scholarly journals Drag and lift forces on clean spherical and ellipsoidal bubbles in a solid-body rotating flow

2011 ◽  
Vol 682 ◽  
pp. 434-459 ◽  
Author(s):  
MARIE RASTELLO ◽  
JEAN-LOUIS MARIÉ ◽  
MICHEL LANCE
Keyword(s):  
Aspect Ratio ◽  
Drag Coefficient ◽  
Solid Body ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
Uniform Flow ◽  
Rotating Flow ◽  
Wide Range ◽  
Spherical Bubbles ◽  
Drag And Lift

A single bubble is placed in a solid-body rotating flow of silicon oil. From the measurement of its equilibrium position, lift and drag forces are determined. Five different silicon oils have been used, providing five different viscosities and Morton numbers. Experiments have been performed over a wide range of bubble Reynolds numbers (0.7 ≤ Re ≤ 380), Rossby numbers (0.58 ≤ Ro ≤ 26) and bubble aspect ratios (1 ≤ χ ≤ 3). For spherical bubbles, the drag coefficient at the first order is the same as that of clean spherical bubbles in a uniform flow. It noticeably increases with the local shear S = Ro−1, following a Ro−5/2 power law. The lift coefficient tends to 0.5 for large Re numbers and rapidly decreases as Re tends to zero, in agreement with existing simulations. It becomes hardly measurable for Re approaching unity. When bubbles start to shrink with Re numbers decreasing slowly, drag and lift coefficients instantaneously follow their stationary curves versus Re. In the standard Eötvös–Reynolds diagram, the transitions from spherical to deformed shapes slightly differ from the uniform flow case, with asymmetric shapes appearing. The aspect ratio χ for deformed bubbles increases with the Weber number following a law which lies in between the two expressions derived from the potential flow theory by Moore (J. Fluid Mech., vol. 6, 1959, pp. 113–130) and Moore (J. Fluid Mech., vol. 23, 1965, pp. 749–766) at low- and moderate We, and the bubble orients with an angle between its minor axis and the direction of the flow that increases for low Ro. The drag coefficient increases with χ, to an extent which is well predicted by the Moore (1965) drag law at high Re and Ro. The lift coefficient is a function of both χ and Re. It increases linearly with (χ − 1) at high Re, in line with the inviscid theory, while in the intermediate range of Reynolds numbers, a decrease of lift with aspect ratio is observed. However, the deformation is not sufficient for a reversal of lift to occur.

Bubble behaviour in a horizontal high-speed solid-body rotating flow

2021 ◽  
Vol 925 ◽  
Author(s):  
Majid Rodgar ◽  
Hélène Scolan ◽  
Jean-Louis Marié ◽  
Delphine Doppler ◽  
Jean-Philippe Matas
Keyword(s):  
Aspect Ratio ◽  
Solid Body ◽  
High Speed ◽  
Lift Coefficient ◽  
Rotating Flow ◽  
Axis Of Rotation ◽  
Large Fluctuations ◽  
The Mean ◽  
Drag And Lift ◽  
The Impact

We study experimentally the behaviour of a bubble injected into a horizontal liquid solid-body rotating flow, in a range of rotational velocities where the bubble is close to the axis of rotation. We first study the stretching of the bubble as a function of its size and of the rotation of the cell. We show that the bubble aspect ratio can be predicted as a function of the bubble Weber number by the model of Rosenthal (J. Fluid Mech., vol. 12, 1962, 358–366) provided an appropriate correction due to the impact of buoyancy is included. We next deduce the drag and lift coefficients from the mean bubble position. For large bubbles straddling the axis of rotation, we show that the drag coefficient $C_D$ is solely dependent on the Rossby number $Ro$, with $C_D \approx 1.5/Ro$. In the same limit of large bubbles, we show that the lift coefficient $C_L$ is controlled by the shear Reynolds number $Re_{shear}$ at the scale of the bubble. For $Re_{shear}$ larger than 3000 we observe a sharp transition, wherein large fluctuations in the bubble aspect ratio and mean position occur, and can lead to the break-up of the bubble. We interpret this regime as a resonance between the periodic forcing of the rotating cell and the eigenmodes of the stretched bubble.

