Drag Coefficient

The curveball is a classic example of complex projectile motion in sports, it is known for its deceptive, arcing path to the batter. Unlike a simple projectile whose trajectory is determined solely by gravity and initial velocity, the curveball's path is significantly altered by aerodynamic forces. The primary physical principle responsible for this deviation is the Magnus effect, a phenomenon where a lift force is generated by a spinning object moving through a fluid (in this case, air). This case study will analyze the role of kinematics, rotational motion, and fluid dynamics to quantify how a baseball's spin creates its characteristic "break," causing it to drop more than it would under the influence of gravity and air resistance alone.

In the PILPS Phase 2a experiment, 23 land-surface schemes were compared in an off-line control experiment using observed meteorological data from Cabauw, the Netherlands. Two simple sensitivity experiments were also undertaken in which the observed surface air temperature was artificially increased or decreased by 2 K while all other factors remained as observed. On the annual timescale, all schemes show similar responses to these perturbations in latent, sensible heat flux, and other key variables. For the 2-K increase in temperature, surface temperatures and latent heat fluxes all increase while net radiation, sensible heat fluxes, and soil moistures all decrease. The results are reversed for a 2-K temperature decrease. The changes in sensible heat fluxes and, especially, the changes in the latent heat fluxes are not linearly related to the change of temperature. Theoretically, the nonlinear relationship between air temperature and the latent heat flux is evident and due to the convex relationship between air temperature and saturation vapor pressure. A simple test shows that, the effect of the change of air temperature on the atmospheric stratification aside, this nonlinear relationship is shown in the form that the increase of the latent heat flux for a 2-K temperature increase is larger than its decrease for a 2-K temperature decrease. However, the results from the Cabauw sensitivity experiments show that the increase of the latent heat flux in the ϩ2-K experiment is smaller than the decrease of the latent heat flux in the Ϫ2-K experiment (we refer to this as the asymmetry). The analysis in this paper shows that this inconsistency between the theoretical relationship and the Cabauw sensitivity experiments results (or the asymmetry) is due to (i) the involvement of the ␤ g formulation, which is a function of a series stress factors that limited the evaporation and whose values change in the Ϯ2-K experiments, leading to strong modifications of the latent heat flux; (ii) the change of the drag coefficient induced by the changes in stratification due to the imposed air temperature changes (Ϯ2 K) in parameterizations of latent heat flux common in current land-surface schemes. Among all stress factors involved in the ␤ g formulation, the soil moisture stress in the ϩ2-K experiment induced by the increased evaporation is the main factor that contributes to the asymmetry.

The wake of a square cylinder at zero angle of incidence oscillating inline with the incoming stream has been experimentally studied. Measurement data are reported for Reynolds numbers of 170 and 355. The cylinder aspect ratio is set equal to 28 and a limited study at an aspect ratio of 16 has been carried out. The frequency of oscillation is varied around the Strouhal frequency of a stationary cylinder, and the amplitude of oscillation is 10–30% of the cylinder size. Spatial and temporal flow fields in the cylinder wake have been studied using particle image velocimetry and hot-wire anemometry, the former providing flow visualization images as well. A strong effect of forcing frequency is clearly seen in the near wake. With an increase in frequency, the recirculation length substantially reduces and diminishes the time-averaged drag coefficient. The time-averaged vorticity contours show that the large-scale vortices move closer to the cylinder. The rms values of velocity fluctuatio...

Increased accuracy in fertilizer spreading performance is required to maximize the farmers’ profit and reduce several ecological effects. To allow for proper spreader calibration, a research system was developed to predict the spread pattern of centrifugal spreaders. By measuring the ejection parameters of the fertilizer grains and applying these in a ballistic flight model, the landing positions of these particles can be calculated, from which the spread pattern can be simulated. Simulations indicate the high sensitivity of the predicted spread pattern to the drag coefficient of the particles. In literature, this coefficient has mostly been determined at terminal velocity and/or for perfectly spherical particles. This paper describes a new method to determine the drag coefficient at velocities similar to those imposed by a centrifugal spreader. The ejection parameters of a single fertilizer particle were determined by means of image processing. Three dimensional information was obt...

Stereovision can be used to characterize of the fertilizer centrifugal spreading process and to control the spreading fertilizer distribution pattern on the ground reference. Fertilizer grains, however, resemble each other and the grain images contain little information on texture. Therefore, the accuracy of stereo matching algorithms in literature cannot be used as a reference for stereo images of fertilizer grains. In order to evaluate stereo matching algorithms applied to images of grains a generator of synthetic stereo particle images is presented in this paper. The particle stereo image generator consists of two main parts: the particle 3D position generator and the virtual stereo rig. The particle 3D position generator uses a simple ballistic flight model and the disc characteristics to simulate the ejection and the displacement of grains. The virtual stereo rig simulates the stereo acquisition system and generates stereo images, a disparity map and an occlusion map. The results are satisfying and present an accurate reference to evaluate stereo particles matching algorithms.

