scholarly journals Observations on Rotating Instabilities and Spike Type Stall Inception in a High-Speed Multistage Compressor

2017 ◽  
Vol 2017 ◽  
pp. 1-11 ◽  
Author(s):  
Johannes Schreiber ◽  
Benoit Paoletti ◽  
Xavier Ottavy
Keyword(s):  
High Frequency ◽  
High Speed ◽  
Stall Inception ◽  
Time Period ◽  
Type Flow ◽  
Different Types ◽  
Multistage Compressors ◽  
Multistage Compressor ◽  
Field Modulation ◽  
Rotating Instability

This work investigates high-frequency measurements for the contribution to the understanding of different stall inception types in high-speed multistage compressors. A 3.5-stage high-speed axial multistage compressor is investigated with a 2 MW test rig in the Laboratoire de Mécanique des Fluides et d’Acoustique (LMFA) at Ecole Centrale de Lyon, France. Two different types of instabilities arise in this compressor as a function of shaft speed. At part speed, a controversy called “rotating instability” type flow field modulation is identified with the measurements. New results are the demonstration of the periodic behavior of this instability and the analogy to classical frequency modulation, periodic to one revolution of the instability. Furthermore, the amplitude of the instability is modulated by the time period of a rotor revolution. At nominal speed, the abrupt spike type stall inception is detected, taking usually less than five rotor revolutions.

Influence of Rotor Tip Flow Field Mis-Prediction on Rotating Disturbance Near Surge in a High Speed Multistage Compressor

2016 ◽  
Author(s):  
Johannes Schreiber ◽  
Xavier Ottavy ◽  
Ghislaine Ngo Boum ◽  
Nicolas Gourdain
Keyword(s):  
Flow Field ◽  
High Frequency ◽  
High Speed ◽  
Periodic Oscillation ◽  
Aircraft Engine ◽  
Numerical Results ◽  
Operating Point ◽  
Stall Inception ◽  
Frequency Measurements ◽  
Multistage Compressor

In this work, unsteady numerical results and high-frequency measurements are investigated from nominal to loaded operating points with the objective to contribute to the understanding of pre-stall rotating disturbances. A 3.5 stages high speed axial multistage compressor is investigated on a 2 MW test rig in the laboratory of fluid mechanics (LMFA) at Ecole Centrale de Lyon, France. The compressor has been built by Snecma, and is representative of modern high-pressure rear blocks of a modern aircraft engine. The unsteady numerical results predict a rotating disturbance in the tip flow field of the rotor 2 at the loaded operating point. It causes a frequency which is not a multiple of the periodicity of the compressor, and is rotating at about 72% of the shaft speed. The mesh independency of this disturbance is ensured. The analysis of the circumferential and axial propagation of the disturbance reveals a rotating instability like phenomenon. Most characteristic is the very important periodic oscillation of the tip leakage vortex trajectory, leading to a modulation of the leakage flow in the neighboring tip gap. The influence of the neighboring blade rows is investigated by filtering their unsteady contribution by means of mixing planes up and/or downstream of the rotor 2. In either case, the rotating disturbance is found to be still present. There are no traces of this rotating disturbance in the high-frequency measurements investigated at a near surge operating point. A spike like stall inception and almost instantaneous surge inception is identified. The mis-prediction of the tip region flow field in the rotors 2 and 3 is believed to cause the mis-prediction of the pre-stall disturbance.

Characteristics and Origin of Loess Landslides on Loess Terraces at Heifangtai, Gansu Province, China

2014 ◽  
Vol 694 ◽  
pp. 455-461 ◽  
Author(s):  
Wei Jiang Wu ◽  
Xing Su ◽  
Xing Min Meng
Keyword(s):  
High Frequency ◽  
Short Distance ◽  
High Speed ◽  
Yellow River ◽  
Gansu Province ◽  
Long Distance ◽  
Freeze Thaw ◽  
Different Types ◽  
Loess Landslides

Over-irrigation can induce serious landslides on the slopes of loess terraces. Typical examples are the series of landslides that happened in the last few decades on the Forth Terraces of the Yellow River at Heifangtai, Yongjing County, Gansu Province. Agricultural irrigations began on the Heifangtai terraces in 1960s. Due to the specific geological and geomorphological conditions of the thick loess terraces, a great amount of irrigation water infiltrated into the loess causing serious landslide problems. The landslides at the Heifangtai can be classified into two different types based on their composition: loess landslides and loess-bedrock landslides, characterized by high-speed, long-distance sliding and low-speed, short-distance sliding respectively. Landslides caused by over-irrigation have a special phenomenon of hysteresis development following long-term of irrigation, occurring in groups and with high frequency. Most of the landslides happen in rainy seasons and freeze-thaw periods.

