, “Tailored Structural Design and Aeromechanical Control of Axial Compressor Stall—Part I: Development of Models and Metrics, ASME J. Turbomach, 126(1), pp. 52–62; Fréchette et al., 2004, “Tailored Structural Design and Aeromechanical Control of Axial Compressor Stall—Part II: Evaluation of Approaches,” ASME J. Turbomach., 126(1), pp. 63–72), the present study shows that the most promising aeromechanical designs and controls for a class of high-speed compressors were the use of dynamic fluid injection. Dynamic compensations involving variable duct geometries and dynamically-re-staggered IGV and rotor blades were predicted to yield less controllability under high-speed flow environments. The aeromechanical interaction of a flexible casing wall was predicted to be destabilizing, and thus should be avoided in high-speed compression systems as in low-speed ones by designing sufficiently rigid structures to prevent casing ovalization or other structurally-induced variations in tip clearance.