Feature Correlation Velocimetry for Measuring Instantaneous Liquid Sheet Velocity

2017 ◽  
Vol 139 (9) ◽  
Author(s):  
K. S. Siddharth ◽  
Mahesh V. Panchagnula ◽  
T. John Tharakan
Keyword(s):  
Short Wavelength ◽  
High Speed ◽  
Cross Correlation ◽  
Ambient Air ◽  
Liquid Sheet ◽  
Bias Error ◽  
High Speed Camera ◽  
Model Predictions ◽  
Feature Correlation ◽  
Spatial Locations

We describe a novel nonintrusive velocimetry technique for measuring the instantaneous velocity field on a liquid sheet. Short wavelength corrugations are naturally formed on the surface of a liquid sheet when the sheet interacts with ambient air. This method, called feature correlation velocimetry (FCV), relies on cross-correlation of such short wavelength corrugations visualized on the liquid sheet surface when captured using a high-speed camera. An experimental setup was created for producing a liquid sheet of known thickness and velocity. After imaging the liquid sheet with a high-speed camera, cross-correlation was employed at various spatial locations on the liquid sheet. To examine the fidelity of the method, laser Doppler velocimetry (LDV) measurements were obtained for a range of flow rates at the same spatial locations and were compared with the FCV values. The FCV values were found to be consistently within 7% of the LDV readings with the FCV measurements being consistently less than those from the LDV. In order to examine the cause of the bias error, a theoretical model of the liquid sheet has been developed. Based on the model predictions, the bias error was observed to scale as U3/2, where U is the local instantaneous liquid sheet velocity. After correcting for this bias error, a good match was observed between the FCV and the LDV readings. As an application of the FCV method, the near-nozzle region of an annular sheet exiting a spray injector has been characterized.

Global and Local Measurements and Proper Orthogonal Decomposition of a Swirling Conical Liquid Sheet

2016 ◽  
Author(s):  
Pretam K. Choudhury ◽  
Ashkan Davanlou ◽  
Eduardo Castillo Orozco ◽  
Ranganathan Kumar
Keyword(s):  
Traveling Waves ◽  
High Speed ◽  
Cone Angle ◽  
Ambient Air ◽  
Liquid Sheet ◽  
Linear Instability ◽  
Image Processing Technique ◽  
High Speed Imaging ◽  
Global And Local ◽  
Proper Orthogonal

In this work, ultra-high speed imaging of conical liquid sheets allows for non-invasive measurements of both global and local features of a swirling conical liquid sheet. The breakup of the swirling conical liquid sheet is visualized and the interface tracked between the conical liquid sheet and the ambient air. The applied experimental technique and the image processing technique capture planar images that are capable of tracking the dynamic behavior of the conical liquid sheet. Cone angle is shown to increase up to a critical Weber Number. The film length is obtained by identifying singular points in the signal response of the radial fluctuations. The results of the proper orthogonal modes indicate the existence of traveling waves on the interface of the swirling conical liquid sheet. Wavelength measurements of the traveling waves are comparable with linear instability analysis.

scholarly journals Properties of Fuel Spray Obtained by Electrohydrodynamic Atomization

2017 ◽  
Author(s):  
Michel Daaboul ◽  
Nicolas Saba ◽  
Jihad Rishmany ◽  
Christophe Louste
Keyword(s):  
High Speed ◽  
Air Flow ◽  
Mesh Size ◽  
Liquid Sheet ◽  
High Speed Camera ◽  
Aircraft Engines ◽  
Shear Forces ◽  
Dielectric Barrier ◽  
Air Stream ◽  
Air Flow Velocity

Airblast atomization is com monly used to atomize fuel in aircraft engines. An annular liquid sheet is atomized bythe shear forces exerted by the co-flowing air stream. Nevertheless, this technique is less effe ctive in some specific cases, e.g. when the external air flow velocity is relatively low. Electrohydrodynamic (EHD) atomization can constitute a solution in these cases. It consists of applying an electric field between two electrodes and electricallycharging the passing carburant. This phenomenon will create instabilities within the liquid, provoking therefore its atomization. The main objective is therefore to electrically atomize a liquid sheet without the application of an external air flow like in airblast atomizers.This paper presents a novel actuator, based on dielectric barrier injection, used to induce instabilities within a plane liquid sheet of fuel similar to the annular sheet in aircraft engines. The behaviour of this atomizer was described in previous works. Several modes were observed, sometimes leading to a complete atomization, or just inducing instabilities and oscillating the liquid sheet. In the present study, only the cases where the liquid sheet is completely atomized are investigated. Images were reco rded with the help of a high speed camera. Primary atomization is only studied, secondaryatomization being neglected. The properties of the spray obtained by EHD atomization are investigated thoroughly, namely the breakup length, the mesh size, the drople t diameter, thedroplet count, etc.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.5018 

