scholarly journals Análise espacial dos ventos no Centro de Lançamento de Alcântara, Maranhão

2018 ◽  
Vol 40 ◽  
pp. 57
Author(s):  
Vinicius Milanez Couto ◽  
Gilberto Fisch
Keyword(s):  
Sea Breeze ◽  
Surface Flow ◽  
Surface Boundary ◽  
Trade Winds ◽  
Surface Boundary Layer ◽  
Weather Forecasts ◽  
Fifth Generation ◽  
Average Wind ◽  
Spatial Differences ◽  
Atmospheric Phenomena

The wind at the Alcântara Launch Center (ALC), which presents as main characteristics an oceanic behavior, influenced by the trade winds and the sea breeze, and modified by the ocean-continent interface and local topography. Therefore, it is necessary to study the characteristics of the site flow, highlighting the influence of the surface boundary layer and the validity of the surface flow homogeneity. In this study will be used the data of two anemometric towers installed in the ALC to evaluate spatial differences in the characteristics of the average wind and its daily cycle. For comparison, data from the ERA5 reanalysis, the fifth generation created by European Centre for Medium-Range Weather Forecasts (ECMWF). The results show that the anemometric towers present, on average, similar characteristics and that the data from the reanalysis can be used for studies of mesoscale atmospheric phenomena that occur on the surface.

scholarly journals Some cavitation experiments with dilute polymer solutions

1970 ◽  
Vol 44 (1) ◽  
pp. 51-63 ◽  
Author(s):  
Christopher Brennen
Keyword(s):  
Surface Flow ◽  
Cavity Surface ◽  
Surface Boundary ◽  
Surface Boundary Layer ◽  
Dilute Polymer Solutions ◽  
Turbulent Drag ◽  
Boundary Layer Instability ◽  
Drag Reducing Additive ◽  
Principal Subject ◽  
Initial Objective

Experiments on fully developed cavity flows were carried out with the prime initial objective of investigating the effects of the addition of small quantities of ‘turbulent drag reducing additive’ upon the cavity-surface boundary-layer instability and transition reported in the previous paper (Brennen 1970). However, in most instances, the additives were found to cause an unforeseen instability in the wetted surface flow around the headform. Upon convection, the resulting disturbances dramatically disfigured the cavity surface, thus negating the original purpose. This new phenomenon warranted investigation and became the principal subject of this paper.

scholarly journals Numerical investigations of the free surface flow around a surface piercing hydrofoil

2021 ◽  
Vol 44 ◽  
pp. 87-94
Author(s):  
Costel Ungureanu
Keyword(s):  
Free Surface ◽  
Free Surface Flow ◽  
Efficiency Index ◽  
Surface Flow ◽  
Point Of View ◽  
Breaking Wave ◽  
Surface Boundary ◽  
Surface Boundary Layer ◽  
Boundary Layer Interaction ◽  
Wave Effects

Starting with January 2013, naval architects faces new challenges, as all ships greater than 400 tons must comply with energy efficiency index (MPEC 62, 2011). From ship hydrodynamics point of view one handy solution is using Energy Saving Devices (ESD), with the main purpose to improve the flow parameters entering the propeller. For ballast loading condition the ESD may intersect the free surface disturbing and complicating the flow due to free surface /boundary layer interaction, turbulence and breaking wave effects that coexist and which are not completely clarified so far. Therefore, a free surface flow around a NACA 0012 surface piercing hydrofoil is numerically investigated and the results are compared to experimental results obtained in the Towing Tank of the Naval Architecture Faculty, “Dunarea de Jos” University of Galati. The comparison includes drag and free surface elevation on hydrofoil surface together with numerical uncertainty.

scholarly journals Fire Whirl Evolution Observed during a Valley Wind-Sea Breeze Reversal

2011 ◽  
Vol 2011 ◽  
pp. 1-12 ◽  
Author(s):  
Daisuke Seto ◽  
Craig B. Clements
Keyword(s):  
Wind Shear ◽  
Vertical Wind Shear ◽  
Sea Breeze ◽  
Atmospheric Environment ◽  
Surface Boundary ◽  
Valley Wind ◽  
Surface Boundary Layer ◽  
Near Surface ◽  
Fire Front ◽  
Fire Whirl

This observational study documented the atmospheric environment of a prescribed fire conducted in a narrow valley when a small fire whirl developed during a mesoscale wind reversal. Based on analysis of in situ meteorological measurements, it is hypothesized that the fire whirl formed due to the presence of strong vertical wind shear caused by the interaction of a sea breeze front with a weaker up-valley wind. Vorticity generated by the interaction of the wind shear and the fire front was estimated to be ~0.2 s−1. Peak turbulence kinetic energy was caused by the wind shear rather than the buoyancy generated by the fire front. It was also found that the convective Froude number itself may not be sufficient for fire whirl prediction since it is less relevant to the near-surface boundary-layer turbulence generated by environmental wind shear. Observations from this case study indicate that even low-intensity prescribed fires can result in the formation of fire whirls due to mesoscale changes in the ambient atmospheric environment.

