Journal articles: 'Impinging Sheet'

1

Ibrahim, E. A., and B. E. Outland. "A non-linear model for impinging jets atomization." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 222, no. 2 (February 1, 2008): 213–24. http://dx.doi.org/10.1243/09544062jmes710.

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The problem considered is predicting the characteristics of the spray produced by atomization of an attenuating liquid sheet formed by the impingement of two liquid jets of equal diameters and momenta. A second-order non-linear perturbation analysis is employed to model the evolution of harmonic instability waves that lead to sheet distortion and fragmentation. The onset of atomization occurs when the uneven surface modulations of the thinning sheet bring its upper and lower interfaces in contact. It is found that the sheet is torn into ligaments at each half wavelength. The instability of the ligaments causes their eventual disintegration into drops. The results indicate that sheet breakup length, time, and resultant drop size decrease as Weber number is increased. A higher Weber number induces a greater sheet breakup thickness. The breakup length, thickness, time, and drop size are diminished at larger impingement angles. The theoretical predictions of the present non-linear model are in good agreement with available experimental data and empirical correlations for sheet breakup length and drop size.

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2

Beck, J. E., Arthur H. Lefebvre, and T. R. Koblish. "LIQUID SHEET DISINTEGRATION BY IMPINGING AIR STREAMS." Atomization and Sprays 1, no. 2 (1991): 155–70. http://dx.doi.org/10.1615/atomizspr.v1.i2.20.

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3

Wang, En Dong, Yan Yin, and Qing Du. "Study on some Aspects of Breakup Characteristics of Power-Law Fluid with Impinging Jets Based on Mechanics Properties." Advanced Materials Research 625 (December 2012): 57–60. http://dx.doi.org/10.4028/www.scientific.net/amr.625.57.

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Shear-thinning power-law fluid is a kind of non-Newtonian fluid in which the viscosity is a function of shear rate. Impinging jets system is used to study the breakup characteristics of power-law liquid sheets formed by two symmetrical round jets in this study. High quality images are obtained from the experiment with a high speed camera and breakup length is extracted from the images. Closed-rim sheet, web-like sheet and ligaments sheet are observed with the increase of jet velocity. A series of images show that the wave length on the surface of sheets tends to decline as the jet velocity increases. At a low We number, the breakup length increases with an increasing We number. However, it first increases and then decreases when the liquid sheet breaks up at a high We number. The liquid jets with larger diameter collide to each other and lead to a liquid sheet with a smaller breakup length.

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4

Kim, Hyuntak, Hongjae Kang, and Sejin Kwon. "Liquid Sheet–Sheet Impinging Structure for Pintle Injector with Nontoxic Hypergolic Bipropellant." Journal of Propulsion and Power 36, no. 2 (March 2020): 302–7. http://dx.doi.org/10.2514/1.b37645.

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5

Xia, Yakang, Lyes Khezzar, Shrinivas Bojanampati, and Arman Molki. "Breakup of the Water Sheet Formed by Two Liquid Impinging Jets." International Journal of Chemical Engineering 2019 (February 3, 2019): 1–8. http://dx.doi.org/10.1155/2019/9514848.

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Flow visualization experiments are carried out to study the flow regimes and breakup length of the water sheet generated by two impinging liquid jets from an atomizer made of two identical tubes 0.686 mm in diameter. These experiments cover liquid jet Reynolds numbers based on the pipe diameter in the range of 1541 to 5394. The effects of the jet velocities and impingement angle between the two jets on the breakup performance are studied. Four spray patterns are recognized, which are presheet formation, smooth sheet, ruffled sheet, and open-rim sheet regimes. Water sheet breakup length is found to be consistent with previous experimental and theoretical results in the lower Weber number (based on water jet diameter and velocity) range. In the relatively high Weber number range, the breakup length tends to a constant value with increasing Weber number, and some discrepancies between experimental and theoretical predictions do exist. Measured water sheet area increases with increasing liquid jet Reynolds numbers and impingement angle within the range of the current study.

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6

Honda, H., S. Nozu, and Y. Takeda. "A Theoretical Model of Film Condensation in a Bundle of Horizontal Low Finned Tubes." Journal of Heat Transfer 111, no. 2 (May 1, 1989): 525–32. http://dx.doi.org/10.1115/1.3250709.

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The previous theoretical model of film condensation on a single horizontal low finned tube is extended to include the effect of condensate inundation. Based on the flow characteristics of condensate on a vertical column of horizontal low finned tubes, two major flow modes, the column mode and the sheet mode, are considered. In the column mode, the surface of the lower tubes is divided into the portion under the condensate column where the condensate flow is affected by the impinging condensate from the upper tubes, and the portion between the condensate columns where the condensate flow is not affected by the impinging condensate. In the sheet mode, the whole tube surface is assumed to be affected by the impinging condensate. Sample calculations for practical conditions show that the effects of the fin spacing and the number of vertical tube rows on the heat transfer performance is significant for R-12, while the effects are small for steam. The predicted value of the heat transfer coefficient for each tube row compares well with available experimental data, including four fluids and five tube bundles.

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7

Dollar, Anna, and Paul S. Steif. "A Tension Crack Impinging Upon Frictional Interfaces." Journal of Applied Mechanics 56, no. 2 (June 1, 1989): 291–98. http://dx.doi.org/10.1115/1.3176081.

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A crack impinging normally upon a frictional interface is studied theoretically. We employ a solution technique which superposes the solution of a crack in a perfectly-bonded elastic medium with a continuous distribution of dislocations which represent slippage at the frictional interface. This procedure reduces the problem to a singular integral equation which is solved numerically. Specifically, we consider the problem of an infinite sheet subjected to uniaxial tension containing a finite crack which lies normal to the tension axis and has both crack tips impinging normally on frictional interfaces. The limiting problem of a semi-infinite crack impinging on a frictional interface is considered as well. Posed as model problems for cracking in weakly bonded fiber composites, these studies reveal the effective blunting that can result when a weak interface serves to deflect a propagating crack.

