Estimation Of Drag Coefficient Research Articles

Comparative Analysis of Satellite Aerodynamics and Its Application to Space-Object Identification

The accuracy of atmospheric density measurements inferred from satellite drag is limited by errors in drag coefficient estimates. In this work, we use a unique opportunity in which the Drag and Atmospheric Neutral Density Explorer satellite and three Polar Orbiting Passive Atmospheric Calibration Spheres are deployed from a common launch vehicle. Each object flies through similar atmospheric conditions but has a different area-to-mass ratio. This allows aerodynamic analysis that is independent of atmospheric density via comparisons of measured and modeled ballistic coefficient ratios. A test particle method combined with a satellite energy accommodation model is used to model the aerodynamics of these objects. Fitted ballistic coefficients computed as a result of special-perturbations orbit analysis are then compared to the model results. The drag coefficient model and observations agree at the 1–2% level when coefficient ratios are compared. Comparisons of an additional shape with model predictions are made possible when one of the satellites shed its launch adapter. This work validates the aerodynamic model used here and can be applied in future research to improve models of atmospheric density and predictions of satellite drag. Beyond potential improvements to atmospheric models, the technique presented here is shown to identify objects based on their aerodynamic signature.

Pressure-field extraction from Lagrangian flow measurements: first experiences with 4D-PTV data

As a follow-up to a previous proof-of-principle study, a novel Lagrangian pressure-extraction technique is analytically evaluated, and experimentally validated using dense 4D-PTV data. The technique is analytically evaluated using the semi-three-dimensional Taylor–Green vortex, and it is found that the Lagrangian technique out-performs the standard Eulerian technique when Dirichlet boundary conditions are enforced. However, the Lagrangian technique produces worse estimates of the pressure field when Neumann boundary conditions are enforced on boundaries with strong pressure gradients. The technique is experimentally validated using flow data obtained for the case of a free-falling, index-matched sphere at \(Re=2100\). The experimental data were collected using a four-camera particle tracking velocimetry measurement system, and processed using 4D-PTV. The pressure field is then extracted using both the Eulerian and Lagrangian techniques, and the resulting pressure fields are compared. Qualitatively, the pressure fields agree; however, quantitative differences are found with respect to the magnitude of the pressure minima on the side of the sphere. Finally, the pressure-drag coefficient is estimated using each technique, and the two techniques are found to be in very close agreement. A comparison to a reference value from literature confirms that the drag coefficient estimates are reasonable, demonstrating the validity of the technique.

Turbulent production in an internal wave bottom boundary layer maintained by a vertically propagating seiche

AbstractInternal seiches, which supply the energy responsible for mixing many lakes, are often modeled as vertically standing waves. However, recent observations of vertical seiche propagation in a small lake are inconsistent with the standard, vertically standing model. To examine the processes responsible for such propagation, drag and turbulent production in the bottom boundary layer of a small lake are related to the energy supplied by a propagating seiche (period 10–24 h). Despite complex and fluctuating stratification, which often inhibited mixing within 0.4 m of the bed, bottom stress was well represented by a simple drag coefficient model (drag coefficient 1.5 × 10−3). The net supply of seiche energy to the boundary layer was estimated by fitting a model for internal wave vertical propagation to velocity profiles measured above the boundary layer (1–4.5 m above lakebed). Fitted reflection coefficients ranged from 0.3 at 1 cycle/d frequency to 0.7 at 2.4 cycles/d (cf. near‐unity coefficients of classical seiche theories). The net supply of seiche energy approximately balanced boundary layer turbulent production. Three of four peaks in production and energy flux occurred 0.8–2.2 days after strong oscillating winds, a delay comparable to the time required for seiche energy to propagate to the lakebed. A model based on the estimated drag coefficient predicted the observed frequency dependence of the seiche reflection coefficient. For flat‐bed regions in narrow lakes, the model predicts that reflection is controlled by the ratio of water velocity to vertical wave propagation speed, with sufficiently large ratios leading to weak reflection, and clear vertical seiche propagation.