Nowadays farmers recognize the importance of a correct and precise fertiliser application: non-uniform spread patterns cause extra pressure on the environment and might result in economic losses for the farmer. In Europe most spreading is done by centrifugal fertilizer spreaders but their spreading process is not easy to monitor and to control. To perform a precise fertilization farmers need proper tools to determine and evaluate the spread patterns at farm level. Therefore the Flemish Institute for Agricultural and Fisheries Research (ILVO) and its partners are exploring and developing a fast and accurate technique for measuring the spread pattern of conventional centrifugal spreaders. This method aims to be low cost and applicable at the farm level. Also, the proposed solution has to be mobile to the extent that the device can be built up on-site to test several machines. The device should enable the adjustment of the spreader in such a way that a uniform spread pattern is obtained. At a later stage, an onboard sensor could be envisaged. Three main approaches for evaluating the spread pattern are currently available: the experimental collector tray method, the full modelling approach like the Discrete Element Method (DEM), and the hybrid approach that combines measurements and modelling. In this research the hybrid approach was applied: the spread pattern was predicted with a ballistic flight model based on the measurement of the horizontal outlet angle, the vertical outlet angle, the grain diameter, the grain density and the initial velocity. In a first step, a 2-dimensional imaging technique was used with a small field of view (0.33m x 0.25m) to measure the horizontal outlet angle and the speed of the grains at different camera positions at the circumference of the disk. The vertical outlet angle and the mass distribution were measured with a cylindrical collector. The grains flying under the measurement unit were imaged using two different techniques: the high speed technique and a newly developed multi-exposure imaging technique. For the high speed technique a camera, type MotionXtra HG 100K (Roper Scientific, New Jersey, USA), was used. The stroboscopic technique combined a specially designed LED stroboscope with a Nikon D 100 camera. Overall the stroboscopic technique and the high speed technique were capable of measuring the outlet angle and the outlet speed. Small differences between the measurements with both techniques existed, but ultimately in the aim is the determination of the resulting spread pattern in the field. When comparing the simulated and the measured spread pattern, relative errors amounted up to 30%. Therefore, in the next phase the twodimensional imaging technique was adapted with a much larger field of view (1m x 1m), improved lighting system and motion estimation algorithms, resulting in lower relative errors between the simulated and the measured cylindrical spread pattern. At the moment a 3D Proceedings International Conference of Agricultural Engineering, Zurich, 06-10.07.2014 -www.eurageng.eu 2/8 stereovision set-up (and related algorithms) to further improve the simulation of the spread pattern is being developed.

Flood flows have the potential to cause substantial damage to infrastructure, mankind, livestock and agricultural land which all stacks up to greatly affect the financial condition of the region. During 2010 Pakistan floods, more than two million houses were damaged partly or totally [1]. To minimize these types of destructions, inland vegetation can be considered a natural barrier to dissipate the energy of flood flow and limits widespread inundation. This study involves volume of fluid (VOF) modelling approach to figure out the role of vegetation of finite width in energy reduction of flood flow, in front of houses, against: vegetation of varying Aspect Ratio (A/R width-length ratio) and distance between vegetation & houses (Lr). Channel domain was built in ANSYS workbench toolkit and meshing was done in meshing building toolkit. For the postprocessing and simulation, FLUENT was used. Various contour plots & profiles of cross stream-wise velocities and water level measurements are presented in this paper. The simulation results of cross stream-wise velocities and water level measurements were identical with experimental data. At vegetation upstream and downstream, velocity reduction observed in higher A/R (2.40) compared to vegetation of A/R-1. Whereas, outside the vegetation and near the walls of channel domain flow velocities were high. The water level was raised on the upstream side of the vegetation due to resistance offered by vegetation. On the upstream side of vegetation, the rise in backwater depth increased by increasing A/R. Contrarily, on the downstream side of vegetation, an undular hydraulic jump was observed in between vegetation and a house. By increasing A/R, the energy loss increases under constant vegetation conditions (G/d = 0.24, Fro = 0.70; G = spacing of each cylinder in cross-stream direction and d= diameter of cylinder and Fro = initial Froude number) and increase in house distance from 1W to 2W, the energy reduction increased from 2.40% to 3.15% which was further increased to 5.04% for another 5W increase in house distance, where W is the vegetation width. Simulation results also shown that with increasing Froude no from 0.60 to 0.70 water level depth has also an incremental pattern which ultimately results in increase in energy dissipation along the varying building distance (1W, 2W & 5W). Thus, to minimize the structural damage, a structure must be located at a safe distance away from the vegetation where flow becomes sub-critical.

The Imaging Wind and Rain Arborne Profilers OWRAP) is a dual-frequency, conically-scanning Doppler radar that measures high-resolution, dual-polarized, multi-beam C-and Ku-band reflectivity and Doppler velocity profiles of the atmospheric boundary layer (ABL) within the inner core of hurricanes. From the datasets acquired during the 2002 through 2UO5 hurricane seasons as part of the ONR Coupled Boundary Layer Air-Sea 'Itansfer (CBLAST) program and the NOAAfl'iESDIS Ocean Winds and Rain experiments, very high resolution radar observations of hurricanes have been acquired and made available to the CBLAST community. Of particular interest am the ABL wind fields and 3-D structures found within the inner core of hurricanes. As a result of these analysis, a limitation in the ability to retrieve the ABL wind field at very low altitudes was identified. This paper shows how thii limitation has been removed and presents initial results demonstrating its new capabilities to derive the ABL wind field within the inner a r e of hurricanes to much lower altitudes than the ones the original system was capable of.

