scholarly journals Direct Breaking of the Internal Tide near Topography: Kaena Ridge, Hawaii

2008 ◽  
Vol 38 (2) ◽  
pp. 380-399 ◽  
Author(s):  
Jody M. Klymak ◽  
Robert Pinkel ◽  
Luc Rainville
Keyword(s):  
Internal Tide ◽  
Leading Edge ◽  
Open Ocean ◽  
Small Scale ◽  
Mixing Processes ◽  
Ridge Crest ◽  
Vertical Scale ◽  
Lee Wave ◽  
Mixing Rates ◽  
New Phenomena

Abstract Barotropic to baroclinic conversion and attendant phenomena were recently examined at the Kaena Ridge as an aspect of the Hawaii Ocean Mixing Experiment. Two distinct mixing processes appear to be at work in the waters above the 1100-m-deep ridge crest. At middepths, above 400 m, mixing events resemble their open-ocean counterparts. There is no apparent modulation of mixing rates with the fortnightly cycle, and they are well modeled by standard open-ocean parameterizations. Nearer to the topography, there is quasi-deterministic breaking associated with each baroclinic crest passage. Large-amplitude, small-scale internal waves are triggered by tidal forcing, consistent with lee-wave formation at the ridge break. These waves have vertical wavelengths on the order of 400 m. During spring tides, the waves are nonlinear and exhibit convective instabilities on their leading edge. Dissipation rates exceed those predicted by the open-ocean parameterizations by up to a factor of 100, with the disparity increasing as the seafloor is approached. These observations are based on a set of repeated CTD and microconductivity profiles obtained from the research platform (R/P) Floating Instrument Platform (FLIP), which was trimoored over the southern edge of the ridge crest. Ocean velocity and shear were resolved to a 4-m vertical scale by a suspended Doppler sonar. Dissipation was estimated both by measuring overturn displacements and from microconductivity wavenumber spectra. The methods agreed in water deeper than 200 m, where sensor resolution limitations do not limit the turbulence estimates. At intense mixing sites new phenomena await discovery, and existing parameterizations cannot be expected to apply.

Flow Physics and Vortex Evolution in Annular Turbine Cascades

2002 ◽  
Author(s):  
M. Treiber ◽  
R. S. Abhari ◽  
M. Sell
Keyword(s):  
Leading Edge ◽  
Operating Conditions ◽  
Experimental Results ◽  
Small Scale ◽  
Test Case ◽  
Mixing Processes ◽  
Substantial Impact ◽  
Aerodynamic Loss ◽  
Spatially Resolved ◽  
Exit Mach Number

The evolution of flow vortices downstream of annular cascades with a specific focus upon the association between vorticity and the mechanisms of aerodynamic loss generation has been experimentally investigated. Spatially-resolved experimental results on an unstructured measurement pattern is used to identify small scale flow structures on the surface of the investigated blades and downstream of two different cascades. The test case comparison is based upon two moderately loaded turbine blade profiles, one stacked prismatically and the other on a bowed stacking line. The design operating conditions for both cascade is at a nominal exit Mach number of 0.5. The measurements were made using an ultra miniature (0.9 mm Dia) 5-hole probe. The measurement were made on 4 planes behind and one plane in front of the trailing and leading edge of the cascade respectively. The experimental results clearly show the influence of the flow structure on the evolution of the stream wise vorticities behind the blading. Detailed measurements are used to compare and evaluate the mixing processes downstream of these two cascades. It is shown that the interaction of the different vortices with the endwall boundary layer has a substantial impact on the overall total pressure loss generation.

Observed coastal sea level changes in Southeast Asia from retracked altimetry over 2002-present

2020 ◽  
Author(s):  
Yvan Gouzènes ◽  
Fabien Léger ◽  
Anny Cazenave ◽  
Florence Birol ◽  
Marcello Passaro ◽  
...  
Keyword(s):  
Time Series ◽  
Southeast Asia ◽  
Sea Level ◽  
Processing System ◽  
Leading Edge ◽  
Open Ocean ◽  
Small Scale ◽  
Coastal Zones ◽  
Sea Level Changes ◽  
Coastal Sea

