Re-Oriented POD for Feature Extraction From Time Resolved Reacting Flow Datasets

2019 ◽  
Author(s):  
H. Ek ◽  
W. Proscia ◽  
T. Lieuwen ◽  
B. Emerson
Keyword(s):  
High Speed ◽  
Stereoscopic Particle Image Velocimetry ◽  
Phase Portraits ◽  
Quality Data ◽  
Reacting Flow ◽  
Axial Distance ◽  
Swirl Combustor ◽  
Time Resolved ◽  
Convective Structures ◽  
Types Of Information

Abstract Recent improvements in computational and experimental combustion have led to an increased availability of high-fidelity data sets. With the surge of high-quality data, the reduction and analysis of this information become a key aspect in improving our understanding of highly dynamic, reacting flow fields. This work utilizes simultaneous high-speed stereoscopic particle image velocimetry (sPIV), OH-planar laser induced fluorescence (PLIF) and fuel-PLIF measurements in a high pressure, liquid fueled swirl combustor. This work extends one of the most commonly used modal analysis techniques, proper orthogonal decomposition (POD). Instead of decomposing the data as a series of time coefficients and spatial modes, which is the result of snap-shot POD, the data is re-oriented such that the coefficients are a function of the transverse distance and the modes are a function of axial distance and time. This reoriented POD method, referred to as spatio-temporal POD, allows us to directly target convective flow structures while still extracting the same types of information as from snap-shot POD. Additionally, since the modes contain temporal information, phase speeds associated with the convective structures can easily be calculated from the phase portraits. This paper presents results of this analysis, allowing us to track the growth of coherent structures, their phase speeds, and their subsequent decay.

scholarly journals Impact of a Centrebody on the Unsteady Flow Dynamics of A Swirl Nozzle: Intermittency of PVC Oscillations

2021 ◽  
Author(s):  
Saarthak Gupta ◽  
Santosh Hemchandra ◽  
Masayasu Shimura ◽  
Santosh Shanbhogue ◽  
Ahmed Ghoniem
Keyword(s):  
Nozzle Exit ◽  
High Speed ◽  
Vortex Breakdown ◽  
Flow Dynamics ◽  
Reacting Flow ◽  
Exit Plane ◽  
Swirl Combustor ◽  
Time Resolved ◽  
Precessing Vortex Core ◽  
The Impact

Abstract The precessing vortex core (PVC) is a self-excited flow oscillation state occurring in swirl nozzles. This is caused by the presence of a marginally unstable hydrodynamic helical mode that induces precession of the vortex breakdown bubble (VBB) around the flow axis. The PVC can impact emissions and thermoacoustic stability characteristics of combustors in various ways, as several prior studies have shown. In this paper, we examine the impact of centrebody diameter (Dc) on the PVC in a non-reacting flow in a single nozzle swirl combustor. Time resolved high speed stereoscopic PIV (sPIV) measurements are performed for combinations of two swirl numbers, S = 0.67 and 1.17 and Dc = 9.5 mm, 4.73 mm and 0 (i.e. no centrebody). The bulk flow velocity at the nozzle exit plane is kept constant as Ub = 8 m/s for all cases (Re ∼ 20,000). The centrebody end face lies in the nozzle exit plane. A new modal decomposition technique based on wavelet filtering and proper orthogonal decomposition (POD) provides insight into flow dynamics in terms of global modes extracted from the data. The results show that without a centrebody, a coherent PVC is present in the flow as expected. The introduction of a centrebody makes the PVC oscillations intermittent. These results suggest two routes to intermittency as follows. For S = 0.67, the vortex breakdown bubble (VBB) and centrebody wake recirculation zone (CWRZ) regions are nominally distinct. Intermittent separation and merger due to turbulence result in PVC oscillations due to the de-stabilization of the hydrodynamic VBB precession mode of the flow. In the S = 1.17 case, the time averaged VBB position causes it to engulf the centrebody. In this case, the emergence of intermittent PVC oscillations is a result of the response of the flow to broadband stochastic forcing imposed on the time averaged vorticity field due to turbulence.

