On standing gravity wave-depression cavity collapse and jetting

2019 ◽  
Vol 866 ◽  
pp. 112-131 ◽  
Author(s):  
D. Krishna Raja ◽  
S. P. Das ◽  
E. J. Hopfinger
Keyword(s):  
Wave Amplitude ◽  
Bond Number ◽  
Working Fluid ◽  
Cavity Depth ◽  
Depth Limit ◽  
Cavity Collapse ◽  
Jet Velocity ◽  
Surface Jet ◽  
Singular Wave ◽  
Surface Jets

Parametrically forced gravity waves can give rise to high-velocity surface jets via the wave-depression cavity implosion. The present results have been obtained in circular cylindrical containers of 10 and 15 cm in diameter (Bond number of order $10^{3}$) in the large fluid depth limit. First, the phase diagrams of instability threshold and wave breaking conditions are determined for the working fluid used, here water with 1 % detergent added. The collapse of the wave-depression cavity is found to be self-similar. The exponent $\unicode[STIX]{x1D6FC}$ of the variation of the cavity radius $r_{m}$ with time $\unicode[STIX]{x1D70F}$, in the form $r_{m}/R\propto \unicode[STIX]{x1D70F}^{\unicode[STIX]{x1D6FC}}$, is close to 0.5, indicative of inertial collapse, followed by a viscous cut-off of $\unicode[STIX]{x1D6FC}\approx 1$. This supports a Froude number scaling of the surface jet velocity caused by cavity collapse. The dimensionless jet velocity scales with the cavity depth that is shown to be proportional to the last stable wave amplitude. It can be expressed by a power law or in terms of finite time singularity related to a singular wave amplitude that sets the transition from a non-pinching to pinch-off cavity collapse scenario. In terms of forcing amplitude, cavity collapse and jetting are found to occur in bands of events of non-pinching and pinching of a bubble at the cavity base. At large forcing amplitudes, incomplete cavity collapse and splashing can occur and, at even larger forcing amplitudes, wave growth is again stable up to the singular wave amplitude. When the cavity is formed, an impulse model shows the importance of the singular cavity diameter that determines the strength of the impulse.

Jet emerging from an annular nozzle and impinging onto cylindrical cavity: Effect of jet velocity on flow structure and heat transfer rates

2008 ◽  
Vol 222 (6) ◽  
pp. 1021-1031 ◽  
Author(s):  
S Z Shuja ◽  
B S Yilbas ◽  
S M A Khan
Keyword(s):  
Heat Transfer ◽  
Flow Structure ◽  
Cylindrical Cavity ◽  
Substrate Material ◽  
Working Fluid ◽  
Cavity Surface ◽  
Annular Nozzle ◽  
Transfer Rates ◽  
Jet Velocity

In laser gas assisting processes, nozzles are used to accelerate the impinging gas and attain a proper flow structure to improve the quality of the end product. In this study, the jet emerging from an annular nozzle and impinging onto a cylindrical cavity is considered. The effects of jet velocity at nozzle exit onto the flow structure in the region of the cavity and heat transfer rates from the cavity surface are examined. To resemble the laser-produced cavity, the cavity wall temperature is kept elevated (almost the melting temperature of the substrate material). Reynolds stress turbulence model is exploited to account for the turbulence. In the simulations, four jet velocities, two outer angles of the annular nozzle, and two depths of the cylindrical cavity are employed while air is used for the working fluid. It is found that jet velocity has a significant effect on the heat transfer rates and skin friction, which is more pronounced with increasing cavity depths.

On the scaling of jetting from bubble collapse at a liquid surface

2017 ◽  
Vol 822 ◽  
pp. 791-812 ◽  
Author(s):  
Sangeeth Krishnan ◽  
E. J. Hopfinger ◽  
Baburaj A. Puthenveettil
Keyword(s):  
Power Law ◽  
Scaling Laws ◽  
Liquid Surface ◽  
Limited Range ◽  
Capillary Waves ◽  
Bubble Collapse ◽  
Jet Formation ◽  
Cavity Depth ◽  
Jet Breakup ◽  
Jet Velocity

We present scaling laws for the jet velocity resulting from bubble collapse at a liquid surface which bring out the effects of gravity and viscosity. The present experiments conducted in the range of Bond numbers $0.004<Bo<2.5$ and Ohnesorge numbers $0.001<Oh<0.1$ were motivated by the discrepancy between previous experimental results and numerical simulations. We show here that the actual dependence of $We$ on $Bo$ is determined by the gravity dependency of the bubble immersion (cavity) depth which has no power-law variation. The power-law variation of the jet Weber number, $We\sim 1/\sqrt{Bo}$, suggested by Ghabache et al. (Phys. Fluids, vol. 26 (12), 2014, 121701) is only a good approximation in a limited range of $Bo$ values ($0.1<Bo<1$). Viscosity enters the jet velocity scaling in two ways: (i) through damping of precursor capillary waves which merge at the bubble base and weaken the pressure impulse, and (ii) through direct viscous damping of the jet formation and dynamics. These damping processes are expressed by a dependence of the jet velocity on Ohnesorge number from which critical values of $Oh$ are obtained for capillary wave damping, the onset of jet weakening, the absence of jetting and the absence of jet breakup into droplets.