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8

Wang, Zhi-liang, S. P. Lin, and Zhe-wei Zhou. "Formation of radially expanding liquid sheet by impinging two round jets." Applied Mathematics and Mechanics 31, no. 8 (July 24, 2010): 937–46. http://dx.doi.org/10.1007/s10483-010-1328-x.

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9

Weidman, Patrick. "Axisymmetric rotational stagnation point flow impinging on a radially stretching sheet." International Journal of Non-Linear Mechanics 82 (June 2016): 1–5. http://dx.doi.org/10.1016/j.ijnonlinmec.2016.01.016.

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10

Mabood, F., and W. A. Khan. "Analytical study for unsteady nanofluid MHD Flow impinging on heated stretching sheet." Journal of Molecular Liquids 219 (July 2016): 216–23. http://dx.doi.org/10.1016/j.molliq.2016.02.071.

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11

Pansang, Rattanakorn, Makatar Wae-Hayee, Passakorn Vessakosol, and Chayut Nuntadusit. "Heat Transfer Enhancement of Impinging Row Jets in Cross-Flow with Mounting Baffles on Surface." Advanced Materials Research 931-932 (May 2014): 1218–22. http://dx.doi.org/10.4028/www.scientific.net/amr.931-932.1218.

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The aim of this research is to enhance heat transfer on a surface of row of impinging jets in cross-flow by mounting some baffles on the surface. A row of 4 jets with inline arrangement discharging from round orifices impinged normally on inner surface of wind tunnel with simulated cross-flow. The orifice diameter (D) was 13.2 mm. The jet-to-surface distance and jet-to-jet distance were fixed at H=2D and S=3D, respectively. Four couples of baffles with V-shaped arrangement at attack angle, θ=30o, were mounted on surface in upstream or downstream of impinging jets and the location of baffles attachment is L=1.5D apart from the jet impingement region. The velocity ratios (Jet velocity/cross-flow velocity) were varied from VR=3, 5 and 7 while the jet velocity was kept constant corresponding to Re=13,400. The experimental investigation was carried out for heat transfer characteristic by using Thermochromic Liquid Crystal sheet, and heat transfer coefficient distributions were evaluated using an image processing method. The results show that the impinging jets with mounting the baffles in the upstream region of jet impingement region can enhance the heat transfer rate throughout VR.

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12

Yang, Li-jun, Peng-hui Li, and Qing-fei Fu. "Liquid sheet formed by a Newtonian jet obliquely impinging on pro/hydrophobic surfaces." International Journal of Multiphase Flow 125 (April 2020): 103192. http://dx.doi.org/10.1016/j.ijmultiphaseflow.2019.103192.

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13

Yang, Li-jun, Qing-fei Fu, Yuan-yuan Qu, Bin Gu, and Meng-zheng Zhang. "Breakup of a power-law liquid sheet formed by an impinging jet injector." International Journal of Multiphase Flow 39 (March 2012): 37–44. http://dx.doi.org/10.1016/j.ijmultiphaseflow.2011.11.003.

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14

Choo, Y. J., and B. S. Kang. "Parametric study on impinging-jet liquid sheet thickness distribution using an interferometric method." Experiments in Fluids 31, no. 1 (July 1, 2001): 56–62. http://dx.doi.org/10.1007/s003480000258.

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15

Shen, Y. B., and D. Poulikakos. "Thickness Variation of a Liquid Sheet Formed by Two Impinging Jets Using Holographic Interferometry." Journal of Fluids Engineering 120, no. 3 (September 1, 1998): 482–87. http://dx.doi.org/10.1115/1.2820688.

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In the work presented in this paper a real time holographic interferometry technique is developed to measure instantaneously and nonintrusively the thickness distribution of a liquid sheet formed by the impingement of two liquid jets. The experimental results are compared with earlier largely unverified analytical predictions. It is shown that the assumption that the sheet thickness is inversely proportional to the radial distance from the impingement point is in principle good. The dependence of the theoretically obtained proportionality constant on the azimuthal angle, however, while exhibiting the same trend it also shows some quantitative differences. Reasons are given in the context of the work. In addition, a weak effect of the jet velocity on the proportionality constant is found to exist. In the theories no such effect was modeled. Finally, comparisons between theoretical and experimental isothickness contours show differences. Overall, there appears to be a justification for improved theoretical studies including effects such as that of gravitation.

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16

Goldstein, R. J., and M. E. Franchett. "Heat Transfer From a Flat Surface to an Oblique Impinging Jet." Journal of Heat Transfer 110, no. 1 (February 1, 1988): 84–90. http://dx.doi.org/10.1115/1.3250477.

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Experiments are conducted to determine the heat transfer to a jet impinging at different oblique angles to a plane surface. The main portion of the test plate contains a composite sheet of temperature-sensitive liquid crystal, which is sandwiched between a thin metallic-foil heater and a specially designed liquid bath. The results indicate a displacement of the peak heat transfer from the geometric center of the jet origin, the displacement being a function primarily of impingement angle. Contours of constant heat transfer coefficient are obtained and correlated with an empirical equation that permits determination of average Nusselt numbers over areas of interest.

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17

Nuntadusit, Chayut, and Makatar Waehahyee. "Drying of Rubber Sheet Using Impingement of Multiple Hot Air Jets." Advanced Materials Research 844 (November 2013): 502–6. http://dx.doi.org/10.4028/www.scientific.net/amr.844.502.