scholarly journals Submesoscale Vorticity and Divergence in the Alboran Sea: Scale and Depth Dependence

2021 ◽  
Vol 8 ◽  
Author(s):  
Giovanni Esposito ◽  
Maristella Berta ◽  
Luca Centurioni ◽  
Shaun Johnston ◽  
John Lodise ◽  
...  
Keyword(s):  
World Ocean ◽  
Surface Flow ◽  
Surface Boundary ◽  
Wind Effects ◽  
Alboran Sea ◽  
Surface Boundary Layer ◽  
Positive Vorticity ◽  
Area Of Interest ◽  
Turbulent Process ◽  
Alborán Sea

The statistics of submesoscale divergence and vorticity (kinematic properties, KPs) in the Alboran Sea (Mediterranean Sea) are investigated, using data from drifters released during two experiments in June 2018 and April 2019 in the framework of the Coherent Lagrangian Pathways from the Surface Ocean to Interior (CALYPSO) project. Surface drifters sampling the first meter of water (CARTHE and CODE) and 15 m drifters (SVP) are considered. The area of interest is dominated by processes of strong frontogenesis and eddy formation as well as mixing, related to the high lateral gradients between Mediterranean and Atlantic waters. Drifter coverage and distribution allow to investigate the dependence of KPs on horizontal scales in a range between 1 and 16 km, that effectively bridges submesoscale and mesoscale processes, and at two depths, of 1 and 15 m. For both experiments, the surface flow is highly ageostrophic at 1 km scale, with positive vorticity skewness indicating the presence of submesoscale features. Surface divergence quickly decreases at increasing scales with a slope compatible with a turbulent process with broadband wavenumber spectrum, suggesting the influence of surface boundary layer processes such as wind effects, waves and Langmuir cells at the smaller scales. Vorticity, on the other hand, has a significantly slower decay, suggesting interaction between submesoscale and mesoscale dynamics. Results at 15 m are characterized by reduced ageostrophic dynamics with respect to the surface, especially for divergence. Submesoscale processes are present but appear attenuated in terms of KP magnitude and skewness. The results are generally consistent for the two experiments, despite the observed differences in the mixed layer stratification, suggesting that submesoscale instabilities occur mostly at surface fronts associated with filaments of Atlantic and Mediterranean waters that are present in both cases. The results are compared with previous literature results in other parts of the world ocean and a synthesis is provided. Good agreement with previous surface results is found, suggesting some general properties for divergence and vorticity scale dependence. The importance of further investigating very high resolution frontal processes at scales of tens of meters, as well as processes of interaction with high wind effects is highlighted.

scholarly journals THE SHEAR STEESS OF SEA BREEZE ON A SWASH ZONE

1970 ◽  
Vol 1 (12) ◽  
pp. 15 ◽  
Author(s):  
Shih-Ang Hsu
Keyword(s):  
Shear Stress ◽  
Sea Breeze ◽  
Surface Boundary ◽  
Neutral Stability ◽  
Temperature Profiles ◽  
Swash Zone ◽  
Unstable Condition ◽  
Surface Boundary Layer ◽  
Stress Coefficient ◽  
Fort Walton

Measurements of shear stress under the effect of a sea hreeze were made by simultaneous wind and temperature profiles over a shore near Fort Walton Beach, Florida It was found that the sea breeze In the surface boundary layer is in the atmospheric free-convection, regime The measured shear stress coefficient is in conformity with that obtained by other investigators by the sea surface tilt method under the unstable condition For coastal applications, the result is found to be more reliable than those assumed coefficients obtained under neutral stability for this localized coastal wind system.

Prediction of Atmospheric Turbulence Characteristics for Surface Boundary Layer using Empirical Spectral Methods

2020 ◽  
Author(s):  
Yagya Dutta Dwivedi ◽  
Vasishta Bhargava Nukala ◽  
Satya Prasad Maddula ◽  
Kiran Nair
Keyword(s):  
Boundary Layer ◽  
Time Series ◽  
Surface Roughness ◽  
Wind Speed ◽  
Atmospheric Turbulence ◽  
Surface Boundary ◽  
Low Frequencies ◽  
Surface Boundary Layer ◽  
Power Spectral ◽  
Mean Wind Speed

Abstract Atmospheric turbulence is an unsteady phenomenon found in nature and plays significance role in predicting natural events and life prediction of structures. In this work, turbulence in surface boundary layer has been studied through empirical methods. Computer simulation of Von Karman, Kaimal methods were evaluated for different surface roughness and for low (1%), medium (10%) and high (50%) turbulence intensities. Instantaneous values of one minute time series for longitudinal turbulent wind at mean wind speed of 12 m/s using both spectra showed strong correlation in validation trends. Influence of integral length scales on turbulence kinetic energy production at different heights is illustrated. Time series for mean wind speed of 12 m/s with surface roughness value of 0.05 m have shown that variance for longitudinal, lateral and vertical velocity components were different and found to be anisotropic. Wind speed power spectral density from Davenport and Simiu profiles have also been calculated at surface roughness of 0.05 m and compared with k−1 and k−3 slopes for Kolmogorov k−5/3 law in inertial sub-range and k−7 in viscous dissipation range. At high frequencies, logarithmic slope of Kolmogorov −5/3rd law agreed well with Davenport, Harris, Simiu and Solari spectra than at low frequencies.