<p>We present results of contemporary coastal sea level changes along the coasts of different<br>regions of Southeast Asia derived from a dedicated reprocessing of satellite altimetry data.<br>This work is performed in the context of the ESA ‘Climate Change Initiative’ sea level project<br>dedicated to provide altimetry-based sea level time series in the world coastal zones. Here is<br>focus on Southeast Asian Seas. High-frequency (20 Hz) sea level data from the Jason-1,<br>Jason-2 and Jason-3 missions are considered. The data are first retracked using the ALES<br>adaptive leading edge subwaveform retracker and further combined with the X-TRACK<br>processing system developed to optimize the accuracy of the sea level time series in coastal<br>oceans. Rates of sea level change are estimated over the period 2002-present along the Jasontracks,<br>from the open ocean to the coast. Different coastal sea level trend behaviors are<br>observed over the study period: constant trends from open ocean to the coast, sometimes<br>decreasing trends, or increasing trends within the last few km to the coast. We compare the<br>computed coastal trends in Southeast Asia with results we previously obtained in other<br>regions (Mediterranean Sea, Western Africa, Northeastern Europe). We further discuss the<br>various small-scale processes able to explain departure of the coastal sea level rate from the<br>offshore (open ocean) rate.</p>

The Triggering of Orographic Rainbands by Small-Scale Topography

2007 ◽  
Vol 64 (5) ◽  
pp. 1530-1549 ◽  
Author(s):  
Daniel J. Kirshbaum ◽  
George H. Bryan ◽  
Richard Rotunno ◽  
Dale R. Durran
Keyword(s):  
Flow Direction ◽  
Cross Flow ◽  
Leading Edge ◽  
Static Stability ◽  
Precipitation Event ◽  
Small Scale ◽  
Band Formation ◽  
Lee Waves ◽  
Lee Wave ◽  
Orographic Cloud

Abstract The triggering of convective orographic rainbands by small-scale topographic features is investigated through observations of a banded precipitation event over the Oregon Coastal Range and simulations using a cloud-resolving numerical model. A quasi-idealized simulation of the observed event reproduces the bands in the radar observations, indicating the model’s ability to capture the physics of the band-formation process. Additional idealized simulations reinforce that the bands are triggered by lee waves past small-scale topographic obstacles just upstream of the nominal leading edge of the orographic cloud. Whether a topographic obstacle in this region is able to trigger a strong rainband depends on the phase of its lee wave at cloud entry. Convective growth only occurs downstream of obstacles that give rise to lee-wave-induced displacements that create positive vertical velocity anomalies wc and nearly zero buoyancy anomalies bc as air parcels undergo saturation. This relationship is quantified through a simple analytic condition involving wc, bc, and the static stability N 2m of the cloud mass. Once convection is triggered, horizontal buoyancy gradients in the cross-flow direction generate circulations that align the bands parallel to the flow direction.

Small-scale spatial and temporal variations in mid-ocean ridge crest magmatic processes

Geology ◽  
1994 ◽  
Vol 22 (4) ◽  
pp. 375-379 ◽  
Author(s):  
M. R. Perfit ◽  
D. J. Fornari ◽  
M. C. Smith ◽  
J. F. Bender ◽  
C. H. Langmuir ◽  
...  
Keyword(s):  
Temporal Variations ◽  
Spatial And Temporal Variations ◽  
Small Scale ◽  
Ridge Crest ◽  
Mid Ocean Ridge ◽  
Magmatic Processes ◽  
Ocean Ridge

Dissipating and reflecting internal waves

2021 ◽  
Author(s):  
Callum J. Shakespeare ◽  
Brian K. Arbic ◽  
Andrew McC. Hogg
Keyword(s):  
Numerical Simulations ◽  
Linear Theory ◽  
Internal Waves ◽  
Energy Flux ◽  
Internal Tide ◽  
Internal Tides ◽  
Linear Wave ◽  
Lee Waves ◽  
Lee Wave ◽  
Upper Boundary

AbstractInternal waves generated at the seafloor propagate through the interior of the ocean, driving mixing where they break and dissipate. However, existing theories only describe these waves in two limiting cases. In one limit, the presence of an upper boundary permits bottom-generated waves to reflect from the ocean surface back to the seafloor, and all the energy flux is at discrete wavenumbers corresponding to resonant modes. In the other limit, waves are strongly dissipated such that they do not interact with the upper boundary and the energy flux is continuous over wavenumber. Here, a novel linear theory is developed for internal tides and lee waves that spans the parameter space in between these two limits. The linear theory is compared with a set of numerical simulations of internal tide and lee wave generation at realistic abyssal hill topography. The linear theory is able to replicate the spatially-averaged kinetic energy and dissipation of even highly non-linear wave fields in the numerical simulations via an appropriate choice of the linear dissipation operator, which represents turbulent wave breaking processes.