Field measurements of drag force on Sargassum horneri (Turner) C. Agardh towed by a boat and estimation of drag coefficient

Field measurements of drag force on <i>Sargassum horneri</i> (Turner) C. Agardh towed by a boat and estimation of drag coefficient

Estimation of Shear-Induced Lift Force in Laminar and Turbulent Flows

The goal of the present study is to demonstrate that direct numerical simulations (DNS) coupled with interface tracking methods can be used to estimate interfacial forces in two-phase flows. Current computational multiphase fluid dynamics codes model interfacial forces utilizing closure laws that are heavily dependent on limited experimental data and simplified analytical approximations. In the present work, a method for improving the current interfacial force database has been developed by using DNS to quantify the lift and drag forces on a single bubble in laminar and turbulent shear flows. A proportional-integral-derivative–based controller was implemented into the finite element–based, multiphase flow solver [PHASTA (Parallel, Hierarchic, higher-order accurate, Adaptive, Stabilized, finite element method Transient Analysis)] to control the bubble position. This capability allowed for utilization of a steady-state force balance on the bubble to determine lift and drag coefficients in various shear flows. Specifically, for low shear flows (2.0 s−1), the effect of the wall presence is analyzed, and for high shear flows, the effect of turbulence is studied. A number of uniform shear (10.0 to 470.0 s−1) laminar flows were simulated to assess lift and drag force behavior as the kinetic energy of the flow increased. Two high shear (236.0 and 470.0 s−1) turbulent flows were simulated to understand bubble-turbulence interaction influence on the drag and lift phenomena. Two uniform shear rates (20.0 and 100 s−1) were simulated utilizing pressurized water reactor fluid properties. The lift and drag coefficients estimated in this work are in agreement with models developed for low shear laminar flows, whereas for high shear laminar and turbulent flows, bubble-turbulence interaction became a dominating influence in the lift and drag coefficient estimation. The novel results and method presented in this paper offer a path to simulating full-fledged reactor coolant environments where the lift and drag forces on a single bubble can be studied.

Using corner chamfers to reduce the drag of flat-sided columns

A comprehensive study of the drag forces acting on flat-sided columns is presented. The study considers a range of plane-sided column sections, from a sharp-cornered square section to varying degrees of corner chamfering and a full octagonal section. All chamfering was found to reduce the drag compared with the sharp-cornered case. It was also found there is a slight decrease in the drag coefficient as the Reynolds number of the fluid increases. For all cases except the octagonal section, drag increases significantly with increasing angle of attack. For the octagonal section, the drag coefficient increases then decreases as the angle of attack changes. The results agree with corresponding cases in the literature. The results are presented in a sequence of tables that allow users to estimate drag coefficients for any of the cases presented in the paper. As such, the study can serve as an archival repository for drag coefficient information. Comparisons of flow patterns are made, particularly in the wake region. It was found that the wake region becomes smaller as the chamfer becomes larger. The findings are important for the prediction of dynamic loads on exposed flat-sided columns above and below water, such as bridge pylons and offshore platform legs.

Turbulence characteristics of favorable pressure gradient flows in gravel-bed channel with vegetated walls

Abstract Field observations showed that in many gravel-bed rivers, rice stems and gravel interact with each other and affect the flow structure. This calls to conduct research in more details in laboratory to better understand impacts of interaction between rice stems and gravel bed rivers on the flow structure. The outcome of such investigations can improve the estimation of drag coefficient in hydrodynamic models. Experiments were carried out in a flume with gravel bed and the vegetated vertical flume walls to investigate turbulence characteristics under favorable pressure gradient flows. Results showed that the stress fraction involves both the sweep and ejection dominance near the vegetated flume walls, showing no negative Reynolds shear stress near water surface. The values of exuberance ratio play a significant role on the magnitude of the Reynolds shear stress which varies with the distance from the vegetation. Quadrant analysis reveals that a major part of the momentum flux is transported during a short period of strong turbulence activity near the bed at the central axis. Augmentation of the hole size makes difference between contributions of sweep and ejection with those of the outward and inward interactions near the bed, however, the hole size doesn’t play any role near the water surface.

キャノピー内部の抗力係数分布を考慮した樹木群を過ぎる流れのLES

The influence of the model drag coefficient on prediction accuracy of flows past emergent vegetation canopies by a classical canopy model has been examined. Two types of numerical simulations are carried out: The preliminary analysis based on a two-dimensional immersed boundary method gives an estimate of the spatial distribution of the drag coefficient over the vegetation canopy of the target flow. The estimated drag coefficient is introduced into the main analysis where a three-dimensional large-eddy simulation (LES) together with the canopy model is employed. The prediction accuracy of the main analysis is discussed against the corresponding experimental data and another LES result with a uniform drag coefficient in the canopy. The present LES with the estimated drag coefficient shows an improved prediction especially on stagnation phenomena at the leading edge of the vegetation patches. The improvement, however, is found mainly at the time-averaged flow level only. This is because the estimated drag coefficient is obtained from the time-averaged flow and does not reflect the instantaneous flow features directly.