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In the process for producing ribbed smoked rubber sheet, the rubber sheet drying is the most time and energy consumption process. This research study the possibility in develop new drying system using array of hot air jets impinging directly on rubber sheet in order to reduce time for drying rubber in smoked room and increase productivity of rubber sheets. In the study, the array of jets from jet plate with drilled jet holes in staggered arrangement impinged on the both side of rubber sheet. The effects of jet velocity (Vj=10, 16, 23 m/s), jet temperature (Tj=50, 60, 70°C) and the distance from jet outlet to rubber surface (L=4D, 6D, 8D which D is diameter of jet hole) on drying rate were investigated by measuring weight of rubber sheet change with time. The heat transfer rate on impinged surface was also measured by attaching a heat flux sensor on impinged wall. The results showed that the convective heat transfer coefficient increased when the jet velocity was increased and when the distance from jet was decreased particularly in jet directly impinged region. It was found that the enhancement in heat transfer rate from jets cannot increase the rubber drying rate for all cases because the drying rate depend on rubber property. The process of rubber sheet drying can be divided in 2 periods; in the first drying period, the drying rate decreases with decreased moisture content. The drying rate depended on the initial moisture content and the condition of external effect such as jet velocity, jet temperature and distance from jet outlet to rubber surface. In second drying period, the moisture content is below 20% dry basis. In this period, the drying rate is almost constant near zero. It was also found that the drying for case of L=6D was higher than case of L=4D and 8D. The optimum condition for rubber sheet drying without defects on rubber property after drying was L=6D and Tj=70°C.

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18

Liang Gang-Tao, Guo Ya-Li, and Shen Sheng-Qiang. "Analysis of liquid sheet and jet flow mechanism after droplet impinging onto liquid film." Acta Physica Sinica 62, no. 2 (2013): 024705. http://dx.doi.org/10.7498/aps.62.024705.

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19

Etteneni, Nikhil Kumar, and Madan Mohan Avulapati. "AN EXPERIMENTAL INVESTIGATION ON LIQUID SHEET BREAKUP DUE TO PERFORATIONS IN IMPINGING JET ATOMIZATION." Atomization and Sprays 32, no. 2 (2022): 35–54. http://dx.doi.org/10.1615/atomizspr.2021037826.

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20

Choo, Y. J., and B. S. Kang. "The velocity distribution of the liquid sheet formed by two low-speed impinging jets." Physics of Fluids 14, no. 2 (February 2002): 622–27. http://dx.doi.org/10.1063/1.1429250.

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21

Akbar, N. S., Z. H. Khan, R. U. Haq, and S. Nadeem. "Dual solutions in MHD stagnation-point flow of Prandtl fluid impinging on shrinking sheet." Applied Mathematics and Mechanics 35, no. 7 (May 31, 2014): 813–20. http://dx.doi.org/10.1007/s10483-014-1836-9.

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22

Bernard, A., L. E. Brizzi, and J. L. Bousgarbie`s. "Study of Several Jets Impinging on a Plane Wall: Visualizations and Laser Velocimetry Investigations." Journal of Fluids Engineering 121, no. 4 (December 1, 1999): 808–12. http://dx.doi.org/10.1115/1.2823541.

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Different experimental techniques have been used in order to describe the flow pattern generated by fifteen jets impinging on a plane wall. The spreading over method revealed the jet influence on the impinged surface, particularly reattachment and detachment lines. The laser sheet visualizations show complex vortical structures such as the ground vortex and secondary rolling-ups near the target plate have been deduced. Velocity measurements have been realised to confirm these observations and to specify the flow pattern. A schema of the flow near the impinged wall is thus drawn.

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23

Luo, H. A., and Q. Wang. "Stress Concentrations in an Intermingled Hybrid Composite." Journal of Applied Mechanics 64, no. 4 (December 1, 1997): 738–42. http://dx.doi.org/10.1115/1.2788977.

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This paper studies the stress redistribution in a tensile hybrid composite sheet due to the breakage of a high modulus fiber. Employing a continuous distribution of dislocations, a set of singular integral equations is established to analyze the fiber crack impinging upon weakly bonded fiber-matrix interfaces. After solving the integral equations numerically, the stress concentration factors of both high modulus and low modulus fibers are evaluated as a function of loading stress and interfacial parameters. The results are compared with those obtained from shear-lag model solution.

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24

Mabood, Fazle, and Stanford Shateyi. "Multiple Slip Effects on MHD Unsteady Flow Heat and Mass Transfer Impinging on Permeable Stretching Sheet with Radiation." Modelling and Simulation in Engineering 2019 (February 12, 2019): 1–11. http://dx.doi.org/10.1155/2019/3052790.

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This paper reports multiple slip effects on MHD unsteady flow heat and mass transfer over a stretching sheet with Soret effect; suction/injection and thermal radiation are numerically analyzed. We consider a time-dependent applied magnetic field and stretching sheet which moves with nonuniform velocity. Suitable similarity variables are used to transform governing partial differential equations into a system of coupled nonlinear ordinary differential equations. The transformed equations are then solved numerically by applying an implicit finite difference method with quasi-linearization technique. The influences of the various parameters on the velocity temperature and concentration profiles as well as on the skin friction coefficient and Sherwood and Nusselt numbers are discussed by the aid of graphs and tables.

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25

Ljung, Anna-Lena, L. Robin Andersson, Anders G. Andersson, T. Staffan Lundström, and Mats Eriksson. "Modelling the Evaporation Rate in an Impingement Jet Dryer with Multiple Nozzles." International Journal of Chemical Engineering 2017 (2017): 1–9. http://dx.doi.org/10.1155/2017/5784627.

