Study on Flow Characteristics in Volute of Centrifugal Pump Based on Dynamic Mode Decomposition

To investigate the unsteady flow characteristics and their influence mechanism in the volute of centrifugal pump, the Reynolds time-averaged N-S equation, RNG k-ε turbulence model, and structured grid technique are used to numerically analyze the transient flow-field characteristics inside the centrifugal pump volute. Based on the quantified parameters of flow field in the volute of centrifugal pump, the velocity mode contours and oscillation characteristics of the mid-span section of the volute of centrifugal pump are obtained by dynamic mode decomposition (DMD) for the nominal and low flow-rate condition. The research shows that the first-order average flow mode extracted by DMD is the dominant flow structure in the flow field of the volute. The second-order and third-order modes are the most important oscillation modes causing unsteady flow in the volute, and the characteristic frequency of the two modes is consistent with the blade passing frequency and the 2x blade passing frequency obtained by the fast Fourier transform (FFT). By reconstructing the internal flow field of the volute with the blade passing frequency for the nominal flow-rate condition, the periodic variation of the unsteady flow structure in the volute under this frequency is visually reproduced, which provides some ideas for the study of the unsteady structure in the internal flow field of centrifugal pumps.

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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 Analysis on the Unsteady Flow Field in the Tip Region for an Axial Compressor Rotor

2020 IEEE 2nd International Conference on Civil Aviation Safety and Information Technology (ICCASIT ◽

10.1109/iccasit50869.2020.9368797 ◽

2020 ◽

Author(s):

Liu Zhenxiong ◽

Hu Bo

Keyword(s):

Flow Field ◽

Unsteady Flow ◽

Decomposition Analysis ◽

Axial Compressor ◽

Dynamic Mode Decomposition ◽

Dynamic Mode ◽

Compressor Rotor ◽

Mode Decomposition

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Numerical Analysis of the Flow around Two Square Cylinders in a Tandem Arrangement with Different Spacing Ratios Based on POD and DMD Methods

Processes ◽

10.3390/pr8080903 ◽

2020 ◽

Vol 8 (8) ◽

pp. 903

Author(s):

Feng Wang ◽

Xiaodong Zheng ◽

Jianming Hao ◽

Hua Bai

Keyword(s):

Flow Field ◽

Flow Characteristics ◽

Dynamic Mode Decomposition ◽

Dynamic Mode ◽

Square Cylinder ◽

Main Mode ◽

Square Cylinders ◽

Mode Decomposition ◽

The Difference ◽

Proper Orthogonal

To more clearly understand the changes in flow characteristics around two square cylinders with different spacing ratios, the main mode of the flow field was extracted by using the Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) methods. The changes in the main mode of the flow field at different spacing ratios and the difference of the time series were analyzed and compared. This processing can separate the mixed information in the flow field and obtain the dominant modes in the flow field. These main modes can clearly reflect the dominant flow characteristics in the flow field. The analysis results show that when L/D = 2, the flow field structure is consistent with the flow field around a single square cylinder. When L/D = 2.5–3.5, the vortex shedding from upstream cylinders combines with the vortex near the downstream cylinders. This mutual coupling causes a significant change in the drag coefficient value of the downstream cylinder. When L/D = 4, the main vortex from the upstream cylinder can be completely shed, which means that the upstream and downstream square cylinder vortices start to become independent. The main focus of this paper is to use the advantages of POD and DMD to obtain several modes with higher energy in the flow field. Furthermore, it can be considered that these main modes can fully reflect the flow characteristics of the flow field.

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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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Dynamic mode decomposition analysis of the flow characteristics in a centrifugal compressor with vaned diffuser

Proceedings of the Institution of Mechanical Engineers Part A Journal of Power and Energy ◽

10.1177/0957650920913464 ◽

2020 ◽

pp. 095765092091346

Author(s):

Xiaojian Li ◽

Yijia Zhao ◽

Zhengxian Liu ◽

Ming Zhao

Keyword(s):

Flow Rate ◽

Centrifugal Compressor ◽

Flow Characteristics ◽

Leading Edge ◽

Dynamic Mode Decomposition ◽

Flow Structures ◽

Dynamic Mode ◽

Tip Leakage ◽

Mode Decomposition ◽

Dynamic Structures

To understand the flow dynamic characteristics of a centrifugal compressor, the dynamic mode decomposition (DMD) method is introduced to decompose the complex three-dimensional flow field. Three operating conditions, peak efficiency (OP1), peak pressure ratio (OP2), and small mass flow rate (near stall, OP3) conditions, are analyzed. First, the physical interpretations of main dynamic modes at OP1 are identified. As a result, the dynamic structures captured by DMD method are closely associated with the flow characteristics. In detail, the BPF/2BPF (blade passing frequency) corresponds to the impeller–diffuser interaction, the rotor frequency (RF) represents the tip leakage flow (TLF) from leading edge, and the 4RF is related to the interaction among the downstream TLF, the secondary flow, and the wake vortex. Then, the evolution of the dynamic structures is discussed when the compressor mass flow rate consistently declines. In the impeller, the tip leakage vortex near leading edge gradually breaks down due to the high backpressure, resulting in multi-frequency vortices. The broken vortices further propagate downstream along streamwise direction and then interact with the flow structures of 4RF. As a result, the 8RF mode can be observed in the whole impeller, this mode is transformed from upstream RF and 4RF modes, respectively. On the other hand, the broken vortices show broadband peak spectrum, which is correlated to the stall inception. Therefore, the sudden boost of energy ratio of 14RF mode could be regarded as a type of earlier signal for compressor instability. In the diffuser, the flow structures are affected by the perturbation from the impeller. However, the flow in diffuser is more stable than that in impeller at OP1–OP3, since the leading modes are stable patterns of BPF/2BPF.

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