Dynamic mode decomposition for the stability analysis of the Molten Salt Fast Reactor core

Abstract Complex unsteady phenomena can appear in turbomachinery components and result in the self-sustained oscillatory motion of the fluid as found in aeronautical engines or rocket turbopumps for example. The origin of these oscillations often results from the complex coupling between flow non linearities and structure motion generating major risks for the operation of the engine and even undermining its components. For instance, in turbines, the internal components that are most liable to vibrate are the blades and discs. In this context, it is critical to understand the effect of the vibrating components on the flow stability in rotor/stator cavities. In order to address this problem, an academic rotor/stator cavity subject to periodic wall oscillations is investigated in the current paper where the frequency of the vibrations are imposed and correspond to the previously identified unstable fluid modes inside the cavity. The objective is to understand the behavior of the flow when subject to a periodic forcing imposed by the rotor motion. To do so, predictive numerical strategies are established based on Large Eddy Simulation (LES) in conjunction to a global stability analysis which seem to be a promising method to capture flow instabilities. Focus is here brought to the underlying pressure fluctuations found inside the cavity using spectral analysis complemented with the global stability analysis, demonstrating that such tools can address forced flow problems. More specifically and for all simulations, the results of the global stability analysis are compared to a Dynamic Mode Decomposition (DMD) of LES predictions by reconstructing the corresponding modes through a spatio-temporal approach showing that the new fluid limit cycles present modes that shift or completely disappear compared to the unforced case, the forcing mechanism altering the stability of the entire system.

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Comprehensive Combustion Stability Analysis Using Dynamic Mode Decomposition

Energy & Fuels ◽

10.1021/acs.energyfuels.8b02433 ◽

2018 ◽

Vol 32 (9) ◽

pp. 9990-9996 ◽

Cited By ~ 6

Author(s):

Rajavasanth Rajasegar ◽

Jeongan Choi ◽

Brendan McGann ◽

Anna Oldani ◽

Tonghun Lee ◽

...

Keyword(s):

Stability Analysis ◽

Dynamic Mode Decomposition ◽

Combustion Stability ◽

Dynamic Mode ◽

Mode Decomposition

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Global linear stability analysis of jets in cross-flow

Journal of Fluid Mechanics ◽

10.1017/jfm.2017.489 ◽

2017 ◽

Vol 828 ◽

pp. 812-836 ◽

Cited By ~ 6

Author(s):

Marc A. Regan ◽

Krishnan Mahesh

Keyword(s):

Stability Analysis ◽

Shear Layer ◽

Linear Stability ◽

Linear Stability Analysis ◽

Velocity Ratio ◽

Cross Flow ◽

Dynamic Mode Decomposition ◽

Dynamic Mode ◽

Mode Decomposition ◽

Implicitly Restarted Arnoldi

The stability of low-speed jets in cross-flow (JICF) is studied using tri-global linear stability analysis (GLSA). Simulations are performed at a Reynolds number of 2000, based on the jet exit diameter and the average velocity. A time stepper method is used in conjunction with the implicitly restarted Arnoldi iteration method. GLSA results are shown to capture the complex upstream shear-layer instabilities. The Strouhal numbers from GLSA match upstream shear-layer vertical velocity spectra and dynamic mode decomposition from simulation (Iyer & Mahesh, J. Fluid Mech., vol. 790, 2016, pp. 275–307) and experiment (Megerian et al., J. Fluid Mech., vol. 593, 2007, pp. 93–129). Additionally, the GLSA results are shown to be consistent with the transition from absolute to convective instability that the upstream shear layer of JICFs undergoes between $R=2$ to $R=4$ observed by Megerian et al. (J. Fluid Mech., vol. 593, 2007, pp. 93–129), where $R=\overline{v}_{jet}/u_{\infty }$ is the jet to cross-flow velocity ratio. The upstream shear-layer instability is shown to dominate when $R=2$, whereas downstream shear-layer instabilities are shown to dominate when $R=4$.

