Empirical Drag Coefficient Research Articles

Can solar wind viscous drag account for coronal mass ejection deceleration?

The forces acting on solar Coronal Mass Ejections (CMEs) in the interplanetary medium have been evaluated so far in terms of an empirical drag coefficient CD ∼ 1 that quantifies the role of the aerodynamic drag experienced by a typical CME due to its interaction with the ambient solar wind. We use a microphysical prescription for viscosity in the turbulent solar wind to obtain an analytical model for the drag coefficient CD. This is the first physical characterization of the aerodynamic drag experienced by CMEs. We use this physically motivated prescription for CD in a simple, 1D model for CME propagation to obtain velocity profiles and travel times that agree well with observations of deceleration experienced by fast CMEs.

The Drag Coefficient and the Shape for a Single Bubble Rising in Non-Newtonian Fluids

The dynamical characteristic of a single bubble rising in non-Newtonian fluid was investigated experimentally. The bubble aspect ratio and rising velocity were measured by high speed camera. The shape regimes for bubbles in non-Newtonian fluids was plotted by means of Reynolds number Re, Eötvös number Eo and Morton number Mo. The effects of bubble shape and liquid rheological property on the total bubble drag coefficient were studied. A new empirical drag coefficient correlation covering spherical bubble and deformed bubble was proposed, the predicted results shows good conformity to experimental values over a wide range of 0.05 < Re < 300.

Drag force on a vegetation field due to long-crested and short-crested nonlinear random waves

This paper provides a practical method for estimating the drag force on a vegetation field exposed to long-crested (2D) and short-crested (3D) nonlinear random waves. This is achieved by using a simple drag formula together with an empirical drag coefficient given by Mendez et al. (1999), in conjunction with a stochastic approach. Here the waves are assumed to be a stationary narrow-band random process. Effects of nonlinear waves are included by adopting the Forristall (2000) wave crest height distribution representing both 2D and 3D random waves.

Drag Coefficient of a Spherical Particle Attached on the Flat Surface

The previous analytical solution for the drag coefficient (Cd) for a spherical particle attached on the flat surface, which was derived by O’Neill (1968), is only valid in the creeping flow conditions. It is important to extend O’Neill’s formula to cover a wide range of particle Reynolds number (Rep). In this study, the drag coefficient was calculated numerically to cover Rep from 0.1 to 250. For a particle suspended in the air, an empirical drag coefficient exists, which is defined as Cd = f × 24/Rep, where f is a correction factor depending on Rep. The applicability of the correction factor f for O’Neill’s analytical equation for the spherical particle attached on the flat surface for Rep = 0.1 to 250 was examined in this study.

Large-scale laboratory measurements of solitary wave inundation on a 1:20 slope

The run-up flow and related pressure of solitary waves breaking on a 1:20 plane beach were investigated experimentally in a super tank (300 m × 5 m × 5.2 m). Swash flow measurements of flow velocities are compared with an existing analytical solution. By incorporating an analytical solution, the hydrodynamic pressure for a quasi-steady flow state is determined and compared with laboratory data. Concerning the evident extra pressure exerted by the impact of swash flow, an empirical drag coefficient for a circular plate is also suggested in the present study.

Nonlinear random wave-induced drag force on a vegetation field

This paper provides a practical method by which the drag force on a vegetation field beneath nonlinear random waves can be estimated. This is achieved by using a simple drag formula together with an empirical drag coefficient given by Mendez et al. (Mendez, F.J., Losada, I.J., Losada, M.A., 1999. Hydrodynamics induced by wind waves in a vegetation field. J. Geophys. Res. 104 (C8), 18383–18396). Effects of nonlinear waves are included by using Stokes second order wave theory where the basic harmonic motion is assumed to be a stationary Gaussian narrow–band random process. An example of calculation is also presented.