Analysis of Buoyant Surface Jets

1976 ◽  
Vol 98 (3) ◽  
pp. 367-372 ◽  
Author(s):  
M. A. Shirazi ◽  
L. R. Davis
Keyword(s):  
Power Plants ◽  
Present Model ◽  
Laboratory Data ◽  
Steam Power ◽  
Thermal Plumes ◽  
Steam Power Plants ◽  
Analysis Computer ◽  
Surface Jet ◽  
Surface Jets ◽  
Best Fit

To obtain improved prediction of heated plume characteristics from a surface jet, an integral analysis computer model was modified and a comprehensive set of field and laboratory data available from the literature was gathered, analyzed, and correlated for estimating the magnitude of certain coefficients that are normally introduced in these analyses to achieve closure. The parameters so estimated include the coefficients for entrainment, turbulent exchange, drag, and shear. Since there appeared considerable scatter in the data, even after appropriate subgrouping to narrow the influence of various flow conditions on the data, only statistical procedures could be applied to find the best fit. This and other analyses of its type have been widely used in industry and government for the prediction of thermal plumes from steam power plants. Although the present model has many shortcomings, a recent independent and exhaustive assessment of such predictions revealed that in comparison with other analyses of its type the present analysis predicts the field situations more successfully.

scholarly journals The water entry of multi-droplet streams and jets

2018 ◽  
Vol 844 ◽  
pp. 1084-1111 ◽  
Author(s):  
Nathan B. Speirs ◽  
Zhao Pan ◽  
Jesse Belden ◽  
Tadd T. Truscott
Keyword(s):  
Low Frequency ◽  
Bond Number ◽  
Water Entry ◽  
Liquid Pool ◽  
Scaling Analysis ◽  
Cavity Depth ◽  
Solid Objects ◽  
Jet Impact ◽  
Energy Scaling ◽  
Quiescent Liquid

Water entry has been studied for over a century, but few studies have focused on multiple droplets impacting on a liquid bath sequentially. We connect multi-droplet streams, jets and solid objects with physical-based scaling arguments that emphasize the intrinsically similar cavities. In particular, the cavities created by the initial impact of both droplet streams and jets on an initially quiescent liquid pool exhibit the same types of cavity seal as hydrophobic spheres at low Bond number, some of which were previously unseen for jets and droplet streams. Low-frequency droplet streams exhibit an additional three new cavity seal types unseen for jets or solid spheres that can be predicted with a new non-dimensional frequency. The cavity depth and cavity velocity for both droplet and jet impact are rationalized by an energy scaling analysis and the Bernoulli equation.

The mechanics of locomotion in the squid Loligo pealei: locomotory function and unsteady hydrodynamics of the jet and intramantle pressure

2000 ◽  
Vol 203 (18) ◽  
pp. 2851-2863 ◽  
Author(s):  
E.J. Anderson ◽  
M.E. DeMont
Keyword(s):  
Mantle Cavity ◽  
Volume Flow ◽  
Working Fluid ◽  
Bernoulli Equation ◽  
Cavity Volume ◽  
Propulsive Efficiency ◽  
Jet Velocity ◽  
Loligo Pealei ◽  
Unsteady Effects

High-speed, high-resolution digital video recordings of swimming squid (Loligo pealei) were acquired. These recordings were used to determine very accurate swimming kinematics, body deformations and mantle cavity volume. The time-varying squid profile was digitized automatically from the acquired swimming sequences. Mantle cavity volume flow rates were determined under the assumption of axisymmetry and the condition of incompressibility. The data were then used to calculate jet velocity, jet thrust and intramantle pressure, including unsteady effects. Because of the accurate measurements of volume flow rate, the standard use of estimated discharge coefficients was avoided. Equations for jet and whole-cycle propulsive efficiency were developed, including a general equation incorporating unsteady effects. Squid were observed to eject up to 94 % of their intramantle working fluid at relatively high swimming speeds. As a result, the standard use of the so-called large-reservoir approximation in the determination of intramantle pressure by the Bernoulli equation leads to significant errors in calculating intramantle pressure from jet velocity and vice versa. The failure of this approximation in squid locomotion also implies that pressure variation throughout the mantle cannot be ignored. In addition, the unsteady terms of the Bernoulli equation and the momentum equation proved to be significant to the determination of intramantle pressure and jet thrust. Equations of propulsive efficiency derived for squid did not resemble Froude efficiency. Instead, they resembled the equation of rocket motor propulsive efficiency. The Froude equation was found to underestimate the propulsive efficiency of the jet period of the squid locomotory cycle and to overestimate whole-cycle propulsive efficiency when compared with efficiencies calculated from equations derived with the squid locomotory apparatus in mind. The equations for squid propulsive efficiency reveal that the refill period of squid plays a greater role, and the jet period a lesser role, in the low whole-cycle efficiencies predicted in squid and similar jet-propelled organisms. These findings offer new perspectives on locomotory hydrodynamics, intramantle pressure measurements and functional morphology with regard to squid and other jet-propelled organisms.

