Evolution of the ejecta sheet from the impact of a drop with a deep pool

2011 ◽  
Vol 690 ◽  
pp. 5-15 ◽  
Author(s):  
L. V. Zhang ◽  
J. Toole ◽  
K. Fezzaa ◽  
R. D. Deegan
Keyword(s):  
Reynolds Number ◽  
Deep Layer ◽  
Power Laws ◽  
Single Drop ◽  
X Ray ◽  
X Ray Imaging ◽  
Time Position ◽  
High Reynolds ◽  
The Impact ◽  
Two Jets

AbstractWe used optical and X-ray imaging to observe the formation of jets from the impact of a single drop with a deep layer of the same liquid. For high Reynolds number there are two distinct jets: the thin, fast and early-emerging ejecta; and the slow, thick and late-emerging lamella. For low Reynolds number the two jets merge into a single continuous jet, the structure of which is determined by the distinct contributions of the lamella and the ejecta. We measured the emergence time, position and speed of the ejecta sheet, and find that these scale as power laws with the impact speed and the viscosity. We identified the origin of secondary droplets with the breakup of the lamella and the ejecta jets, and show that the size of the droplets is not a good indicator of their origin.

Drop impact into a deep pool: vortex shedding and jet formation

2015 ◽  
Vol 764 ◽  
Author(s):  
G. Agbaglah ◽  
M.-J. Thoraval ◽  
S. T. Thoroddsen ◽  
L. V. Zhang ◽  
K. Fezzaa ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
High Speed ◽  
Single Drop ◽  
Jet Formation ◽  
X Ray Imaging ◽  
Multiple Jets ◽  
Experimental Parameters ◽  
Single Jet ◽  
The Impact ◽  
Two Jets

AbstractOne of the simplest splashing scenarios results from the impact of a single drop on a deep pool. The traditional understanding of this process is that the impact generates an axisymmetric sheet-like jet that later breaks up into secondary droplets. Recently it was shown that even this simplest of scenarios is more complicated than expected because multiple jets can be generated from a single impact event and there are transitions in the multiplicity of jets as the experimental parameters are varied. Here, we use experiments and numerical simulations of a single drop impacting on a deep pool to examine the transition from impacts that produce a single jet to those that produce two jets. Using high-speed X-ray imaging methods we show that vortex separation within the drop leads to the formation of a second jet long after the formation of the ejecta sheet. Using numerical simulations we develop a phase diagram for this transition and show that the capillary number is the most appropriate order parameter for the transition.

Experimental study of single vs. two-close-frequency heating impact on confinement and losses dynamics in ECR Ion Sources plasmas by means of X-ray spectroscopy and imaging

2021 ◽  
Author(s):  
David Mascali ◽  
Eugenia Naselli ◽  
Richard Racz ◽  
Sándor Biri ◽  
Luigi Celona ◽  
...  
Keyword(s):  
Ion Source ◽  
Single Frequency ◽  
Specific Power ◽  
Imaging Method ◽  
X Ray ◽  
Plasma Chamber ◽  
X Ray Imaging ◽  
Close Frequency ◽  
The Impact ◽  
Frequency Heating

Abstract We hereby report the study of confinement and electron losses dynamics in the magnetic trap of an Electron Cyclotron Resonance Ion Source (ECRIS) using a special multi-diagnostic setup that has allowed the simultaneous collection of plasma radio-self-emission and X-ray images in the range 500 eV - 20 keV. Argon plasmas were generated in single and two close frequency heating (TCFH) modes. Evidences of turbulent regimes have been found: for stable and unstable configurations quantitative characterizations of the plasma radio self-emission have been carried out, then compared with local measurement of plasma energy content evaluated by X-ray imaging. This imaging method is the only one able to clearly separate X-ray radiation coming from the plasma from the one coming from the plasma chamber walls. X-ray imaging has been also supported and benchmarked by volumetric spectroscopy performed via SDD and HPGe detectors. The obtained results in terms of X-ray intensity signal coming from the plasma core and from the plasma chamber walls have permitted to estimate the average ratio: plasma vs. walls (i.e., plasma losses) as a function of input RF power and pumping wave frequency, showing an evident increase (above the experimental errors) of the intensity in the 2-20 keV energy range due to the plasma losses in case of unstable plasma. This ratio was well correlated with the strength of the instabilities, in single frequency heating (SFH) operation mode; in TCFH mode, under specific power balance conditions and frequency combinations, it was possible to damp the instabilities, thus the plasma losses were observed to decrease and a general reconfiguration of the spatial plasma structure occurred (the X-ray emission was more concentrated in the center of the plasma chamber). In the end, a simplified model has been used to simulate electron heating under different pumping frequencies, discussing the impact of velocity anisotropy vs. the onset of the instability, and the mechanism of particles diffusion in the velocity space in stable and unstable regimes.

