Investigation of rotating instability characteristics in an axial compressor with different tip clearances

It is believed that the rotating instability phenomenon originating in the compressor tip region is due to leakage flow, which is closely associated with the blade tip clearance. In this work, we have studied the correlation between the dynamic characteristics of blade tip flow and the size of tip clearance for a single-stage low-speed compressor rotor, so as to unveil the mechanism of rotating instability. The full-passage numerical simulations were carried out to obtain the variations in frequency, circumferential mode, and spatial flow field associated with rotating instability. The results of spatial mode decomposition with open clearance show the number of predominate instability modes identified are 25 and 30, respectively. By diminishing the blade tip clearance, all these unstable modes greatly diminished. The formation and propagation of the tip leakage vortex were described in detail to show the development of rotating instability. Two flow field reduced-order methods, proper orthogonal decomposition and dynamic mode decomposition, were used to analyze the flow field, energy proportion, and stability of related modes under different tip clearances. The results show that the first several modes with strong stability account for a large proportion of energy and make a major contribution to flow unsteadiness. The energy proportion and stability of rotating instability decrease as the tip clearance becomes smaller. The blade-passing frequency and its multiples emerge as the main components of the flow field.

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Rotating Instabilities in a Low-Speed Single Compressor Rotor Row with Varying Blade Tip Clearance

Energies ◽

10.3390/en14248369 ◽

2021 ◽

Vol 14 (24) ◽

pp. 8369

Author(s):

Xiangyi Chen ◽

Björn Koppe ◽

Martin Lange ◽

Wuli Chu ◽

Ronald Mailach

Keyword(s):

Chord Length ◽

Tip Clearance ◽

Dynamic Mode Decomposition ◽

Dynamic Mode ◽

Dynamic Feature ◽

Tip Leakage Flow ◽

Tip Leakage ◽

Compressor Rotor ◽

Blade Tip ◽

Blade Tip Clearance

When a compressor is throttled to the near stall point, rotating instability (RI) is often observed as significant increases of amplitude within a narrow frequency band which can be regarded as a pre-stall disturbance. In the current study, a single compressor rotor row with varying blade tip clearance (1.3%, 2.6% and 4.3% chord length) was numerically simulated using the zonal large eddy simulation model. The mesh with six blade passages was selected to capture the proper dynamic feature after being validated in comparison to the measured data, and the dynamic mode decomposition (DMD) approach was applied to the numerical temporal snapshots. In the experimental results, RIs are detected in the configurations with middle and large tip gaps (2.6% and 4.3% chord length), and the corresponding characterized frequencies are about 1/2 and 1/3 of the blade passing frequency, respectively. Simulations provide remarkable performance in capturing the measured flow features, and the DMD modes corresponding to the featured RI frequencies are successfully extracted and then visualized. The analysis of DMD results indicates that RI is essentially a presentation of the pressure wave propagating over the blade tip region. The tip leakage vortex stretches to the front part of the adjacent blade and consequently triggers the flow perturbations (waves). The wave influences the pressure distribution, which, in turn, determines the tip leakage flow and finally forms a loop.

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Analysis of transonic buffet using dynamic mode decomposition

Experiments in Fluids ◽

10.1007/s00348-020-03111-5 ◽

2021 ◽

Vol 62 (4) ◽

Author(s):

Antje Feldhusen-Hoffmann ◽

Christian Lagemann ◽

Simon Loosen ◽

Pascal Meysonnat ◽

Michael Klaas ◽

...

Keyword(s):

Shock Wave ◽

Flow Field ◽

Acoustic Waves ◽

Feedback Loop ◽

Measurement Data ◽

Dynamic Mode Decomposition ◽

Recirculation Region ◽

Dynamic Mode ◽

Mode Decomposition ◽

Transonic Buffet

AbstractThe buffet flow field around supercritical airfoils is dominated by self-sustained shock wave oscillations on the suction side of the wing. Theories assume that this unsteadiness is driven by a feedback loop of disturbances in the flow field downstream of the shock wave whose upstream propagating part is generated by acoustic waves. High-speed particle-image velocimetry measurements are performed to investigate this feedback loop in transonic buffet flow over a supercritical DRA 2303 airfoil. The freestream Mach number is $$M_{\infty } = 0.73$$ M ∞ = 0.73 , the angle of attack is $$\alpha = 3.5^{\circ }$$ α = 3 . 5 ∘ , and the chord-based Reynolds number is $${\mathrm{Re}}_{c} = 1.9\times 10^6$$ Re c = 1.9 × 10 6 . The obtained velocity fields are processed by sparsity-promoting dynamic mode decomposition to identify the dominant dynamic features contributing strongest to the buffet flow field. Two pronounced dynamic modes are found which confirm the presence of two main features of the proposed feedback loop. One mode is related to the shock wave oscillation frequency and its shape includes the movement of the shock wave and the coupled pulsation of the recirculation region downstream of the shock wave. The other pronounced mode represents the disturbances which form the downstream propagating part of the proposed feedback loop. The frequency of this mode corresponds to the frequency of the acoustic waves which are generated by these downstream traveling disturbances and which form the upstream propagating part of the proposed feedback loop. In this study, the post-processing, i.e., the DMD, is highlighted to substantiate the existence of this vortex mode. It is this vortex mode that via the Lamb vector excites the shock oscillations. The measurement data based DMD results confirm numerical findings, i.e., the dominant buffet and vortex modes are in good agreement with the feedback loop suggested by Lee. Graphic abstract