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Stability analysis for flow past a cylinder via lattice Boltzmann method and dynamic mode decomposition

Chinese Physics B ◽

10.1088/1674-1056/24/6/064701 ◽

2015 ◽

Vol 24 (6) ◽

pp. 064701 ◽

Cited By ~ 1

Author(s):

Wei Zhang ◽

Yong Wang ◽

Yue-Hong Qian

Keyword(s):

Stability Analysis ◽

Lattice Boltzmann Method ◽

Lattice Boltzmann ◽

Dynamic Mode Decomposition ◽

Dynamic Mode ◽

Flow Past ◽

Mode Decomposition ◽

Flow Past A Cylinder ◽

Boltzmann Method

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Local and Global Stability Analysis of an Academic Rotor/Stator Cavity

Volume 2A: Turbomachinery ◽

10.1115/gt2018-75008 ◽

2018 ◽

Author(s):

Matthieu Queguineur ◽

Thibault Bridel-Bertomeu ◽

Laurent Gicquel ◽

Gabriel Staffelbach

Keyword(s):

Structural Integrity ◽

Flow Instability ◽

Dynamic Mode Decomposition ◽

Dynamic Mode ◽

Cavity Flows ◽

Space Applications ◽

Sustained Oscillations ◽

Mode Decomposition ◽

Large Eddy ◽

The Stability

Self-sustained oscillations of rotor/stator cavity flows are well known to industry. This unsteady phenomenon can be very dangerous and jeopardize the structural integrity of aeronautical engines by damaging turbomachinery components or turbopumps in the context of space applications. Today, the origin of such flow instability and resulting limit-cycle is not well understood and still difficult to predict numerically. In order to have more insight of this phenomenon dynamic, an academic rotor/stator cavity is investigated in the present paper. The main motivation of this study is to highlight the benefit of conjunct numerical strategies relying on Large Eddy Simulations (LES) and flow stability analyses to understand driving instability mechanisms. More specifically, results of a local and global methods are devised and compared to a Dynamic Mode Decomposition (DMD) of LES predictions. Good agreements between the stability methods studied and the present features in the LES limitcycle are found. On this basis, a sensitivity and receptivity analysis of the flow is realized to point the origin of the two most unstable modes: i.e the position within the flow where the problem issues.

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Experimental Measurement of In-Plane Rolling Nonpneumatic Tire Vibrations Using High-Speed Imaging

Tire Science and Technology ◽

10.2346/tire.18.470101 ◽

2019 ◽

Vol 47 (3) ◽

pp. 196-210

Author(s):

Meghashyam Panyam ◽

Beshah Ayalew ◽

Timothy Rhyne ◽

Steve Cron ◽

John Adcox

Keyword(s):

High Speed ◽

Image Correlation ◽

Dynamic Mode Decomposition ◽

Dynamic Mode ◽

High Speed Imaging ◽

Correlation Algorithm ◽

Mode Decomposition ◽

Series Of Experiments ◽

Plane Deformations ◽

Dominant Frequencies

ABSTRACT This article presents a novel experimental technique for measuring in-plane deformations and vibration modes of a rotating nonpneumatic tire subjected to obstacle impacts. The tire was mounted on a modified quarter-car test rig, which was built around one of the drums of a 500-horse power chassis dynamometer at Clemson University's International Center for Automotive Research. A series of experiments were conducted using a high-speed camera to capture the event of the rotating tire coming into contact with a cleat attached to the surface of the drum. The resulting video was processed using a two-dimensional digital image correlation algorithm to obtain in-plane radial and tangential deformation fields of the tire. The dynamic mode decomposition algorithm was implemented on the deformation fields to extract the dominant frequencies that were excited in the tire upon contact with the cleat. It was observed that the deformations and the modal frequencies estimated using this method were within a reasonable range of expected values. In general, the results indicate that the method used in this study can be a useful tool in measuring in-plane deformations of rolling tires without the need for additional sensors and wiring.

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