Aims. We study the formation of a hypothetical terrestrial-type body in the equilateral Lagrange points of a giant extrasolar planet. Starting from a swarm of planetesimals in stable tadpole orbits, we simulate its dynamical and collisional evolution under a wide range of different initial conditions and masses for both the Trojan population and its planetary companion. We also analyze the effects of gas drag from the interaction of the planetesimals with the nebular disk. Methods. The formation process is simulated with an N-body code that considers full gravitational interactions between the planetesimals and the giant planet. Gas interaction is modeled with Stokes and Epstein drags, where the drag coefficients are chosen following the results of full hydrodynamic simulations performed with the 2D public hydro-code FARGO. Results. In both gas-free and gas-rich scenarios, we have been able to obtain a single final terrestrial-type body in a stable tadpole orbit around one of the triangular Lagrange points of the system. However, due to gravitational instabilities within the swarm, the accretional process is not very efficient and the mass of the final planet never seems to exceed ∼0.6 Earth masses, even when the total mass of the swarm is five times this value. Finally, we also included an orbital decay of the giant planet due to a type II migration. Although the accretional process shows evidence of a lower efficiency, a small terrestrial planet is still able to form, and follows the giant planet towards the habitable zone of the hosting star.

Entrainment of river bed particles by turbulent flow is a core matter of study in river hydrodynamics. It is of great interest to river engineers to evaluate the shear stress for initiating river bed motion. The main objective is to calculate transport rates for bed load, to predict changes in bed level which are scoured or aggraded and to design a stable channel. Forces acting upon the particle especially fluid forces which give a major role in the incipient motion of the particle on the rough boundary. For calculation generally use shield's diagram but some other modified methods and approaches are discussed. Modeling criteria are discussed for the hydraulically smooth and rough boundary depending on Reynolds number. In the past, experimental studies on tractive shear stress have been done by many researchers but consideration of lift force to analyze the movement of sediment is very limited. For suspended load transport, a detailed analysis of lift force is required. Based on the study it has been observed that shear stress depends on channel slope not only due to gravitational force but also many other factors like drag force, lift force, friction angle, fluctuations, velocity profile, etc. Complete analysis of these factors provides slope dependency over shear stress. To improve past studies, some factors have been discussed, to give a more correct force balance equation. This is very difficult task to analyze more and more variable's dependency on the slope. Consideration of the possible number of variable holds complete analysis of experimental study. This paper also reviews the effect of particle Reynolds number and relative submergence over critical shield stress.

The innovative bus designs, inspired by the whales, have been developed. The designs are confined to the frontal area of the buses. The new designs are named as the Beluga buses. Several variants of the models all mimicking Beluga whales are proposed. Both numerical analysis and experimental have been conducted to determine the drag coefficients of various models. The ANSYS CFD program was used for numerical simulations. WT tests were conducted to experimentally determine the drag coefficients. Both methods indicate that the beluga-inspired buses offer significant reductions in drag, which can lead to lower fuel consumption. The new beluga design is expected to reduce fuel consumption by 12.64%. Comparing the experimental and numerical results, a 6.4% discrepancy in the drag coefficients is observed at low Reynolds numbers, which became negligible at higher Reynolds numbers. The new geometry is expected to offer an economical solution for reducing fuel consumption.

This article describes the bed expansion characteristics of a down-flow anaerobic fluidized bed reactor treating a synthetic wastewater. Experiments were carried out in a 0.08 m diameter and 1 m length PVC column. The carrier used was ground perlite (an expanded volcanic rock). Particles characteristics were 0.968 mm in diameter, specific density of 213 kg ⅐ m -3 and U mf (minimal fluidization velocity): 2.3 m ⅐ h -1 . Experimental data of terminal velocities and bed expansion parameters at several biofilm thicknesses were compared to different models predicting the bed expansion of up-flow and downflow fluidized beds. Measured bed porosities at different liquid superficial velocities for the different biofilm thicknesses were in agreement with the Richardson-Zaki model, when U t (particle terminal velocity) and n (expansion coefficient) were calculated by linear regression of the experimental data. Terminal velocities of particles at different biofilm thicknesses calculated from experimental bed expansion data, were found to be much smaller than those obtained when C d (drag coefficient) is determined from the standard drag curve or with others' correlations (Karamanev and Nikolov, 1992a,b). This difference could be explained by the fact that free-rising particles do not obey Newton's law for free-settling, as proposed by Karamanev and Nikolov (1992a,b) and . In the present study, the same freerising behavior was observed for all particles (densities between 213 and 490 kg ⅐ m -3 ).

This is my review Einstein's Special Theory of Relativity in which I have shown that the quantity of work varies from MV in Perfect Motion, to nMV in Normal Motion and to MV 2 in Stubborn Motion, that Einstein's Special Theory of Relativity is a wrong concept and his most famous equation: E=MC 2 is not the Mass-Energy Equivalence Formula, but the quantity of work required for Stubborn Motion at speed C Voigt's Theories of Length Contraction and Time Dilation, Lorentz's proposal of Length Contraction due to compressive strain impacted by stationary Aether, and the misconception of the application of Maxwell's Equations, and contributions of many other Physicists like Abraham, Kaufmann, Thomas et al helped Einstein to formulate his theory of Special Relativity. James Clark Maxwell's equations were meant only for static bodies, but he applied them on moving bodies to create his Special Theory of Relativity.

