Axial Transonic Rotor and Stage Behavior Near the Stability Limit

2010 ◽  
Author(s):  
Anthony J. Gannon ◽  
Garth V. Hobson ◽  
William L. Davis
Keyword(s):  
High Speed ◽  
Axisymmetric Flow ◽  
Low Frequency ◽  
Stability Limit ◽  
Stable Operation ◽  
Inlet Flow ◽  
Flow Angle ◽  
The Stability ◽  
Lower Magnitude ◽  
Transonic Rotor

Transient casing pressure data from a transonic rotor and rotor-stator stage measured using high-speed pressure probes embedded in the casewall over the rotor tips is analyzed. Using long data sets sampled at a high frequency, low-frequency (less than once-per-revolution) non-axisymmetric flow phenomena were detected while operating at steady-state conditions near stall. Both the rotor and stage cases are investigated and the difference in behavior of a rotor with and without a stator blade row is investigated. Data for both cases over the speed range 70–100% of design and from choke to near the stability limit (stall or surge) is presented. The root mean square power of the low-frequency signal as well as its fraction of the total pressure signal is presented. It was thought that the behavior of these signals as stall was approached could lead to some method of detecting the proximity of stall. For the rotor-only configuration the strength of these non-axisymmetric phenomena increased as stall was approached for all speed-lines. However for the stage configuration, more representative of an operational machine, these were of a lower magnitude and did not exhibit a clearly increasing trend as stall was approached. This would seem to indicate that the stator suppressed these signals somewhat. It is also shown that these non-axisymmetric phenomena led to a significant variation of the mean relative inlet flow angle into the rotor blade. During stable operation near to stall at 100% speed for the rotor-only case a 1.9° variation of this angle was measured. This compared with a 5.6° variation over the entire speed line. Further it was observed that while the rotor and stage cases had different stability limits their peak relative inlet flow angles near stall were similar for both along most speed-lines.

Axial Transonic Rotor and Stage Behavior Near the Stability Limit

2011 ◽  
Vol 134 (1) ◽  
Author(s):  
Anthony J. Gannon ◽  
Garth V. Hobson ◽  
William L. Davis
Keyword(s):  
High Speed ◽  
Low Frequency ◽  
Stability Limit ◽  
Stable Operation ◽  
Inlet Flow ◽  
Flow Angle ◽  
The Difference ◽  
The Stability ◽  
Lower Magnitude ◽  
Transonic Rotor

Transient casing pressure data from a transonic rotor and rotor-stator stage measured using high-speed pressure probes embedded in the casewall over the rotor tips are analyzed. Using long data sets sampled at a high frequency, low-frequency (less than once-per-revolution) nonaxisymmetric flow phenomena were detected while operating at steady-state conditions near stall. Both the rotor and stage cases are investigated, and the difference in behavior of a rotor with and without a stator blade row is investigated. Data for both cases over the speed range 70–100% of design and from choke to near the stability limit (stall or surge) are presented. The root mean square power of the low-frequency signal as well as its fraction of the total pressure signal is presented. It was thought that the behavior of these signals as stall was approached could lead to some method of detecting the proximity of stall. For the rotor-only configuration, the strength of these nonaxisymmetric phenomena increased as stall was approached for all speed-lines. However, for the stage configuration, more representative of an operational machine, these were of a lower magnitude and did not exhibit a clearly increasing trend as stall was approached. This would seem to indicate that the stator suppressed these signals somewhat. It is also shown that these nonaxisymmetric phenomena led to a significant variation of the mean relative inlet flow angle into the rotor blade. During stable operation near to stall at 100% speed for the rotor-only case, a 1.9 deg variation of this angle was measured. This compared with a 5.6 deg variation over the entire speed-line. Further, it was observed that while the rotor and stage cases had different stability limits, their peak relative inlet flow angles near stall were similar for both along most speed-lines.

Criteria for the Stability Limit Prediction of High Speed Centrifugal Compressors With Vaneless Diffuser: Part I — Flow Structure Analysis

2020 ◽  
Author(s):  
Carlo Cravero ◽  
Davide Marsano
Keyword(s):  
Rotational Speed ◽  
High Speed ◽  
Stability Limit ◽  
Vaneless Diffuser ◽  
Centrifugal Compressors ◽  
Vaned Diffuser ◽  
High Rotational Speed ◽  
Lower Accuracy ◽  
The Stability ◽  
Computational Resources

Abstract High-speed centrifugal compressor requirements include a wide operating range between choking and stall especially for turbocharging applications. The prediction of the stability limit at different speeds is still challenging. In literature, several studies have been published on the phenomena that trigger the compressor instability. However, a comprehensive analysis of criteria that can be used in the first steps of centrifugal compressors design to predict the stability limit is still missing. In previous work the authors have already presented a criterion, so called “Stability Parameter”, to predict the surge line of centrifugal compressors based on a simplified CFD approach that does not require excessive computational resources and that can be efficiently used in the preliminary design phases. The above methodology has demonstrated its accuracy for centrifugal compressors with vaned diffuser, but a lower accuracy has been detected for vaneless diffusers. Before proceeding to identify additional criteria focused on compressors with vaneless diffuser, an in-depth fluid dynamics analysis has been necessary. This analysis has been also carried out through fully 3D unsteady simulations to allow identifying the real phenomena linked to the trigger of the instability of centrifugal compressors. It has been found how these phenomena are strongly related to the rotational speed, in particular have been shown the key role of the volute at high rotational speed.

