Stable–streamlined and helical cavities following the impact of Leidenfrost spheres

2017 ◽  
Vol 823 ◽  
pp. 716-754 ◽  
Author(s):  
M. M. Mansoor ◽  
I. U. Vakarelski ◽  
J. O. Marston ◽  
T. T. Truscott ◽  
S. T. Thoroddsen
Keyword(s):  
Experimental Study ◽  
Contact Line ◽  
Room Temperature ◽  
Reynolds Numbers ◽  
Physical Contact ◽  
Friction Drag ◽  
Drag Effect ◽  
Wall Effects ◽  
The Impact ◽  
Stable Cavity

We report results from an experimental study on the formation of stable–streamlined and helical cavity wakes following the free-surface impact of Leidenfrost spheres. Similar to the observations of Mansoor et al. (J. Fluid Mech., vol. 743, 2014, pp. 295–326), we show that acoustic ripples form along the interface of elongated cavities entrained in the presence of wall effects as soon as the primary cavity pinch-off takes place. The crests of these ripples can act as favourable points for closure, producing multiple acoustic pinch-offs, which are found to occur in an acoustic pinch-off cascade. We show that these ripples pacify with time in the absence of physical contact between the sphere and the liquid, leading to extremely smooth cavity wake profiles. More importantly, the downward-facing jet at the apex of the cavity is continually suppressed due to a skin-friction drag effect at the colliding cavity-wall junction, which ultimately produces a stable–streamlined cavity wake. This streamlined configuration is found to experience drag coefficients an order of a magnitude lower than those acting on room-temperature spheres. A striking observation is the formation of helical cavities which occur for impact Reynolds numbers $Re_{0}\gtrsim 1.4\times 10^{5}$ and are characterized by multiple interfacial ridges, stemming from and rotating synchronously about an evident contact line around the sphere equator. The contact line is shown to result from the degeneration of Kelvin–Helmholtz billows into turbulence which are observed forming along the liquid–vapour interface around the bottom hemisphere of the sphere. Using sphere trajectory measurements, we show that this helical cavity wake configuration has 40 %–55 % smaller force coefficients than those obtained in the formation of stable cavity wakes.

Experimental Study on the Response Characteristics of Oilcans under High-Velocity Fragment Impact

2012 ◽  
Vol 510 ◽  
pp. 500-506
Author(s):  
Chang Hai Chen ◽  
Xi Zhu ◽  
Hai Liang Hou ◽  
Li Jun Zhang ◽  
Ting Tang
Keyword(s):  
Experimental Study ◽  
High Velocity ◽  
High Speed ◽  
Room Temperature ◽  
Experimental Results ◽  
Fuel Oil ◽  
High Speed Camera ◽  
Response Characteristics ◽  
Fuel Oils ◽  
The Impact

To explore the deflagration possibility of the warship cabin filled with fuel oil under impact of high-speed fragments in the condition of room temperature, experiments were carried out employing the small aluminium oilcans filled with fuel oil. Response processes of the oilcans were observed with the help of a high-speed camera. The disintegration as well as flying scattering of the oilcans were analyzed. The reasons for atomization of the fuel oils were presented. Finally, the deflagration possibility of warship oil cabin was analyzed. Results show that the pressure inside the oilcan is quite great under the impact of the high-speed fragment, which makes the oilcan disintegration and flying scattering. Simultaneously, fuel oils inside the oilcans are atomized quickly followed by ejected in front and back directions. Under the same condition as in present tests, deflagration will not occur for fuel oils used by warships. Experimental results will provide valuable references for the deflagration analysis of warship fuel oil cabins subjected to the impact of high-velocity fragments.

