scholarly journals Combined Diagnostic Analysis of Dynamic Combustion Characteristics in a Scramjet Engine

Energies ◽  
2020 ◽  
Vol 13 (15) ◽  
pp. 4029
Author(s):  
Seung-Min Jeong ◽  
Jeong-Yeol Choi
Keyword(s):  
Flame Structure ◽  
Injection Pressure ◽  
Combustion Characteristics ◽  
Dynamic Mode Decomposition ◽  
Mode Analysis ◽  
Dynamic Mode ◽  
Diagnostic Analysis ◽  
Detached Eddy Simulation ◽  
Scramjet Engine ◽  
Dynamic Combustion

In this work, the dynamic combustion characteristics in a scramjet engine were investigated using three diagnostic data analysis methods: DMD (Dynamic Mode Decomposition), STFT (Short-Time Fourier Transform), and CEMA (Chemical Explosive Mode Analysis). The data for the analyses were obtained through a 2D numerical experiment using a DDES (Delayed Detached Eddy Simulation) turbulence model, the UCSD (University of California at San Diego) hydrogen/oxygen chemical reaction mechanism, and high-resolution schemes. The STFT was able to detect that oscillations above 50 kHz identified as dominant in FFT results were not the dominant frequencies in a channel-type combustor. In the analysis using DMD, it was confirmed that the critical point that induced a complete change of mixing characteristics existed between an injection pressure of 0.75 MPa and 1.0 MPa. A combined diagnostic analysis that included a CEMA was performed to investigate the dynamic combustion characteristics. The differences in the reaction steps forming the flame structure under each combustor condition were identified, and, through this, it was confirmed that the pressure distribution upstream of the combustor dominated the dynamic combustion characteristics of this scramjet engine. From these processes, it was confirmed that the combined analysis method used in this paper is an effective approach to diagnose the combustion characteristics of a supersonic combustor.

A comparative study of DES type methods for mild flow separation prediction on a NACA0015 airfoil

2017 ◽  
Vol 27 (11) ◽  
pp. 2528-2543 ◽  
Author(s):  
Liang Wang ◽  
Liying Li ◽  
Song Fu
Keyword(s):  
Separated Flow ◽  
Dynamic Mode Decomposition ◽  
Dynamic Mode ◽  
Detached Eddy Simulation ◽  
Reynolds Stresses ◽  
Content Type ◽  
Eddy Simulation ◽  
Mode Decomposition ◽  
Flow Phenomena ◽  
Critical Dynamic

Purpose The purpose of this paper is to numerically investigate the mildly separated flow phenomena on a near-stall NACA0015 airfoil, by using Detached-Eddy Simulation (DES) type methods. It includes a comparison of different choices of underlying Reynolds-averaged Navier–Stokes model as well as subgrid-scale stress model in Large-Eddy simulation mode. Design/methodology/approach The unsteady flow phenomena are simulated by using delayed DES (DDES) and improved DDES (IDDES) methods, with an in-house computational fluid dynamics solver. Characteristic frequencies in different flow regions are extracted using fast Fourier transform. Dynamic mode decomposition (DMD) method is applied to uncover the critical dynamic modes. Findings Among all the DES type methods investigated in this paper, only the Spalart–Allmaras-based IDDES captures the separation point as measured in the experiments. The classical vortex-shedding and the shear-layer flapping modes for airfoil flows with shallow separation are also found from the IDDES results by using DMD. Originality/value The value of this paper lies in the assessment of five different DES-type models through the detailed investigation of the Reynolds stresses as well as the separation and reattachment.

