scholarly journals Quantifying the Airflow Distortion over Merchant Ships. Part I: Validation of a CFD Model

2006 ◽  
Vol 23 (3) ◽  
pp. 341-350 ◽  
Author(s):  
Bengamin I. Moat ◽  
Margaret J. Yelland ◽  
Robin W. Pascal ◽  
Anthony F. Molland
Keyword(s):  
Wind Speed ◽  
Charles Darwin ◽  
Reverse Direction ◽  
Cfd Model ◽  
Mean Flow ◽  
Flow Distortion ◽  
Flux Measurements ◽  
Computational Fluid Dynamics Cfd ◽  
The Mean

Abstract The effects of flow distortion created by the ship’s hull and superstructure bias wind speed measurements made from anemometers located on ships. Flow distortion must be taken into account if accurate air–sea flux measurements are to be achieved. Little work has been undertaken to examine the wind speed bias due to flow distortion in wind speed reports from voluntary observing ships (VOS). In this first part of a two-part paper the accuracy of the computational fluid dynamics (CFD) code VECTIS in simulating the airflow over VOS is investigated. Simulations of the airflow over a representation of the bridge of a VOS are compared to in situ wind speed measurements made from six anemometers located above the bridge of the RRS Charles Darwin. The ship’s structure was ideal for reproducing the flow over VOS when the wind is blowing onto either beam. The comparisons showed VECTIS was accurate to within 4% in predicting the wind speed over ships, except in extreme cases such as wake regions or the region close to the bridge top where the flow may be stagnant or reverse direction. The study showed that there was little change in the numerically predicted flow pattern above the bridge with change in Reynolds number between 2 × 105 and 1 × 107. The findings showed that the CFD code VECTIS can reliably be used to determine the mean flow above typical VOS.

scholarly journals Direct Flux Measurements from Mobile Platforms at Sea: Motion and Airflow Distortion Corrections Revisited

2015 ◽  
Vol 32 (6) ◽  
pp. 1163-1178 ◽  
Author(s):  
Sebastian Landwehr ◽  
Niall O’Sullivan ◽  
Brian Ward
Keyword(s):  
Wind Speed ◽  
Correction Method ◽  
New Method ◽  
Wind Vector ◽  
Mean Flow ◽  
Mobile Platforms ◽  
Flow Distortion ◽  
Scalar Fluxes ◽  
Flux Measurements ◽  
Bulk Model

AbstractShip-based measurements of wind speed and direct fluxes are affected by airflow distortion that can lead to a tilt of the wind vector as well as acceleration or deceleration of the wind speed. Direct flux measurements are additionally affected by the fluctuating velocity of the platform. The classic approach is to first correct the wind speed for angular and translational platform velocities and thereafter rotate the wind vector into the mean flow. This study finds that for ships under way, this leads to an overestimation of the vector tilt and biased flux estimates. This may explain the common observation that flux estimates from ships in transit have lower quality than measurements taken on station. Here an alternative approach is presented, where the flow-distortion-induced tilt of the wind vector is estimated from the 3D wind speed measurements and applied to the apparent wind vector. The tilt correction is carried out after correction for the fluctuating part of the platform velocity but before removing the ship’s mean translational velocity. This new method significantly improved the agreement of direct momentum flux measurements made from a ship under way with the parameterization of the COARE3.5 bulk model. The sensitivity of the eddy covariance measurements of momentum and scalar fluxes to the choice of the tilt-motion correction method is analyzed, and this study proposes that a reanalysis of previous direct flux measurements with the new method discussed here can improve researchers’ understanding of air–sea interaction.

scholarly journals Linking aerosol fluxes in street canyons to urban city-scale emissions

2009 ◽  
Vol 9 (5) ◽  
pp. 18065-18112
Author(s):  
B. K. Tay ◽  
G. B. McFiggans ◽  
D. P. Jones ◽  
M. W. Gallagher ◽  
C. Martin ◽  
...  
Keyword(s):  
Eddy Viscosity ◽  
Field Experiments ◽  
Ultrafine Particle ◽  
Cfd Model ◽  
Mean Flow ◽  
Street Canyons ◽  
First Order ◽  
Urban City ◽  
Flux Measurements ◽  
Computational Fluid Dynamics Cfd