Impacts of wave and current on drag coefficient and wind stress over the tropical and northern Pacific

By taking into consideration the effects of ocean surface wave-induced Stokes drift velocity Ūw and current velocity Ūc on the drag coefficient, the spatial distributions of drag coefficient and wind stress in 2004 are computed over the tropical and northern Pacific using an empirical drag coefficient parameterization formula based on wave steepness and wind speed. The global ocean current field is generated from the Hybrid Coordinate Ocean Model (HYCOM) and the wave data are generated from Wavewatch III (WW3). The spatial variability of the drag coefficient and wind stress is analyzed. Preliminary results indicate that the ocean surface Stokes drift velocity and current velocity exert an important influence on the wind stress. The results also show that consideration of the effects of the ocean surface Stokes drift velocity and current velocity on the wind stress can significantly improve the modeling of ocean circulation and air-sea interaction processes.

Windage Power Loss Modeling of a Smooth Rotor Supported by Homopolar Active Magnetic Bearings

Rotors supported by active magnetic bearings (AMBs) can spin at high surface speeds with relatively low power losses. This makes them particularly attractive for use in flywheels for energy storage in applications such as electric vehicles and uninterruptible power supplies. In order to optimize efficiency in these and other applications, the loss mechanisms associated with magnetic bearings and rotating machinery must be well understood. The primary parasitic loss mechanisms in an AMB include complex magnetic losses, due to eddy currents and hysteresis, and windage losses along the entire rotor in nonvacuum environments. In low-loss magnetic bearing designs, the windage loss component along the rotor can become dominant at high speeds, and the need for accurate windage models becomes even more critical. This study extends previous AMB power loss work by evaluating five different windage loss models using the experimental rundown data from the previous work. Each of the five windage models, along with standard models of eddy current and hysteresis losses, are used to reduce the rundown data into the associated power loss components. A comparison is then completed comparing the windage power loss component extracted through the rundown data reduction scheme to the associated analytical windage prediction in order to identify the most accurate model for calculating windage losses along a smooth rotor. Five empirical flat-plate drag coefficient models are implemented, four turbulent and one laminar. An empirical flat-plate turbulent boundary layer formula (referred to here as “Model 2”) developed by Prandtl and Schlichting displayed the best agreement between experimentally extracted and analytically predicted windage loss values. The most accurate model formula (Model 2) dictates that the frequency dependency of windage loss is both logarithmic and power based and represents the minimum error between experimentally extracted and analytically predicted losses of all models in the study of high-speed power losses in a smooth rotor supported in AMBs.

310 高粒子体積率で存在する粒子に負荷する流体抵抗力の検証(2)(OS3-2 噴流,後流,せん断流の構造・普遍的特性(後流2),OS3噴流,後流,せん断流の構造・普遍的特性)

The drag coefficient of solid particles falling in the air has been investigated experimentally. Small spherical particles free-fall through quiescent or turbulent flow in which the turbulent level is kept constant with rotating grids as a turbulent generator. Averaged flow property that is changed depending on the charge of the particles is measured by means of LDV. Particle velocity is measured by means of 2D-PTV with laser sheet and CMOS camera. In still flow, by increasing particle volume fraction (up to O(10^<-3>)) the drag force for each particle changes, while in the turbulent flow the drag force for each particle is changed with the change of volume fraction but is relatively insensitive to turbulent intensity. Consequently, the existing empirical drag coefficient for solid particle, which depends only on the particle Reynolds number, is insufficient and it depends on the volume fraction of solid particles and ambient turbulent statistics.

Turbulent structures in partly vegetated open-channel flows with LDA and PI V measurements

The effects of vegetation growing in rivers in and at ihe edge of the water on turbulent structures and the associated sediment transport are not claritied yet. in spite of their importance for hydraulics and river engineering. In this study, turbulence measurements of open-channel flows with a vegetated zone at a half channel width were conducted by making use of both, a laser Doppler anemometer! LDA) and the particle-image velocinietry(PIV). It was found that the intensities of ihe secondary currents and the turbulent energy increase with an increase of the Froude number. The turbulence is adveeted span wisely near the free surface by the secondary currents, which are generated by the anisotropy of turbulence. The horizontal vortices near the free surface are generated by the velocity inflectional instability, which increases w ith an increase of Froude number and the vegetation density. The bed (wall) shear stress in the vegetated zone was calculated by the Reynolds equation with the aid of the empirical drag coefficient.