Experimental studies on thermosyphon using low global warming potential refrigerant HFE7000 and nanorefrigerant HFE7000/Al2O3

2020 ◽  
pp. 095440891989669
Author(s):  
R S Anand ◽  
C P Jawahar ◽  
A Brusly Solomon ◽  
Varghese Benson ◽  
Ashie Alan K ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Volume Concentration ◽  
Experimental Studies ◽  
Bond Number ◽  
Considerable Effect ◽  
Economic Feasibility ◽  
Working Fluid ◽  
Two Phase ◽  
Technology Advancement ◽  
Natural Refrigerant

Thermosyphon is used in numerous applications such as permafrost, cooling building and structures, Alaska pipeline, electronic cooling, and other applications. Improving the performance of thermosyphon is essential for technology advancement. Therefore, experimentation is conducted to improve the efficiency of thermosyphon with the natural refrigerant hydrofluoroether (HFE) and Al2O3/HFE7000 nanorefrigerant. The Al2O3 nanoparticle is chosen based on its economic feasibility and better thermo-physical properties with the refrigerants. Firstly, the preparation of Al2O3/HFE7000 nanorefrigerant is carried out specifically at different volume concentrations of the nanoparticle to check the long-term stability. Secondly, the heat transfer characteristics of the thermosyphon charged Al2O3/HFE7000 nanorefrigerant of 0.025%, 0.05%, and 0.075% volume concentration and pure HFE7000 is investigated experimentally. The nanorefrigerant charged thermosyphon experimented for different inclinations and different volume concentrations as the working fluid. It was observed that the two-phase closed thermosyphon charged with Al2O3/HFE7000 nanorefrigerant enhanced its evaporator heat transfer performance also decreased the thermal resistance of 57.5% compared with the pure HFE7000 and was at its peak for 0.05% volume concentration. The heat transfer of nanorefrigerant Al2O3/HFE7000 0.025%, 0.05%, and 0.075% volume concentration is increases 41.61%, 88.414%, and 74.362% than HFE7000. In conclusion, the results of the experiments suggest that the use of Al2O3/HFE7000 nanofluid produce a significant thermal enhancement in thermosyphon. This research also discloses the effect of dimensionless parameters such as the Bond number of the boiling phenomenon, Prandtl and condensation number of conduction phenomenon, and Ohensorge number of buoyancy phenomenon in thermosyphon with Al2O3/HFE7000 nanorefrigerant. It is identified that the volume concentration of 0.05% Al2O3/HFE7000 has a considerable effect on nondimensional parameters.

Characteristics of a Jet in the Vicinity of a Free Surface

2012 ◽  
Vol 134 (3) ◽  
Author(s):  
Jiahao Tian ◽  
Vesselina Roussinova ◽  
Ram Balachandar
Keyword(s):  
Shear Stress ◽  
Free Surface ◽  
Normal Component ◽  
Central Plane ◽  
Free Jets ◽  
Piv Measurements ◽  
Free Jet ◽  
Double Peaks ◽  
Surface Jet ◽  
Surface Jets

In this study, the characteristics of a round turbulent jet in the vicinity of a free surface are investigated. The jet issued from a nozzle located at a depth five times the nozzle diameter (d = 10 mm) below and parallel to the free surface. The jet exit velocity was 2.8 m/s and the resulting Reynolds number was 28,000. Instantaneous two-dimensional PIV measurements were obtained in the vertical central plane and in several horizontal planes at various distances (y/d = 0,±1,±2,±3± 4) from the axis of the nozzle. All fields-of-view were positioned at streamwise locations in the range of 28 < x/d < 62, where the jet interacts significantly with the free surface. The results reveal that the behavior of the surface jet is very similar to that of the free jet before it interacts with the free surface which occurs at about x/d = 30. Beyond this, the velocity normal to the free surface is diminished and those parallel to the free surface are enhanced in the region near the free surface. In the horizontal plane near the free surface (y/d = +4), the spreading of the surface jet is significantly greater than that of the free jet. The mean lateral flow in this region tends to be outward everywhere for the surface jet, while the opposite trend occurs in the free jet. Turbulence intensities in all three directions are reduced by the effect of the free surface confinement. Near the free surface, at y/d = +4, unlike the single peak streamwise turbulence intensity profile noticed in the case of the free jet, the off-axis double peaks reappear in the case of the surface jet. The magnitude of shear stress in the vertical central plane of the surface jet is smaller than that noticed in the free jet near the free surface. In identical horizontal planes, the shear stress (-uw¯) profiles are similar in both free jets and surface jets in regions where the interaction with the free surface is not significant (x/d ≈ 30). As the downstream distance increases near the free surface, the magnitudes of the shear stress profiles are larger compared to that of the free jet. An increase in the normal component of vorticity is observed in the horizontal planes near the free surface.

