Measured Drag Coefficients Research Articles

Rotational and translational drags of a Janus particle close to a wall and a lipid membrane

HypothesisMeasuring rotational and translational Brownian motion of single spherical particles reveals dissipations due to the interaction between the particle and the environment. ExperimentsIn this article, we show experiments where the in-plane translational and the two rotational drag coefficients of a single spherical Brownian particle can be measured. These particle drags are functions of the particle size and of the particle–wall distance, and of the viscous dissipations at play. We measure drag coefficients for Janus particles close to a solid wall and close to a lipid bilayer membrane. FindingsFor a particle close to a wall, we show that according to hydrodynamic models, particle–wall distance and particle size can be determined. For a particle partially wrapped by lipid membranes, in absence of strong binding interactions, translational and rotational drags are significantly larger than the ones of non-wrapped particles. Beside the effect of the membrane viscosity, we show that dissipations in the deformed membrane cap region strongly contribute to the drag coefficients.

Microwave Flux-flow Hall Effect in a Multi-band Superconductor FeSe

We have measured the flux-flow Hall effect in a multi-band superconductor FeSe pure single crystal to investigate the nature of the vortex core state by means of the cross-shaped bimodal cavity technique. We found that the flux-flow Hall angle of FeSe at low temperatures is about 0.5, which is equal to or smaller than that evaluated by the effective viscous drag coefficient measurements. This feature is in contrast to the cuprate superconductors. The conductivity tensor of multi-band superconductors that are contributed from holes and electrons shows partial cancellation of the flux-flow Hall voltage by the electrons and holes, which can explain the observed feature. Therefore, our study suggests the appearance of the multi-band nature in the vortex dynamics.

Experimental Assessment of Drag Coefficient for Quasi-Radially-Symmetric Microplastic Particles Sinking in Water Stream

Microplastics (MPs) are found to be omnipresent in marine environments and their production and disposal are constantly increasing. In order to control and mitigate their negative effects on the environment, it is important to understand the processes involved in their transport and sinking. Most of the conducted experimental studies on MP in water have focused on exploring the settling behavior of MP particles under static flow conditions. This paper presents the results of an experimental study of MP particles in a horizontal stream of water. A series of laboratory experiments were carried out to measure the drag coefficient of quasi-radially-symmetric MP particles with different shapes (spheres, cubes, and crosses) and sizes (1.5 to 3.0 mm). In the study, the relationship between the drag coefficient and flow conditions represented by the local Reynolds number is investigated. The experimental procedure was validated, and a total of 400 measurements were performed. Values of the measured drag coefficient ranged from 0.8 to 2.5 for the values of Re from 40 to 300. The results show that the shape of MP particles in the water stream considerably influences the particle drag coefficient, with a rather complex relationship between the drag coefficient and flow conditions.

Experimental Measurements of Drag and Lift Coefficient on Building with an Elliptical Cross-section

Abstract The characteristics of aerodynamic forces acting on an elliptic cylinder with an aspect ratio of 0.5 with a wind attack angle from 0 to 90° and subjected to the boundary layer wind tunnel were investigated. The model was initially calibrated and compared with the existing work. The aspect ratio of the investigated model was 0.5, and the model was emerging in a turbulent flow. The mean and fluctuating drag and lift coefficients were investigated. The minimum drag coefficient occurred in the wind direction of 0° and the maximum at 90°. The lift coefficient was the largest in the 30° wind direction and the smallest at 0°. Fluctuating coefficients were similar profiles as the mean coefficients. Around the 30° wind direction, an inappropriate phenomenon occurred, caused by the generation of asymmetrical vortices structures and wake instabilities.