Numerical and Experimental Investigation of the CeCOST Swirl Burner

2018 ◽  
Author(s):  
Erdzan Hodzic ◽  
Senbin Yu ◽  
Arman Ahamed Subash ◽  
Xin Liu ◽  
Xiao Liu ◽  
...  
Keyword(s):  
High Speed ◽  
Swirling Flow ◽  
Combustion Process ◽  
Stability Limit ◽  
Swirl Burner ◽  
Current Configuration ◽  
Stable Case ◽  
Eddy Simulation ◽  
Computational Fluid Dynamics Cfd ◽  
The Stability

Clean technology has become a key feature due to increasing environmental concerns. Swirling flows, being directly associated with combustion performance and hence minimized pollutant formation, are encountered in most propulsion and power-generation combustion devices. In this study, the development process of the conceptual swirl burner developed at the Swedish National Centre for Combustion and Technology (CeCOST), is presented. Utilizing extensive computational fluid dynamics (CFD) analysis, both the lead time and cost in manufacturing of the different burner parts were significantly reduced. The performance maps bounded by the flashback and blow-off limits for the current configuration were obtained and studied in detail using advanced experimental measurements and numerical simulations. Utilizing high speed OH-chemiluminescence, OH/CH2O-PLIF and Large Eddy Simulation (LES), details of the combustion process and flame-flow interaction are presented. The main focus is on three different cases, a stable case, a case close to blow-off and flashback condition. We show the influence of the flame on the core flow and how an increase in swirl may extend the stability limit of the anchored flame in swirling flow burners.

Deficiencies in Turbulence Modelling for the Prediction of the Stability Boundary in Highly Loaded Compressors

2019 ◽  
Author(s):  
Jose Moreno ◽  
John Dodds ◽  
Mehdi Vahdati ◽  
Sina Stapelfeldt
Keyword(s):  
High Speed ◽  
Stability Boundary ◽  
Turbulence Models ◽  
Stability Limit ◽  
Major Effect ◽  
Navier Stokes ◽  
Tip Leakage Flow ◽  
Stall Margin ◽  
Multi Stage ◽  
The Stability

Abstract Reynolds-averaged Navier-Stokes (RANS) equations are employed for aerodynamic and aeroelastic modelling in axial compressors. Their solutions are highly dependent on the turbulence models for closure. The main objective of this work is to assess the widely used Spalart-Allmaras model’s suitability for compressor flows. For this purpose, an extensive investigation of the sources of uncertainties in a high-speed multi-stage compressor rig was carried out. The grid resolution near the casing end wall, which affects the tip leakage flow and casing boundary layer, was found to have a major effect on the stability limit prediction. Refinements in this region led to a stall margin loss prediction. It was found that this loss was exclusively due to the destruction term in the SA model.

Bandwidth enhancement in damping control for piezoelectric nanopositioning stages with load uncertainty: Design and implementation

2020 ◽  
pp. 107754632094170
Author(s):  
Jie Ling ◽  
Zhao Feng ◽  
Xi Kang ◽  
Xiaohui Xiao
Keyword(s):  
High Speed ◽  
Low Frequency ◽  
Bandwidth Enhancement ◽  
Load Variations ◽  
Fast Tracking ◽  
Damping Control ◽  
Positive Acceleration ◽  
High Bandwidth ◽  
Small Gain ◽  
The Stability

High bandwidth and fast tracking of desired trajectories are eagerly required in various applications that use piezoelectric nanopositioning stages, especially in atomic force microscopes where the vibration stemming from lightly damped modes of stages is a challenging control problem. In this study, a bandwidth-enhanced positive acceleration, velocity, and position feedback damping controller is presented to achieve the tracking bandwidth exceeding the first resonant frequency through using a novel pole-shift method. The stability of the positive feedback damped loop is examined by a mixed passivity, small-gain approach, and Nyquist theorem framework. Also, in conjunction with a proportional–integral tracking controller, robust stability is addressed for load uncertainties. Experimental application to a piezoelectric nanopositioning stage demonstrates that a closed-loop bandwidth of 282.5 Hz is achieved, which exceeds the dominating resonance of the stage at 210 Hz. The achieved bandwidth is 1.35 times larger than the dominating resonance, which is a competitive result among most existing damping control approaches. Comparative tracking results verify the effectiveness of the proposed control scheme on the suppression of low-frequency hysteresis and tracking performance of high-speed triangular waves under load variations.