scholarly journals Growth and instability of the liquid rim in the crown splash regime

2014 ◽  
Vol 752 ◽  
pp. 485-496 ◽  
Author(s):  
G. Agbaglah ◽  
R. D. Deegan
Keyword(s):  
Thin Film ◽  
High Speed ◽  
Unstable Mode ◽  
Linear Stability Theory ◽  
Scaling Relations ◽  
X Ray ◽  
X Ray Imaging ◽  
Secondary Droplets ◽  
The Impact ◽  
Good Agreement

AbstractWe study the formation, growth and disintegration of jets following the impact of a drop on a thin film of the same liquid for $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}\mathit{We}<1000$ and $\mathit{Re}<2000$ using a combination of numerical simulations and linear stability theory (Agbaglah, Josserand & Zaleski, Phys. Fluids, vol. 25, 2013, 022103). Our simulations faithfully capture this phenomena and are in good agreement with experimental profiles obtained from high-speed X-ray imaging. We obtain scaling relations from our simulations and use these as inputs to our stability analysis. The resulting predictions for the most unstable wavelength are in excellent agreement with experimental data. Our calculations show that the dominant destabilizing mechanism is a competition between capillarity and inertia but that deceleration of the rim provides an additional boost to growth. We also predict over the entire parameter range of our study the number and timescale for formation of secondary droplets formed during a splash, based on the assumption that the most unstable mode sets the droplet number.

Influence of Rotation on Heat Transfer in a Two-Pass Channel With Impingement Under High Reynolds Number

2015 ◽  
Author(s):  
Li Yang ◽  
Kartikeya Tyagi ◽  
Srinath Ekkad ◽  
Jing Ren
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Coriolis Force ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Internal Cooling ◽  
Channel Diameter ◽  
Turbine Cooling ◽  
High Reynolds ◽  
The Impact

Effect of rotation on turbine blade internal cooling is an important factor in gas turbine cooling systems. In order to minimize the impact from the Coriolis force, cooling structures with less rotation-dependent cooling effectiveness are needed. This study presents an impingement design in a two pass channel to reduce impact of rotational forces on non-uniform heat transfer behavior inside these complex channels. A Transient Liquid Crystal(TLC) method was employed to obtain local heat transfer coefficient measurements in a rotating environment. The channel Reynolds number based on the channel diameter ranges from 25,000 to 100,000. The rotation number ranges from 0 to 0.14. A series of computational simulations with the SST model were also utilized to understand the flow field behavior that impacts the heat transfer distributions on the walls. A 1-D correlation of zone averaged Nusselt number distribution was derived from the measurements. Results show that rotation reduces the heat transfer on both sides of the impingement, which is due to the Coriolis force and the pressure redistribution. The local change in the present study is about 25%. Rotation significantly enhances the heat transfer near the closed end because of the centrifugal force and the ‘pumping’ effect. Within the parameters of this test, the magnitude of enhancement is 25% to 75%. Compared to U-bended two pass channel, impingement channel has advantages in the upstream channel and the end region, but performance is not beneficial on the leading side of the downstream channel.

Life of a smooth liquid sheet

2002 ◽  
Vol 462 ◽  
pp. 307-340 ◽  
Author(s):  
CHRISTOPHE CLANET ◽  
EMMANUEL VILLERMAUX
Keyword(s):  
Reynolds Number ◽  
High Reynolds Number ◽  
Stationary Regime ◽  
Liquid Sheet ◽  
Liquid Sheets ◽  
Small Disc ◽  
High Reynolds ◽  
The Impact

We report on experiments with liquid sheets formed through the impact of a slender jet on a small disc at high Reynolds number. When the interaction with the surrounding air is negligible, the sheet spreads out radially and remains smooth. The study extends over the whole life of the sheet, considering the dynamics of its formation and destruction and paying special attention to the stationary regime, in which the transition from sheet to drops occurs.

Robust learning-based X-ray image denoising - potential pitfalls, their analysis and solutions

2021 ◽  
Author(s):  
Sai Gokul Hariharan ◽  
Christian Kaethner ◽  
Norbert Strobel ◽  
Markus Kowarschik ◽  
Rebecca Fahrig ◽  
...  
Keyword(s):  
Low Dose ◽  
Noise Model ◽  
X Ray ◽  
Robust Learning ◽  
Noise Characteristics ◽  
Imaging Model ◽  
X Ray Imaging ◽  
Dose Levels ◽  
The Impact