The aerodynamic performance of an aircraft mainly depends on the lift force, drag force, and the lift to drag ratio. The geometric shapes of aircraft wings are considered crucial for this aerodynamic performance. The purpose of this study is to determine the most efficient wing shape that improves the aerodynamic performance of the airfoil. For that purpose, a numerical comparative study was carried out between the rectangular and tapered wing shapes of the NACA 4412 airfoil for a wide range of angles of attack in the subsonic regime. ANSYS Fluent software, based on the finite volume method, was used for the numerical resolution of the governing equations. The Realizable k-ε model was chosen for the turbulence modeling. The numerical procedure was validated based on experimental results obtained from the literature. The results show an improvement in the lift coefficient and a reduction in the drag coefficient of the Tapered shape compared to the rectangular shape at all angles of a...

We propose an empirical model to determine the form of energy loss of charm quarks due to multiple scatterings in quark gluon plasma by demanding a good description of production of D mesons and non-photonic electrons in relativistic collision of heavy nuclei at RHIC and LHC energies. Best results are obtained when we approximate the momentum loss per collision ∆p T = α p T , where α is a constant depending on the centrality and the centre of mass energy. Comparing our results with those obtained earlier for drag coefficients estimated using Langevin equation for heavy quarks we find that up to half of the energy loss of charm quarks at top RHIC energy could be due to collisions while that at LHC energy at 2760 GeV/A the collisional energy loss could be about one third of the total. Estimates are obtained for azimuthal anisotropy in momentum spectra of heavy mesons, due to this energy loss. We further suggest that energy loss of charm quarks may lead to an enhanced production of D-mesons and single electrons at low p T in AA collisions.

In this paper we report on (two-component) LDV experiments in a fully developed turbulent pipe flow with a drag-reducing polymer (partially hydrolyzed polyacrylamide) dissolved in water. The Reynolds number based on the mean velocity, the pipe diameter and the local viscosity at the wall is approximately 10000. We have used polymer solutions with three different concentrations which have been chosen

When swimming at the surface, swimmers will experience wave drag. It is observed that above a certain speed, wave height grows rapidly with further speed increase, suggesting that wave drag cannot be neglected at high speed. Therefore, the magnitude of this component of ...

In India, open sea cage culture has been successfully demonstrated and several experimental offshore cages for mariculture were installed along the coast for on-farm demonstration by the Central Marine Fisheries Research Institute, Cochin. In the present study, a model cage was fabricated and tested in a towing tank under different waves and current load conditions. The tension on the mooring chain was measured during the experimental study, besides the towing speed and wave parameters. Based on the experimental data, drag coefficient for the cage net twine was estimated. The tensions in the mooring chain and the cage net twine of the prototype cage were predicted based on the model data. The maximum tension on a single twine of the outer and inner fish net were estimated as 0.15 N and 0.028 N respectively. The force on the net was more than 1.7 times the force on the floating collar and sinker pipe. The tension in the mooring line is mainly due to the force on the net. Further it w...

In this paper, author solve numerically, using the method of finite differences, the transfer equations, laminar, three-dimensional, between inclined isothermal ellipsoid of revolution, and a newtonian fluid in vertical upward flow generated by the natural convection. In the boundary layer, the results concerning the dimensionless velocity fields and temperatures as well as the Nusselt number and the friction coefficients, are represented graphically. With respect to the angle of inclination of the ellipsoid, the author put in evidence of the privileged points on the partition of the body. Secondly, the influence of the geometry of the body was also considered, in order to assess the adherence of the fluid on the wall and locate the boundary layer separation points.

Using a new approach, we propose an analog of the Fizeau effect for massive and massless particles in an effective optical medium derived from the static, spherically symmetric gravitational field. The medium is naturally perceived as a dispersive medium by matter de Broglie waves. Several Fresnel drag coefficients are worked out, with appropriate interpretations of the wavelengths used. In two cases, it turns out that the coefficients become independent of the wavelength even if the equivalent medium itself is dispersive. A few conceptual issues are also addressed in the process of derivation. It is shown that some of our results complement recent works dealing with real fluid or optical black holes.