Impedance Control of Gyroscopic Power Generator

2011 ◽  
Author(s):  
Tomoyuki Takahashi ◽  
Jun Iwasaki ◽  
Hiroshi Hosaka
Keyword(s):  
Steady State ◽  
Phase Difference ◽  
High Speed ◽  
Control Method ◽  
Impedance Control ◽  
Low Frequency ◽  
Power Generator ◽  
Communication Devices ◽  
High Speed Rotation ◽  
The Stability

The gyroscopic power generator produces a high-speed rotation of magnets from low-frequency vibrations and supplies electric power to information and communication devices that use human vibrations in daily life. In this paper, in order to increase the stability and the output power of the generator, a simple equation that indicates the steady state approximate solution of the phase difference is derived. From the derived solution, a control method for the steady state is verified by the simulations. In order to maintain the stability and high power generation for variable input vibrations, the impedance control method using the phase difference is developed and verified experimentally.

scholarly journals DETERMINING THE STABILITY CONDITIONS OF THE TRACK-DRIVEN VEHICLE WHILE STAIR CLIMBING AND DESCENDING

2012 ◽  
Vol 15 (1) ◽  
pp. 36-42
Author(s):  
Khoi Duc Pham ◽  
Ha Thi Thu Thai
Keyword(s):  
Mass Velocity ◽  
Research Method ◽  
Stability Limit ◽  
Stair Climbing ◽  
Stability Conditions ◽  
Stable Operation ◽  
Constraint Equations ◽  
The Stability

This article presents the method of determining the stability limit of the vehicle (robots or electric wheelchairs) that use tracks (chain, belt) for climbing and descending stairs. Research method was conducted by modeling vehicle which is working under the influence of some elements such as geometric, mass, velocity, acceleration, friction...Afterthat, we identify some conditions which lead to tipping. Finally, the results of research are constraint equations in order to ensure stable operation of vehicle.

Criteria for the Stability Limit Prediction of High Speed Centrifugal Compressors With Vaneless Diffuser: Part II — The Development of Prediction Criteria

2020 ◽  
Author(s):  
Carlo Cravero ◽  
Davide Marsano
Keyword(s):  
High Speed ◽  
Numerical Models ◽  
Fluid Dynamic ◽  
Stability Limit ◽  
Design Phase ◽  
Vaneless Diffuser ◽  
Centrifugal Compressors ◽  
Vaned Diffuser ◽  
The Stability ◽  
Computational Resources

Abstract The challenge to be able to predict the stability limit in high speed centrifugal compressor is particularly strategic in an initial design phase. Furthermore, to be able to predict the limit massflow rate through the use of simplified numerical models (which does not require excessive computational resources) is very important. In the literature there are several methods to predict the chocking condition, while there is a lack as regards the surge condition. The authors have already presented a criterion to predict the surge line valid for centrifugal compressors with vaned diffuser. Instead those with vaneless diffuser have a very different behavior. For this reason, in the first paper an in-depth fluid dynamic analysis has been carried out, in order to identify the main phenomena linked to the trigger of instability in this type of compressors. This analysis has allowed understanding that the rotational speed is a discriminating factor in the phenomenology. In this second part, using the previous information, different criteria to predict the limit massflow rate for centrifugal compressors with vaneless diffuser are described. All the criteria are based on different simplified CFD approaches that can be routinely used during the design phase.

scholarly journals Self-Recirculating Casing Treatment Concept for Enhanced Compressor Performance

2002 ◽  
Author(s):  
Michael D. Hathaway
Keyword(s):  
High Speed ◽  
Flow Characteristics ◽  
Treatment Concept ◽  
Casing Treatment ◽  
Compressor Performance ◽  
And Performance ◽  
The Stability ◽  
The Impact ◽  
Compressor Efficiency ◽  
Transonic Rotor

A state-of-the-art CFD code (APNASA) was employed in a computationally based investigation of the impact of casing bleed and injection on the stability and performance of a moderate speed fan rotor wherein the stalling mass flow is controlled by tip flow field breakdown. The investigation was guided by observed trends in endwall flow characteristics (e.g., increasing endwall aerodynamic blockage) as stall is approached, and based on the hypothesis that application of bleed or injection can mitigate these trends. The “best” bleed and injection configurations were then combined to yield a self-recirculating casing treatment concept. The results of this investigation yielded: 1) identification of the fluid mechanisms which precipitate stall of tip critical blade rows, and 2) an approach to recirculated casing treatment which results in increased compressor stall range with minimal or no loss in efficiency. Subsequent application of this approach to a high speed transonic rotor successfully yielded significant improvements in stall range with no loss in compressor efficiency.

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