Numerical investigation of aerodynamic and acoustic characteristics of bionic airfoils inspired by bird wing

2018 ◽  
Vol 233 (11) ◽  
pp. 4004-4016 ◽  
Author(s):  
Menghao Wang ◽  
Xiaomin Liu
Keyword(s):  
Sound Pressure Level ◽  
Sound Pressure ◽  
Leading Edge ◽  
Pressure Level ◽  
Aerodynamic Noise ◽  
Small Scale ◽  
Airfoil Surface ◽  
Acoustic Characteristics ◽  
Bionic Coupling ◽  
Bionic Airfoil

Airfoil is the basic element of fluid machinery and aircraft, and the noise generated from that is an important research aspect. Aiming to reduce the aerodynamic noise around the airfoil, this study proposes an airfoil inspired by the long-eared owl wing and another airfoil coupled with the bionic airfoil profile, leading edge waves, and trailing edge serrations. Numerical simulations dependent on the large eddy simulation method coupled with the wall-adapting local eddy-viscosity model and the Ffowcs Williams and Hawkings equation are conducted to compare the aerodynamic and acoustic characteristics of two types of bionic airfoils at low Reynolds number condition. The simulations reveal the dipole characteristic of acoustic source and sound pressure level distribution at various frequencies. Two types of bionic airfoils show lower noise compared with the conventional NACA 0012 airfoil with a similar relative thickness of 12%. Compared with the bionic airfoil, the average value of sound pressure level at the monitoring points around the bionic coupling airfoil is decreased by 9.94 dB, meanwhile the lift-to-drag ratio also keep higher. The bionic coupling airfoil exerts a suppression of sound pressure fluctuation on the airfoil surfaces, which result from that the range and size of separation vortices are reduced and the distance between vortices and airfoil surface are increased. The tube-shaped vortices in the wake of airfoil are effectively restrained and split into small scale vortices, which are important to cause less aerodynamic noise around the bionic coupling airfoil. Consequently, a novel bionic coupling airfoil is developed with the excellent aerodynamic and acoustic performance.

scholarly journals On the structure of the self-sustaining cycle in separating and reattaching flows

2018 ◽  
Vol 857 ◽  
pp. 907-936 ◽  
Author(s):  
A. Cimarelli ◽  
A. Leonforte ◽  
D. Angeli
Keyword(s):  
Shear Layer ◽  
Rectangular Plate ◽  
Large Scale ◽  
Reverse Flow ◽  
Leading Edge ◽  
Streamwise Velocity ◽  
The Self ◽  
Small Scale ◽  
Spectral Evolution ◽  
Mean Velocity

The separating and reattaching flows and the wake of a finite rectangular plate are studied by means of direct numerical simulation data. The large amount of information provided by the numerical approach is exploited here to address the multi-scale features of the flow and to assess the self-sustaining mechanisms that form the basis of the main unsteadinesses of the flows. We first analyse the statistically dominant flow structures by means of three-dimensional spatial correlation functions. The developed flow is found to be statistically dominated by quasi-streamwise vortices and streamwise velocity streaks as a result of flow motions induced by hairpin-like structures. On the other hand, the reverse flow within the separated region is found to be characterized by spanwise vortices. We then study the spectral properties of the flow. Given the strongly inhomogeneous nature of the flow, the spectral analysis has been conducted along two selected streamtraces of the mean velocity field. This approach allows us to study the spectral evolution of the flow along its paths. Two well-separated characteristic scales are identified in the near-wall reverse flow and in the leading-edge shear layer. The first is recognized to represent trains of small-scale structures triggering the leading-edge shear layer, whereas the second is found to be related to a very large-scale phenomenon that embraces the entire flow field. A picture of the self-sustaining mechanisms of the flow is then derived. It is shown that very-large-scale fluctuations of the pressure field alternate between promoting and suppressing the reverse flow within the separation region. Driven by these large-scale dynamics, packages of small-scale motions trigger the leading-edge shear layers, which in turn created them, alternating in the top and bottom sides of the rectangular plate with a relatively long period of inversion, thus closing the self-sustaining cycle.