Numerical and Experimental Investigation on Spray Flux Distribution Produced by Liquid Sheet Atomization

2015 ◽  
Author(s):  
Chihiro Inoue ◽  
Atsushi Shimizu ◽  
Toshinori Watanabe ◽  
Takehiro Himeno ◽  
Seiji Uzawa
Keyword(s):  
Hybrid Method ◽  
Mass Flux ◽  
High Speed ◽  
Flux Distribution ◽  
Transient State ◽  
Ambient Air ◽  
Video Camera ◽  
Liquid Sheet ◽  
Spray Characteristics ◽  
High Speed Video Camera

Eulerian-Lagrangian hybrid method is implemented for the prediction of liquid atomization phenomena produced by 2 liquid water jets impinging by an angle of 40 deg. in quiet ambient air. To calculate the flow fields with liquid/gas interface, Eulerian analyses are conducted inside a fixed computational grid system. After the atomization occurs, every droplet is converted to a spherical particle. The motion of particles are tracked in Lagrangian form. For the validation of the developed Eulerian-Lagrangian hybrid method, flow visualization by using a high-speed video camera is carried out. To obtain quantitative values of spray characteristics, the liquid mass flux distribution in space is measured by utilizing a patternator. Numerical and experimental results of atomization process and mass flux distribution of spray show a similarity, and thus the developed method is evaluated that it has potential to predict spray characteristics produced by liquid sheet atomization. The developed numerical method can calculate unsteady spray distributions not only at the plane close to the injector but also far downstream. The spray mass flux distribution in the transient state, which is hard to measure by experiment, is demonstrated.

scholarly journals Tracking by Deblatting

2021 ◽  
Author(s):  
Denys Rozumnyi ◽  
Jan Kotera ◽  
Filip Šroubek ◽  
Jiří Matas
Keyword(s):  
High Speed ◽  
High Performance ◽  
Motion Blur ◽  
Velocity Estimation ◽  
High Speed Camera ◽  
Trajectory Function ◽  
Novel Approach ◽  
Blind Deblurring ◽  
Object Trajectories ◽  
Complex Trajectories

AbstractObjects moving at high speed along complex trajectories often appear in videos, especially videos of sports. Such objects travel a considerable distance during exposure time of a single frame, and therefore, their position in the frame is not well defined. They appear as semi-transparent streaks due to the motion blur and cannot be reliably tracked by general trackers. We propose a novel approach called Tracking by Deblatting based on the observation that motion blur is directly related to the intra-frame trajectory of an object. Blur is estimated by solving two intertwined inverse problems, blind deblurring and image matting, which we call deblatting. By postprocessing, non-causal Tracking by Deblatting estimates continuous, complete, and accurate object trajectories for the whole sequence. Tracked objects are precisely localized with higher temporal resolution than by conventional trackers. Energy minimization by dynamic programming is used to detect abrupt changes of motion, called bounces. High-order polynomials are then fitted to smooth trajectory segments between bounces. The output is a continuous trajectory function that assigns location for every real-valued time stamp from zero to the number of frames. The proposed algorithm was evaluated on a newly created dataset of videos from a high-speed camera using a novel Trajectory-IoU metric that generalizes the traditional Intersection over Union and measures the accuracy of the intra-frame trajectory. The proposed method outperforms the baselines both in recall and trajectory accuracy. Additionally, we show that from the trajectory function precise physical calculations are possible, such as radius, gravity, and sub-frame object velocity. Velocity estimation is compared to the high-speed camera measurements and radars. Results show high performance of the proposed method in terms of Trajectory-IoU, recall, and velocity estimation.

