scholarly journals The Impacts of Gustiness on Air–Sea Momentum Flux

Fluids ◽  
2021 ◽  
Vol 6 (10) ◽  
pp. 336
Author(s):  
Meng Lyu ◽  
Henry Potter ◽  
Clarence O. Collins
Keyword(s):  
Drag Coefficient ◽  
Momentum Flux ◽  
Aerodynamic Drag ◽  
Critical Threshold ◽  
Wind Speeds ◽  
The Earth ◽  
Momentum Fluxes ◽  
Aerodynamic Drag Coefficient ◽  
Turbulent Spectra ◽  
The Impact

The exchange of momentum across the air–sea boundary is an integral component of the earth system and its parametrization is essential for climate and weather models. This study focuses on the impact of gustiness on the momentum flux using three months of direct flux observations from a moored surface buoy. Gustiness, which quantifies the fluctuations of wind speed and direction, is shown to impact air–sea momentum fluxes. First, we put forward a new gustiness formula that simultaneously evaluates the impact of fluctuations in wind direction and speed. A critical threshold is established using a cumulative density function to classify runs as either gusty or non-gusty. We find that, during runs classified as gusty, the aerodynamic drag coefficient is increased up to 57% when compared to their non-gusty counterparts. This is caused by a correlated increase in vertical fluctuations during gusty conditions and explains variability in the drag coefficient for wind speeds up to 20 m/s. This increase in energy is connected with horizontal fluctuations through turbulent interactions between peaks in the turbulent spectra coincident with peaks in the wave spectra. We discus two potential mechanistic explanations. The results of this study will help improve the representation of gustiness in momentum flux parameterizations leading to more accurate ocean models.

Experimental Model of the Aerodynamic Drag Coefficient in Alpine Skiing

2004 ◽  
Vol 20 (2) ◽  
pp. 167-176 ◽  
Author(s):  
Caroline Barelle ◽  
Anne Ruby ◽  
Michel Tavernier
Keyword(s):  
Wind Tunnel ◽  
Drag Coefficient ◽  
Experimental Model ◽  
Aerodynamic Drag ◽  
Aerodynamic Force ◽  
Alpine Skiing ◽  
Aerodynamic Properties ◽  
Speed Performance ◽  
Aerodynamic Drag Coefficient ◽  
The Impact

Aerodynamic properties are one of the factors that determine speed performance in Alpine skiing. Many studies have examined the consequences of this factor in downhill skiing, and the impact of postural modifications on speed is now well established. To date, only wind tunnel tests have enabled one to measure aerodynamic drag values (a major component of the aerodynamic force in Alpine skiing). Yet such tests are incompatible with the constraints of a regular and accurate follow-up of training programs. The present study proposes an experimental model that permits one to determine a skier's aerodynamic drag coefficient (SCx) based on posture. Experimental SCx measurements made in a wind tunnel are matched with the skier's postural parameters. The accuracy of the model was determined by comparing calculated drag values with measurements observed in a wind tunnel for different postures. For postures corresponding to an optimal aerodynamic penetration (speed position), the uncertainty was 13%. Although this model does not permit an accurate comparison between two skiers, it does satisfactorily account for variations observed in the aerodynamic drag of the same skier in different postures. During Alpine ski training sessions and races, this model may help coaches assess the gain or loss in time induced by modifications in aerodynamic drag corresponding to different postures. It may also be used in other sports to help determine whether the aerodynamic force has a significant impact on performance.

scholarly journals Experimental Determination of the Impact of Floats on the Aerodynamic Characteristics of an OSA Model in Symmetric Flow

2021 ◽  
Vol 12 (1) ◽  
pp. 41-58
Author(s):  
Michał FRANT ◽  
Stanisław WRZESIEŃ ◽  
Maciej MAJCHER
Keyword(s):  
Drag Coefficient ◽  
Aerodynamic Drag ◽  
Lift Coefficient ◽  
Aerodynamic Characteristics ◽  
Symmetric Flow ◽  
Aerodynamic Drag Coefficient ◽  
The Impact ◽  
Drag Ratio ◽  
Lift To Drag Ratio