Abstract. In this study we investigate ultrafine particle (UFP) fluxes using a first order eddy viscosity turbulence closure Computational Fluid Dynamics (CFD) model and determine the different factors that influence emissions of UFP into the urban boundary layer. Both vertical turbulent fluxes as well as the fluxes due to mean flow are shown to contribute to the overall ventilation characteristics of street canyons. We then derive a simple parameterised numerical prediction model for canyon top UFP venting which is then compared with tower based micrometeorological flux measurements obtained during the REPARTEE and CityFlux field experiments.

scholarly journals Investigation of dominant traveling 10-day wave components using long-term MERRA-2 database

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Chunming Huang ◽  
Wei Li ◽  
Shaodong Zhang ◽  
Gang Chen ◽  
Kaiming Huang ◽  
...  
Keyword(s):  
Flow Instability ◽  
Transmission Condition ◽  
Wave Number ◽  
Mean Flow ◽  
Excited Wave ◽  
Propagating Waves ◽  
Zonal Wave Number ◽  
The Mean

AbstractThe eastward- and westward-traveling 10-day waves with zonal wavenumbers up to 6 from surface to the middle mesosphere during the recent 12 years from 2007 to 2018 are deduced from MERRA-2 data. On the basis of climatology study, the westward-propagating wave with zonal wave number 1 (W1) and eastward-propagating waves with zonal wave numbers 1 (E1) and 2 (E2) are identified as the dominant traveling ones. They are all active at mid- and high-latitudes above the troposphere and display notable month-to-month variations. The W1 and E2 waves are strong in the NH from December to March and in the SH from June to October, respectively, while the E1 wave is active in the SH from August to October and also in the NH from December to February. Further case study on E1 and E2 waves shows that their latitude–altitude structures are dependent on the transmission condition of the background atmosphere. The presence of these two waves in the stratosphere and mesosphere might have originated from the downward-propagating wave excited in the mesosphere by the mean flow instability, the upward-propagating wave from the troposphere, and/or in situ excited wave in the stratosphere. The two eastward waves can exert strong zonal forcing on the mean flow in the stratosphere and mesosphere in specific periods. Compared with E2 wave, the dramatic forcing from the E1 waves is located in the poleward regions.

scholarly journals The influence of idealized surface heterogeneity on virtual turbulent flux measurements

2018 ◽  
Vol 18 (7) ◽  
pp. 5059-5074 ◽  
Author(s):  
Frederik De Roo ◽  
Matthias Mauder
Keyword(s):  
Energy Budget ◽  
Turbulent Flux ◽  
Surface Heterogeneity ◽  
Surface Fluxes ◽  
Convective Conditions ◽  
Mean Flow ◽  
Flux Divergence ◽  
Length Scales ◽  
Flux Measurements ◽  
The Mean

Abstract. The imbalance of the surface energy budget in eddy-covariance measurements is still an unsolved problem. A possible cause is the presence of land surface heterogeneity, which affects the boundary-layer turbulence. To investigate the impact of surface variables on the partitioning of the energy budget of flux measurements in the surface layer under convective conditions, we set up a systematic parameter study by means of large-eddy simulation. For the study we use a virtual control volume approach, which allows the determination of advection by the mean flow, flux-divergence and storage terms of the energy budget at the virtual measurement site, in addition to the standard turbulent flux. We focus on the heterogeneity of the surface fluxes and keep the topography flat. The surface fluxes vary locally in intensity and these patches have different length scales. Intensity and length scales can vary for the two horizontal dimensions but follow an idealized chessboard pattern. Our main focus lies on surface heterogeneity of the kilometer scale, and one order of magnitude smaller. For these two length scales, we investigate the average response of the fluxes at a number of virtual towers, when varying the heterogeneity length within the length scale and when varying the contrast between the different patches. For each simulation, virtual measurement towers were positioned at functionally different positions (e.g., downdraft region, updraft region, at border between domains, etc.). As the storage term is always small, the non-closure is given by the sum of the advection by the mean flow and the flux-divergence. Remarkably, the missing flux can be described by either the advection by the mean flow or the flux-divergence separately, because the latter two have a high correlation with each other. For kilometer scale heterogeneity, we notice a clear dependence of the updrafts and downdrafts on the surface heterogeneity and likewise we also see a dependence of the energy partitioning on the tower location. For the hectometer scale, we do not notice such a clear dependence. Finally, we seek correlators for the energy balance ratio in the simulations. The correlation with the friction velocity is less pronounced than previously found, but this is likely due to our concentration on effectively strongly to freely convective conditions.