Drag coefficient of circular cylinder in axial flow of water for a wide range of length to diameter ratios

ABSTRACT An experimental campaign was conducted to determine drag coefficients of circular cylinders in axial flow of water for a wide range of length-to-diameter ratios (L/D) from 2 to 35. Drag force acting on the circular cylinders was acquired at a velocity of 2 to 6 m/s, which corresponds to the Reynolds numbers of 2.2 × 105 to 7.0 × 105. The experimental data were validated by analysis using the commercial CFD code, Star-CCM+. The measured drag coefficients increased monotonically as the L/D increased with the range of Reynolds numbers, and were almost constant regardless of the Reynolds number. The drag coefficient was decomposed by the term of form drag and skin friction. As the value of L/D increased, the drag coefficient increased due to the skin friction drag term. The drag coefficient correlation was proposed as a function of L/D. The predicted values were consistent with both the experimental data and numerical simulation results. Furthermore, this correlation was applied to a fuel assembly with a channel box, it was shown that the drag coefficient can be predicted for a wide range of Reynolds numbers by specifying an appropriate form drag term.

Large Hall angle of vortex motion in high- Tc cuprate superconductors revealed by microwave flux-flow Hall effect

We investigated the nature of the quasi-particle state in the vortex core by means of the flux-flow Hall effect measurements at 15.8 GHz. We measured the flux-flow Hall effect in cuprate superconductors, Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{y}$ and YBa$_{2}$Cu$_{3}$O$_{y}$ single crystals, whose equilibrium $B$-$T$ phase diagrams were different. As a result, we found that the Hall angle is independent of the magnetic field, and reaches an order of unity at low temperatures in BSCCO. However, in YBCO, the angle increases with increasing magnetic field even at low temperatures. We understood that this difference in the magnetic field dependence of the Hall angle is due to the difference in the influence of the pinning, which originated from the difference in the vortex state (liquid vs. solid) between the two materials. However, as a common feature, both materials showed a large tangent of the Hall angle at low temperatures, which was larger by an order of magnitude than those obtained in the effective viscous drag coefficient measurements. We discussed the origin of the discrepancy both in terms of the possible nonlinearity of the viscous drag force and possible hidden dissipation mechanisms. The unexpectedly large Hall angle of the vortex motion in cuprates revealed in our flux-flow Hall effect study poses a serious question on the fundamental understanding of the motion of the quantized vortex in superconductors, and it deserves further investigation.

Towards a model of hydrodynamic damping for a circular cylinder with helical strakes at low KC

This paper investigates the hydrodynamic damping of a circular cylinder with helical strakes at Keulegan-Carpenter (KC) number from 0.07 to 3 in the presence of steady currents. Experiments were performed with a straked cylinder oscillating in either in-line or cross currents over Reynolds number (based on the oscillating velocity amplitude) varying from 1260 to 54,000. With in-line current being present, the measured drag coefficients of the straked cylinder are found to depend on the ratio between the oscillating velocity amplitude and the steady current velocity. This phenomenon is further confirmed by computational fluid dynamics using large-eddy simulations. The drag coefficients obtained from the numerical simulations agree well with the experimentally determined values. Similar phenomenon is observed for the cases with cross background current. Based on the experimental data, empirical formulae are proposed to evaluate drag coefficients. These results are of importance in estimating the resonant motion and the fatigue life of risers, e.g. water intake risers, in the flow regime of low KC. Finally, recommendations are provided for fatigue analysis of risers with helical strakes from the perspective of engineering practice.

Drag coefficients of air rifle pellets with wide range of geometries

Air rifle and air pistol target shooting are included in major intentional and national sports competitions and are also highly popular sport pastimes. Published scientific studies of pellet drag are very rare, in contrast to a large number of scientific studies published on aerodynamic drag of sports balls and other sports projectiles. Measurements are presented of the drag coefficients for 31 air rifle pellets of mainly 4.5 mm (0.177 in) calibre having a wide range of geometries. The drag coefficient measurements were made with a low-turbulence open wind tunnel at flow velocity of 200 m/s (Mach and Reynolds numbers 0.57 and 56,000 for 4.5 mm pellets). The detailed geometry of some pellets was altered systematically in order to improve understanding of how pellet geometry affects drag coefficient. The drag coefficient for the 31 pellets varied widely from 0.36 to 0.78, and it was influenced substantially by the curvature of the flow separating from the pellet head rim. Large curvatures delayed flow re-attachment onto the pellet tail, thereby lowering pellet base pressure and increasing the value of drag coefficient. Pellets with hemi-spherical or ogive-shaped noses generally had lower values of drag coefficient than pellets with other nose shapes. The presence of the pellet tail was beneficial by providing a surface onto which the flow detaching from the pellet rim could re-attach. However, for minimisation of drag coefficient, the pellet tail had to be of a certain optimum length which depended on the shape of the pellet nose. Small differences in pellet geometry had significant influence on the value of drag coefficient. Increase in air velocity from 120 to 200 m/s had small influence on the value of drag coefficient for three common sports pellets having flat, conical and dome-shaped noses.