Abstract Purpose: Since guidance based on X-ray imaging is an integral part of interventional procedures, continuous efforts are taken towards reducing the exposure of patients and clinical staff to ionizing radiation. Even though a reduction in the X-ray dose may lower associated radiation risks, it is likely to impair the quality of the acquired images, potentially making it more difficult for physicians to carry out their procedures. Method: We present a robust learning-based denoising strategy involving model- based simulations of low-dose X-ray images during the training phase. The method also utilizes a data-driven normalization step - based on an X-ray imaging model - to stabilize the mixed signal-dependent noise associated with X-ray images. We thoroughly analyze the method's sensitivity to a mismatch in dose levels used for training and application. We also study the impact of differing noise models used when training for low and very low-dose X-ray images on the denoising results. Results: A quantitative and qualitative analysis based on acquired phantom and clinical data has shown that the proposed learning-based strategy is stable across different dose levels and yields excellent denoising results, if an accurate noise model is applied. We also found that there can be severe artifacts when the noise characteristics of the training images are significantly different from those in the actual images to be processed. This problem can be especially acute at very low dose levels. During a thorough analysis of our experimental results, we further discovered that viewing the results from the perspective of denoising via thresholding of sub-band co efficients can be very beneficial to get a better understanding of the proposed learning-based denoising strategy. Conclusion: The proposed learning-based denoising strategy provides scope for significant X-ray dose reduction without the loss of important image information if the characteristics of noise is accurately accounted for during the training ph

scholarly journals The making of a splash

2011 ◽  
Vol 690 ◽  
pp. 1-4 ◽  
Author(s):  
S. T. Thoroddsen
Keyword(s):  
Experimental Study ◽  
Full Description ◽  
Small Length ◽  
Length Scales ◽  
X Ray ◽  
X Ray Imaging ◽  
The Impact

AbstractThe splash resulting from the impact of a drop onto a pool is a particularly beautiful manifestation of a canonical problem, where a mass of fluid breaks up into smaller pieces. Despite over a century of experimental study, the splashing mechanics have eluded full description, the details often being obscured by the very rapid motions and small length scales involved. Zhang et al. (J. Fluid Mech., vol. 690, 2012, pp. 5–15) introduce a powerful new tool to the experimental arsenal, when they apply X-ray imaging to study the fine ejecta sheets which emerge during the earliest contact of the drop. Their images reveal hidden details and complex underlying dynamics, which will directly affect the size and velocity of the splashing droplets.

Effect of γ irradiation on the impact response of rigid polyurethane foam

2016 ◽  
Vol 36 (8) ◽  
pp. 829-835 ◽  
Author(s):  
Sagar Chandra ◽  
Sudhanshu Sharma ◽  
Hajrat Ali ◽  
Jotiram V. Mane ◽  
Yeshwant P. Naik ◽  
...  
Keyword(s):  
Polyurethane Foam ◽  
Phase Contrast ◽  
Testing Machine ◽  
Impact Response ◽  
Rigid Polyurethane Foam ◽  
Dynamic Tests ◽  
Γ Irradiation ◽  
X Ray ◽  
X Ray Imaging ◽  
The Impact

Abstract An experimental study to observe the change in impact response of rigid polyurethane foam due to γ irradiation is presented. The foam samples were irradiated using a 60Co based γ irradiator, γ Chamber 5000. Dynamic tests were performed on unirradiated and irradiated cubical foam specimens in a drop weight testing machine to characterize the mechanical properties. Structural characterization was performed using phase-contrast X-ray imaging and scanning electron microscopy (SEM). The results reveal a significant change in the dynamic response of polyurethane foam after irradiation due to change in structure. The response of foam gets stiffer in the initial linear phase, and densification (lockup) occurs well below the strains at which lockup occurs for an unirradiated foam. The ramifications of this study towards the application of polyurethane foam as an impact limiter in nuclear shipping casks are discussed.

scholarly journals Optimizing the energy bandwidth for transmission full-field X-ray microscopy experiments

2022 ◽  
Vol 29 (1) ◽  
Author(s):  
Malte Storm ◽  
Florian Döring ◽  
Shashidhara Marathe ◽  
Silvia Cipiccia ◽  
Christian David ◽  
...  
Keyword(s):  
Limited Effect ◽  
Double Crystal ◽  
Full Field ◽  
X Ray ◽  
Double Crystal Monochromator ◽  
X Ray Imaging ◽  
Order Of Magnitude ◽  
Chromatic Aberrations ◽  
The Impact ◽  
Theoretical Considerations

Full-field transmission X-ray microscopy (TXM) is a very potent high-resolution X-ray imaging technique. However, it is challenging to achieve fast acquisitions because of the limited efficiency of the optics. Using a broader energy bandwidth, for example using a multilayer monochromator, directly increases the flux in the experiment. The advantage of more counts needs to be weighed against a deterioration in achievable resolution because focusing optics show chromatic aberrations. This study presents theoretical considerations of how much the resolution is affected by an increase in bandwidth as well as measurements at different energy bandwidths (ΔE/E = 0.013%, 0.27%, 0.63%) and the impact on achievable resolution. It is shown that using a multilayer monochromator instead of a classical silicon double-crystal monochromator can increase the flux by an order of magnitude with only a limited effect on the resolution.

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