Drag and lift forces on bubbles in a rotating flow

2007 ◽  
Vol 571 ◽  
pp. 439-454 ◽  
Author(s):  
ERNST A. VAN NIEROP ◽  
STEFAN LUTHER ◽  
JOHANNA J. BLUEMINK ◽  
JACQUES MAGNAUDET ◽  
ANDREA PROSPERETTI ◽  
...  
Keyword(s):  
Solid Body ◽  
Slip Velocity ◽  
Strong Dependence ◽  
Bubble Diameter ◽  
Rotating Flow ◽  
Viscous Effects ◽  
Wide Range ◽  
Theoretical Predictions ◽  
Lift Forces ◽  
Drag And Lift

The motion of small air bubbles in a horizontal solid-body rotating flow is investigated experimentally. Bubbles with a typical radius of 1 mm are released in a liquid-filled horizontally rotating cylinder. We measure the transient motion of the bubbles in solid-body rotation and their final equilibrium position from which we compute drag and lift coefficients for a wide range of dimensionless shear rates 0.1<Sr<2 (Sr is the velocity difference over one bubble diameter divided by the slip velocity of the bubble) and Reynolds numbers 0.01<Re<500 (Re is based on the slip velocity and bubble diameter). For large Sr, we find that the drag force is increased by the shear rate. The lift force shows strong dependence on viscous effects. In particular, for Re<5, we measure negative lift forces, in line with theoretical predictions.

scholarly journals Drag and lift forces on a counter-rotating cylinder in rotating flow

2010 ◽  
Vol 664 ◽  
pp. 150-173 ◽  
Author(s):  
CHAO SUN ◽  
TOM MULLIN ◽  
LEEN VAN WIJNGAARDEN ◽  
DETLEF LOHSE
Keyword(s):  
Lift Force ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
Rotating Cylinder ◽  
Rotating Drum ◽  
Rotation Rates ◽  
Counter Rotation ◽  
Image Velocimetry ◽  
Wide Range ◽  
Drag And Lift

Results are reported of an experimental investigation into the motion of a heavy cylinder free to move inside a water-filled drum rotating around its horizontal axis. The cylinder is observed to either co-rotate or, counter-intuitively, counter-rotate with respect to the rotating drum. The flow was measured with particle image velocimetry, and it was found that the inner cylinder significantly altered the bulk flow field from the solid-body rotation found for a fluid-filled drum. In the counter-rotation case, the generated lift force allowed the cylinder to freely rotate without contact with the drum wall. Drag and lift coefficients of the freely counter-rotating cylinder were measured over a wide range of Reynolds numbers, 2500 < Re < 25000, dimensionless rotation rates, 0.0 < α < 1.2, and gap to cylinder diameter ratios 0.003 < G/2a < 0.5. Drag coefficients were consistent with previous measurements on a cylinder in a uniform flow. However, for the lift coefficient, considerably larger values were observed in the present measurements. We found the enhancement of the lift force to be mainly caused by the vicinity of the wall.

Drag and lift forces on particles in a rotating flow

2009 ◽  
Vol 643 ◽  
pp. 1-31 ◽  
Author(s):  
J. J. BLUEMINK ◽  
D. LOHSE ◽  
A. PROSPERETTI ◽  
L. VAN WIJNGAARDEN
Keyword(s):  
Solid Body ◽  
Numerical Results ◽  
Rotating Flow ◽  
Cylinder Axis ◽  
Drag Coefficients ◽  
Rotating Sphere ◽  
Particle Spin ◽  
Wide Range ◽  
Drag And Lift ◽  
Lift And Drag

A freely rotating sphere in a solid-body rotating flow is experimentally investigated. When the sphere is buoyant, it reaches an equilibrium position from which drag and lift coefficients are determined over a wide range of particle Reynolds numbers (2 ≤ Re ≤ 1060). The wake behind the sphere is visualized and appears to deflect strongly when the sphere is close to the cylinder axis. The spin rate of the sphere is recorded. In fluids with low viscosity, spin rates more than twice as large as the angular velocity of the cylinder can be observed. By comparing numerical results for a fixed but freely spinning sphere with a fixed non-spinning sphere for Re ≤ 200, the effect of the sphere spin on the lift coefficient is determined. The experimentally and numerically determined lift and drag coefficients and particle spin rates all show excellent agreement for Re ≤ 200. The combination of the experimental and numerical results allows for a parameterization of the lift and drag coefficients of a freely rotating sphere as function of the Reynolds number, the particle spin and the location of the particle with respect to the cylinder axis. Although the effect of the flow rotation on the particle spin is different in shear flow and solid-body rotating flow, the effect of spin on lift is found to be comparable for both types of flow.