The majority of wind power is currently produced on high wind speed sites by large wind turbine, whereas small wind turbines often operate in light wind conditions. Small capacity wind turbines have not received the same engineering attention as their large counterparts. This is partially due to a number of unique problems that small wind turbines experience. The most relevant are: low operating Reynolds number (Re<500,000) and high angles of attack. Several studies have suggested that flow control devices such as the spherical tubercle could be used to increase lift before stall and generate more power in such situations. The aim of this study is to determine the effect of tubercle amplitude on aerodynamic performance of an airfoil at low-Re numbers (Re=300,000 & Re=400,000). Three amplitudes were considered in this study: A1=0.005c, A2=0.01c, and A3=0.03c. A detailed 2D simulation study is carried out using a calibrated Transition SST k-ω turbulence model to obtain aerodynamic coefficients and flow characteristics. Results indicate that small tubercles perform better overall than larger tubercles. The airfoil with the smallest tubercle outperforms the unmodified airfoil at both studied Reynolds numbers at angles of attack 0° -4°. The analysis of the aerodynamic coefficients indicates that the improvement of the aerodynamic performance of the airfoils with tubercles is due to the reduction of the drag coefficient. Pressure, intermittency and wall shear stress contours suggest that the overall drag reduction is achieved through the decrease of friction drag. En la actualidad, la mayor parte de la energía eólica se produce en emplazamientos con vientos fuertes mediante grandes aerogeneradores, mientras que los pequeños suelen funcionar con vientos flojos. Los aerogeneradores de pequeña potencia no han recibido la misma atención técnica que sus homólogos de gran tamaño. Esto se debe en parte a una serie de problemas específicos que experimentan los aerogeneradores pequeños. Los más importantes son el bajo número de Reynolds operativo (Re<500.000) y los elevados ángulos de ataque. Varios estudios han sugerido que los dispositivos de control de flujo, como el tubérculo esférico, podrían utilizarse para aumentar la sustentación antes de la entrada en pérdida y generar más potencia en estas situaciones. El objetivo de este estudio es determinar el efecto de la amplitud del tubérculo en el rendimiento aerodinámico de un perfil aerodinámico con números de Re bajos (Re=300.000 y Re=400.000). En este estudio se consideraron tres amplitudes: A1=0,005c, A2=0,01c, y A3=0,03c. Se lleva a cabo un estudio detallado de simulación 2D utilizando un modelo de turbulencia k-ω de Transition SST calibrado para obtener los coeficientes aerodinámicos y las características del flujo. Los resultados indican que los tubérculos pequeños presentan un mejor comportamiento general que los tubérculos más grandes. El perfil con el tubérculo más pequeño supera al perfil no modificado en los dos números de Reynolds estudiados para ángulos de ataque de 0° -4°. El análisis de los coeficientes aerodinámicos indica que la mejora del rendimiento aerodinámico de los perfiles con tubérculos se debe a la reducción del coeficiente de resistencia. Los contornos de presión,

&amp;amp;lt;p&amp;amp;gt;The fluid dynamics of different sedimentological processes are often studied and interpreted by using models based on a combination of Newton dynamics and an empirical expression of the drag force in function of the drag coefficient. However, neither the expression of the drag force nor the value of the drag have a unique expression, depending on the state of the fluid (laminar, transitional, and turbulent) and on the shape and dimensions of the sediments. These (semi-) empirical models are often inaccurate, in particular in planetary sciences when gravity plays a determining role, like, for example, when calculating the terminal settling velocity of natural sediments on Mars. In this work, a numerical simulation code based on the Lattice Boltzmann Method (LBM) is used to study how settling velocity of some reference spherical particles changes at different gravity conditions, ranging from hyper to reduced gravity. LBM is a discrete computational method based on the kinetic Boltzmann equation that describes the dynamics of a fluid on a mesoscopic scale. This study shows that, despite the LB model has been calibrated and validated using only the set of experimental data collected during a parabolic flight, its validity goes beyond, being able to predict the correct terminal velocity of different particles, with different density and diameters. In addition, the same settings can be used to simulate other important processes that occur when sediments interact with each other and the fluid phase, such as hindered settling and the drafting, kissing, and tumbling phenomenon. This makes the Lattice Boltzmann method an ideal candidate for studying a wide range of sedimentological processes where a mesoscale accurate description is crucial to understand macroscale phenomena.&amp;amp;lt;/p&amp;amp;gt;

There is an increasing need to accurately predict the behaviour of fluid in the different flow geometry as applicable in the industries. The prediction of drag reduction phenomenon observed during the two-phase oil-water flow with drag reducing polymers in horizontal pipes was investigated. The Power law model was adopted in this study to empirically correlate the data acquired from our earlier experimental works in a 12-mm ID and 20-mm ID pipes. The model accurately predicts the drag reduction across the horizontal pipes. The agreement between the predicted and experimental drag reductions was better in the 12-mm ID pipe than in the 20-mm ID pipe. More work and data is needed to enhance the predictive accuracy of applicable models.

An unprecedented observational analysis of a category-5 hurricane suggests a mechanism by which high-entropy air inside the low-level eye can sustain the storm at an intensity above the currently formulated upper bound for tangential wind speed.

We apply the Finite Volume Coastal Ocean Model to simulate the Hurricane Ike storm surge using two-dimensional (2-D) and three-dimensional (3-D) formulations. The high resolution, unstructured grid extends over the Gulf of Mexico with open boundaries in the Straits of Florida and the Yucatan Channel. With the same wind and pressure forcing, the bottom drag coefficients for the baseline 2-D and 3-D simulations are determined by spatially varying Manning coefficients and constant bottom roughness, respectively. The baseline 2-D model simulates both the forerunner and the surge, whereas the baseline 3-D model simulates the surge, but underestimates the forerunner. Increasing the minimum Manning coefficient reduces the 2-D forerunner and the surge. Manning coefficient and bottom roughness parameterizations produce different bottom drag coefficients. Using the same bottom drag coefficient, the 2-D simulation yields a smaller surge than in three dimensions. This is investigated for scenarios of either constant or variable bottom roughness where the bottom roughness is determined through Manning coefficient transformation. These sensitivity studies indicate that storm surges, simulated either in two dimensions or three dimensions, depend critically upon the parameterizations and the parameter values used for specifying bottom stress (and similar may be said of surface stress). Given suitable calibration, 2-D and 3-D models may adequately simulate storm surge. However, it is unclear that a calibration for a given storm and location may apply generally. Hence additional experimental guidance is required on the parameterizations and the parameter values used for both the surface and bottom stresses under severe wind conditions.