Investigation of the stability of transverse hydrogen injection combustion caused by plate vibration using the dynamic mode decomposition method

2021 ◽  
pp. 095441002110301
Author(s):  
Kun Ye ◽  
Liuzhen Qin ◽  
Zhenghao Feng ◽  
Zhengyin Ye
Keyword(s):  
Shock Wave ◽  
Growth Rate ◽  
Flame Structure ◽  
Wave Structure ◽  
Dynamic Mode Decomposition ◽  
Reflected Shock Wave ◽  
Dynamic Mode ◽  
Plate Vibration ◽  
Shock Wave Structure ◽  
Reflected Shock

This article investigated the stability of transverse hydrogen injection combustion caused by the plate vibration. The finite-rate method is used to simulate the combustion. The unsteady flow field in the unstable phase of combustion is extracted. The unstable mode of the shock wave structure and the flame structure during the stage of combustion instability, the spatial and temporal characteristics of the dominant modes, as well as their stability are analyzed based on the dynamic mode decomposition (DMD) method. The results indicate that, according to the sequence of energy, the extracted first six orders modes of the shock wave structure and the flame structure have relatively low frequency with a negative growth rate and small numerical value, which presents a trend of weak convergence. The characteristics of the dominant structure of DMD modes show that the plate vibration has great effects on the reflected shock wave structure near the plate and on the upper wall surface, as well as the flame structure near the plate. According to the sequence of the mode energy and the growth rate, respectively, the extracted first six orders modes have relatively high frequency. Simultaneously, the structures of the modes extracted by the sequence of mode energy are more regular, while those extracted by the sequence of growth rate are more disorderly. The unstable shock wave structure is mainly manifested by the reflected shock wave in the vibration region and the shock wave structure reflected by the upper wall surface. The unstable flame structure is mainly concentrated near the vibration region and downstream areas.

scholarly journals Robust Mode Analysis

Mathematics ◽  
2021 ◽  
Vol 9 (9) ◽  
pp. 1057
Author(s):  
Gemunu H. Gunaratne ◽  
Sukesh Roy
Keyword(s):  
Experimental Data ◽  
Bluff Body ◽  
Numerical Solutions ◽  
Dynamic Mode Decomposition ◽  
Mode Analysis ◽  
Jet Flows ◽  
Dynamic Mode ◽  
Reacting Flow ◽  
Model Free ◽  
Wide Range

In this paper, we introduce a model-free algorithm, robust mode analysis (RMA), to extract primary constituents in a fluid or reacting flow directly from high-frequency, high-resolution experimental data. It is expected to be particularly useful in studying strongly driven flows, where nonlinearities can induce chaotic and irregular dynamics. The lack of precise governing equations and the absence of symmetries or other simplifying constraints in realistic configurations preclude the derivation of analytical solutions for these systems; the presence of flow structures over a wide range of scales handicaps finding their numerical solutions. Thus, the need for direct analysis of experimental data is reinforced. RMA is predicated on the assumption that primary flow constituents are common in multiple, nominally identical realizations of an experiment. Their search relies on the identification of common dynamic modes in the experiments, the commonality established via proximity of the eigenvalues and eigenfunctions. Robust flow constituents are then constructed by combining common dynamic modes that flow at the same rate. We illustrate RMA using reacting flows behind a symmetric bluff body. Two robust constituents, whose signatures resemble symmetric and von Karman vortex shedding, are identified. It is shown how RMA can be implemented via extended dynamic mode decomposition in flow configurations interrogated with a small number of time-series. This approach may prove useful in analyzing changes in flow patterns in engines and propulsion systems equipped with sturdy arrays of pressure transducers or thermocouples. Finally, an analysis of high Reynolds number jet flows suggests that tests of statistical characterizations in turbulent flows may best be done using non-robust components of the flow.

Comparison of hydrodynamic and acoustic pressure on automotive front side window

2021 ◽  
pp. 095440702110343
Author(s):  
Haidong Yuan ◽  
Zhigang Yang
Keyword(s):  
Large Scale ◽  
Acoustic Pressure ◽  
Hydrodynamic Pressure ◽  
Dynamic Mode Decomposition ◽  
Diffusion Field ◽  
Dynamic Mode ◽  
Detached Eddy Simulation ◽  
Front Side ◽  
Side Window ◽  
Eddy Simulation