scholarly journals Influence of Large Relative Tip Clearances for a Micro Radial Fan and Design Guidelines for Increased Efficiency

2020 ◽  
Author(s):  
Patrick H. Wagner ◽  
Jan Van herle ◽  
Lili Gu ◽  
Jürg Schiffmann
Keyword(s):  
Pressure Rise ◽  
Leading Edge ◽  
High Sensitivity ◽  
Design Guidelines ◽  
Tip Clearance ◽  
Small Scale ◽  
Blade Tip ◽  
Dynamics Simulations ◽  
Experimental Findings ◽  
Blade Tip Clearance

Abstract The blade tip clearance loss was studied experimentally and numerically for a micro radial fan with a tip diameter of 19.2mm. Its relative blade tip clearance, i.e., the clearance divided by the blade height of 1.82 mm, was adjusted with different shims. The fan characteristics were experimentally determined for an operation at the nominal rotational speed of 168 krpm with hot air (200 °C). The total-to-total pressure rise and efficiency increased from 49 mbar to 68 mbar and from 53% to 64%, respectively, by reducing the relative tip clearance from 7.7% to the design value of 2.2%. Single and full passage computational fluid dynamics simulations correlate well with these experimental findings. The widely-used Pfleiderer loss correlation with an empirical coefficient of 2.8 fits the numerical simulation and the experiments within +2 efficiency points. The high sensitivity to the tip clearance loss is a result of the design specific speed of 0.80, the highly-backward curved blades (17°), and possibly the low Reynolds number (1 × 105). The authors suggest three main measures to mitigate the blade tip clearance losses for small-scale fans: (1) utilization of high-precision surfaced-grooved gas-bearings to lower the blade tip clearance, (2) a mid-loaded blade design, and (3) an unloaded fan leading edge to reduce the blade tip clearance vortex in the fan passage.

scholarly journals Physical Transport Processes that Affect the Distribution of Oil in the Gulf of Mexico: Observations and Modeling

Oceanography ◽  
2021 ◽  
Vol 34 (1) ◽  
pp. 58-75
Author(s):  
Michel Boufadel ◽  
◽  
Annalisa Bracco ◽  
Eric Chassignet ◽  
Shuyi Chen ◽  
...  
Keyword(s):  
Gulf Of Mexico ◽  
Physical Environment ◽  
Large Scale ◽  
Transport Processes ◽  
Small Scale ◽  
Surface Mixed Layer ◽  
Physical Processes ◽  
Mixing Processes ◽  
Near Surface ◽  
Wide Range

Physical transport processes such as the circulation and mixing of waters largely determine the spatial distribution of materials in the ocean. They also establish the physical environment within which biogeochemical and other processes transform materials, including naturally occurring nutrients and human-made contaminants that may sustain or harm the region’s living resources. Thus, understanding and modeling the transport and distribution of materials provides a crucial substrate for determining the effects of biological, geological, and chemical processes. The wide range of scales in which these physical processes operate includes microscale droplets and bubbles; small-scale turbulence in buoyant plumes and the near-surface “mixed” layer; submesoscale fronts, convergent and divergent flows, and small eddies; larger mesoscale quasi-geostrophic eddies; and the overall large-scale circulation of the Gulf of Mexico and its interaction with the Atlantic Ocean and the Caribbean Sea; along with air-sea interaction on longer timescales. The circulation and mixing processes that operate near the Gulf of Mexico coasts, where most human activities occur, are strongly affected by wind- and river-induced currents and are further modified by the area’s complex topography. Gulf of Mexico physical processes are also characterized by strong linkages between coastal/shelf and deeper offshore waters that determine connectivity to the basin’s interior. This physical connectivity influences the transport of materials among different coastal areas within the Gulf of Mexico and can extend to adjacent basins. Major advances enabled by the Gulf of Mexico Research Initiative in the observation, understanding, and modeling of all of these aspects of the Gulf’s physical environment are summarized in this article, and key priorities for future work are also identified.

Sign in / Sign up

Export Citation Format

Share Document