An experimental study on the impact of double bending at room temperature on the performance of YBCO coated conductors

2021 ◽  
pp. 1-1
Author(s):  
Marco Breschi ◽  
Andrea Musso ◽  
Pier Luigi Ribani ◽  
Alberto Amaduzzi ◽  
Therese Chabert ◽  
...  
Keyword(s):  
Experimental Study ◽  
Room Temperature ◽  
Coated Conductors ◽  
The Impact ◽  
Ybco Coated Conductors

Cavity formation by the impact of Leidenfrost spheres

2012 ◽  
Vol 699 ◽  
pp. 465-488 ◽  
Author(s):  
J. O. Marston ◽  
I. U. Vakarelski ◽  
S. T. Thoroddsen
Keyword(s):  
Free Surface ◽  
Contact Line ◽  
Liquid Pool ◽  
Physical Contact ◽  
Cavity Formation ◽  
Cavity Structure ◽  
Leidenfrost Effect ◽  
Contact Line Pinning ◽  
The Impact ◽  
Initial Entry

AbstractWe report observations of cavity formation and subsequent collapse when a heated sphere impacts onto a liquid pool. When the sphere temperature is much greater than the boiling point of the liquid, we observe an inverted Leidenfrost effect where the sphere is encompassed by a vapour layer that prevents physical contact with the liquid. This creates the ultimate non-wetting scenario during sphere penetration through a free surface, producing very smooth cavity walls. In some cases during initial entry, however, the liquid contacts the sphere at the equator, leading to the formation of a dual cavity structure. For cold sphere impacts, where a contact line is observed, we reveal details of the contact line pinning, which initially forms a sawtooth pattern. We also observe surface waves on the cavity interface for cold spheres. We compare our experimental results to previous studies of cavity dynamics and, in particular, the influence of hydrophobicity on the entry of the sphere.

The Impact of a Vortex Induced by a Baffle on the Turbulent Structure

2008 ◽  
Author(s):  
Shivani T. Gajusingh ◽  
Nasiruddin Shaikh ◽  
Kamran Siddiqui
Keyword(s):  
Experimental Study ◽  
Reynolds Stress ◽  
Reynolds Numbers ◽  
Velocity Fields ◽  
Turbulent Structure ◽  
Turbulent Regime ◽  
Two Dimensional ◽  
Square Channel ◽  
Order Of Magnitude ◽  
The Impact

An experimental study was conducted to investigate the impact of a rectangular baffle inside a square channel. PIV was used to measure the two-dimensional velocity fields. The measurements were conducted for two Reynolds numbers (Reτ) equal to 134 and 152 in the turbulent regime. Results show that the turbulent intensities and the Reynolds Stress are enhanced by more than an order of magnitude in the presence of a baffle. Significant enhancement was observed in a region up to two times the baffle height.

Experimental study of thermohydraulic characteristics and irreversibility analysis of novel axial corrugated tube with spring tape inserts

2020 ◽  
Vol 92 (3) ◽  
pp. 30901
Author(s):  
Suvanjan Bhattacharyya ◽  
Debraj Sarkar ◽  
Ulavathi Shettar Mahabaleshwar ◽  
Manoj K. Soni ◽  
M. Mohanraj
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Thermal Performance ◽  
Working Fluid ◽  
The Novel ◽  
Heat Exchanger Tube ◽  
Heat Transfer Augmentation ◽  
Corrugated Tube ◽  
The Impact ◽  
Exchanger Tube

The current study experimentally investigates the heat transfer augmentation on the novel axial corrugated heat exchanger tube in which the spring tape is introduced. Air (Pr = 0.707) is used as a working fluid. In order to augment the thermohydraulic performance, a corrugated tube with inserts is offered. The experimental study is further extended by varying the important parameters like spring ratio (y = 1.5, 2.0, 2.5) and Reynolds number (Re = 10 000–52 000). The angular pitch between the two neighboring corrugations and the angle of the corrugation is kept constant through the experiments at β = 1200 and α = 600 respectively, while two different corrugations heights (h) are analyzed. While increasing the corrugation height and decreasing the spring ratio, the impact of the swirling effect improves the thermal performance of the system. The maximum thermal performance is obtained when the corrugation height is h = 0.2 and spring ratio y = 1.5. Eventually, correlations for predicting friction factor (f) and Nusselt number (Nu) are developed.