The unsteady flow in the front side window region of the vehicle can generate hydrodynamic and acoustic pressure on the front side window, which can influence the interior sound field. The hydrodynamic pressure on the front side window was achieved by the incompressible wall-modeled large-scale eddy simulation (WMLES) or improved delayed detached eddy simulation (IDDES), and the hybrid computational aeroacoustics (CAA) method based on acoustic perturbation equations (APE) was employed to achieve the acoustic pressure on the front side window. The numerical results of both hydrodynamic and acoustic pressure ware validated by the wind tunnel experiment, especially the corrected force analysis technique (CFAT) is employed to validate the acoustic pressure. The comparison of hydrodynamic and acoustic pressure on the front side window was performed by the Dynamic Mode Decomposition (DMD). Results show that the hydrodynamic pressure regionally distributes on the front side window and most energy concentrates on area interacted with the side mirror wake, while the acoustic pressure distributes uniformly on the front side window acting as a diffusion field and the energy disperses in frequency region.

scholarly journals Deciphering Exhaled Aerosol Fingerprints for Early Diagnosis and Personalized Therapeutics of Obstructive Respiratory Diseases in Small Airways

2021 ◽  
Vol 2 (3) ◽  
pp. 94-117
Author(s):  
Xiuhua April Si ◽  
Jinxiang Xi
Keyword(s):  
Feature Extraction ◽  
Respiratory Diseases ◽  
Airway Remodeling ◽  
Dynamic Mode Decomposition ◽  
Mode Analysis ◽  
Support Vector ◽  
Dynamic Mode ◽  
Small Airways ◽  
Early Stages ◽  
Breath Testing

Respiratory diseases often show no apparent symptoms at their early stages and are usually diagnosed when permanent damages have been made to the lungs. A major site of lung pathogenesis is the small airways, which make it highly challenging to detect using current techniques due to the diseases’ location (inaccessibility to biopsy) and size (below normal CT/MRI resolution). In this review, we present a new method for lung disease detection and treatment in small airways based on exhaled aerosols, whose patterns are uniquely related to the health of the lungs. Proof-of-concept studies are first presented in idealized lung geometries. We subsequently describe the recent developments in feature extraction and classification of the exhaled aerosol images to establish the relationship between the images and the underlying airway remodeling. Different feature extraction algorithms (aerosol density, fractal dimension, principal mode analysis, and dynamic mode decomposition) and machine learning approaches (support vector machine, random forest, and convolutional neural network) are elaborated upon. Finally, future studies and frequent questions related to clinical applications of the proposed aerosol breath testing are discussed from the authors’ perspective. The proposed breath testing has clinical advantages over conventional approaches, such as easy-to-perform, non-invasive, providing real-time feedback, and is promising in detecting symptomless lung diseases at early stages.

scholarly journals Effects of Bogies on the Wake Flow of a High-Speed Train

2019 ◽  
Vol 9 (4) ◽  
pp. 759 ◽  
Author(s):  
Wen Liu ◽  
Dilong Guo ◽  
Zijian Zhang ◽  
Dawei Chen ◽  
Guowei Yang
Keyword(s):  
High Speed ◽  
Wake Flow ◽  
Dynamic Mode Decomposition ◽  
Dynamic Mode ◽  
High Speed Train ◽  
Detached Eddy Simulation ◽  
Wake Flows ◽  
Delayed Detached Eddy Simulation ◽  
Mode Decomposition ◽  
Unsteady Characteristics

The wake region of high-speed trains is an area of complex turbulent flow characterized by the periodic generation and shedding of vortices, which causes discomfort to passengers and affects the stability and safety of the train. In this study, the unsteady characteristics of the wake flows of three 1:1 scale China Railway High-Speed 380A (CRH380A) high-speed train models with different degrees of simplification were numerically investigated using the improved delayed detached eddy simulation (IDDES) method. Analyses of the aerodynamic forces, train-induced slipstream, and turbulent kinetic energy (TKE) were conducted to determine the effects of the bogies on the wake flow of the high-speed train. It was found that the existence of bogies on the bottom of the train, especially the last bogie, not only enhanced the wake flow but also introduced large perturbances into the wake flow. Moreover, the generation and evolution of the vortices in the wake flows were determined by analyzing the instantaneous flow fields and coherent flow structures that were obtained by the dynamic mode decomposition (DMD) method. The results showed that a pair of large, counter-rotating streamwise vortices in the real model of the high-speed train was generated by the cowcatcher and their intensity was significantly enhanced by perturbances that were introduced by the bogies on the bottom of the train.