Development of empirical models with high accuracy for estimation of drag coefficient of flow around a smooth sphere: An evolutionary approach

An accurate correlation for the smooth sphere drag coefficient with wide range of applicability is a useful tool in the field of particle technology. The present study focuses on the development of high accurate drag coefficient correlations from low to very high Reynolds numbers (up to 106) using a multi-gene Genetic Programming (GP) procedure. A clear superiority of GP over other methods is that GP is able to determine the structure and parameters of the model, simultaneously, while the structure of the model is imposed by the user in traditional regression analysis, and only the parameters of the model are assigned. In other words, in addition to the parameters of the model, the structure of it can be optimized using GP approach. Among two new and high accurate models of the present study, one of them is acceptable for the region before drag dip, and the other is applicable for the whole range of Reynolds numbers up to 106 including the transient region from laminar to turbulent. The performances of the developed models are examined and compared with other reported models. The results indicate that these models respectively give 16.2% and 69.4% better results than the best existing correlations in terms of the sum of squared of logarithmic deviations (SSLD). On the other hand, the proposed models are validated with experimental data. The validation results show that all of the estimated drag coefficients are within the bounds of ±7% of experimental values.

Estimation of aerodynamic coefficients for a ball by using characteristics of trajectory

We investigate estimation methods of aerodynamic coefficients for a ball in sports by using characteristic quantities of its trajectory. One method is based on the quantities representing the whole shape of trajectory while the other utilizes local quantities such as curvature and/or torsion. In the former, the flight distance and the maximum height are measured, and the motion equation predicts numerical values of these quantities with measured initial conditions and preset aerodynamic coefficients. Then the optimal combination of the aerodynamic coefficients is determined by minimizing the error between the measured and estimated values of the characteristic quantities. This method is applied to estimate drag and lift coefficients of a soccer ball in back-spinning, and the result shows that the averaged values of CD and CL are 0.205 and 0.237, respectively. In the latter method, the expressions between the aerodynamic coefficients and the geometrical quantities of trajectory are derived, which suggests that the piecewise quadratic interpolation on a trajectory provides the aerodynamic coefficients. This method enables to locally estimate the coefficients, and therefore clarifies the variation of the coefficients along a trajectory. Measured data for a table tennis ball is analyzed with the method and we obtain successfully the drag and lift coefficients in flight condition. The results indicate the qualitative difference of spinning effect in drag and lift coefficients.

Momentum and heat transfer from a heated circular cylinder in Bingham plastic fluids

In this work, heat and momentum transfer characteristics of a heated circular cylinder submerged in Bingham plastic fluids over wide ranges of conditions as: plastic Reynolds number, 1⩽Re⩽40, Prandtl number, 1⩽Pr⩽100 and Bingham number, 0⩽Bn⩽104 have been studied numerically. The governing equations in conjunction with the Papanastasiou regularization for the discontinuous-viscosity behavior of a Bingham fluid have been solved using the finite element method. Extensive new results on streamlines, distribution of shear rate and velocity, morphology of yielded/unyielded regions and drag coefficient are presented and discussed to delineate the influence of the fluid yield stress on the structure of flow field. As expected, while the yield stress acts to stabilize the flow by suppressing the phenomenon of flow detachment, the inertial forces act to destabilize the flow. A delicate balance thus exists between the viscous and yield stress effects on one hand and the inertial effects on the other. For a fixed Reynolds number, there exists a critical Bingham number beyond which no flow separation is observed. Also, the laminar forced convection heat characteristics have been analyzed in terms of the isotherm contours, local Nusselt number and average Nusselt number. In order to facilitate the estimation of drag coefficient and Nusselt number in a new application, the present numerical values have been correlated in terms of the pertinent dimensionless parameters with acceptable levels of accuracy. Finally, due to the occurrence of steeper gradients in Bingham plastic fluids otherwise under identical conditions (same Reynolds and Prandtl numbers), the drag is augmented by 37–100% and the Nusselt number by ∼30–57% over and above its value in Newtonian fluids (Bn=0) over the range of conditions spanned here.