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Impinging jets are often used in industry to dry, cool, or heat items. In this work, a two-dimensional Computational Fluid Dynamics model is created to model an impingement jet dryer with a total of 9 pairs of nozzles that dries sheets of metal. Different methods to model the evaporation rate are studied, as well as the influence of recirculating the outlet air. For the studied conditions, the simulations show that the difference in evaporation rate between single- and two-component treatment of moist air is only around 5%, hence indicating that drying can be predicted with a simplified model where vapor is included as a nonreacting scalar. Furthermore, the humidity of the inlet air, as determined from the degree of recirculating outlet air, has a strong effect on the water evaporation rate. Results show that the metal sheet is dry at the exit if 85% of the air is recirculated, while approximately only 60% of the water has evaporated at a recirculation of 92,5%.

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26

Kline, M. C., R. D. Woodward, R. L. Burch, F. B. Cheung, and Kenneth K. Kuo. "IMAGING OF IMPINGING JET BREAKUP AND ATOMIZATION PROCESSES USING COPPER-VAPOR-LASER-SHEET-ILLUMINATED PHOTOGRAPHY." International Journal of Energetic Materials and Chemical Propulsion 3, no. 1-6 (1994): 552–68. http://dx.doi.org/10.1615/intjenergeticmaterialschemprop.v3.i1-6.560.

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27

Kang, B. S., Y. B. Shen, and D. Poulikakos. "HOLOGRAPHY EXPERIMENTS IN THE BREAKUP REGION OF A LIQUID SHEET FORMED BY TWO IMPINGING JETS." Atomization and Sprays 5, no. 4-5 (1995): 387–402. http://dx.doi.org/10.1615/atomizspr.v5.i45.20.

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28

Luo, Yi Cheng, Wang, Yong Jin, and Yang. "Study on the Mixing Behavior of Thin Liquid-Sheet Impinging Jets Using the PLIF Technique." Industrial & Engineering Chemistry Research 45, no. 2 (January 2006): 863–70. http://dx.doi.org/10.1021/ie050963c.

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29

Mabood, Fazle, Giulio Lorenzini, Nopparat Pochai, and Stanford Shateyi. "Homotopy Analysis Method for Radiation and Hydrodynamic-Thermal Slips Effects on MHD Flow and Heat Transfer Impinging on Stretching Sheet." Defect and Diffusion Forum 388 (October 2018): 317–27. http://dx.doi.org/10.4028/www.scientific.net/ddf.388.317.

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This article deals with the analytical study of MHD flow and heat transfer over a permeable stretching sheet via homotopy analysis method (HAM). The effect of thermal radiation is included in the energy equation, while velocity and thermal slips are included in the boundary conditions. The governing boundary layer equations are transformed into a set of ordinary differential equations by means of similarity transformations. The effects of different parameters on the flow field and heat transfer characteristics are examined. The results obtained were shown to compare well with the numerical results and for some special cases with the published data available in the literature, which are in favorable agreement. Keywords: MHD; Slip flow; Stretching sheet; Thermal radiation; Homotopy analysis method

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30

Khayat, Roger E. "Impinging planar jet flow on a horizontal surface with slip." Journal of Fluid Mechanics 808 (October 28, 2016): 258–89. http://dx.doi.org/10.1017/jfm.2016.620.

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The flow of a planar jet (sheet) impinging onto a solid flat plate with slip is examined theoretically. The jet is assumed to spread out in a thin layer bounded by a hydraulic jump, and draining at the edge of the plate. In contrast to an adhering jet, a slipping jet does not admit a similarity solution. Taking advantage of the different scaling in each region, series expansions are used in the developing and fully viscous layers, which are matched at the transition point. We show that a slipping film exhibits a singularity in the normal stress at the leading edge of the boundary layer, as opposed to the singularity in velocity and shear stress for an adhering film. The boundary-layer and film heights are both found to decrease with slip relative to a smooth substrate, roughly like $\sqrt{30x/Re}-2S$, whereas the slip velocity intensifies like $S\sqrt{Re/30x}$ with slip. Here, $x$ is the distance along the plate, $S$ is the slip length and $Re$ is the Reynolds number (in units of the jet width). The transition is delayed by slip. Guided by the measurements of Duchesne et al. (Europhys. Lett., vol. 107, 2014, p. 54002) for a circular adhering jet, the hydraulic-jump height and location are determined for a planar jet, and are found to increase with the Froude number (flow rate) like $Fr^{1/4}$ and $Fr^{5/8}$ respectively, essentially independently of slip length.

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31

Mabood, F., W. A. Khan, and A. I. Md Ismail. "MHD stagnation point flow and heat transfer impinging on stretching sheet with chemical reaction and transpiration." Chemical Engineering Journal 273 (August 2015): 430–37. http://dx.doi.org/10.1016/j.cej.2015.03.037.

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32

Zhang, Jun, Peng-Fei Liang, Ying Luo, Ying Guo, and You-Zhi Liu. "Liquid Sheet Breakup Mode and Droplet Size of Free Opposed Impinging Jets by Particle Image Velocimetry." Industrial & Engineering Chemistry Research 59, no. 24 (May 22, 2020): 11296–307. http://dx.doi.org/10.1021/acs.iecr.9b06354.

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33

Ichimiya, K. "Heat Transfer and Flow Characteristics of an Oblique Turbulent Impinging Jet Within Confined Walls." Journal of Heat Transfer 117, no. 2 (May 1, 1995): 316–22. http://dx.doi.org/10.1115/1.2822523.

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Experiments were conducted to determine the turbulent heat transfer and flow characteristics of an oblique impinging circular jet within closely confined walls using air as a working fluid. The local temperature distribution on the impingement surface was obtained in detail by a thermocamera using a liquid crystal sheet. A correction to the heat flux was evaluated by using the detailed temperature distribution and solving numerically the three-dimensional equation of heat conduction in the heated section. Two-dimensional profiles of the local Nusselt numbers and temperatures changed with jet angle and Reynolds number. These showed a peak shift toward the minor flow region and a plateau of the local heat transfer coefficients in the major flow region. The local velocity and turbulent intensity in the gap between the confined insulated wall and impingement surface were also obtained in detail by a thermal anemometer.