Numerical Simulation of Flow Instabilities in High Speed Multistage Compressors

2010 ◽  
Author(s):  
Huan Zhang ◽  
Jun Hu ◽  
Baofeng Tu ◽  
Zhiqiang Wang
Keyword(s):  
High Speed ◽  
Rotating Stall ◽  
Flow Instabilities ◽  
Two Dimensional ◽  
Duct Flow ◽  
Disk Model ◽  
Stall Inception ◽  
Axial Compressors ◽  
Multistage Compressors ◽  
The Stability

In the present paper, a nonlinear multi “actuator disk” model is proposed to analyze the dynamic behavior of flow instabilities, including rotating stall and surge, in high speed multistage axial compressors. The model describes the duct flow fields using two dimensional, compressible and unsteady Euler equations, and accounts for the influences of downstream plenum and throttle in the system as well. It replaces each blade row of multistage compressors with a disk. For numerical calculations, the time marching procedure, using MacCormack two steps scheme, is used. The main purpose of this paper is to predict the mechanism of two dimensional short wavelength rotating stall inception, the interaction between blade rows in high speed multistage compressors and the influence of rotating inlet distortion on the stability. It has been demonstrated that the model has the ability to predict those phenomena, and the results show that some system parameters have a strong effect on the stall features as well. Results for a five stage high speed compressor are analyzed in detail, and comparison with the experimental data demonstrates that the model and calculating results are reliable.

scholarly journals Earthquake-induced snow avalanches: II. Experimental study

2010 ◽  
Vol 56 (197) ◽  
pp. 447-458 ◽  
Author(s):  
Evgeny A. Podolskiy ◽  
Kouichi Nishimura ◽  
Osamu Abe ◽  
Pavel A. Chernous
Keyword(s):  
High Frequency ◽  
High Speed ◽  
Shear Plane ◽  
Shaking Table ◽  
Snow Avalanches ◽  
Weak Layer ◽  
Different Types ◽  
The Stability ◽  
The Moment ◽  
Snow Samples

AbstractWe conducted experiments on the stability of snow, subjecting snow to vibrations, with the aim of improving our understanding of poorly studied mechanisms behind the triggering of avalanches during earthquakes. Most experiments were carried out on a specially constructed shaking table using artificial snowpacks containing a weak layer. Accelerations in the snow samples were measured using high-frequency sensors, enabling calculation of vibration-induced stresses within the snow at the moment of fracture. We used a high-speed camera to film different types of fracturing. In all cases, the vibrations caused failure of the snow by fracturing along the weak layer or at the base of the snow sample. An additional inertial stress induced by accelerations normal to the shear plane was quantified. We find that this stress can be related to smaller values of the shear strength in snow.

Experimental Study of Surge Precursors in a High-Speed Multistage Compressor

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
Nicolas Courtiade ◽  
Xavier Ottavy
Keyword(s):  
High Frequency ◽  
High Speed ◽  
Rotation Speed ◽  
Characteristic Line ◽  
Pressure Measurements ◽  
High Frequency Response ◽  
Stable Operating ◽  
Variable Duration ◽  
Multistage Compressor ◽  
Operating Points

Pressure measurements using high frequency response sensors have been carried out on the third rotor of the 3.5-stage high speed compressor CREATE (rotation speed: 11,543 RPM, Rotor 1 tip speed: 313 m/s) over the complete characteristic line and during the surge transient. Precursors to the instabilities occurring near surge are observable at stable operating points. Just before surge, these precursors characterized as rotating disturbances grow in amplitude and provoke the onset a stall cell after a variable duration, which finally triggers surge. This paper presents a detailed analysis of the phenomena of rotating instabilities and surge transient and shows that it is possible to develop an antisurge active control system based on the early detection of the precursors.

Experimental Investigation of Rotating Stall in a Mismatched Three-Stage Axial Flow Compressor

1989 ◽  
Vol 111 (4) ◽  
pp. 418-425 ◽  
Author(s):  
G. L. Giannissis ◽  
A. B. McKenzie ◽  
R. L. Elder
Keyword(s):  
High Speed ◽  
Measurement Techniques ◽  
Axial Flow ◽  
Fast Response ◽  
Rotating Stall ◽  
Response Measurement ◽  
Stall Inception ◽  
Axial Flow Compressor ◽  
Multistage Compressors ◽  
Flow Compressor

This paper reports on an examination of rotating stall in a low-speed three-stage axial flow compressor operating with various degrees of stage mismatch. The objective of this study was to simulate the mismatching that occurs in high-speed multistage compressors when operating near surge. The study of the stall zones involved the use of fast response measurement techniques. The study clearly shows how stages can operate in an axisymmetric fashion even when heavily stalled, since rotating stall inception requires the stall of more than one stage. The study also compares conditions required for full-span and part-span stall and suggests that the part-span stall structure is more relevant to high-speed multistage compressors.