The current paper summarizes the findings of a Computational Fluid Dynamics (CFD) study performed for the improvement of ASDE-X antenna operation. The vibration and noise generation of the newly developed ASDE-X radar antenna as shown in Figure is a serious problem that jeopardizes the successful deployment of this new airport ground traffic control system. The most significant problem areas are aerodynamically induced noise and vibration. The overall project has three main areas of investigation.

The aim of the present study is to investigate the accuracy of two different dynamic stall approaches for windturbine airfoils. The first approach is the semi-empirical Leishman-Beddoes model (L-B), and the second is the computational fluid dynamic (CFD) results. National Renewable-Energy Laboratory (NREL) S series airfoils are used, and the simulations are performed in Re=10 6 . For both approaches, aerodynamic coefficients are represented and compared to experimental data. Validation data refer to Ohio State University (OSU) experiments, which are for pitch oscillation. Results show that the accuracy of the L-B and CFD methods is dependent on mean angle of attack, reduced frequency and the phase of motion. The semi-empirical model has appropriate accuracy as well as low computational cost while the CFD unsteady simulation could be properly used to predict the drag coefficient.

Approximately 25% of the aerodynamic drag of passenger vehicles is contributed by the wheels. Small features in the tire geometry and the contact area between tire and ground can induce flow separation. Thus, the wheel wake features complex flow phenomena. To understand the appearing flow phenomena, a correct geometry representation of the rotating tire in CFD is essential. The model has to cover the rotating tread, the deformation due to weight and centrifugal forces. Realistic detailed and/or deformed tires are investigated with OpenFOAM® employing a hybrid approach to study the influence of geometrical features on the flow field and coefficients.

Approximately 25% of the aerodynamic drag of passenger vehicles is contributed by the wheels. Small features in the tire geometry and the contact area between tire and ground can induce flow separation. Thus, the wheel wake features complex flow phenomena. To understand the appearing flow phenomena, a correct geometry representation of the rotating tire in CFD is essential. The model has to cover the rotating tread, the deformation due to weight and centrifugal forces. Realistic detailed and/or deformed tires are investigated with OpenFOAM® employing a hybrid approach to study the influence of geometrical features on the flow field and coefficients.

The drag coefficient C D is generally expressed as a function only of the wind speed U 10 . However, there exists considerable disagreement among the observed values of C D . In this study, we investigate the variation of C D by using data sets, including directional wave spectral data in long period measurements. Wind and wave data obtained at a coastal tower operated by the Shirahama Oceanographic Observatory of the Disaster Prevention Research Institute (DPRI) at Kyoto University in Japan, together with data sets obtained by Suzuki et al. (2002), were used. The directional wave spectra were separated into four different groups: the following and cross swell cases, mixed swell case, and pure wind-wave case. The data sets also showed variation in wind speed regions higher than 20 m/s in the C D -U 10 diagram. It was shown that this variation is the effect of the natural fluctuation of wind. We also observed C D values by using the windsea Reynolds number R B proposed by Toba et al. (2006). In the following swell cases, C D values are slightly smaller. In the cross swell cases, when the difference in direction between the wind and waves is greater than 70 degrees, C D has larger values. However, C D has similar values in the following swell cases when the difference in direction between the wind and waves is less than 70 degrees.

Within the AdS/CFT correspondence, we review the studies of field theories with a large number of adjoint and fundamental fields, in the Veneziano limit. We concentrate in set-ups where the fundamentals are introduced by a smeared set of D-branes. We make emphasis on the general ideas and then in subsequent chapters that can be read independently and describe particular considerations in various different models. Some new material is presented along the various sections.

In the repowering of conventional steam power plants, we face off-design conditions. In this paper, a numerical study of the steam flow in the blades of the last stage of the low-pressure turbine of the Neka thermal power plant was carried out. To analyze the steam flow in the turbine, one design mode and two off-design modes including part-load and overload were considered. In this research, three-dimensional Reynolds-averaged Navier-Stokes equations were simulated by using Ansys CFX software. Also, the SST k-ω method was used to model the turbulent flow. According to the obtained results, the effect of steam mass flow rate changes on the low-pressure turbine performance, such as velocity triangles, pressure, Mach number, and temperature distribution on blade surfaces, flow angles, degree of reaction, back pressure, steam quality, and efficiency, was investigated. For example, the loss of isentropic efficiency of the last stage in the off-design mode was less than 0.37% compared to the design conditions. Furthermore, the changes in the degree of reaction of the blades due to the changes in the mass flow rate of the fluid were less than 3%. Validation of the numerical solution was done in two-dimensional and three-dimensional models, and the results showed that there was a good agreement between numerical simulation and experimental data.

A micro energy harvesting device proposed in the literature, is numerically studied. It consists of two bluff bodies in a micro-channel and a flexible diaphragm at its upper wall. Vortex shedding behind bodies induces pressure fluctuation causing vibration of the diaphragm that converts me-chanical energy to electrical by means of a piezoelectric membrane. Research on enhancing vortex shedding is justified due to the low power output of the device. Amplitude and frequency of un-steady pressure fluctuation on the diaphragm center are numerically predicted. Vortex shedding severity is mainly assessed in terms of pressure amplitude. The CFD model set-up is described in detail and appropriate metrics to assess energy harvesting potential are defined. Several cases are simulated to study the effect of inlet Reynolds number and channel blockage ratio on the prospec-tive performance of the device. Furthermore, the critical blockage ratio leading to vortex shedding suppression is sought. Hi...