TRAIL part 2: A comprehensive assessment of ice particle fall speed parametrisations

AbstractResults are presented from a comprehensive experimental campaign studying the aerodynamics of 3D‐printed analogues of ice particles. Measurements of the drag coefficient of the analogues were acquired by using a novel experimental approach to digitally reconstruct the analogues' trajectory and orientation as they fall through a quiescent viscous liquid, using images acquired by a series of digital cameras. The data are used to evaluate commonly used parametrisations of ice particle fall speeds. We find that the accuracy of each of the parametrisations reduces at Reynolds numbers greater than approximately 100, as a result of effects associated with the onset of unsteady oscillating, fluttering or tumbling motions as the analogues fall. We propose a new fall speed parametrisation that predicts the measured drag coefficients at high Reynolds number with an accuracy consistent with that of the leading parametrisation at low Reynolds number.

Multi-fidelity drag prediction for base bleed projectile

A computational study is performed to predict the drag reduction for a base bleed projectile. 2-D and 3-D simulations are conducted to describe the flow past a projectile with base bleed. The calculated computational results are compared with measurements of total drag coefficients based on published results for 155mm K307 projectiles with live/dummy base bleed grain. In addition, the mean drag coefficient measurements based on live firing tests for a five K307 projectiles with live BB grain at different Mach numbers are used to validate results obtained from the computational results. Differences between the drag coefficient calculated from computational and published live firing measurements of the drag coefficient for K307 are less than 5.2% and 6.8% for projectile with dummy and live BB, respectively. On the other hand, the maximum deviation between computational results and real measurements from the live firing tests of live BB projectiles is 2.75%.

Wind tunnel measurement of overall and sectional drag coefficients for a super high-rise steel tube transmission tower

Wind tunnel tests on models of a 1000 ​kV super high-rise tubular steel transmission tower were carried out under two wind fields. In order that the boundary conditions for the tower section models be consistent with those of the actual structure, a new experimental method is proposed. The results show the drag coefficients in a thick turbulent boundary layer are generally less than those in uniform flow, as expected, the drag coefficient of a lattice tower section is related not only to the solidity ratio but also to its geometric shape and oncoming flow turbulence intensity. The effective projected areas (EPA) calculated by wind tunnel tests were compared to the regulations in some applicable codes. The results for the wind loads on the superstructure show that the calculation method should take into account the geometric shape, both in the transverse and longitudinal direction, and be distinguished from the methods for cross-arm and tower body. The test values for the cross-arm are in best agreement with the data from the Chinese code, while the results for the whole tower and tower sections match better with the values from the USA code. The European code generally underestimates the wind loads for all the test models.

Statistical Engineering for Wind Tunnel Testing of Mars Parachute Designs

Formal experiment design and analysis techniques featuring design of experiments were applied to a Mars parachute wind tunnel test. The experiments were part of an extensive study conducted in 2014 by the NASA Engineering and Safety Center to evaluate the performance of two candidate parachute systems. Reduced scale models of the legacy Disk-Gap-Band (DGB) parachute and new Supersonic Ringsail (SSRS) were compared for both model fidelity and performance measures. Two tests, conducted in the NASA Langley Transonic Dynamics Tunnel, are described with emphasis on statistical engineering principles. The first test compared drag coefficients between models of the same canopy at Earth atmospheric pressure but at mission dynamic pressures. The experiment proved that any manufacturing differences between models were not detectable in drag coefficient measurements. The second test focused on parachute drag coefficient modeling for both canopy designs and two fabric permeabilities over a representative range of mission dynamic pressures and Mach numbers. The SSRS was found to have higher drag coefficients in comparison to the DGB for both canopy material permeabilities over the operational range of Mach numbers and dynamic pressures.