Experimental Study of Surge Precursors in a High-Speed Multistage Compressor

2012 ◽  
Author(s):  
Nicolas Courtiade ◽  
Xavier Ottavy
Keyword(s):  
High Frequency ◽  
High Speed ◽  
Rotation Speed ◽  
Critical Size ◽  
Rotating Stall ◽  
Characteristic Line ◽  
High Frequency Response ◽  
Stable Operating ◽  
Multistage Compressor ◽  
Operating Points

Pressure measurements using high frequency response sensors have been carried out on the 3rd rotor of the 3 1/2-stage high speed compressor CREATE (rotation speed: 11543 RPM, Rotor 1 tip speed: 313 m/s), over the complete characteristic line and during the surge transient. It seems that precursors to the instabilities occurring near surge are observable at stable operating points. Just before the surge, these precursors characterized as rotating disturbances transition smoothly to part span rotating stall cells, and bring the machine to surge as they grow and reach a critical size: this paper presents a detailed analysis of the phenomena of rotating stall and surge transient and shows that it is possible to develop an anti-surge active control system based on the early detection of the precursors.

scholarly journals Does the Opening of High-Speed Railway Lines Reduce the Carbon Intensity of China’s Resource-Based Cities?

Energies ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4648
Author(s):  
Zhipeng Tang ◽  
Ziao Mei ◽  
Jialing Zou
Keyword(s):  
High Speed ◽  
National Average ◽  
Carbon Intensity ◽  
Time Varying ◽  
Low Carbon ◽  
High Speed Railway ◽  
Different Types ◽  
Endogenous Selection ◽  
Mode Of Development ◽  
The Impact

The carbon intensity of China’s resource-based cities (RBCs) is much higher than the national average due to their relatively intensive mode of development. Low carbon transformation of RBCs is an important way to achieve the goal of reaching the carbon emissions peak in 2030. Based on the panel data from 116 RBCs in China from 2003 to 2018, this study takes the opening of high-speed railway (HSR) lines as a quasi-experiment, using a time-varying difference-in-difference (DID) model to empirically evaluate the impact of an HSR line on reducing the carbon intensity of RBCs. The results show that the opening of an HSR line can reduce the carbon intensity of RBCs, and this was still true after considering the possibility of problems with endogenous selection bias and after applying the relevant robustness tests. The opening of an HSR line is found to have a significant reducing effect on the carbon intensity of different types of RBC, and the decline in the carbon intensity of coal-based cities is found to be the greatest. Promoting migration of RBCs with HSR lines is found to be an effective intermediary way of reducing their carbon intensity.

scholarly journals The Reduction of Initial Reserves Using the Optimal Reinsurance Chains in Non-Life Insurance

Mathematics ◽  
2021 ◽  
Vol 9 (12) ◽  
pp. 1350
Author(s):  
Galina Horáková ◽  
František Slaninka ◽  
Zsolt Simonka
Keyword(s):  
Life Insurance ◽  
Continuous Time ◽  
Ruin Probability ◽  
Proportional Reinsurance ◽  
Insurance Risk ◽  
Optimal Reinsurance ◽  
Insurance Contracts ◽  
Time Period ◽  
Different Types ◽  
Capital Injections

The aim of the paper is to propose, and give an example of, a strategy for managing insurance risk in continuous time to protect a portfolio of non-life insurance contracts against unwelcome surplus fluctuations. The strategy combines the characteristics of the ruin probability and the values VaR and CVaR. It also proposes an approach for reducing the required initial reserves by means of capital injections when the surplus is tending towards negative values, which, if used, would protect a portfolio of insurance contracts against unwelcome fluctuations of that surplus. The proposed approach enables the insurer to analyse the surplus by developing a number of scenarios for the progress of the surplus for a given reinsurance protection over a particular time period. It allows one to observe the differences in the reduction of risk obtained with different types of reinsurance chains. In addition, one can compare the differences with the results obtained, using optimally chosen parameters for each type of proportional reinsurance making up the reinsurance chain.

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