A Novel Vibrating Ribbon Technique

2005 ◽  
Author(s):  
Jonathan H. Watmuff
Keyword(s):  
Test Section ◽  
Vibration Amplitude ◽  
Wave Amplitude ◽  
Separation Bubble ◽  
Wind Tunnel Test ◽  
Mean Flow ◽  
Test Plate ◽  
Numerical Predictions ◽  
The Mean

A novel vibrating ribbon apparatus is described that is active over the full span of a wind tunnel test section. The spanwise uniformity of the vibration amplitude and other ribbon characteristics are considered in detail. The height of each end of the ribbon above the test plate can be adjusted in situ, while the ribbon is vibrating and with flow in the test section, thereby allowing the response of the layer to be easily tuned. The growth of the wave amplitude downstream of the ribbon is shown to agree with numerical predictions. However, two or three wavelengths of development are required before the wave amplitude follows the predicted growth. The flow around an inactive ribbon is examined using a commercial CFD solver and features such as a miniature separation bubble just downstream of the ribbon are revealed. The distance required for the mean flow to recover from the disturbance introduced by the ribbon is greater when the ribbon is located further from the wall. The mean flow recovers to form a boundary layer that is slightly thicker than the undisturbed flow. Experimental measurements indicate that the distance required for the wave motions to follow predicted behavior is about 4 or 5 times larger than distance for recovery of the mean flow.

scholarly journals Experimental verification of a CFD model for the closed plant factory under artificial lighting

2020 ◽  
Vol 213 ◽  
pp. 03013
Author(s):  
Wei Lu ◽  
Yiwen Hu ◽  
Shenghan Zhou ◽  
Xin Zhang ◽  
Quan Yuan ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Air Temperature ◽  
Experimental Verification ◽  
Cfd Model ◽  
Air Velocity ◽  
Artificial Lighting ◽  
Mean Relative Error ◽  
Plant Factory ◽  
Computational Fluid Dynamics Cfd ◽  
The Mean

A computational fluid dynamics (CFD) model for the closed plant factory under artificial lighting has been developed in this study, the experimental verification of CFD model with the air velocity value was compared with the measured air temperature value. The results showed that the mean relative error of validation with the air velocity was 15%, and comparable with experimentally observed air temperature profile inside the plant factory with RMSE of 3% which show the utility of CFD to study plant factory microclimatic parameters.

scholarly journals Influence of Parapets on Wave Overtopping on Mound Breakwaters with Crown Walls

2019 ◽  
Vol 11 (24) ◽  
pp. 7109 ◽  
Author(s):  
Jorge Molines ◽  
Arnau Bayon ◽  
M. Esther Gómez-Martín ◽  
Josep R. Medina
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Laboratory Tests ◽  
Cfd Model ◽  
Wave Overtopping ◽  
Numerical Tests ◽  
Computational Fluid Dynamics Cfd ◽  
The Mean

Background literature on the influence of parapets on the overtopping of mound breakwaters is limited. In this study, numerical tests were conducted using computational fluid dynamics (CFD) to analyze the influence of nine crown wall geometries (seven with parapets). The CFD model was implemented in OpenFOAM® and successfully validated with laboratory tests. A new estimator of the dimensionless mean wave-overtopping discharges (logQ) on structures with parapets is proposed. The new estimator depends on the estimation of logQ of the same structure without a parapet. The effects on wave overtopping of the parapet angle (εp), parapet width (wp), and parapet height (hp) were analyzed. Low values of εp and wp/hp ≈ 1 produced the highest parapet effectiveness to reduce the mean wave-overtopping discharges.

scholarly journals Mapping flow distortion on oceanographic platforms using computational fluid dynamics