Hydrodynamic damping of a circular cylinder at low KC: Experiments and an associated model

This paper investigates the hydrodynamic damping of a smooth circular cylinder undergoing forced oscillations at Keulegan-Carpenter (KC) numbers smaller than 5 and Reynolds (Re) numbers from 103–105 with and without background steady currents. A series of experiments are conducted with a circular cylinder oscillating in still water, in-line currents and cross currents. The measured drag coefficients of the smooth cylinder in the still water condition match with the well-published results and the theoretical solution of Stokes and Wang at very small KC numbers. The hydrodynamic damping increases with the in-line steady current whereas it remains almost constant at small transverse velocities and increases notably when the latter becomes large. To predict the hydrodynamic damping in in-line steady currents, the performance of the Morison equation based on relative velocity and independent velocity is explored, respectively. The latter model, by separating the drag into two independent parts, leads to a better fit of the drag force than the former, which is not surprising. However, the former is still a preferable option for engineering design due to its simplicity. The experimental data suggest that the existing design guidelines such as ISO-19902 or DNVGL-RP-C205 should be used with caution for KC < 5.

Particle tracking velocimetry of porous sphere settling under gravity: Preparation of the model porous particle and measurement of drag coefficients

Porous particles are widely used in liquid–solid and gas-liquid-solid reactors, and accurate prediction of drag coefficients (CD) for porous particles is essential for designing and optimizing these reactors. The drag coefficients for porous particles, however, have been mainly obtained via theoretical analysis and numerical simulations. Only three experimental studies were carried out to study the drag force on porous spherical particles due to the difficulties in the preparation of model porous spheres with a homogeneous porosity and homogeneous surface properties. In this paper, a method to prepare model porous spheres which have a homogeneous porosity and homogeneous surface properties with a good sphericity for a wider range of relative permeability β has been presented. The details of this method were documented, and it showed that the porous spheres constructed could withstand rigid collisions at the maximum terminal velocity of 1m/s and keep the structure intact with a negligible quantity of binders. Then gravity-driven settling experiments of a single porous sphere by use of particle tracking velocimetry (PTV) method were carried out to evaluate the feasibility of the use of the prepared porous spheres. Experimental results for 12 porous spheres, with particle Reynolds number (Re) ranging from 1 to 108 and relative permeability β from 21.6 to 315.6, agreed well with the previous results in the literature. The porous particles prepared by our proposed method can be potentially used for measuring drag coefficients of the porous permeable spheres in a wider range of particle Reynolds number and permeability and studying the complex interaction between the porous particles and the surrounding fluid.

Determination of aerodynamic drag coefficients using a drop test with a wireless accelerometer and its application to model rockets

The use of drag coefficients to quantify the drag force on objects moving through air is a key concept in aerodynamics. However, gaining access to a wind tunnel, the conventionally used apparatus with which to measure drag coefficients, can be difficult for students and educators at the undergraduate level. Several methods have been proposed as alternatives to the wind tunnel, but these often suffer from experimental complexity. In this paper, we propose a straightforward method using a wireless accelerometer to eliminate several common drawbacks of previous methods, enabling a simpler and direct analysis of drag. Here, we describe the method and its validation along with an application to model rockets as a possible undergraduate laboratory experiment. We also discuss an inconsistency regarding the drag coefficient of a typical model rocket and use it as an example of not taking published results at face value.