scholarly journals Cloud Radar Observations of Diurnal and Seasonal Cloudiness over Reunion Island

Atmosphere ◽  
2021 ◽  
Vol 12 (7) ◽  
pp. 868
Author(s):  
Jonathan Durand ◽  
Edouard Lees ◽  
Olivier Bousquet ◽  
Julien Delanoë ◽  
François Bonnardot
Keyword(s):  
Sea Breeze ◽  
Satellite System ◽  
Research Infrastructure ◽  
Weather Data ◽  
Reunion Island ◽  
Wet Season ◽  
Trade Winds ◽  
Cloud Radar ◽  
Réunion Island ◽  
Global Navigation Satellite

In November 2016, a 95 GHz cloud radar was permanently deployed in Reunion Island to investigate the vertical distribution of tropical clouds and monitor the temporal variability of cloudiness in the frame of the pan-European research infrastructure Aerosol, Clouds and Trace gases Research InfraStructure (ACTRIS). In the present study, reflectivity observations collected during the two first years of operation (2016–2018) of this vertically pointing cloud radar are relied upon to investigate the diurnal and seasonal cycle of cloudiness in the northern part of this island. During the wet season (December–March), cloudiness is particularly pronounced between 1–3 km above sea level (with a frequency of cloud occurrence of 45% between 12:00–19:00 LST) and 8–12 km (with a frequency of cloud occurrence of 15% between 14:00–19:00 LST). During the dry season (June–September), this bimodal vertical mode is no longer observed and the vertical cloud extension is essentially limited to a height of 3 km due to both the drop-in humidity resulting from the northward migration of the ITCZ and the capping effect of the trade winds inversion. The frequency of cloud occurrence is at its maximum between 13:00–18:00 LST, with a probability of 35% at 15 LST near an altitude of 2 km. The analysis of global navigation satellite system (GNSS)-derived weather data also shows that the diurnal cycle of low- (1–3 km) and mid-to-high level (5–10 km) clouds is strongly correlated with the diurnal evolution of tropospheric humidity, suggesting that additional moisture is advected towards the island by the sea breeze regime. The detailed analysis of cloudiness observations collected during the four seasons sampled in 2017 and 2018 also shows substantial differences between the two years, possibly associated with a strong positive Indian Ocean Southern Dipole (IOSD) event extending throughout the year 2017.

scholarly journals Aerodynamics of smooth and rough square-section prisms at incidence in very high Reynolds-number cross-flows

2021 ◽  
Vol 62 (3) ◽  
Author(s):  
Nils Paul van Hinsberg
Keyword(s):  
Reynolds Number ◽  
Cross Sections ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Surface Boundary ◽  
Experimental Proof ◽  
Surface Boundary Layer ◽  
Pitch Moment ◽  
The Mean ◽  
High Reynolds

Abstract The aerodynamics of smooth and slightly rough prisms with square cross-sections and sharp edges is investigated through wind tunnel experiments. Mean and fluctuating forces, the mean pitch moment, Strouhal numbers, the mean surface pressures and the mean wake profiles in the mid-span cross-section of the prism are recorded simultaneously for Reynolds numbers between 1$$\times$$ × 10$$^{5}$$ 5 $$\le$$ ≤ Re$$_{D}$$ D $$\le$$ ≤ 1$$\times$$ × 10$$^{7}$$ 7 . For the smooth prism with $$k_s$$ k s /D = 4$$\times$$ × 10$$^{-5}$$ - 5 , tests were performed at three angles of incidence, i.e. $$\alpha$$ α = 0$$^{\circ }$$ ∘ , −22.5$$^{\circ }$$ ∘ and −45$$^{\circ }$$ ∘ , whereas only both “symmetric” angles were studied for its slightly rough counterpart with $$k_s$$ k s /D = 1$$\times$$ × 10$$^{-3}$$ - 3 . First-time experimental proof is given that, within the accuracy of the data, no significant variation with Reynolds number occurs for all mean and fluctuating aerodynamic coefficients of smooth square prisms up to Reynolds numbers as high as $$\mathcal {O}$$ O (10$$^{7}$$ 7 ). This Reynolds-number independent behaviour applies to the Strouhal number and the wake profile as well. In contrast to what is known from square prisms with rounded edges and circular cylinders, an increase in surface roughness height by a factor 25 on the current sharp-edged square prism does not lead to any notable effects on the surface boundary layer and thus on the prism’s aerodynamics. For both prisms, distinct changes in the aerostatics between the various angles of incidence are seen to take place though. Graphic abstract

Sign in / Sign up

Export Citation Format

Share Document