Influence of Main Swirler Vane Angle on the Ignition Performance of TeLESS-II Combustor

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Bo Wang ◽  
Chi Zhang ◽  
Yuzhen Lin ◽  
Xin Hui ◽  
Jibao Li
Keyword(s):  
High Speed ◽  
Inlet Temperature ◽  
Main Stage ◽  
Ignition Process ◽  
High Speed Camera ◽  
Fuel Distribution ◽  
Fuel Droplets ◽  
Planar Laser ◽  
Cfd Method ◽  
Vane Angle

In order to balance the low emission and wide stabilization for lean premixed prevaporized (LPP) combustion, the centrally staged layout is preferred in advanced aero-engine combustors. However, compared with the conventional combustor, it is more difficult for the centrally staged combustor to light up as the main stage air layer will prevent the pilot fuel droplets arriving at igniter tip. The goal of the present paper is to study the effect of the main stage air on the ignition of the centrally staged combustor. Two cases of the main swirler vane angle of the TeLESS-II combustor, 20 deg and 30 deg are researched. The ignition results at room inlet temperature and pressure show that the ignition performance of the 30 deg vane angle case is better than that of the 20 deg vane angle case. High-speed camera, planar laser induced fluorescence (PLIF), and computational fluids dynamics (CFD) are used to better understand the ignition results. The high-speed camera has recorded the ignition process, indicated that an initial kernel forms just adjacent the liner wall after the igniter is turned on, the kernel propagates along the radial direction to the combustor center and begins to grow into a big flame, and then it spreads to the exit of the pilot stage, and eventually stabilizes the flame. CFD of the cold flow field coupled with spray field is conducted. A verification of the CFD method has been applied with PLIF measurement, and the simulation results can qualitatively represent the experimental data in terms of fuel distribution. The CFD results show that the radial dimensions of the primary recirculation zone of the two cases are very similar, and the dominant cause of the different ignition results is the vapor distribution of the fuel. The concentration of kerosene vapor of the 30 deg vane angle case is much larger than that of the 20 deg vane angle case close to the igniter tip and along the propagation route of the kernel, therefore, the 30 deg vane angle case has a better ignition performance. For the consideration of the ignition performance, a larger main swirler vane angle of 30 deg is suggested for the better fuel distribution when designing a centrally staged combustor.

scholarly journals Leader-chasing behavior in negative artificial triggered lightning flashes

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Fukun Wang ◽  
Jianguo Wang ◽  
Li Cai ◽  
Rui Su ◽  
Wenhan Ding ◽  
...  
Keyword(s):  
High Speed ◽  
The Other ◽  
Lightning Flash ◽  
High Speed Camera ◽  
Return Stroke ◽  
Catching Up ◽  
Special Cases ◽  
Triggered Lightning

AbstractTwo special cases of dart leader propagation were observed by the high-speed camera in the leader/return stroke sequences of a classical triggered lightning flash and an altitude-triggered lightning flash, respectively. Different from most of the subsequent return strokes preceded by only one leader, the return stroke in each case was preceded by two leaders occurring successively and competing in the same channel, which herein is named leader-chasing behavior. In one case, the polarity of the latter leader was opposite to that of the former leader and these two combined together to form a new leader, which shared the same polarity with the former leader. In the other case, the latter leader shared the same polarity with the former leader and disappeared after catching up with the former leader. The propagation of the former leader in this case seems not to be significantly influenced by the existence of the latter leader.

scholarly journals Interactive Effects in Two-Droplets Combustion of RP-3 Kerosene under Sub-Atmospheric Pressure

Processes ◽  
2021 ◽  
Vol 9 (7) ◽  
pp. 1229
Author(s):  
Hongtao Zhang ◽  
Zhihua Wang ◽  
Yong He ◽  
Jie Huang ◽  
Kefa Cen
Keyword(s):  
Burning Rate ◽  
Atmospheric Pressure ◽  
High Speed ◽  
Ambient Pressure ◽  
Interactive Effects ◽  
Propagation Time ◽  
High Speed Camera ◽  
Single Droplet ◽  
Fuel Droplets ◽  
Spacing Distance

To improve our understanding of the interactive effects in combustion of binary multicomponent fuel droplets at sub-atmospheric pressure, combustion experiments were conducted on two fibre-supported RP-3 kerosene droplets at pressures from 0.2 to 1.0 bar. The burning life of the interactive droplets was recorded by a high-speed camera and a mirrorless camera. The results showed that the flame propagation time from burning droplet to unburned droplet was proportional to the normalised spacing distance between droplets and the ambient pressure. Meanwhile, the maximum normalised spacing distance from which the left droplet can be ignited has been investigated under different ambient pressure. The burning rate was evaluated and found to have the same trend as the single droplet combustion, which decreased with the reduction in the pressure. For every experiment, the interactive coefficient was less than one owing to the oxygen competition, except for the experiment at L/D0 = 2.5 and P = 1.0 bar. During the interactive combustion, puffing and microexplosion were found to have a significant impact on secondary atomization, ignition and extinction.

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