Plane Turbulent Surface Jets in Shallow Tailwater

2000 ◽  
Vol 123 (1) ◽  
pp. 121-127 ◽  
Author(s):  
S. A. Ead ◽  
N. Rajaratnam
Keyword(s):  
Laboratory Study ◽  
Momentum Flux ◽  
Return Flow ◽  
Volume Flux ◽  
Limited Extent ◽  
Ambient Fluid ◽  
Forward Flow ◽  
Velocity Scale ◽  
Surface Jet ◽  
Surface Jets

This paper presents a theoretical and laboratory study of plane turbulent surface jets in shallow tailwater. The main objective was to show that when the depth of tailwater is finite, the momentum flux in the forward flow in the surface jet decays appreciably with the distance from the nozzle producing the surface jet. This decay is shown to be due to the entrainment of the return flow which has negative momentum and an increase in the tailwater depth further away from the nozzle produces this return flow. An extensive set of experiments, with different Froude numbers and offset ratios, was conducted to observe and quantify the growth of the surface jet, the decay of the velocity scale, and the momentum flux and the variation of the volume flux. On the whole, the results from this study highlight the effect of the tailwater depth on the behavior of plane turbulent surface jets when the ambient fluid has a limited extent.

Flow impinging onto a conical cavity: A conical and annular nozzle combination

2009 ◽  
Vol 223 (11) ◽  
pp. 2583-2593
Author(s):  
S Z Shuja ◽  
B S Yilbas ◽  
S A Khan
Keyword(s):  
Shear Stress ◽  
Nusselt Number ◽  
Cone Angle ◽  
Working Fluid ◽  
Cavity Surface ◽  
Annular Nozzle ◽  
Cavity Depth ◽  
Conical Cavity ◽  
Transfer Rates ◽  
Laser Heated

Flow emanating from a combined conical and annular nozzle and impinging onto a conical cavity is considered. Two cone angles of the nozzle and two cavity depths are simulated for flow field around the nozzle and the cavity as well as for the heat transfer rates from the cavity surface. The conical cavity wall is assumed at 1500 K to resemble a laser-heated cavity and air is used as a working fluid. The Reynolds stress turbulence model is incorporated to account for the turbulence. It is found that the Nusselt number along the cavity surface is influenced by the cavity depth. The Nusselt number attains high values in the region close to the cavity edge. The wall shear stress at the cavity edge is influenced by the nozzle cone angle such that the shear stress increases for the nozzle cone angle of 70° in this region over values for the cone angle of 55°.

ASETS-II Oscillating Heat Pipe Space Flight Experiment: Ground Truth Results

2017 ◽  
Author(s):  
Brent S. Taft ◽  
Sally M. Smith
Keyword(s):  
Single Layer ◽  
Ground Truth ◽  
Bond Number ◽  
Working Fluid ◽  
Oscillating Heat Pipe ◽  
Ground Testing ◽  
Loop Design ◽  
The Difference ◽  
R 134A ◽  
Flight Hardware

The ASETS-II experiment consists of three oscillating heat pipes (OHPs), an electronics box, and mounting structures that control boundary conditions. Each OHP consists of 34 channels in a typical single-layer closed loop design. Butane was selected as the working fluid for OHP #1 and #2 for its performance stability. R-134a was selected for OHP #3 in order to explore the Bond number limit’s influence on OHP operation in microgravity. The ASETS-II Flight and Flight Spare hardware were subjected to a comprehensive set of ground testing to baseline performance prior to flight testing. For most test conditions, the Flight and Flight Spare test results for OHP #1 and OHP #2 are within the margin of uncertainty in the measurements. OHP #3 on the Flight hardware performs similarly to OHP #3 on the Flight Spare hardware; however, the difference in performance is outside the margin of uncertainty in the measurements. This variation in performance may be attributable to the fact that OHP #3 is being pushed to operate near its Bond number limit.

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