This paper presents the results of experimental determination of the impact of floats on the aerodynamic characteristics of an OSA model in symmetric flow. The studies have been performed in the low-speed wind tunnel at the Military University of Technology (MUT, Warsaw, Poland). The aircraft model was examined at the dynamic pressure q = 500 Pa in the following angle of attack range = -2828. The investigations have been performed for an aircraft model under plain configuration with floats and without floats. The influence of elevator and flap inclination on the aerodynamic characteristics of the model has also been analysed. The obtained values of aerodynamic drag coefficient, lift coefficient, pitching moment coefficient and lift-to-drag ratio have been presented in the form of tables and graphs. The studies performed demonstrated that the use of floats causes the increase of aerodynamic drag coefficient CD, maximum lift coefficient CLmax as well as critical angle of attack cr. The decrease of lift-to-drag ratio has also been observed. Its value in the case of the model with floats was up to 20% lower than in the model without floats. The studies also showed that the model equipped with floats had a lower longitudinal static stability margin than the model without floats.

scholarly journals A Physics-Based Parameterization of Air–Sea Momentum Flux at High Wind Speeds and Its Impact on Hurricane Intensity Predictions

2007 ◽  
Vol 135 (8) ◽  
pp. 2869-2878 ◽  
Author(s):  
Il-Ju Moon ◽  
Isaac Ginis ◽  
Tetsu Hara ◽  
Biju Thomas
Keyword(s):  
Drag Coefficient ◽  
Momentum Flux ◽  
Surface Wind ◽  
Wind Pressure ◽  
Central Pressure ◽  
Geophysical Fluid Dynamics Laboratory ◽  
High Wind ◽  
Wind Speeds ◽  
Gfdl Model ◽  
The Impact

Abstract A new bulk parameterization of the air–sea momentum flux at high wind speeds is proposed based on coupled wave–wind model simulations for 10 tropical cyclones that occurred in the Atlantic Ocean during 1998–2003. The new parameterization describes how the roughness length increases linearly with wind speed and the neutral drag coefficient tends to level off at high wind speeds. The proposed parameterization is then tested on real hurricanes using the operational Geophysical Fluid Dynamics Laboratory (GFDL) coupled hurricane–ocean prediction model. The impact of the new parameterization on the hurricane prediction is mainly found in increased maximum surface wind speeds, while it does not appreciably affect the hurricane central pressure prediction. This helps to improve the GFDL model–predicted wind–pressure relationship in strong hurricanes. Attempts are made to provide physical explanations as to why the reduced drag coefficient affects surface wind speeds but not the central pressure in hurricanes.

scholarly journals A Novel Sea Surface Roughness Parameterization Based on Wave State and Sea Foam

2021 ◽  
Vol 9 (3) ◽  
pp. 246
Author(s):  
Difu Sun ◽  
Junqiang Song ◽  
Xiaoyong Li ◽  
Kaijun Ren ◽  
Hongze Leng
Keyword(s):  
Surface Roughness ◽  
Wind Speed ◽  
Drag Coefficient ◽  
Sea Surface ◽  
High Wind Speed ◽  
Wave State ◽  
Wind Speeds ◽  
Sea Surface Roughness ◽  
Extreme Wind ◽  
The Impact

A wave state related sea surface roughness parameterization scheme that takes into account the impact of sea foam is proposed in this study. Using eight observational datasets, the performances of two most widely used wave state related parameterizations are examined under various wave conditions. Based on the different performances of two wave state related parameterizations under different wave state, and by introducing the effect of sea foam, a new sea surface roughness parameterization suitable for low to extreme wind conditions is proposed. The behaviors of drag coefficient predicted by the proposed parameterization match the field and laboratory measurements well. It is shown that the drag coefficient increases with the increasing wind speed under low and moderate wind speed conditions, and then decreases with increasing wind speed, due to the effect of sea foam under high wind speed conditions. The maximum values of the drag coefficient are reached when the 10 m wind speeds are in the range of 30–35 m/s.

Influence of Engine Cabin Simplification on Aerodynamic Characteristics of Car

2014 ◽  
Vol 1042 ◽  
pp. 188-193 ◽  
Author(s):  
Xing Jun Hu ◽  
Jing Chang
Keyword(s):  
Numerical Simulation ◽  
Aerodynamic Drag ◽  
Aerodynamic Characteristics ◽  
Thin Plates ◽  
Average Thickness ◽  
Two Dimensional ◽  
Engine Cooling ◽  
Aerodynamic Drag Coefficient ◽  
Simulation Results ◽  
The Impact