Form drag on pressure ridges and drag coefficient in the northwestern Weddell Sea, Antarctica, in winter

AbstractSurface elevation data for sea ice in the northwesternty - Weddell Sea, Antarctica, collected by a helicopter-borne laser altimeter during the Winter Weddell Outflow Study 2006, were used to estimate the form drag on pressure ridges and its contribution to the total wind drag, and the air-ice drag coefficient at a reference height of 10 m under neutral stability conditions (Cdn(10)). This was achieved by partitioning the total wind drag into two components: form drag on pressure ridges and skin drag over rough sea-ice surfaces. The results reveal that for the compacted ice field, the contribution of form drag on pressure ridges to the total wind drag increases with increasing ridging intensity Ri (where Ri is the ratio of mean ridge height to spacing), while the contribution decreases with increasing roughness length. There is also an increasing trend in the air-ice drag coefficient Cdn(10) as ridging intensity Ri increases. However, as roughness length increases, Cdn(10) increases at lower ridging intensities (Ri &lt; 0.023) but decreases at lower ridging intensities (0.023 &lt; Ri &lt; 0.05). These opposing trends are mainly caused by the dominance of the form drag on pressure ridges and skin drag over rough ice surfaces. Generally, the form drag becomes dominant only when the ridging intensity is sufficiently large, while the skin drag is the dominant component at relatively larger ridging intensities. These results imply that a large value of Cdn(10) is caused not only by the form drag on pressure ridges, but also by the skin drag over rough ice surfaces. Additionally, the estimated drag coefficients are consistent with reported measurements in the northwestern Weddell Sea, further demonstrating the feasibility of the drag partition model.

波浪データに基づく海面抵抗係数の風速依存性に関する研究

For the purpose of clarifying the appropriate values of the sea surface drag coefficient in high wind speed, the ADWAM was modified to estimate the sea surface drag coefficients as its control variables of the model. In this study, we apply the method to the actual wave observation data to investigate the sea surface drag coefficient. As a result, we confirm that the sea surface drag coefficient was automatically corrected to appropriate values (similar to Mitsuyasu & Honda's equation in wind speed less than 30m/s) from arbitrary initial values with the method. It was also confirmed that the possibility of the estimation of the sea surface drag coefficient under stormy conditions on the basis of the wave data remotely observed from storms.

Drag Coefficient and Two-Phase Friction Multiplier on Tube Bundles Subjected to Two-Phase Cross-Flow

An approximate analytical model, to predict the drag coefficient on a cylinder and the two-phase Euler number for upward two-phase cross-flow through horizontal bundles, has been developed. To verify the model, two sets of experiments were performed with an air–water mixture for a range of pitch mass fluxes and void fractions. The experiments were undertaken using a rotated triangular (RT) array of cylinders having a pitch-to-diameter ratio of 1.5 and cylinder diameter 38 mm. The void fraction model proposed by Feenstra et al. was used to estimate the void fraction of the flow within the tube bundle. An important variable for drag coefficient estimation is the two-phase friction multiplier. A new drag coefficient model has been developed, based on the single-phase flow Euler number formulation proposed by Zukauskas et al. and the two-phase friction multiplier in duct flow formulated by various researchers. The present model is developed considering the Euler number formulation by Zukauskas et al. as well as existing two-phase friction multiplier models. It is found that Marchaterre's model for two-phase friction multiplier is applicable to air–water mixtures. The analytical results agree reasonably well with experimental drag coefficients and Euler numbers in air–water mixtures for a sufficiently wide range of pitch mass fluxes and qualities. This model will allow researchers to provide analytical estimates of the drag coefficient, which is related to two-phase damping.

Effect of an external vortex on the uav aerodynamic performances

In this present work, the CFD and wind tunnel are used to investigate the effect of an external vortex around an UAV in order to obtain initial estimates of lift and drag coefficients with flow velocity of 30 meters per second for various angles of attack. The model of Spalart- Allmaras turbulence is used for the investigation of the complex flow around the UAV. The wind tunnel and CFD results are compared and appropriate error bands placed on the data.

A new approach for the determination of the drag coefficient from the upper ocean response to a tropical cyclone: a feasibility study

We seek to determine if a small number of measurements of upper ocean temperature and currents can be used to make estimates of the drag coefficient that have a smaller range of uncertainty than previously found. We adopt a numerical approach using forward models of the ocean’s response to a tropical cyclone, whereby the probability density function of drag coefficient values as a function of wind speed that results from adding realistic levels of noise to the simulated ocean response variables is sought. Allowing the drag coefficient two parameters of freedom, namely the values at 35 and at 45 m/s, we found that the uncertainty in the optimal value is about 20% for levels of instrument noise up to 1 K for a misfit function based on temperature, or 1.0 m/s for a misfit function based on 15 m velocity components. This is within tolerable limits considering the spread of measurement-based drag coefficient estimates. The results are robust for several different instrument arrays; the noise levels do not decrease by much for arrays with more than 40 sensors when the sensor positions are random. Our results suggest that for an ideal case, having a small number of sensors (20–40) in a data assimilation problem would provide sufficient accuracy in the estimated drag coefficient.