High‐Speed Drag Measurements of Aluminum Particles in Free Molecular Flow

AbstractHigh‐speed drag in a free molecular flow is still poorly understood despite playing an important role in a variety of physical situations, including meteor ablation in the upper atmosphere, the orbits of satellites, and the dynamics of cosmic dust grains. To measure drag at high speeds, small aluminum spheres 0.1–2.1 μm in radius were shot at 1–10 km/s into air, N2, Ar, and CO2 using an electrostatic dust accelerator. The measured drag coefficient in air is Γ = 1.29 ± 0.13, with similar values for the other gases. The measurement constrains the heating coefficient to Λ = 0.58 ± 0.37 in air assuming the gas molecules reflect diffusely from the particles' surfaces. The drag appears to be independent of the molecular structures of the four gases tested but has a slight dependence on molecular mass. The drag is also higher than frequently assumed, which has implications for the modeling of high‐speed objects in free molecular flows.

Measurement of Net Water Drag Coefficients in Polymer Electrolyte Fuel Cells under Cathode-Dry Conditions

For polymer electrolyte fuel cell (PEFC) systems in vehicle applications, removal of external humidifiers from the cathode is desirable to reduce system efficiency, cost, space and weight, and thus PEFCs should achieve continuous self-humidification operation under cathode-dry conditions. A critical index to judge the success or failure of self-humidification is net water drag coefficient (αNWD). Self-humidification operation requires αNWD to be negative. Here, αNWD is experimentally evaluated using cells with different configurations of gas diffusion layer (GDL), membrane, and flow channel geometry. Experimental results confirmed that αNWD remains negative under cathode-dry conditions at a cell temperature of 60°C, and that current density – net water drag coefficient (i − αNWD) characteristics are immune to configurations compared with the cell performance, when the flow rate of air at the cathode is low enough to keep αNWD low. In addition, under these conditions, the effect of flow velocity and pressure on the i − αNWD characteristics was limited. On the other hand, as expected, a thinner membrane promotes back-diffusion of water to the anode. In conclusion, the flow rate of air should be determined carefully so that the cell performance is maintained while self-humidification is achieved.

Accurate Radar Measurements of Drag Coefficients in Free Flight

Undergraduate lab design balances several factors: 1) simple experiments connected with learning objectives, 2) experiments sufficiently accurate for comparisons between theory and measurements without gaps when students ascribe discrepancies to confounding factors (imperfect simplifying assumptions, measurement uncertainties, and “human error”), and 3) experiments capturing student attention to ensure due diligence in execution and analysis. Drag coefficient measurements are a particular challenge, though there has been some success using accurate measurements of terminal velocities. Video shows promise in several areas of kinematics, but the number of trials in a reasonable time is limited, and analysis techniques to determine drag coefficients often include numerical integration of differential equations. Here we demonstrate a technique with potential to measure drag coefficients to near 1% accuracy using an affordable 2.4 GHz Doppler radar system and round plastic pellets from an Airsoft launcher.

Computational analysis of compressibility effects on cavity dynamics in high-speed water-entry

The objective of this study is to analyze the compressibility effects of multiphase cavitating flow during the water-entry process. For this purpose, the water-entry of a projectile at transonic speed is investigated computationally. A temperature-adjusted Tait equation is used to describe the compressibility effects in water, and air and vapor are treated as ideal gases. First, the computational methodology is validated by comparing the simulation results with the experimental measurements of drag coefficient and the theoretical results of cavity shape. Second, based on the computational methodology, the hydrodynamic characteristics of flow are investigated. After analyzing the cavitating flow in compressible and incompressible fluids, the characteristics under compressible conditions are focused upon. The results show that the compressibility effects play a significant role in the development of cavitation and the pressure inside the cavity. More specifically, the drag coefficient and cavity size tend to be larger in the compressible case than those in the incompressible case. Furthermore, the influence of entry velocities on the hydrodynamic characteristics is investigated to provide an insight into the compressibility effects on cavitating flow. The results show that the drag coefficient and the impact pressure vary with the entry velocity, and the prediction formulas for drag coefficient and impact pressure are established respectively in the present study.

Experimental Measurement and Numerical Model of Dunes Drag Coefficients

Experimental Measurement and Numerical Model of Dunes Drag Coefficients