In order to analyze the impact of engine cabin parts on aerodynamic characteristics, the related parts are divided into three categories except the engine cooling components: front thin plates (average thickness of 2mm), bottom-suspension and interior panels. The aerodynamic drag coefficient (Cd) were obtained upon the combination schemes consisting of the three types of parts by numerical simulation. Results show that Cd by simulation is closer to the test value gained by the wind tunnel experiment when front thin plates were simplified to the two-dimensional interface with zero thickness. The error is only 5.23%. Meanwhile this scheme reduces grid numbers, thus decreasing the calculating time. As the front thin plates can guide the flow, there is no difference on the Cd values gained from the model with or without bottom-suspension or interior panels when the engine cabin contains the front thin plates; while only both bottom-suspension and interior panels are removed, the Cd value can be reduced when the cabin doesn’t contain the front thin plates.

scholarly journals The “Bag Breakup” Spume Droplet Generation Mechanism at High Winds. Part II: Contribution to Momentum and Enthalpy Transfer

2018 ◽  
Vol 48 (9) ◽  
pp. 2189-2207 ◽  
Author(s):  
Yu. Troitskaya ◽  
O. Druzhinin ◽  
D. Kozlov ◽  
S. Zilitinkevich
Keyword(s):  
High Speed ◽  
Aerodynamic Drag ◽  
Stable Stratification ◽  
Noticeable Increase ◽  
Wind Speeds ◽  
Breakup Mechanism ◽  
Hurricane Wind ◽  
Exchange Processes ◽  
Aerodynamic Drag Coefficient ◽  
High Winds

AbstractIn Part I of this study, we used high-speed video to identify “bag breakup” fragmentation as the dominant mechanism by which spume droplets are generated at gale-force and hurricane wind speeds. We also constructed a spray generation function (SGF) for the bag-breakup mechanism. The distinctive feature of this new SGF is the presence of giant (~1000 μm) droplets, which may significantly intensify the exchange between the atmosphere and the ocean. In this paper, Part II, we estimate the contribution of the bag-breakup mechanism to the momentum and enthalpy fluxes, which are known to strongly affect the development and maintenance of hurricanes. We consider three contributions to the spray-mediated aerodynamic drag: 1) “bags” as obstacles before fragmentation, 2) acceleration of droplets by the wind in the course of their production, and 3) stable stratification of the marine atmospheric boundary layer due to levitating droplets. Taking into account all of these contributions indicates a peaking dependence of the aerodynamic drag coefficient on the wind speed, which confirms the results of field and laboratory measurements. The contribution of the spray-mediated flux to the ocean-to-atmosphere moist enthalpy is also estimated using the concept of “reentrant spray,” and the equation for the enthalpy flux from a single droplet to the atmosphere is derived from microphysical equations. Our estimates show that a noticeable increase in the enthalpy exchange coefficient at winds exceeding 30–35 m s−1 is due to the enhancement of the exchange processes caused by the presence of giant droplets originating from bag-breakup fragmentation.

scholarly journals Relationship between Sea Surface Drag Coefficient and Wave State

2021 ◽  
Vol 9 (11) ◽  
pp. 1248
Author(s):  
Jian Shi ◽  
Zhihao Feng ◽  
Yuan Sun ◽  
Xueyan Zhang ◽  
Wenjing Zhang ◽  
...  
Keyword(s):  
Drag Coefficient ◽  
Momentum Flux ◽  
Sea Surface ◽  
Sea Spray ◽  
Wave Age ◽  
High Wind ◽  
Surface Drag ◽  
Wave State ◽  
Wind Speeds ◽  
Strong Winds

The sea surface drag coefficient plays an important role in momentum transmission between the atmosphere and the ocean, which is affected by ocean waves. The total air–sea momentum flux consists of effective momentum flux and sea spray momentum flux. Sea spray momentum flux involves sea surface drag, which is largely affected by the ocean wave state. Under strong winds, the sea surface drag coefficient (CD) does not increase linearly with the increasing wind speed, namely, the increase of CD is inhibited by strong winds. In this study, a sea surface drag coefficient is constructed that can be applied to the calculation of the air–sea momentum flux under high wind speed. The sea surface drag coefficient also considers the influence of wave state and sea spray droplets generated by wave breaking. Specially, the wave-dependent sea spray generation function is employed to calculate sea spray momentum flux. This facilitates the analysis not only on the sensitivity of the sea spray momentum flux to wave age, but also on the effect of wave state on the effective CD (CD, eff) under strong winds. Our results indicate that wave age plays an important role in determining CD. When the wave age is >0.4, CD decreases with the wave age. However, when the wave age is ≤0.4, CD increases with the wave age at low and moderate wind speeds but tends to decrease with the wave age at high wind speeds.

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