Experimental investigations of flow over NACA airfoils 0021 and 4412 of wind turbine blades with and without Tubercles

2021 ◽  
pp. 0309524X2110071
Author(s):  
Usman Butt ◽  
Shafqat Hussain ◽  
Stephan Schacht ◽  
Uwe Ritschel
Keyword(s):  
Wind Tunnel ◽  
Drag Coefficient ◽  
Wind Turbine ◽  
Critical Region ◽  
Lift Coefficient ◽  
Turbine Blades ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Experimental Investigations ◽  
Wind Turbine Blades

Experimental investigations of wind turbine blades having NACA airfoils 0021 and 4412 with and without tubercles on the leading edge have been performed in a wind tunnel. It was found that the lift coefficient of the airfoil 0021 with tubercles was higher at Re = 1.2×105 and 1.69×105 in post critical region (at higher angle of attach) than airfoils without tubercles but this difference relatively diminished at higher Reynolds numbers and beyond indicating that there is no effect on the lift coefficients of airfoils with tubercles at higher Reynolds numbers whereas drag coefficient remains unchanged. It is noted that at Re = 1.69×105, the lift coefficient of airfoil without tubercles drops from 0.96 to 0.42 as the angle of attack increases from 15° to 20° which is about 56% and the corresponding values of lift coefficient for airfoil with tubercles are 0.86 and 0.7 at respective angles with18% drop.

scholarly journals A Study of Drag Reduction on Cylinders with Different V-Groove Depths on the Surface

Water ◽  
2021 ◽  
Vol 14 (1) ◽  
pp. 36
Author(s):  
Jiyang Qi ◽  
Yue Qi ◽  
Qunyan Chen ◽  
Fei Yan
Keyword(s):  
Drag Reduction ◽  
Drag Coefficient ◽  
Vortex Structure ◽  
Lift Coefficient ◽  
Pressure Coefficient ◽  
Reynolds Numbers ◽  
Groove Surface ◽  
Smooth Cylinder ◽  
Groove Structure ◽  
Reduction Effect

In this study, the drag reduction effect is studied for a cylinder with different V-groove depths on its surface using a k-ω/SST (Shear Stress Transport) turbulence model of computational fluid dynamics (CFD), while a particle image velocimetry (PIV) system is employed to analyze the wake characteristics for a smooth cylinder and a cylinder with different V-groove depths on its surface at different Reynolds numbers. The study focuses on the characteristics of the different V-groove depths on lift coefficient, drag coefficient, the velocity distribution of flow field, pressure coefficient, vortex shedding, and vortex structure. In comparison with a smooth cylinder, the lift coefficient and drag coefficient can be reduced for a cylinder with different V-groove depths on its surface, and the maximum reduction rates of lift coefficient and drag coefficient are about 34.4% and 16%, respectively. Otherwise, the vortex structure presents a complete symmetry for the smooth cylinder, however, the symmetry of the vortex structure becomes insignificant for the V-shaped groove structure with different depths. This is also an important reason for the drag reduction effect of a cylinder with a V-groove surface.

On the Motion of Rectangular Prismatic Bodies

1979 ◽  
Vol 101 (2) ◽  
pp. 193-199 ◽  
Author(s):  
M. Poreh ◽  
R. N. Wray
Keyword(s):  
Aspect Ratio ◽  
Rotational Speed ◽  
Lift Coefficient ◽  
Moment Of Inertia ◽  
Secondary Effects ◽  
Rotational Mode ◽  
Atmospheric Flows ◽  
Prismatic Bodies ◽  
Drag And Lift ◽  
Rotating Bodies

Rectangular prismatic bodies can assume either a translatory or an auto-rotating mode of motion during free motion in the atmosphere. The translatory mode is stable only when the dimensionless moment of inertia of the bodies is large, however, large perturbations will always start auto-rotation. The characteristics of the auto-rotational mode are shown to depend primarily on the aspect ratio of the bodies which determines the dimensionless rotational speed and the lift coefficient. Both the average drag and lift-coefficients of auto-rotating bodies are estimated, but it is shown that secondary effects make it impossible to determine their exact trajectories in atmospheric flows.