scholarly journals Experimental Study of Transient Mechanisms of Bi-Stable Flame Shape Transitions in a Swirl Combustor

2017 ◽  
Author(s):  
Michael Stöhr ◽  
Kilian Oberleithner ◽  
Moritz Sieber ◽  
Zhiyao Yin ◽  
Wolfgang Meier
Keyword(s):  
Gas Turbines ◽  
High Speed ◽  
Hydrodynamic Instability ◽  
Mean Flow ◽  
Swirl Combustor ◽  
Time Resolved ◽  
Precessing Vortex Core ◽  
Amplification Process ◽  
Flame Shape ◽  
Shape Transitions

Sudden changes of flame shape are an undesired, yet poorly understood feature of swirl combustors used in gas turbines. The present work studies flame shape transition mechanisms of a bistable turbulent swirl flame in a gas turbine model combustor, which alternates intermittently between an attached V-form and a lifted M-form. Time-resolved velocity fields and 2D flame structures were measured simultaneously using high-speed stereo-PIV and OH-PLIF at 10 kHz. The data analysis is performed using two novel methods that are well adapted to the study of transient flame shape transitions: Firstly, the linear stability analysis (LSA) of a time-varying mean flow and secondly the recently proposed spectral proper orthogonal decomposition (SPOD). The results show that the transitions are governed by two types of instability, namely a hydrodynamic instability in the form of a precessing vortex core (PVC) and a thermoacoustic (TA) instability. The LSA shows that the V-M transition implies the transient formation of a PVC as the result of a self-amplification process. The V-M transition, on the other hand, is induced by the appearance of a TA instability that suppresses the PVC and thereby modifies the flow field such that the flame re-attaches at the nozzle. In summary these results provide novel insights into the complex interactions of TA and hydrodynamic instabilities that govern the shape of turbulent swirl-stabilized flames.

scholarly journals The wake of hovering flight in bats

2015 ◽  
Vol 12 (109) ◽  
pp. 20150357 ◽  
Author(s):  
Jonas Håkansson ◽  
Anders Hedenström ◽  
York Winter ◽  
L. Christoffer Johansson
Keyword(s):  
High Speed ◽  
Time History ◽  
Energy Conversion Efficiency ◽  
Flapping Flight ◽  
Stereoscopic Particle Image Velocimetry ◽  
Hovering Flight ◽  
Time Resolved ◽  
Nectar Feeding ◽  
Weight Support ◽  
Mechanical Power Output

Hovering means stationary flight at zero net forward speed, which can be achieved by animals through muscle powered flapping flight. Small bats capable of hovering typically do so with a downstroke in an inclined stroke plane, and with an aerodynamically active outer wing during the upstroke. The magnitude and time history of aerodynamic forces should be reflected by vorticity shed into the wake. We thus expect hovering bats to generate a characteristic wake, but this has until now never been studied. Here we trained nectar-feeding bats, Leptonycteris yerbabuenae , to hover at a feeder and using time-resolved stereoscopic particle image velocimetry in conjunction with high-speed kinematic analysis we show that hovering nectar-feeding bats produce a series of bilateral stacked vortex loops. Vortex visualizations suggest that the downstroke produces the majority of the weight support, but that the upstroke contributes positively to the lift production. However, the relative contributions from downstroke and upstroke could not be determined on the basis of the wake, because wake elements from down- and upstroke mix and interact. We also use a modified actuator disc model to estimate lift force, power and flap efficiency. Based on our quantitative wake-induced velocities, the model accounts for weight support well (108%). Estimates of aerodynamic efficiency suggest hovering flight is less efficient than forward flapping flight, while the overall energy conversion efficiency (mechanical power output/metabolic power) was estimated at 13%.