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34

Deng, Han-Yu, Chang-fei Zhuo, and Feng Feng. "A simplified linear model and breakup characteristics of power-law sheet formed by a doublet impinging injector." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 232, no. 6 (December 4, 2017): 1035–46. http://dx.doi.org/10.1177/0954410017708209.

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35

Fan, Boyu, Cecilia Huertas-Cerdeira, Julia Cossé, John E. Sader, and Morteza Gharib. "Effect of morphology on the large-amplitude flapping dynamics of an inverted flag in a uniform flow." Journal of Fluid Mechanics 874 (July 10, 2019): 526–47. http://dx.doi.org/10.1017/jfm.2019.474.

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The stability of a cantilevered elastic sheet in a uniform flow has been studied extensively due to its importance in engineering and its prevalence in natural structures. Varying the flow speed can give rise to a range of dynamics including limit cycle behaviour and chaotic motion of the cantilevered sheet. Recently, the ‘inverted flag’ configuration – a cantilevered elastic sheet aligned with the flow impinging on its free edge – has been observed to produce large-amplitude flapping over a finite band of flow speeds. This flapping phenomenon has been found to be a vortex-induced vibration, and only occurs at sufficiently large Reynolds numbers. In all cases studied, the inverted flag has been formed from a cantilevered sheet of rectangular morphology, i.e. the planform of its elastic sheet is a rectangle. Here, we investigate the effect of the inverted flag’s morphology on its resulting stability and dynamics. We choose a trapezoidal planform which is explored using experiment and an analytical theory for the divergence instability of an inverted flag of arbitrary morphology. Strikingly, for this planform we observe that the flow speed range over which flapping occurs scales approximately with the flow speed at which the divergence instability occurs. This provides a means by which to predict and control flapping. In a biological setting, leaves in a wind can also align themselves in an inverted flag configuration. Motivated by this natural occurrence we also study the effect of adding an artificial ‘petiole’ (a thin elastic stalk that connects the sheet to the clamp) on the inverted flag’s dynamics. We find that the petiole serves to partially decouple fluid forces from elastic forces, for which an analytical theory is also derived, in addition to increasing the freedom by which the flapping dynamics can be tuned. These results highlight the intricacies of the flapping instability and account for some of the varied dynamics of leaves in nature.

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36

Hamdi, Jana, Kamel Abed-Meraïm, Hassan Assoum, Anas Sakout, Marwan Al-Kheir, Tarek Mrach, Laurent Rambault, Sebastien Cauet, and Eric Etien. "Tomographic and Time-Resolved PIV measurement of an Impinging Jet on a Slotted Plate." MATEC Web of Conferences 261 (2019): 03004. http://dx.doi.org/10.1051/matecconf/201926103004.

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In order to reveal the complete topology of unsteady coherent flow structures the instantaneous measurement of the 3D velocity field is being of the great interest in fluid mechanic. Several different methods were proposed to achieve a 3D version of the technique (scanning light sheet, holography, 3D PTV). We aimed in our study to develop a 3D technique than enables to obtain the 3D kinematic field of an impinging jet by using 2D measurements. In this study and in order to validate the proposed technique [1], the tomographic particle image velocimetry technique has been applied to time resolved PIV recordings. The first step before the validation was to study the vortex shedding phenomena between the jet exit and the slotted plate. The experiments were performed at a Re = 4458 with an initial velocity U0=7m/s using three cameras Phantom V711 and a Nd: YLF LDY 300 Litron laser. In the present study, we analyzed the coherent structures organization by a 3D-velocity visualization. Both mean and fluctuating part of velocity were analyzed for several positions in z. The results has shown that a couple of vortex rolls are created downstream the flow at y/H=2.

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37

Inamura, Takao, and Minori Shirota. "Effect of velocity profile of impinging jets on sheet characteristics formed by impingement of two round liquid jets." International Journal of Multiphase Flow 60 (April 2014): 149–60. http://dx.doi.org/10.1016/j.ijmultiphaseflow.2013.12.006.

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38

Wang, Ruixiang, Yong Huang, Xiang Feng, Lei Sun, Di Wang, and Zhilin Liu. "Semi-empirical model for the engine liquid fuel sheet formed by the oblique jet impinging onto a plate." Fuel 233 (December 2018): 84–93. http://dx.doi.org/10.1016/j.fuel.2018.06.028.

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39

Allocca, L., L. Andreassi, and S. Ubertini. "Enhanced Splash Models for High Pressure Diesel Spray." Journal of Engineering for Gas Turbines and Power 129, no. 2 (September 4, 2006): 609–21. http://dx.doi.org/10.1115/1.2432891.

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Mixture preparation is a crucial aspect for the correct operation of modern direct injection (DI) Diesel engines as it greatly influences and alters the combustion process and, therefore, the exhaust emissions. The complete comprehension of the spray impingement phenomenon is a quite complete task and a mixed numerical-experimental approach has to be considered. On the modeling side, several studies can be found in the scientific literature but only in the last years complete multidimensional modeling has been developed and applied to engine simulations. Among the models available in literature, in this paper, the models by Bai and Gosman (Bai, C., and Gosman, A. D., 1995, SAE Technical Paper No. 950283) and by Lee et al. (Lee, S., and Ryou, H., 2000, Proceedings of the Eighth International Conference on Liquid Atomization and Spray Systems, Pasadena, CA, pp. 586–593; Lee, S., Ko, G. H., Ryas, H., and Hong, K. B., 2001, KSME Int. J., 15(7), pp. 951–961) have been selected and implemented in the KIVA-3V code. On the experimental side, the behavior of a Diesel impinging spray emerging from a common rail injection system (injection pressures of 80 and 120MPa) has been analyzed. The impinging spray has been lightened by a pulsed laser sheet generated from the second harmonic of a Nd-yttrium-aluminum-garnet laser. The images have been acquired by a charge coupled device camera at different times from the start of injection. Digital image processing software has enabled to extract the characteristic parameters of the impinging spray with respect to different operating conditions. The comparison of numerical and experimental data shows that both models should be modified in order to allow a proper simulation of the splash phenomena in modern Diesel engines. Then the numerical data in terms of radial growth, height and shape of the splash cloud, as predicted by modified versions of the models are compared to the experimental ones. Differences among the models are highlighted and discussed.