This paper looks at the impact deformation and turnover stability of both feather and synthetic shuttlecocks using a racket based launcher. Flight of a shuttlecock can be described by steady state and unsteady state. Previous works were mainly focused on the steady state flight. While bulk of flight is in the steady state, the transient unsteady state is critical because it determines the initial condition of stabilized flight. The whole phase of rapid angular change during the unsteady state is the turnover process. Impact deformation and turnover response were studied with a racket-based launcher. Angles of attack with respect to time were recorded using high speed capturing. While the resultant plot showed significant variations between shuttles, most completed turnover process within 0.05s to 0.06s. Despite inherent disadvantage in density of the skirt material, turnover stability of synthetic shuttlecock was not compromised. All shuttles exhibited under damped behaviour in angular response and a 2 nd order approximation was identified for the mean response of each. Feather shuttles have higher damping factor and smaller natural period. Higher-grade feather shuttle was observed to maintain skirt structural integrity better than lower tier shuttle in the impact deformation testing. Skirt stiffness is desirable to prevent deformation upon impact at higher racket speed. The practice grade feather shuttle displayed deformation pattern akin to a blooming flower, while the top grade shuttle was able to resist impact deformation at same racket speed. In conclusion, higher-grade shuttles could resist skirt deformation from racket-shuttle impact and attain steady state flight within a shorter time.

The structure of the wake behind a submersed body greatly affects the performance and design of many engineering applications. The behaviour of the wake partially dictates the drag experienced by the body, therefore optimisation of this wake behaviour can have a significant effect on the energy required to move the body relative to the fluid. The formation of wakes over smooth bodies is well understood, however, the implications of surface roughness on the near wake structure are not well known. Surface roughness is known to greatly affect the behaviour of a turbulent boundary layer and the nature of the structures within. The subsequent interaction of these modified boundary layers in the wake modifies the formation of the wake. Roughness can be introduced into a system in a range of ways, such as manufacturing processes, surface finishes and degradation and accumulation of fouling. Therefore, the prevalence of roughness in combination with the importance of wake behaviour on performance is the motivation for the investigation of the implications of surface roughness on plane wake flows. To investigate these implications a series of 2-component -2dimensional particle image velocimetry (2C-2D PIV) measurements were performed on a smooth and rough flat plate in the LTRAC large horizontal water tunnel facility. The boundary layer was tripped at the leading edge and measurements were acquired in the near wake of the blunt trailing edge of the plate. The surface was roughened using commercially available sandpaper adhered to the plate surface.

The unstructured-grid, Finite-Volume Coastal Ocean Model (FVCOM) was used to simulate the flows in Discovery Passage, British Columbia, Canada. Challenges in this numerical study include the strong tidal currents in Seymour Narrows of up to 7.8 m s -1 , small-scale topographic features, and freshwater discharge and stratification. Tidal forcing, freshwater input, the Coriolis effect, and wet and dry regions were considered. The model was integrated for 16 days and model results of the last 14 days were examined. The model was validated using available historical measurements at different sites in Discovery Passage, including water surface elevation and ocean current data, as well as CTD-bottle profile data. Model results are also compared with the recent numerical studies by and by . Model results demonstrated that the unstructured-grid model generated reasonable maps of the very strong currents in tidal channels, with the advantage of high adaptability in resolving the complex geometry of the narrow channels as seen in Discovery Passage. Effects of stratification and freshwater discharge from Campbell River during the study period were investigated.

The settling velocity of porous particles in linear stratification is affected by the diffusive exchange between interstitial and ambient water. The extent to which buoyancy and interstitial mass adaptation alters the settling velocity depends on the ratio of the diffusive and viscous time scales. We conducted schlieren experiments and lattice Boltzmann simulations for highly porous (95 %) but impermeable spheres settling in linear stratification. For a parameter range that resembles marine porous particles, 'marine aggregates', i.e. low Reynolds numbers (0.05 ≤ Re ≤ 10), intermediate Froude numbers (0.1 ≤ Fr ≤ 100) and Schmidt number of salt (Sc = 700), we observe delayed mass adaptation of the interstitial fluid due to lower-density fluid being dragged by a particle that forms a density boundary layer around the particle. The boundary layer buffers the diffusive exchange of stratifying agent with the ambient fluid, leading to an enhanced density contrast of the interstitial pore fluid. Stratification-related drag enhancement by means of additional buoyancy of dragging lighter fluid and buoyancy-induced vorticity resembles earlier findings for solid spheres. However, the exchange between density boundary layer and pore fluid substantially increases stratification drag for small Fr. To estimate the effect of stratification on marine aggregates settling in the ocean, we derived scaling laws and show that small particles (≤0.5 mm) experience enhanced drag which increases retention times by 10 % while larger porous particle (>0.5 mm)

The simulation of a stationary fluid flow past an obstacle by the lattice Boltzmann method ͑LBM͒ in two dimensions is discussed. The combination of second-order expressions for far-field boundary conditions and a suitable treatment of the no-slip boundary condition at the obstacle surface with the nested grid-refinement technique can be applied to the LBM, resulting in a highly efficient method for the treatment of exterior flows. Furthermore, via replacing the nested time stepping by local time stepping, the resolution process can be substantially accelerated. A highly accurate drag coefficient was used to make an error assessment for various no-slip boundary conditions imposed on the obstacle surface. The analysis showed that the equilibrium method for treating the no-slip conditions is superior to halfway bounce-back and full-way bounce-back no-slip conditions when the relaxation time = 1. Also a -dependence test was made to evaluate the performance of different methods in the treatment of the no-slip boundary conditions.