scholarly journals Experimental Study of Transient Mechanisms of Bistable Flame Shape Transitions in a Swirl Combustor

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Michael Stöhr ◽  
Kilian Oberleithner ◽  
Moritz Sieber ◽  
Zhiyao Yin ◽  
Wolfgang Meier
Keyword(s):  
Gas Turbines ◽  
High Speed ◽  
Hydrodynamic Instability ◽  
Mean Flow ◽  
Swirl Combustor ◽  
Time Resolved ◽  
Precessing Vortex Core ◽  
Planar Laser ◽  
Flame Shape ◽  
Shape Transitions

Sudden changes of flame shape are an undesired, yet poorly understood feature of swirl combustors used in gas turbines. The present work studies flame shape transition mechanisms of a bistable turbulent swirl flame in a gas turbine model combustor, which alternates intermittently between an attached V-form and a lifted M-form. Time-resolved velocity fields and two-dimensional flame structures were measured simultaneously using high-speed stereo-particle image velocimetry (PIV) and planar laser-induced fluorescence of OH (OH-PLIF) at 10 kHz. The data analysis is performed using two novel methods that are well adapted to the study of transient flame shape transitions: First, the linear stability analysis (LSA) of a time-varying mean flow and second, the recently proposed spectral proper orthogonal decomposition (SPOD). The results show that the transitions are governed by two types of instability, namely a hydrodynamic instability in the form of a precessing vortex core (PVC) and a thermoacoustic (TA) instability. The LSA shows that the V-M transition implies the transient formation of a PVC as the result of a self-amplification process. The V-M transition, on the other hand, is induced by the appearance of a TA instability that suppresses the PVC and thereby modifies the flowfield such that the flame re-attaches at the nozzle. In summary, these results provide novel insights into the complex interactions of TA and hydrodynamic instabilities that govern the shape of turbulent swirl-stabilized flames.

scholarly journals Impact of a Centrebody On the Unsteady Flow Dynamics of a Swirl Nozzle: Intermittency of PVC Oscillations

2021 ◽  
Author(s):  
Saarthak Gupta ◽  
Santosh Shanbhogue ◽  
Masayasu Shimura ◽  
Ahmed F. Ghoniem ◽  
Santosh Hemchandra
Keyword(s):  
High Speed ◽  
Vortex Breakdown ◽  
Flow Dynamics ◽  
Axial Position ◽  
Intermittent Flow ◽  
Reacting Flow ◽  
Hydrodynamic Mode ◽  
Time Resolved ◽  
Precessing Vortex Core ◽  
The Impact

Abstract The precessing vortex core (PVC) is a self-excited flow oscillation state occurring in swirl nozzles. This is caused by the presence of a marginally unstable hydrodynamic mode that induces precession of the vortex breakdown bubble (VBB) around the flow axis. We examine the impact of a centrebody on PVC dynamics in a non-reacting flow in a swirl nozzle combustor. Time resolved high speed stereoscopic PIV measurements are performed for two swirl numbers, S=0.67 and 1.17 and three centrebody diameters, 9.5mm, 4.73mm and 0 (i.e. no centrebody). The bulk flow velocity at the nozzle exit is kept constant as Ub=8m/s for all cases (Re~20,000). The data is analyzed using a new modal decomposition technique that combines the wavelet transform and proper orthogonal decomposition (WPOD). This gives insight into globally intermittent flow dynamics. A coherent PVC is present in the flow when there is no centrebody. Introducing a centrebody makes the PVC oscillations intermittent. The WPOD results show two qualitatively different intermittent behaviours at S=0.67 and 1.17. For S=0.67, the axial position of the VBB suggests that turbulence destabilizes the PVC mode by causing intermittent separation of the VBB and centrebody wake, resulting in PVC oscillations. For S=1.17, the VBB engulfs the centrebody and stabilizes the PVC mode. Therefore, in this case, PVC oscillations appear to be the flow response to broadband stochastic forcing of the time averaged flow by turbulence.