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40

HANCOCK, MATTHEW J., and JOHN W. M. BUSH. "Fluid pipes." Journal of Fluid Mechanics 466 (September 10, 2002): 285–304. http://dx.doi.org/10.1017/s0022112002001258.

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We present the results of a combined theoretical and experimental investigation of laminar vertical jets impinging on a deep fluid reservoir. We consider the parameter regime where, in a pure water system, the jet is characterized by a stationary field of capillary waves at its base. When the reservoir is contaminated by surfactant, the base of the jet is void of capillary waves, cylindrical and quiescent: water enters the reservoir as if through a rigid pipe. A theoretical description of the resulting fluid pipe is deduced by matching extensional plug flow upstream of the pipe onto entry pipe flow within it. Theoretical predictions for the pipe height are found to be in excellent accord with our experimental results. An analogous theoretical description of the planar fluid pipe expected to arise on a falling fluid sheet is presented.

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41

Rahman, M. M., Teodor Grosan, and Ioan Pop. "Oblique stagnation-point flow of a nanofluid past a shrinking sheet." International Journal of Numerical Methods for Heat & Fluid Flow 26, no. 1 (January 4, 2016): 189–213. http://dx.doi.org/10.1108/hff-10-2014-0315.

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Purpose – The laminar two-dimensional stagnation-point flow and heat transfer of a viscous incompressible nanofluid obliquely impinging on a shrinking surface is formulated as a similarity solution of the Navier-Stokes, energy and concentration equations. The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis. The effect of the dimensionless strain rate, shrinking parameter, Brownian motion parameter and thermophoresis parameter on the flow, temperature and nanoparticle volume fraction is investigated in details. The paper aims to discuss these issues. Design/methodology/approach – The transformed system of ordinary differential equations was solved using the function bvp4c from Matlab. The relative tolerance was set to 10−10. Findings – It is found that dimensionless strain rate and shrinking parameter causes a shift in the position of the point of zero skin friction along the stretching sheet. Obliquity of the flow toward the surface increases as the strain rate intensifies. The results indicate that dual solutions exist for the opposing flow case. Research limitations/implications – The problem is formulated for an incompressible nanofluid with no chemical reactions, dilute mixture, negligible viscous dissipation and negligible radiative heat transfer assuming nanoparticles and base fluid are locally in thermal equilibrium. Beyond the critical point λ c to obtain further solutions, the full basic partial differential equations have to be solved. Originality/value – The present results are original and new for the oblique stagnation-point flow of a nanofluid past a shrinking sheet. Therefore, this study would be important for the researchers working in the relatively new area of nanofluids in order to become familiar with the flow behavior and properties of such nanofluids.

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42

Abiev, Rufat Sh, and Alexey A. Sirotkin. "Influence of Hydrodynamic Conditions on Micromixing in Microreactors with Free Impinging Jets." Fluids 5, no. 4 (October 13, 2020): 179. http://dx.doi.org/10.3390/fluids5040179.

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An experimental study and mathematical modeling of micromixing in a microreactor with free impinging jets (MRFIJ) with a diameter of 1 mm was carried out. In the experimental part, the iodide-iodate technique was used (involving parallel competing Villermaux–Dushman reactions with the formation of I3−). Theoretical assessment revealed that more than 50% of the introduced energy is dissipated in the jets collision region. Through the use of differentiated sampling, an uneven quality distribution of micro mixing in the central and peripheral zones of the reactor was found: at moderate flow rates (700–1000 mL/min, jets velocity of 15–21 m/s) the micromixing in the central part of reactor is up to 12 times better than that in the periphery. Furthermore, the weight fraction of the probes in the central zones of MRFIJ is reduced with increasing jet velocity; this effect is attributed to a more intense formation of ligaments and droplets upon collision of jets and their secondary mixing on the walls of the apparatus. In terms of the weighted average concentration, the best quality of micromixing in the samples is achieved at a flow rate of 300 mL/min. With an increase in the flow rate (and velocity) of the jets, the dependence of the I3− concentration on the flow rate has a nonmonotonic character, which is explained by a change in the nature of the flow in the collision zone of the jets: the transition from the formation of a liquid sheet to the intensive formation of ligaments and drops and secondary mixing of the liquid film formed on the walls of the reactor. The effect of “freshness” of solutions on the concentration of reaction products was studied.

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Panizon, Emanuele, Roberto Guerra, and Erio Tosatti. "Ballistic thermophoresis of adsorbates on free-standing graphene." Proceedings of the National Academy of Sciences 114, no. 34 (August 3, 2017): E7035—E7044. http://dx.doi.org/10.1073/pnas.1708098114.