MAGNETIC FIELD IMPACT UPON TRIBOTECHNICAL CHARACTERISTICS OF PERMANENT CONNECTIONS IN RELATION TO FRICTION SHOCK ABSORBERS

2020 ◽  
Vol 2020 (10) ◽  
pp. 4-11
Author(s):  
Victor Tikhomirov ◽  
Aleksandr Gorlenko ◽  
Stanislav Volohov ◽  
Mikhail Izmerov
Keyword(s):  
Magnetic Field ◽  
Friction Factor ◽  
Physical Contact ◽  
Active Centers ◽  
Press Fit ◽  
Electro Magnetic Field ◽  
Investigation Methods ◽  
Electro Magnetic ◽  
The Impact ◽  
The Magnetic Field

The work purpose is the investigation of magnetic field impact upon properties of friction steel surfaces at fit stripping with tightness through manifested effects and their wear visually observed. On the spots of a real contact the magnetic field increases active centers, their amount and saturation with the time of dislocation outlet, and has an influence upon tribo-mating. The external electro-magnetic field promotes the increase of the number of active centers at the expense of dislocations outlet on the contact surface, and the increase of a physical contact area results in friction tie strengthening and growth of a friction factor. By the example of friction pairs of a spentonly unit in the suspension of coach cars there is given a substantiation of actuality and possibility for the creation of technical devices with the controlled factor of friction and the stability of effects achieved is also confirmed experimentally. Investigation methods: the fulfillment of laboratory physical experiments on the laboratory plant developed and patented on bush-rod samples inserted with the fit and tightness. The results of investigations and novelty: the impact of the magnetic field upon the value of a stripping force of a press fit with the guaranteed tightness is defined. Conclusion: there is a possibility to control a friction factor through the magnetic field impact upon a friction contact.

“New Normal”: Analisis Penerimaan Menggunakan Balance Score Card

2020 ◽  
Vol 3 (2) ◽  
pp. 396-402
Author(s):  
Maria Florentina Rumba ◽  
Margaretha P.N Rozady ◽  
Theresia W. Mado
Keyword(s):  
Higher Education ◽  
Higher Education Institutions ◽  
Normal Phase ◽  
Physical Contact ◽  
New Normal ◽  
Face To Face ◽  
Balance Score Card ◽  
Score Card ◽  
Pros And Cons ◽  
The Impact

Abstrak: Kebiasaan manusia berubah karena adanya wabah COVID-19, hal ini berpengaruh ketika manusia masuk ke dalam fase new normal. New normal diartikan sebagai keadaan yang tidak biasa dilakukan sebelumnya, yang kemudian dijadikan sebagai standar atau kebiasaan baru yang mesti dilakukan manusia untuk dirinya sendiri maupun untuk bersosialisasi dengan orang lain. Kebiasaan baru ini pun menimbulkan pro dan kontra seiring dengan dampak yang timbul. Lembaga pendidikan tinggi merupakan salah satu yang merasakan dampak penerapan new normal. Perkuliahan yang selama ini dilakukan secara online/daring, akan kembali dilakukan secara luring/tatap muka, dengan tetap menerapkan protokol COVID-19 seperti mengenakan masker, menjaga jarak, mengenakan sarung tangan, serta tidak melakukan kontak fisik seperti berjabat tangan. Masalah yang muncul bukan hanya kecemasan orang tua terhadap anak – anaknya, tetapi bagaimana lembaga pendidikan tinggi mengatur segala sumber daya yang dimiliki agar memenuhi standar penerapan new normal. penelitian ini bertujuan untuk mengetahui penerimaan  terhadap kondisi normal yang baru menggunakan Perspektif balance score card. Abstract: Human habits change because of the COVID-19 outbreak, this affects when humans enter the new normal phase. New normal is defined as a condition that is not normally done before, which is then used as a standard or new habits that must be done by humans for themselves or to socialize with others. This new habit also raises the pros and cons along with the impact arising with the new normal. Higher education institutions are the ones who feel the impact of implementing new normal. Lectures that have been conducted online / online will be re-done offline / face to face, while still applying the COVID-19 protocol such as wearing a mask, keeping a distance, wearing gloves, and not making physical contact such as shaking hands. The problem that arises is not only parents' anxiety about their children, but how higher education institutions regulate all available resources to meet new normal implementation standards. This study aims to determine acceptance of new normal conditions using the balance score card Perspective.

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