An Aid to Operating Decisions Based on Nonlinear Response of a Crane Barge in Waves

A nine-degree-of-freedom time domain mathematical model was used to numerically simulate crane ship dynamics. This model considers the elasticity and damping of the hoisting rope assembly and includes arbitrary, biangular swing of the suspended hook load coupled with surge, sway, heave, roll, pitch, and yaw motions of the hull. The linear frequency-dependent hydrodynamic response to the hull’s own motions accounted for memory effects that were approximated in the time domain by a finite state space model. The nonlinear hydrodynamic drag force acting on the oscillating hull was quadratically approximated using an empirical drag coefficient. The incident wave force on the hull consisted of the first-order force oscillating at wave frequency and the second-order slowly varying wave drift force. The nonlinear horizontal mooring system restoring force was approximated by a third-order polynomial. To specify operating limits for a shear-leg crane barge in a heavy lift offshore operation, a stochastic analysis was performed based on the system’s simulated dynamic response in an ensemble of natural seaways.

Modeling Forces on a Beam-Pump System During Pumping of Highly Viscous Crude

SummaryIn previous dynamic predictive models of beam-pump performance, drag forces on the rod string commonly are modeled by an input empirical drag coefficient multiplying the local rod velocity. This paper shows how forces on the rods and pump plunger can be modeled theoretically and calculated for viscous flow. Results of viscous-flow calculations to develop drag coefficients compare well with measured field data.

Hydrodynamic forces acting on cylinders oscillating at small amplitudes

The hydrodynamic forces resulting from small-amplitude harmonic oscillations of arbitrarily shaped cylinders are considered both experimentally and theoretically. The fluid is assumed to be initially at rest. The theoretical model assumes a laminar, nonseparating flow, where the in-line force has two components, one due to normal pressure stresses and one due to skin friction. In the limit of zero amplitude oscillations, comparisons between theory and experiment demonstrate that the nonseparating theoretical model captures the essential behavior of real fluid hydrodynamics. This is valid for a variety of shapes including sharp-edged bodies such as squares. Through model testing, it is possible to estimate an “effective eddy viscosity” which can then be used in conjunction with the theoretical laminar flow model to give empirical drag coefficients.

A MODIFIED EMPIRICAL DRAG COEFFICIENT FOR WATER DROP BALLISTICS

Variation of the empirical drag coefficient, in Seginer's water drop ballistics equation as a function of drop size and velocity, increased the accuracy of predicted velocities when compared to measured values. The velocity exponent, n, used to calculate the drag coefficient in Seginer's equation increases not only with increasing drop size but also increases with increasing fall velocity. Using falling water drop terminal velocities from a meteorological model enables the calculation of water drop ballistics for any air density. The throw distance of drops from an impact sprinkler were simulated with the drag coefficient dependent on drop size and velocity, and show that simulated throw distances are greater for small drops than if the velocity exponent has a typically used constant value of two.

Effect of Ultra-Stokesian Drag and Particle Interception on Impaction Characteristics

The characteristics of impactors with round or rectangular nozzles have been determined by the numerical solution of the Navier-Stokes equations and of the equation of motion of the particles. The sensitivity of this solution to the system of grid lines was investigated by decreasing the spacing between them; these studies yielded sharper curves and higher √St50 for finer grids. The particle trajectory calculation program included an empirical ultra-Stokesian drag coefficient and a facility for handling particle interception. Studies comparing the results of runs made using the ultra-Stokesian drag law with those assuming Stokes law indicated that the latter underpredicts the √St20 by 5 to 10%. The influence of particle interception was found to be small except at very low Reynolds numbers, the characteristics for which demon strated low-efficiency tails. Dimensional analysis of the impactor system required the introduction of a second dimensionless quantity (in addition to the St) to char acterize the pa...