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The textbook thermophoretic force which acts on a body in a fluid is proportional to the local temperature gradient. The same is expected to hold for the macroscopic drift behavior of a diffusive cluster or molecule physisorbed on a solid surface. The question we explore here is whether that is still valid on a 2D membrane such as graphene at short sheet length. By means of a nonequilibrium molecular dynamics study of a test system—a gold nanocluster adsorbed on free-standing graphene clamped between two temperatures ΔT apart—we find a phoretic force which for submicron sheet lengths is parallel to, but basically independent of, the local gradient magnitude. This identifies a thermophoretic regime that is ballistic rather than diffusive, persisting up to and beyond a 100-nanometer sheet length. Analysis shows that the phoretic force is due to the flexural phonons, whose flow is known to be ballistic and distance-independent up to relatively long mean-free paths. However, ordinary harmonic phonons should only carry crystal momentum and, while impinging on the cluster, should not be able to impress real momentum. We show that graphene and other membrane-like monolayers support a specific anharmonic connection between the flexural corrugation and longitudinal phonons whose fast escape leaves behind a 2D-projected mass density increase endowing the flexural phonons, as they move with their group velocity, with real momentum, part of which is transmitted to the adsorbate through scattering. The resulting distance-independent ballistic thermophoretic force is not unlikely to possess practical applications.

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Sader, John E., Julia Cossé, Daegyoum Kim, Boyu Fan, and Morteza Gharib. "Large-amplitude flapping of an inverted flag in a uniform steady flow – a vortex-induced vibration." Journal of Fluid Mechanics 793 (March 18, 2016): 524–55. http://dx.doi.org/10.1017/jfm.2016.139.

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The dynamics of a cantilevered elastic sheet, with a uniform steady flow impinging on its clamped end, have been studied widely and provide insight into the stability of flags and biological phenomena. Recent measurements by Kim et al. (J. Fluid Mech., vol. 736, 2013, R1) show that reversing the sheet’s orientation, with the flow impinging on its free edge, dramatically alters its dynamics. In contrast to the conventional flag, which exhibits (small-amplitude) flutter above a critical flow speed, the inverted flag displays large-amplitude flapping over a finite band of flow speeds. The physical mechanisms giving rise to this flapping phenomenon are currently unknown. In this article, we use a combination of mathematical theory, scaling analysis and measurement to establish that this large-amplitude flapping motion is a vortex-induced vibration. Onset of flapping is shown mathematically to be due to divergence instability, verifying previous speculation based on a two-point measurement. Reducing the sheet’s aspect ratio (height/length) increases the critical flow speed for divergence and ultimately eliminates flapping. The flapping motion is associated with a separated flow – detailed measurements and scaling analysis show that it exhibits the required features of a vortex-induced vibration. Flapping is found to be periodic predominantly, with a transition to chaos as flow speed increases. Cessation of flapping occurs at higher speeds – increased damping reduces the flow speed range where flapping is observed, as required. These findings have implications for leaf motion and other biological processes, such as the dynamics of hair follicles, because they also can present an inverted-flag configuration.

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Kim, Sang Kyun, Jung Chul Lee, Viresh Dutta, Sung Ju Park, and Kyung Hoon Yoon. "The Effect of ZnO:Al Sputtering Condition on a-Si:H / Si Wafer Heterojunction Solar Cells." Solid State Phenomena 124-126 (June 2007): 1015–18. http://dx.doi.org/10.4028/www.scientific.net/ssp.124-126.1015.

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A-Si:H/Si wafer heterojunction solar cells with different ZnO:Al sputtering conditions were fabricated and the effects of sputtering conditions on device performance were evaluated. Various sputter condition(substrate temperature RT~200’C, working pressure 0.5mTorr~15mTorr, thickness 60~100nm) were tested and optimized as 130’C, 0.5mTorr, 80nm by measuring reflectance and sheet resistance of ZnO:Al layer on corning glass. However, when optimal ZnO:Al condition was applied to solar cells, series resistance was high which led to device efficiency ~10%. Dark I-V curves of with and w/o ZnO layer showed large difference, which means there is a kind of barrier to current flow between ZnO:Al and a-Si:H layer. Modified condition with double layer scheme was applied and lower series resistance and device efficiency above 12% could be reached. The improvement may be due to either suppression of Si oxide formation or less defect formation by impinging atoms.

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Gojon, Romain, Christophe Bogey, and Olivier Marsden. "Investigation of tone generation in ideally expanded supersonic planar impinging jets using large-eddy simulation." Journal of Fluid Mechanics 808 (October 26, 2016): 90–115. http://dx.doi.org/10.1017/jfm.2016.628.

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The generation of tones in a supersonic planar jet impinging on a flat plate normally has been investigated by performing compressible large-eddy simulations using low-dissipation and low-dispersion finite differences. At the exit of a straight nozzle of height $h$, the jet is ideally expanded, and has a Mach number of 1.28 and a Reynolds number of $5\times 10^{4}$. Four distances between the nozzle and the plate between $3.94h$ and $9.1h$ have been considered. Flow snapshots and mean velocity fields are first presented. The variations of turbulence intensities and of the convection velocity in the jet shear layers are then examined. The properties of the jet near fields are subsequently described, in particular by applying Fourier decomposition to the pressure fields. Several coexisting tones appear to be generated by aeroacoustic feedback loops establishing between the nozzle lip and the flat plate, which also lead to the presence of hydrodynamic–acoustic standing waves. The tone frequencies are consistent with those given by the aeroacoustic feedback model and with measurements for high-aspect-ratio rectangular jets. The jet oscillation modes at these frequencies are characterized, and found to agree with experimental data. Their symmetric or antisymmetric natures are shown to be well predicted by a wave analysis carried out using a vortex sheet model of the jet, providing the allowable frequency ranges for the upstream-propagating acoustic waves. Thus, it is possible, for an ideally expanded impinging planar jet to predict both the frequencies of the tones and the symmetric or antisymmetric nature of the corresponding oscillation modes by combining the aeroacoustic feedback model and the wave analysis.