Ocean Science ◽  
2013 ◽  
Vol 9 (5) ◽  
pp. 855-866 ◽  
Author(s):  
N. O'Sullivan ◽  
S. Landwehr ◽  
B. Ward
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Wind Speed ◽  
Close Agreement ◽  
Velocity Fields ◽  
Experimental Measurements ◽  
Flow Distortion ◽  
Direct Measurements ◽  
Computational Fluid Dynamics Cfd ◽  
Set Up

Abstract. Wind speed measurements over the ocean on ships or buoys are affected by flow distortion from the platform and by the anemometer itself. This can lead to errors in direct measurements and the derived parametrisations. Here we computational fluid dynamics (CFD) to simulate the errors in wind speed measurements caused by flow distortion on the RV Celtic Explorer. Numerical measurements were obtained from the finite-volume CFD code OpenFOAM, which was used to simulate the velocity fields. This was done over a range of orientations in the test domain from −60 to +60° in increments of 10°. The simulation was also set up for a range of velocities, ranging from 5 to 25 m s−1 in increments of 0.5 m s−1. The numerical analysis showed close agreement to experimental measurements.

The nonlinear stability of a free shear layer in the viscous critical layer régime

1980 ◽  
Vol 293 (1408) ◽  
pp. 643-672 ◽  
Keyword(s):  
Shear Layer ◽  
Critical Layer ◽  
Reynolds Stresses ◽  
Free Shear Layer ◽  
Mean Flow ◽  
Viscous Effects ◽  
Flow Distortion ◽  
Threshold Amplitude ◽  
The Mean ◽  
Valid Solution

The nonlinear evolution of weakly amplified waves in a hyperbolic tangent free shear layer is described for spatially and temporally growing waves when the shear layer Reynolds number is large and the critical layer viscous. An artificial body force is introduced in order to keep the mean flow parallel. Jump conditions on the perturbation velocity and mean vorticity are derived across the critical layer by applying the method of matched asymptotic expansions and it is shown that viscous effects outside the critical layer have to be taken into account in order to obtain a uniformly valid solution. Consequently the true neutral wavenumber and frequency are lower than their inviscid counterparts. When only the harmonic fluctuations are considered, it is known that the Landau constant is negative so that linearly amplified disturbances reach an equilibrium amplitude. It is shown that when the mean flow distortion generated by Reynolds stresses is also included, the Landau constant becomes positive. Thus, in both the spatial and temporal case, linearly amplified waves are further destabilized and damped waves are unstable above a threshold amplitude.

scholarly journals Strong Intraseasonal Variability of Meridional Currents near 5°N in the Eastern Indian Ocean: Characteristics and Causes

2017 ◽  
Vol 47 (5) ◽  
pp. 979-998 ◽  
Author(s):  
Gengxin Chen ◽  
Weiqing Han ◽  
Yuanlong Li ◽  
Michael J. McPhaden ◽  
Ju Chen ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Rossby Waves ◽  
Intraseasonal Variability ◽  
Upper Ocean ◽  
Mean Flow ◽  
Eastern Boundary ◽  
Typical Period ◽  
The Indian Ocean ◽  
The Mean

AbstractThis paper reports on strong, intraseasonal, upper-ocean meridional currents observed in the Indian Ocean between the Bay of Bengal (BOB) and the equator and elucidates the underlying physical processes responsible for them. In situ measurements from a subsurface mooring at 5°N, 90.5°E reveal strong intraseasonal variability of the meridional current with an amplitude of ~0.4 m s−1 and a typical period of 30–50 days in the upper 150 m, which by far exceeds the magnitudes of the mean flow and seasonal cycle. Such prominent intraseasonal variability is, however, not seen in zonal current at the same location. Further analysis suggests that the observed intraseasonal flows are closely associated with westward-propagating eddylike sea surface height anomalies (SSHAs) along 5°N. The eddylike SSHAs are largely manifestations of symmetric Rossby waves, which result primarily from intraseasonal wind stress forcing in the equatorial waveguide and reflection of the equatorial Kelvin waves at the eastern boundary. Since the wave signals are generally symmetric about the equator, similar variability is also seen at 5°S but with weaker intensity because of the inclined coastline at the eastern boundary. The Rossby waves propagate westward, causing pronounced intraseasonal SSHA and meridional current in the upper ocean across the entire southern BOB between 84° and 94°E. They greatly weaken in the western Indian Basin, but zonal currents near the equator remain relatively strong.

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