Estimation of drag coefficient of a real tree considering the vertical stand structure of trunk, branches, and leaves

Drag coefficients of a real tree trunk and branch and the sheltering effects of an upstream trunk or branch on a downstream one in a linear arrangement with different spacings were investigated in detail. Willow and Robinia pseudoacacia, representative and invasive trees in Japanese rivers, respectively, were selected for the study. The drag coefficient of the real tree trunk started to decrease from a relatively low Reynolds number and was smaller than that of a smooth circular cylinder in the entire Reynolds number range investigated. Leaves increased the drag coefficient by around 40–100% in comparison to that of a branch alone and increased with increasing the area ratio of leaves and branches. The sheltering effects of an upstream branch increased with the existence of leaves. The drag coefficient of a downstream branch approached around 95% of that of a single branch with increasing Reynolds number, regardless of the presence of leaves. The moment for drag force of a whole tree was calculated for a strong wind event that overturned trees in the Arakawa River, Japan. The calculated value was compared with the experimental threshold values and was validated within a reasonable limit.

Influence of Particle Shape on Drag Coefficient for Commonly Occuring Sandy Particles in Coastal Areas

A well defined relationship connecting settling velocity with sediment geometry and ambient properties is an essential pre-requisite for coastal and hydraulic engineering studies. An established relationship for settling velocity of sandy particles assuming spherical shape geometry is available in the literature. In reality, the sediment particles need not be spherical at all times, which influences settling velocity that is strongly biased to the drag coefficient. Based on quantitative comparison with measured data collected at Oahu Islands located in the Hawaiian archipelago, USA this work provides a relationship between drag coefficient and particle shape factor for sand grains viz; sand, sandy loam and fine sandy loam typically found in coastal environment (typical size ranges from 0.05 to 2.0 mm). The particle Reynolds number and shape factor are evaluated for each grain. The drag coefficient evaluated as function of nominal diameter and Reynolds number show a positive correlation over a wide range of shape factors used in this study. A comprehensive correlation has been developed of the drag coefficient for non-spherical particles as a function of Reynolds number and particle shape. Further a regression analysis was performed on the functional dependence of drag coefficient on particle shape. Based on this study, it could be advocated the validity of Krumbien shape factor holds well for the above characterized grain size and various particle shapes considered. Hence, the settling velocity of particles has a functional dependence on estimated drag coefficient with important implications for modeling sediment transport and swash zone hydrodynamics.

A posteriori error estimate improvement in mesh adaptation for computer fluid dynamics applications

The objective of this work is to study, in a first part, the impact of mesh adaptation on computational estimates of lift and drag coefficients. The convergence of these quantities with successive adaptation is demonstrated by comparing with experimental results. As a second part, optimization of relevant adaptation parameters to accelerate the convergence is investigated. A combination of adaptation variables is proposed to better capture some physical features that are poorly represented when a single variable is used. On the other hand, a new error metric is derived from both Hessian and gradient that are used separately in the framework of mesh adaptation in general. The impact of the proposed improvements is demonstrated through test cases.

Reliable determination of vortex parameters from measurements of the microwave complex resistivity

We discuss and propose a complete data treatment, in close contact to typical microwave experimental data, in order to derive vortex parameters, such as pinning constant and viscous drag coefficient (also referred to as ``vortex viscosity''), in a way as model independent as possible. We show that many of the accepted models for the complex resistivity can be described by a single, very general analytical expression. Using typical measurements of real and imaginary resistivity as a function of the applied field, we show that, even for single-frequency measurements, it is always possible to obtain (a) estimates of viscous drag coefficient and pinning constant with well-defined upper and lower bounds and (b) quantitative information about thermal creep. It turns out that neglecting thermal creep, in particular and counterintuitively at low temperatures, might result in a severe overestimation of the viscous drag coefficient. We also discuss the impact of thermal creep on the determination of the pinning constant. The present results might lead to a reconsideration of several estimates of the vortex parameters.