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47

Wåhlin, A. K., A. G. C. Graham, K. A. Hogan, B. Y. Queste, L. Boehme, R. D. Larter, E. C. Pettit, J. Wellner, and K. J. Heywood. "Pathways and modification of warm water flowing beneath Thwaites Ice Shelf, West Antarctica." Science Advances 7, no. 15 (April 2021): eabd7254. http://dx.doi.org/10.1126/sciadv.abd7254.

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Thwaites Glacier is the most rapidly changing outlet of the West Antarctic Ice Sheet and adds large uncertainty to 21st century sea-level rise predictions. Here, we present the first direct observations of ocean temperature, salinity, and oxygen beneath Thwaites Ice Shelf front, collected by an autonomous underwater vehicle. On the basis of these data, pathways and modification of water flowing into the cavity are identified. Deep water underneath the central ice shelf derives from a previously underestimated eastern branch of warm water entering the cavity from Pine Island Bay. Inflow of warm and outflow of melt-enriched waters are identified in two seafloor troughs to the north. Spatial property gradients highlight a previously unknown convergence zone in one trough, where different water masses meet and mix. Our observations show warm water impinging from all sides on pinning points critical to ice-shelf stability, a scenario that may lead to unpinning and retreat.

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48

Eiamsa-ard, S., C. Nuntadusit, K. Wongcharee, and V. Chuwattanakul. "An Impingement Cooling Using Swirling Jets Induced by Helical Rod Swirl Generators." International Journal of Turbo & Jet-Engines 35, no. 3 (July 26, 2018): 241–50. http://dx.doi.org/10.1515/tjj-2016-0043.

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Abstract The heat transfer performance of swirling impinging jets (SIJs) was investigated and compared with that of the conventional jet (CIJ). The swirling jets were induced by helical rod inserts (HRs) fitted with pipe nozzles. The helical rod inserts with two different rod diameter to nozzle diameter ratios (d/D) of 0.46 and 0.64 were employed for comparison. Jet-to-plate distance to nozzle diameter ratio (L/D) was varied from 1 to 5 while Reynolds number was fixed at 20,000. The temperature and Nusselt number distributions on the impinged plate were measured and evaluated using thermochromic liquid crystal (TLC) sheet and image processing technique. The experimental results showed that the swirling jet (SJ) at d/D=0.64 gave higher average heat transfer rate than the SJ at d/D=0.46 up to 6.41 % and the conventional jet (CJ) up to 35.05 %. In addition, Nusselt number peak of swirling jets increased as jet-to-plate distance decreased.

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49

Roşca, Natalia C., and Ioan Pop. "A numerical study of the axisymmetric rotational stagnation point flow impinging radially a permeable stretching/shrinking surface in a nanofluid." International Journal of Numerical Methods for Heat & Fluid Flow 27, no. 11 (November 6, 2017): 2415–32. http://dx.doi.org/10.1108/hff-11-2016-0464.

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Purpose The purpose of this study is to analyze numerically the steady axisymmetric rotational stagnation point flow impinging on a radially permeable stretching/shrinking sheet in a nanofluid. Design/methodology/approach Similarity transformation is used to convert the system of partial differential equations into a system of ordinary (similarity) differential equations. This system is then reduced to a system of first-order differential equations and solved numerically using the bvp4c function in MATLAB software. Findings Dual solutions exist when the surface is stretched, as well as when the surface is shrunk. For these solutions, a stability analysis is carried out revealing that the first solution (upper branch) is stable and physically realizable, while the second solution (lower branch) is unstable and therefore not physically realizable. Originality/value The present results are original and new for the study of fluid flow and heat transfer over a stretching/shrinking surface, as they successfully extend the problem considered by Weidman (2016) to the case of nanofluids.

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50

Bogey, Christophe, and Romain Gojon. "Feedback loop and upwind-propagating waves in ideally expanded supersonic impinging round jets." Journal of Fluid Mechanics 823 (June 22, 2017): 562–91. http://dx.doi.org/10.1017/jfm.2017.334.

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The aeroacoustic feedback loop establishing in a supersonic round jet impinging on a flat plate normally has been investigated by combining compressible large-eddy simulations and modelling of that loop. At the exit of a straight pipe nozzle of radius $r_{0}$, the jet is ideally expanded, and has a Mach number of 1.5 and a Reynolds number of $6\times 10^{4}$. Four distances between the nozzle exit and the flat plate, equal to $6r_{0}$, $8r_{0}$, $10r_{0}$ and $12r_{0}$, have been considered. In this way, the variations of the convection velocity of the shear-layer turbulent structures according to the nozzle-to-plate distance are shown. In the spectra obtained inside and outside of the flow near the nozzle, several tones emerge at Strouhal numbers in agreement with measurements in the literature. At these frequencies, by applying Fourier decomposition to the pressure fields, hydrodynamic-acoustic standing waves containing a whole number of cells between the nozzle and the plate and axisymmetric or helical jet oscillations are found. The tone frequencies and the mode numbers inferred from the standing-wave patterns are in line with the classical feedback-loop model, in which the loop is closed by acoustic waves outside the jet. The axisymmetric or helical nature of the jet oscillations at the tone frequencies is also consistent with a wave analysis using a jet vortex-sheet model, providing the allowable frequency ranges for the upstream-propagating acoustic wave modes of the jet. In particular, the tones are located on the part of the dispersion relations of the modes where these waves have phase and group velocities close to the ambient speed of sound. Based on the observation of the pressure fields and on frequency–wavenumber spectra on the jet axis and in the shear layers, such waves are identified inside the present jets, for the first time to the best of our knowledge, for a supersonic jet flow. This study thus suggests that the feedback loop in ideally expanded impinging jets is completed by these waves.

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Journal articles on the topic 'Impinging Sheet'

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