Multiple phase transitions investigated by high-speed TEM

1990 ◽  
Vol 48 (4) ◽  
pp. 550-551
Author(s):  
Oleg Bostanjoglo ◽  
Peter Thomsen-Schmidt
Keyword(s):  
Phase Transitions ◽  
High Speed ◽  
Short Exposure ◽  
Semiconductor Film ◽  
Time Resolved ◽  
Short Exposure Time ◽  
Multiple Phase ◽  
Model Substance ◽  
History Of ◽  
Electron Image

Thin GexTe1-x (x = 0.15-0.8) were studied as a model substance of a composite semiconductor film, in addition being of interest for optical storage material. Two complementary modes of time-resolved TEM were used to trace the phase transitions, induced by an attached Q-switched (50 ns FWHM) and frequency doubled (532 nm) Nd:YAG laser. The laser radiation was focused onto the specimen within the TEM to a 20 μm spot (FWHM). Discrete intermediate states were visualized by short-exposure time doubleframe imaging /1,2/. The full history of a transformation was gained by tracking the electron image intensity with photomultiplier and storage oscilloscopes (space/time resolution 100 nm/3 ns) /3/. In order to avoid radiation damage by the probing electron beam to detector and specimen, the beam is pulsed in this continuous mode of time-resolved TEM,too.Short events ( <2 μs) are followed by illuminating with an extended single electron pulse (fig. 1c)

Structural dynamics of P-type ATPase ion pumps

2019 ◽  
Vol 47 (5) ◽  
pp. 1247-1257 ◽  
Author(s):  
Mateusz Dyla ◽  
Sara Basse Hansen ◽  
Poul Nissen ◽  
Magnus Kjaergaard
Keyword(s):  
Structural Dynamics ◽  
Single Molecule ◽  
New Technologies ◽  
Atp Hydrolysis ◽  
Resonance Energy Transfer ◽  
Resonance Energy ◽  
Time Resolved ◽  
Dynamics Simulations ◽  
Types Of Information ◽  
P Type

Abstract P-type ATPases transport ions across biological membranes against concentration gradients and are essential for all cells. They use the energy from ATP hydrolysis to propel large intramolecular movements, which drive vectorial transport of ions. Tight coordination of the motions of the pump is required to couple the two spatially distant processes of ion binding and ATP hydrolysis. Here, we review our current understanding of the structural dynamics of P-type ATPases, focusing primarily on Ca2+ pumps. We integrate different types of information that report on structural dynamics, primarily time-resolved fluorescence experiments including single-molecule Förster resonance energy transfer and molecular dynamics simulations, and interpret them in the framework provided by the numerous crystal structures of sarco/endoplasmic reticulum Ca2+-ATPase. We discuss the challenges in characterizing the dynamics of membrane pumps, and the likely impact of new technologies on the field.

scholarly journals A 1.55-to-32-Gb/s Four-Lane Transmitter with 3-Tap Feed Forward Equalizer and Shared PLL in 28-nm CMOS

Electronics ◽  
2021 ◽  
Vol 10 (16) ◽  
pp. 1873
Author(s):  
Chen Cai ◽  
Xuqiang Zheng ◽  
Yong Chen ◽  
Danyu Wu ◽  
Jian Luan ◽  
...  
Keyword(s):  
Data Transmission ◽  
High Speed ◽  
Data Rate ◽  
Quality Data ◽  
Cmos Process ◽  
Voltage Controlled Oscillator ◽  
Feed Forward ◽  
Fully Integrated ◽  
Output Driver ◽  
28 Nm

