The Experts below are selected from a list of 1659 Experts worldwide ranked by ideXlab platform
R Leaitch - One of the best experts on this subject based on the ideXlab platform.
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importance of vertical Velocity variations in the cloud droplet nucleation process of marine stratus clouds
Journal of Geophysical Research, 2005Co-Authors: Yiran. Peng, Ulrike Lohmann, R LeaitchAbstract:[1] Eleven cloud cases through marine stratus, obtained during two field experiments in the North Atlantic Ocean, are used to study the sensitivity of cloud droplet nucleation to the vertical Gust Velocity. Selected cloud microphysical data, size-distributed aerosol properties and particle chemistry are applied in an adiabatic parcel model. The nucleated cloud droplet number concentrations (N) predicted using the probability density function (PDF) of the measured in-cloud vertical velocities are compared to predictions using a characteristic Velocity value. In this study, the model-predicted N from the PDF of the measured in-cloud vertical velocities agrees with the observed maximum N (Nmax )t o within 8.6%. The average N (Navg) can be related to Nmax using a power law (Leaitch et al., 1996). If a relationship between Nmax and Navg based on the measurements is applied to obtain the average N from the model-predicted N, then the model-predicted average N agrees with the observed average N to within 13.3%. When a characteristic vertical Velocity (0.8 times the standard deviation of the vertical Velocity distribution in this study) is used in the parcel model to simulate N, the model-predicted N agrees with the observed maximum N to within 5.7% and the model-predicted average N agrees with the observed average N within 8.8%. This indicates that using a characteristic value of the vertical Velocity distribution instead of its PDF is a good approximation for simulating the nucleated cloud droplet number of marine stratus on a cloud scale.
Yiran. Peng - One of the best experts on this subject based on the ideXlab platform.
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importance of vertical Velocity variations in the cloud droplet nucleation process of marine stratus clouds
Journal of Geophysical Research, 2005Co-Authors: Yiran. Peng, Ulrike Lohmann, R LeaitchAbstract:[1] Eleven cloud cases through marine stratus, obtained during two field experiments in the North Atlantic Ocean, are used to study the sensitivity of cloud droplet nucleation to the vertical Gust Velocity. Selected cloud microphysical data, size-distributed aerosol properties and particle chemistry are applied in an adiabatic parcel model. The nucleated cloud droplet number concentrations (N) predicted using the probability density function (PDF) of the measured in-cloud vertical velocities are compared to predictions using a characteristic Velocity value. In this study, the model-predicted N from the PDF of the measured in-cloud vertical velocities agrees with the observed maximum N (Nmax )t o within 8.6%. The average N (Navg) can be related to Nmax using a power law (Leaitch et al., 1996). If a relationship between Nmax and Navg based on the measurements is applied to obtain the average N from the model-predicted N, then the model-predicted average N agrees with the observed average N to within 13.3%. When a characteristic vertical Velocity (0.8 times the standard deviation of the vertical Velocity distribution in this study) is used in the parcel model to simulate N, the model-predicted N agrees with the observed maximum N to within 5.7% and the model-predicted average N agrees with the observed average N within 8.8%. This indicates that using a characteristic value of the vertical Velocity distribution instead of its PDF is a good approximation for simulating the nucleated cloud droplet number of marine stratus on a cloud scale.
Ulrike Lohmann - One of the best experts on this subject based on the ideXlab platform.
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importance of vertical Velocity variations in the cloud droplet nucleation process of marine stratus clouds
Journal of Geophysical Research, 2005Co-Authors: Yiran. Peng, Ulrike Lohmann, R LeaitchAbstract:[1] Eleven cloud cases through marine stratus, obtained during two field experiments in the North Atlantic Ocean, are used to study the sensitivity of cloud droplet nucleation to the vertical Gust Velocity. Selected cloud microphysical data, size-distributed aerosol properties and particle chemistry are applied in an adiabatic parcel model. The nucleated cloud droplet number concentrations (N) predicted using the probability density function (PDF) of the measured in-cloud vertical velocities are compared to predictions using a characteristic Velocity value. In this study, the model-predicted N from the PDF of the measured in-cloud vertical velocities agrees with the observed maximum N (Nmax )t o within 8.6%. The average N (Navg) can be related to Nmax using a power law (Leaitch et al., 1996). If a relationship between Nmax and Navg based on the measurements is applied to obtain the average N from the model-predicted N, then the model-predicted average N agrees with the observed average N to within 13.3%. When a characteristic vertical Velocity (0.8 times the standard deviation of the vertical Velocity distribution in this study) is used in the parcel model to simulate N, the model-predicted N agrees with the observed maximum N to within 5.7% and the model-predicted average N agrees with the observed average N within 8.8%. This indicates that using a characteristic value of the vertical Velocity distribution instead of its PDF is a good approximation for simulating the nucleated cloud droplet number of marine stratus on a cloud scale.
