scholarly journals An Improved Integral Model for a Non-Buoyant Turbulent Jet in Wave Environment

Water ◽  
2019 ◽  
Vol 11 (4) ◽  
pp. 765 ◽  
Author(s):  
Fang ◽  
Chen ◽  
Xu ◽  
Otoo ◽  
Lu
Keyword(s):  
Cross Section ◽  
Near Field ◽  
Spreading Rate ◽  
Turbulent Jet ◽  
Integral Model ◽  
Wave Direction ◽  
Wave Condition ◽  
Initial Dilution ◽  
Improved Model ◽  
Vertical Jet

The integral model developed by Chin (1988) for modelling a non-buoyant turbulent jet in wave environment is improved by introducing two new parameters, i.e., the jet spreading rate c1 and the shortening rate pe. The parameter c1 is used to simplify the model by explicitly describing the radial velocity and scalar profiles under the assumption of “instantaneous” Gaussian distribution. By doing so, the governing equations can be easily solved by simultaneously integrating the conservation laws of momentum and scalars across the jet cross-section. The parameter pe is used to shorten the initial length of zone of flow establishment (ZFE), so as to more accurately account for the wave effect on the jet initial dilution near the jet nozzle. The parameters are calibrated by the particle image velocimetry (PIV)-measured data from three groups of jet experiments, i.e., the group of vertical jet towards the wave direction (vertical jet), the group of horizontal jet along the wave direction (co-wave jet) and the group of horizontal jet opposing to the wave direction (op-wave jet). The results show that both parameters are well related to the ratio of jet and wave characteristic velocities in the same group, but it is not able to be generalized among different groups. Under the same wave condition, the value of c1 in the vertical jet is larger than that of the horizontal jets; while the value of pe in the vertical jet is smaller than that of the horizontal jets, which indicates that the jet has a faster decay rate of centerline velocity and a wider width of jet cross-section profile in the near field when it is vertically discharged into the wave environment. With the well-calibrated parameters, the improved model can achieve a higher accuracy than the original model developed by Chin (1988).

Near-Field Characteristics of a Turbulent Jet With Ring Injectors

2009 ◽  
Author(s):  
Hamid R. Rahai ◽  
Shahab Moayedian
Keyword(s):  
Cross Section ◽  
Near Field ◽  
Turbulent Jet ◽  
Hole Injection ◽  
Mean Velocity ◽  
Blowing Ratio ◽  
Velocity Decay ◽  
Axial Variation ◽  
Inner Diameter ◽  
Axis Switching

Mixing effectiveness of a heated turbulent jet with two-hole and three-hole ring injectors was experimentally investigated. The injectors were rings with square cross section with side dimensions of approximately 5 mm. The ratio of the ring thickness to the jet inner diameter was 4.7%. For the two-hole injector, the injecting holes were at 180 degrees from each other and for the three-hole injectors, the holes were spaced at 120 degrees. The maximum mean velocity of the jet was at approximately 4 m/s which corresponds to an approximate Reynolds number based on the jet inner diameter of 14,676. The total blowing ratio as compared to the axial momentum for each configuration was at 2%. Results indicate significant increases in RMS fluctuation and mean velocity decay with the ring injectors with these effects being more pronounced for the three-hole injection. Axial variation of momentum thicknesses indicates a possibility of axis switching in the near field for the three-hole ring injector.

scholarly journals EFFICIENT SIMULATION TOOL TO CHARACTERIZE THE RADAR CROSS SECTION OF A PEDESTRIAN IN NEAR FIELD

2020 ◽  
Vol 100 ◽  
pp. 145-159
Author(s):  
Giovanni Manfredi ◽  
Paola Russo ◽  
Alfredo De Leo ◽  
Graziano Cerri
Keyword(s):  
Cross Section ◽  
Near Field ◽  
Radar Cross Section ◽  
Simulation Tool ◽  
Efficient Simulation

scholarly journals Dye-doped spheres with plasmonic semi-shells: Lasing modes and scattering at realistic gain levels

2013 ◽  
Vol 4 ◽  
pp. 974-987 ◽  
Author(s):  
Nikita Arnold ◽  
Boyang Ding ◽  
Calin Hrelescu ◽  
Thomas A Klar
Keyword(s):  
Cross Section ◽  
Near Field ◽  
Field Enhancement ◽  
Higher Order ◽  
Silver Layer ◽  
Far Field ◽  
Spectral Features ◽  
Polystyrene Spheres ◽  
Higher Order Modes ◽  
Lasing Modes

We numerically simulate the compensation of absorption, the near-field enhancement as well as the differential far-field scattering cross section for dye-doped polystyrene spheres (radius 195 nm), which are half-covered by a silver layer of 10–40 nm thickness. Such silver capped spheres are interesting candidates for nanoplasmonic lasers, so-called spasers. We find that spasing requires gain levels less than 3.7 times higher than those in commercially available dye-doped spheres. However, commercially available concentrations are already apt to achieve negative absorption, and to narrow and enhance scattering by higher order modes. Narrowing of the plasmonic modes by gain also makes visible higher order modes, which are normally obscured by the broad spectral features of the lower order modes. We further show that the angular distribution of the far-field scattering of the spasing modes is by no means dipole-like and is very sensitive to the geometry of the structure.

scholarly journals The Use of a Numerical Weather Prediction Model to Simulate Near-Field Volcanic Plumes

Atmosphere ◽  
2020 ◽  
Vol 11 (6) ◽  
pp. 594
Author(s):  
Ralph R. Burton ◽  
Mark J. Woodhouse ◽  
Alan M. Gadian ◽  
Stephen D. Mobbs
Keyword(s):  
Numerical Weather Prediction ◽  
Near Field ◽  
Weather Prediction ◽  
Wrf Model ◽  
Integral Model ◽  
Eruption Column ◽  
Volcanic Plumes ◽  
Numerical Weather ◽  
Essential Components ◽  
Nwp Model

In this paper, a state-of the art numerical weather prediction (NWP) model is used to simulate the near-field plume of a Plinian-type volcanic eruption. The NWP model is run at very high resolution (of the order of 100 m) and includes a representation of physical processes, including turbulence and buoyancy, that are essential components of eruption column dynamics. Results are shown that illustrate buoyant gas plume dynamics in an atmosphere at rest and in an atmosphere with background wind, and we show that these results agree well with those from theoretical models in the quiescent atmosphere. For wind-blown plumes, we show that features observed in experimental and natural settings are reproduced in our model. However, when comparing with predictions from an integral model using existing entrainment closures there are marked differences. We speculate that these are signatures of a difference in turbulent mixing for uniform and shear flow profiles in a stratified atmosphere. A more complex implementation is given to show that the model may also be used to examine the dispersion of heavy volcanic gases such as sulphur dioxide. Starting from the standard version of the weather research and forecasting (WRF) model, we show that minimal modifications are needed in order to model volcanic plumes. This suggests that the modified NWP model can be used in the forecasting of plume evolution during future volcanic events, in addition to providing a virtual laboratory for the testing of hypotheses regarding plume behaviour.

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