This paper presents a fully integrated physical layer (PHY) transmitter (TX) suiting for multiple industrial protocols and compatible with different protocol versions. Targeting a wide operating range, the LC-based phase-locked loop (PLL) with a dual voltage-controlled oscillator (VCO) was integrated to provide the low jitter clock. Each lane with a configurable serialization scheme was adapted to adjust the data rate flexibly. To achieve high-speed data transmission, several bandwidth-extended techniques were introduced, and an optimized output driver with a 3-tap feed-forward equalizer (FFE) was proposed to accomplish high-quality data transmission and equalization. The TX prototype was fabricated in a 28-nm CMOS process, and a single-lane TX only occupied an active area of 0.048 mm2. The shared PLL and clock distribution circuits occupied an area of 0.54 mm2. The proposed PLL can support a tuning range that covers 6.2 to 16 GHz. Each lane's data rate ranged from 1.55 to 32 Gb/s, and the energy efficiency is 1.89 pJ/bit/lane at a 32-Gb/s data rate and can tune an equalization up to 10 dB.

scholarly journals Dual-shot dynamics and ultimate frequency of all-optical magnetic recording on GdFeCo

2021 ◽  
Vol 10 (1) ◽  
Author(s):  
Sicong Wang ◽  
Chen Wei ◽  
Yuanhua Feng ◽  
Hongkun Cao ◽  
Wenzhe Li ◽  
...  
Keyword(s):  
Magnetization Reversal ◽  
Energy Efficient ◽  
High Speed ◽  
Data Transfer ◽  
Laser Pulses ◽  
Time Resolved ◽  
All Optical ◽  
Fs Laser ◽  
High Speed Data ◽  
Natural Way

AbstractAlthough photonics presents the fastest and most energy-efficient method of data transfer, magnetism still offers the cheapest and most natural way to store data. The ultrafast and energy-efficient optical control of magnetism is presently a missing technological link that prevents us from reaching the next evolution in information processing. The discovery of all-optical magnetization reversal in GdFeCo with the help of 100 fs laser pulses has further aroused intense interest in this compelling problem. Although the applicability of this approach to high-speed data processing depends vitally on the maximum repetition rate of the switching, the latter remains virtually unknown. Here we experimentally unveil the ultimate frequency of repetitive all-optical magnetization reversal through time-resolved studies of the dual-shot magnetization dynamics in Gd27Fe63.87Co9.13. Varying the intensities of the shots and the shot-to-shot separation, we reveal the conditions for ultrafast writing and the fastest possible restoration of magnetic bits. It is shown that although magnetic writing launched by the first shot is completed after 100 ps, a reliable rewriting of the bit by the second shot requires separating the shots by at least 300 ps. Using two shots partially overlapping in space and minimally separated by 300 ps, we demonstrate an approach for GHz magnetic writing that can be scaled down to sizes below the diffraction limit.

Detector commissioning and development for PETRA-III

2010 ◽  
Vol 1 (SRMS-7) ◽  
Author(s):  
David Pennicard ◽  
Heinz Graafsma ◽  
Michael Lohmann
Keyword(s):  
High Speed ◽  
Materials Science ◽  
Dynamic Range ◽  
Photon Counting ◽  
High Energy ◽  
X Rays ◽  
Silicon Detectors ◽  
Time Resolved ◽  
Wide Range ◽  
Synchrotron Light

The new synchrotron light source PETRA-III produced its first beam last year. The extremely high brilliance of PETRA-III and the large energy range of many of its beamlines make it useful for a wide range of experiments, particularly in materials science. The detectors at PETRA-III will need to meet several requirements, such as operation across a wide dynamic range, high-speed readout and good quantum efficiency even at high photon energies. PETRA-III beamlines with lower photon energies will typically be equipped with photon-counting silicon detectors for two-dimensional detection and silicon drift detectors for spectroscopy and higher-energy beamlines will use scintillators coupled to cameras or photomultiplier tubes. Longer-term developments include ‘high-Z’ semiconductors for detecting high-energy X-rays, photon-counting readout chips with smaller pixels and higher frame rates and pixellated avalanche photodiodes for time-resolved experiments.

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