Babinsky H - One of the best experts on this subject based on the ideXlab platform.
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Non-Circulatory Force on a Finite Thickness Body Encountering a Gust
'American Institute of Aeronautics and Astronautics (AIAA)', 2020Co-Authors: Gehlert P, Babinsky HAbstract:Many low-order models for unsteady flows divide the force into circulatory and non-circulatory components. The former is associated with vorticity in the flow field, whilst the latter is often synonymous with the added mass force. Investigating a cylinder sharp-edged Gust encounter, at a Reynolds number of 6000, probes the origin of these respective forces. Vorticity residing in the flow field does not only originate from the cylinder but it is also located in the Gust shear layers, which delimit the vertical Gust Velocity from the surrounding quiescent fluid. It is possible to represent the body surface by a vortex sheet where individual components, satisfying the non-through flow condition, originate from different sources. All vorticity external to the body generates a complementary contribution to this surface vortex sheet. A further vortex sheet component is uniquely attributed to linear acceleration of a body and linked to the added mass effect. Finally, a non-circulatory vortex sheet forms due to the induced Velocity by the Gust vorticity. In Küssner's potential flow Gust model this latter vortex sheet contribution is attributed to added mass. However, because the Gust encounter is not associated with any body acceleration, the force must rather be linked to the growth and redistribution of this vortex sheet, due to the relative advection of the Gust shear layer vorticity. Particle image velocimetry validates this result using a surging and rotating cylinder at Gust ratios of 0.5 and 1. Force balance measurements show that the force originating from the rate of change of the non-circulatory Gust vortex sheet, unlike in the case for an infinitely thin plate, vastly over-predicts the initial rise in force as the cylinder enters the Gust. This is because, when considering the rate of change of the vortex sheet, it is implicitly assumed that all of the vertical momentum of the Gust flow inside the region occupied by the cylinder, is lost. The overestimation is a result of the rigid shear layer assumption inherent to the Küssner model. In reality, the Gust shear layers deflect, causing a spread of vertical momentum. The deflection of the shear layers can be analytically approximated by removing the contribution due to the rate of change of momentum inside the cylinder. This improves the force prediction but does not fully recover the experimental force measurements during the initial entry into the Gust. On a practical level this suggests that for bodies of finite thickness the non-circulatory force cannot be easily calculated, as it is difficult to quantify the effect of the body volume
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Effect of transverse Gust Velocity profiles
2020Co-Authors: Babinsky H, Biler H, Sedky G, Ar JonesAbstract:© 2020 by I. Andreu-Angulo, H. Babinsky, H. Biler, G. Sedky, and A. R. Jones. A large variety of Gusts that develop in the atmospheric boundary layer affect aerial vehicles. This study, performed in water tow tanks, compares the response of a flat plate wing to transverse vertical Gusts with a top-hat and a sine-squared Velocity profile at Reynolds numbers of 20,000–30,000. Experiments are performed for a wide range of Gust ratios (0.5–1.5) and angles of attack (0–20 deg). Force measurements for a sine-squared Gust show a smoother increase in lift and a lower peak compared with a top-hat Gust for the same Gust ratio. Linear models are found to work reasonably well predicting the force response for the sine-squared Gust, whereas the top-hat Gust exhibits significant nonlinear effects at the largest Gust ratios. This nonlinear behavior is linked to high levels of circulation shed from the wing edges and the development of nonplanar wakes. Nevertheless, the Gust momentum inflow on the wing is directly linked to many characteristics of the lift response, independently of Gust Velocity profile. In addition, the lift response for the two Gusts is found to increase with angle of attack until the wing inclination is large enough to produce a separated wake before Gust entry
Cao Shu-yang - One of the best experts on this subject based on the ideXlab platform.
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Simulation of downburst and its loads with wind tunnel test
Journal of Vibration and Shock, 2009Co-Authors: Cao Shu-yangAbstract:In order to study aerodynamic characteristics of a structure undergoing sudden change flow, a test for simulation of sudden change flow with an active control wind tunnel was introduced. Firstly, a Gust Velocity profile of downburst was simulated with the wind tunnel. Subsequently, a time history of wind speed change was simulated using step flow method. Finally, high-rise structure models were placed in the sudden change flow, and the variation characteristics of wind pressure on the structure surface and aerodynamic parameters in the flow were observed and studied. The results showed that the identities between the Gust Velocity profile simulated with the wind tunnel and the theory formula were more than ninety percent, and sudden change flow could generate a high unsteady lift on the whole high-rise structure and a big unsteady wind pressure on the structure surface meanwhile.