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Analysis of dynamic stall flow field of high bypass fan rotor based on airworthiness certification

Proceedings of the Institution of Mechanical Engineers Part G Journal of Aerospace Engineering ◽

10.1177/0954410020919281 ◽

2020 ◽

Vol 234 (11) ◽

pp. 1757-1769

Author(s):

Kai Zhang ◽

AJ Wang

Keyword(s):

Flow Field ◽

Unsteady Flow ◽

Field Data ◽

Decomposition Methods ◽

Modal Identification ◽

Dynamic Mode Decomposition ◽

Dynamic Mode ◽

Complex Flow ◽

Mode Decomposition ◽

Proper Orthogonal

In order to ensure flight safety, the stall test is one of the most important steps in the airworthiness certification phase of civil aircraft. The twisted-swept fan is one of the most important components of the high bypass ratio engine. The unsteady flow field of the fan rotor stall condition is obtained by numerical simulation. At the same time, the time series flow field data of the stall condition flow field is acquired. The modal analysis of the unsteady flow field at stall condition was performed using the dynamic mode decomposition and proper orthogonal decomposition methods. Through modal identification of a large number of unsteady flow field data, the eigenvalues and corresponding modal information about the unsteady flow field change process are obtained. Finally, the evolution process of the unsteady flow field of the fan rotor under stall condition is visually demonstrated, and the coherent structures of different scales in the complex flow field under stall condition are revealed.

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Dynamic mode decomposition for flow field and scalar field of coaxial jet with swirl

The Proceedings of Conference of Tokai Branch ◽

10.1299/jsmetokai.2017.66.423 ◽

2017 ◽

Vol 2017.66 (0) ◽

pp. 423

Author(s):

Yuta MAEKAWA ◽

Yasumasa ITO ◽

Yasuhiko SAKAI ◽

Koji IWANO ◽

Koji NAGATA ◽

...

Keyword(s):

Scalar Field ◽

Flow Field ◽

Dynamic Mode Decomposition ◽

Dynamic Mode ◽

Mode Decomposition

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High-Precision Extraction Method for Blade Tip-Timing Signal with Eddy Current Sensor

International Journal of Rotating Machinery ◽

10.1155/2020/8882858 ◽

2020 ◽

Vol 2020 ◽

pp. 1-13

Author(s):

Ji-wang Zhang ◽

Ke-qin Ding ◽

Guang Chen

Keyword(s):

Measurement Error ◽

Eddy Current ◽

Background Noise ◽

High Speed ◽

Ensemble Empirical Mode Decomposition ◽

Tip Clearance ◽

Mode Decomposition ◽

Blade Tip ◽

The Asymmetry ◽

Blade Tip Clearance

Online monitoring of high-speed rotating blades has always been a hot topic. Of the various methods, the blade tip timing (BTT) technique, based on eddy current sensors, is considered to be the most promising. However, BTT signals are easily influenced by various factors, which means that the accurate extraction of BTT signals remains a challenge. To try to solve this problem, the causes of measurement error were analyzed. The three main reasons for the error were established: the variation in blade tip clearance, the interference of background noise, and the asymmetry of the blade tip shape. Further, pertinent improvement methods were proposed, and a compensation method was proposed for the errors caused by the variation of tip clearance. A new denoising and shaping algorithm based on ensemble empirical mode decomposition (EEMD) was introduced for the errors caused by background noise. Additionally, an optimal installation position of the sensor was also proposed for the errors caused by the asymmetry of the blade tip shape. Finally, simulations and experiments were used to demonstrate the improved methodology. The results show that the measurement error on vibration amplitude and vibration frequency using the proposed method is less than 2.89% and 0.17%, respectively, which is much lower than the traditional method (24.44% and 0.39%, respectively).

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Design, Fabrication and Characterization of a Mechanical Micropump

Volume 1: Thermal Management ◽

10.1115/ipack2015-48017 ◽

2015 ◽

Author(s):

Bin Duan ◽

Tinghui Guo ◽

Minqing Luo ◽

Xiaobing Luo

Keyword(s):

Flow Field ◽

Flow Rate ◽

Pressure Head ◽

Tip Clearance ◽

Average Deviation ◽

Blade Tip ◽

Computational Fluid Dynamics Cfd ◽

Inlet Angle ◽

Blade Tip Clearance

In this paper, a centrifugal micropump was designed, fabricated and characterized. The proposed micropump is able to provide a 1.4L/min flow rate and a 75KPa pressure head at 24000 rpm with an oversize of 46mm wide and 69mm long. The hydrodynamic components were designed based on partial emission pump. Meanwhile, the geometric profiles of both impeller and volute were simplified for manufacturing. A computational fluid dynamics (CFD) analysis was performed to predict the effects of blade inlet angle and vane number on hydraulic performance. Experiments were conducted at 4 different rotational speeds to validate the numerical results. The results showed that the numerical simulation has a high accuracy to predict the micropump flow field with the overall average deviation less than 3%. As expected, the micropump prototype performed obvious partial emission pump features. In terms of the external characteristic, the pressure head at a given rotational speed decreased little with flow rate increasing. While, in the flow field, complex secondary flow was significant in the impeller passage, due to the joint action of the blade tip clearance leakage and axial vortex. Regression analysis and statistical evaluation showed that the flow nondimensional coefficients at different rotational speeds correlated well, indicating that classical similarity rules was still applicable to this micropump.

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