The Reynolds number and flaperon deflection influence taken into account when optimizing the wing airfoil of an unmanned aerial vehicle

2020 ◽  
Author(s):  
N.I. Kochurova ◽  
Ye.S. Parkhaev ◽  
N.V. Semenchikov
Keyword(s):  
Reynolds Number ◽  
Unmanned Aerial Vehicle ◽  
Multicriteria Optimization ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
Horizontal Flight ◽  
Wide Range ◽  
Aerial Vehicle ◽  
Zero Values ◽  
Wing Airfoil

The paper considers the solutions to the multicriteria problem of optimizing the wing airfoil of a miniature unmanned aerial vehicle (MUAV) under various constraints. The study introduces the statement of the problem of multicriteria optimization of the airfoil shape, following the condition of MUAV horizontal flight, with an additional condition associated with a change in the flight Reynolds number of the MUAV wing. This statement of the problem allows us to optimize the airfoil, taking into account the load on the wing of the designed vehicle. The wing airfoil was optimized in a wide range of lift coefficients of Cya and Reynolds numbers. The study shows that taking into account the Reynolds number makes it possible to improve the quality of the result obtained during optimization, and introduces a technique for multicriteria optimization of the wing airfoil with sealed mechanization, i.e. with flaperon. Findings of research show that for equal values of the relative thickness, the mechanized airfoil obtained as a result of optimization has a lower center line camber (by 1.5%) than the optimized airfoil without mechanization, due to which a gain in the drag coefficient is achieved at close to zero values of the lift coefficient. The study shows how profitable the use of a wing airfoil with a flaperon on MUAV wings can be, in contrast to an airfoil without mechanization.

Drag and lift measurements of solid sports balls in still air

2017 ◽  
Vol 232 (3) ◽  
pp. 255-263 ◽  
Author(s):  
Jeff R Kensrud ◽  
Lloyd V Smith
Keyword(s):  
Surface Roughness ◽  
Wind Tunnel ◽  
Drag Coefficient ◽  
Rough Surface ◽  
Lift Coefficient ◽  
Laboratory Setting ◽  
Air Drag ◽  
High Speeds ◽  
Drag And Lift ◽  
Lift And Drag

The following article considers lift and drag measurements of solid sports balls propelled through still air in a laboratory setting. The balls traveled at speeds ranging from 26 to 134 m/s with spin rates up to 3900 r/min. Light gates measured the speed and location of the balls at two locations from which lift and drag values were determined. Ball roughness varied from polished to rough surface protrusions, that is, seams as high as 1.5 mm. Lift and drag were observed to depend on speed, spin rate, surface roughness, and seam orientation. A drag crisis was observed on smooth balls as well as non-rotating seamed balls with seam heights less than 0.9 mm. The drag coefficient of approximately 0.42 was nearly constant with speed for spinning seamed balls with seam height greater than 0.9 mm. The still air drag coefficient of smooth balls was comparable to wind tunnel drag at low speeds ( Re < 2 × 105) and higher than wind tunnel results at high speeds ( Re > 2 × 105). The lift and drag coefficients of spinning balls increased with increasing spin rate. The lift coefficient of baseballs was not sensitive to ball orientation or seam height.

scholarly journals Drag and lift forces on interface-contaminated bubbles spinning in a rotating flow

2009 ◽  
Vol 624 ◽  
pp. 159-178 ◽  
Author(s):  
MARIE RASTELLO ◽  
JEAN-LOUIS MARIÉ ◽  
NATHALIE GROSJEAN ◽  
MICHEL LANCE
Keyword(s):  
Reynolds Number ◽  
Solid Body ◽  
Equilibrium Position ◽  
Rotating Flow ◽  
Dimensionless Numbers ◽  
Air Bubble ◽  
Demineralized Water ◽  
Drag And Lift ◽  
Area Of Influence ◽  
Eotvos Number

The equilibrium position of a spherical air bubble in a solid body rotating flow around a horizontal axis is investigated experimentally. The flow without bubbles is checked to be solid body rotating. The area of influence of the bubble is characterized to determine for each bubble whether the incoming flow is perturbed or not. The demineralized water used is shown to Tbe contaminated, and spinning of the bubble's interface is observed and measured. From the measurement of the bubble's equilibrium position, drag and lift coefficients are determined. They appear to be dependent on two dimensionless numbers. Eo the Eötvös number and Rω the rotational Reynolds number (or Taylor number Ta) can be varied independently by changing the control parameters, and for that reason are the convenient choice for experiments. (Re, Ro) with Ro the Rossby number is an equivalent choice generally adopted in the literature for numerical simulations, and Re denotes the Reynolds number. When using this second representation, the Ro number appears to be an indicator of the influence on the force coefficients of the shear, of the curvature of the streamlines of the flow and of the bubble's spinning. The bubble's spinning effect on the lift force is far from trivial. Its contribution explains the important gap between lift values for a bubble (not spinning) in a clean fluid and for a bubble (spinning) in a contaminated fluid as present.

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