Fuel efficiency is the prime focus of the present work. Simulations are carried over external aerodynamic body to determine the drag and its coefficient by means of virtual environment with the help of commercial tool. The use of computer software makes it possible to be in time and cost savings. Numerical methods are employed on threedimensional vehicle structure to resolved body forces. The present work is carried using the ANSYS-CFX and the equations governing fluid flow combined with standard model and solved by using the appropriate boundary conditions. The study results of the aerodynamic analysis of the air flow, pressure distribution and drag force on the vehicle. Few design modifications are made in the form of attachable accessories which have been resulted in reduction of the drag coefficient. These modifications have shown a drag reduction of 14.28% at a speed of 60 km/h with the drag coefficient reduced to 0.336 from 0.392, thereby reducing the fuel consumption allotted to external body by an amount of approximately 14.28%, which means, there is a saving of 2.14L of petrol for every full tank refill.

Measurements are presented of response and drag for a flexibly mounted circular cylinder with low mass and damping. In one set of experiments it is free to respond in only the cross-flow direction and in a second it is free to respond in two degrees of freedom. It is shown how vortex-induced vibration can be practically eliminated by using free-to-rotate, two-dimensional control plates. Further it is shown that these devices achieve VIV suppression with drag reduction. The device producing the largest drag reduction was found to have a drag coefficient equal to about 60% of that for a plain, fixed cylinder over the Reynolds number range of the experiments, up to 30 000. The importance of torsional resistance of the devices is discussed and it is shown that if it is too low large oscillations of the device and cylinder will develop and if it is too high galloping is initiated.

Experiments with stationary and yawed cylinders were carried out at a recirculating water channel facility and aimed to study the effects of the inclination in the force coefficients and in the vortex-shedding frequency. The cylinders were inclined at 0 (non-yawed case), 10, 20, 30, and 45 degrees. Force coefficients and the Strouhal number were evaluated by using the Independence Principle (IP), which states a dependence of the flow characteristics only on the component of velocity normal to the cylinder axis. The experimental results showed that when the cylinder was yawed at 45 degrees, there was no regular vortex-shedding regime. A new result is the fact that the lift force spectra, as well as the mean drag coefficient, are different if the cylinder is yawed in upstream or downstream orientation. This difference is associated with the asymmetrical end conditions of the cylinder.

The growth of urbanization has generated an increase in the use of motorized transport, which has intensified problems such as road congestion, environmental impact and health and safety risks. Currently, the automotive field is responsible for more than 10 % of global greenhouse gas (GHG) emissions. In response to this problem, manufacturers have developed several solutions, with electric vehicles playing the leading role as a sustainable alternative. Electric motorcycles have shown a growth in sales in recent years in Ecuador; however, their growth is limited by factors such as lack of infrastructure and government regulations. Manufacturers focus on aerodynamics as a key aspect to improve efficiency; to optimize their design, tools such as wind tunnels or computational simulations are used, the latter being a more accessible option. This study proposes the design of a fairing for an electric motorcycle using CAD/CAE software, based on the IDes process. Three proposals were developed, evaluating their aerodynamic performance under the conditions of Loja province. The results indicated that design 3 obtained the best performance, with an average drag coefficient of 0.283 and a lift coefficient of -0.273, subjected to different speeds. From the structural point of view, epoxy resin with unidirectional prepreg S-glass fiber was selected for its balance between mechanical properties and cost. The simulation showed a maximum deformation of 0.35339 mm under various stresses. Furthermore, in the modal analysis, at 78.802 Hz, the fairing presented a deformation of 15.788 mm with a maximum amplitude of 6.5 Hz, validating its ability to withstand the dynamic conditions of the motorcycle without compromising its structure.

Tropical storm intensity prediction remains a challenge in tropical meteorology. Some tropical storms undergo dramatic rapid intensification and rapid decline. Hurricane researchers have considered particular ambient environmental conditions including the ocean thermal and salinity structure and internal vortex dynamics (e.g., eyewall replacement cycle, hot towers) as factors creating favorable conditions for rapid intensification. At this point, however, it is not exactly known to what extent the state of the sea surface controls tropical cyclone dynamics. Theoretical considerations, laboratory experiments, and numerical simulations suggest that the air-sea interface under tropical cyclones is subject to the Kelvin-Helmholtz type instability. Ejection of large quantities of spray particles due to this instability can produce a two-phase environment, which can attenuate gravity-capillary waves and alter the air-sea coupling. The unified parameterization of waveform and two-phase drag based on the physics of the air-sea interface shows the increase of the aerodynamic drag coefficient C d with wind speed up to hurricane force (U 10 % 35 m s 21 ). Remarkably, there is a local C d minimum-''an aerodynamic drag well''-at around U 10 % 60 m s 21 . The negative slope of the C d dependence on wind-speed between approximately 35 and 60 m s 21 favors rapid storm intensification. In contrast, the positive slope of C d wind-speed dependence above 60 m s 21 is favorable for a rapid storm decline of the most powerful storms. In fact, the storms that intensify to Category 5 usually rapidly weaken afterward.