Low-Memory Reduced-Order Modelling With Dynamic Mode Decomposition Applied on Unsteady Wheel Aerodynamics

2017 ◽  
Author(s):  
Marco Kiewat ◽  
Lukas Haag ◽  
Thomas Indinger ◽  
Vincent Zander
Keyword(s):  
Rotation Frequency ◽  
Dynamic Mode Decomposition ◽  
Dynamic Mode ◽  
Test Case ◽  
Detached Eddy Simulation ◽  
Weighting Method ◽  
Reduced Order ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Mode Decomposition

Wheel aerodynamics has a major impact on the overall aerodynamic performance of a vehicle. Different vortex excitation mechanisms are responsible for the induced forces on the geometry. Due to the high degree of complexity, it is difficult to gain further insight into the vortex structures at the rotating wheel. Therefore, wheel aerodynamics is usually investigated using temporally averaged flow fields. This work presents an approach to apply a recently introduced low-memory variant of Dynamic Mode Decomposition (DMD), namely Streaming Total DMD (STDMD), to investigate temporally resolved simulations in greater detail. The performance of STDMD is shown to be comparable to conventional DMD for a rotating generic closed wheel simulation test case. By creating a Reduced-Order Model (ROM) using a comparably small amount of DMD modes, the amount of complexity in the flow field can be drastically reduced. Orthonormal basis compression, amplitude ordering and a newly introduced amplitude weighting method are analyzed for creating a suitable ROM of DMD modes. A combination of compression and ordering by eigenvalue-weighted amplitude is concluded to be best suited and applied to the Delayed Detached Eddy Simulation (DDES) of the rotating generic closed wheel and a production vehicle rim wheel. The most dominant flow structures are captured at frequencies between 18Hz and 176Hz. Leading modes for both geometries are found close to the wheel rotation frequency and multiples of that frequency. The modes are identified as recirculation modes and vortex shedding.

Investigation of the coherent structures in flow behind a backward-facing step

2016 ◽  
Vol 26 (3/4) ◽  
pp. 1050-1068 ◽  
Author(s):  
Ruyun Hu ◽  
Liang Wang ◽  
Song Fu
Keyword(s):  
Coherent Structure ◽  
Pressure Fluctuations ◽  
Excitation Frequency ◽  
Dynamic Mode Decomposition ◽  
Effective Control ◽  
Dynamic Mode ◽  
Detached Eddy Simulation ◽  
Backward Facing Step ◽  
Recirculation Bubble ◽  
Content Type

Purpose – The purpose of this paper is to investigate the characteristic flow structures behind a backward-facing step. With better understanding of unsteady features, effective control practice with harmonic actuation is illustrated. Design/methodology/approach – The present study employs Improved Delayed Detached Eddy Simulation to resolve flow turbulence with a finite-volume approach on structured grid mesh. The coherent structure is displayed through temporal- and spatial-evolution of pressure fluctuations. Characteristic frequencies in different flow regions are extracted using fast Fourier transform. Dynamic mode decomposition method is applied to uncover the critical dynamic modes. Findings – The time- and spanwise-averaged quantities agree well with experimental data. It is observed that two distinct modes exist: shear layer mode and shedding mode. The former is related to Kelvin-Helmholtz instability mechanism, vortex pairing and step mode with non-dimensional frequency, Sth,st at around 0.2. The latter is of multi-scale, with a typical coherent structure shedding frequency, Sth,st at 0.074. Step mode interacts with shedding mode in the reattachment region, resulting in the low-frequency characteristics. Originality/value – An optimal excitation frequency to reduce recirculation bubble length is obtained at about Sth,st =0.2 with an explanation.

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

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.

Sign in / Sign up

Export Citation Format

Share Document