Inverse Magnus Effect Research Articles

Investigation of the Inverse Magnus Effect on a Rotating Sphere in Hypersonic Rarefied Flow

Explorations involving long-endurance and maneuvering flights in the upper atmosphere, as well as research on atmospheric entries of space debris or asteroids, call for a full understanding of hypersonic rarefied flows. The inverse Magnus effect occurs in the hypersonic rarefied flow past a rotating sphere, but the aerodynamic behavior is contrary to the Magnus effect in the continuum flow regime. In this article, a series of such flows are numerically studied using the direct simulation Monte Carlo (DSMC) method. By analyzing the flow fields, as well as the distributions of pressure and shear stress on the sphere, the formation of the inverse Magnus force can be attributed to the tangential momentum transfer between incident gas molecules and the windward surface. The variation laws of aerodynamic parameters with the rotation rate are presented and discussed.

Laminar separation bubble on a rotating cylinder in uniform flow

We study the effect of spin ( 0 ≤ α ≤ 2) of a cylinder, placed in uniform flow, on the transition of the boundary layer. Large Eddy Simulation, with the Sigma turbulence model to account for the sub-grid scales, is carried out using a stabilized finite element formulation. The Reynolds numbers ( R e = 0.6 × 10 5 and 1.0 × 10 5) lie in the high-subcritical regime for a non-rotating cylinder where the boundary layer separates in a laminar state and does not reattach. Magnus effect is observed at low α wherein separation is delayed on the retreating side and preponed on the advancing side, resulting in a lift force that increases with increase in α. At a certain critical α, the boundary layer on the advancing side transitions to a turbulent state, causing it to reattach. A laminar separation bubble (LSB) forms, significantly delaying the final separation and increasing suction. At R e = 1.0 × 10 5, this suction overcomes that on the retreating side, leading to a reversal in the direction of lift force, referred to as the inverse Magnus effect. The LSB is accompanied by weakened vortex shedding at increased frequency. The spatial extent of the LSB and the magnitude of reverse lift, at a given Re, decreases with increase in α. The lift force changes direction yet again at a certain α marking the end of the inverse Magnus effect regime and beginning of the second Magnus effect regime. The LSB vanishes beyond a certain spin rate, and the boundary layer directly transitions to a turbulent state.

On the Magnus effect of a rotating porous circular cylinder in uniform flow: A lattice Boltzmann study

In this paper, a multiple-relaxation-time–lattice Boltzmann method is used to simulate the steady fluid flow through and around a rotating porous circular cylinder in uniform flow. This study aims at investigating the effect of Darcy number (10−6≤Da≤10−2), velocity ratio (0≤VR≤2), and Reynolds number (Re = 20 and 40) on the Magnus lift as well as on the flow pattern and pressure coefficient inside and around the rotating porous cylinder. The results reveal that besides the enveloping and detached wakes reported in the literature for rotating solid cylinders, in this study, a new type of the wake called confined wake is observed within the rotating porous cylinders at high Darcy numbers and velocity ratios of less than one. It is seen that the Magnus lift increases almost linearly with the velocity ratio for Da≤10−3; however, through curve-fitting, the rate of increase is shown to decrease with Darcy number in a non-linear manner. For Darcy numbers higher than 10−3, the Magnus lift varies non-linearly with both the velocity ratio and Darcy number in such a way that, interestingly, for Re=40 and very high Darcy numbers of 7.5×10−3 and 10−2, the Magnus lift becomes negative showing a behavior called the inverse Magnus effect.

Wake Flow Measurements Behind Rotating Smooth Spheres and Baseballs Near Critical Reynolds Numbers

Abstract The flow field behind spinning baseballs at two different seam orientations was investigated, and compared with a smooth sphere, to isolate effects of seams on the Magnus effect at Reynolds numbers of 5×104 and 1×105. The rotational speed of the three spheres varied from 0 to 2400 rpm, which are typical of spin rates imparted to a thrown baseball. These spin rates are represented nondimensionally as a relative spin rate relating the surface tangential velocity to the freestream velocity, and varied between 0 and 0.94. Mean velocity profiles, streamline patterns, and power spectral density of the velocity signals were taken using hot-wire anemometry and/or stereoscopic particle image velocimetry in the wake region. The sphere wake orientation changed over a range of relative spin rates, indicating an inverse Magnus effect. Vortex shedding at a Strouhal number of 0.25 was present on the sphere at low relative spin rates. However, the seams on the baseball prevented any consequential change in wake orientation and, at most spin rates, suppressed the shedding frequency exhibited by the sphere. Instead, frequencies corresponding to the seam rotation rates were observed in the wake flow. It was concluded that the so-called inverse Magnus effect recorded by previous investigators at specific combinations of Reynolds number and relative spin rate on a sphere exists for a smooth sphere or an axisymmetrically dimpled sphere but not for a baseball near critical Reynolds numbers, where the wake flow pattern is strongly influenced by the raised seams.

Flight and bounce of spinning sports balls

Standard university or high-school physics teaching material on projectile motion is usually based on Newton's second law in vacuum, neglecting aerodynamics. We present a low-cost experiment for teaching projectile motion using the students' cell phones and sports equipment, which allows the students to test theory and numerical simulation against experimental data in the real world. For a shot put, theoretical predictions assuming projectile motion in vacuum agree with experimentally obtained trajectories in air to within a few centimeters. However, for a table tennis ball, vacuum trajectories can be almost three times as long as experimentally obtained trajectories. An equation of motion including the aerodynamic drag force has no analytic solution, but it is straightforward to integrate numerically for high-school or first-year university students. Accounting for aerodynamic drag substantially improves the match with experimental data for any ball. In a second experiment, balls are shot with spin resulting in curveball trajectories. Numerical simulations including the Magnus force can give accurate predictions of 3D curveball trajectories, both curving according to the normal and the inverse Magnus effect. Balls shot with topspin and backspin are also accurately modelled. Finally, we model the bounce of an arbitrarily spinning ball using linear and angular impulse-momentum theorems and coefficients of restitution in vertical and horizontal directions. We find agreement with experimental data to within centimeters.

Computation of Aerodynamic Forces Under Nonequilibrium Conditions: Flow Past a Spinning Cylinder

An alternative methodology to compute aerodynamic coefficients, such as lift and drag, using the direct simulation Monte Carlo method is presented. This methodology, which is valid for all flow conditions, is then applied to investigate the aerodynamic characteristics of nonequilibrium flow past a rotating cylinder. This work focuses specifically on the transition flow regime in which an inverse Magnus effect involving a directional change in lift force can be observed. In particular, the Magnus force and the inverse Magnus effect in subsonic flow are investigated by studying the variation in the aerodynamic coefficients and their normal stress, fluid pressure, and shear stress components. Illustrative results studying the aerodynamic force components as a function of flow rarefaction, Reynolds number, and incomplete surface accommodation are presented, which provide fundamental insight into the physics occurring under nonequilibrium flow conditions.

Gas-induced friction and diffusion of rigid rotors.

We derive the Boltzmann equation for the rotranslational dynamics of an arbitrary convex rigid body in a rarefied gas. It yields as a limiting case the Fokker-Planck equation accounting for friction, diffusion, and nonconservative drift forces and torques. We provide the rotranslational friction and diffusion tensors for specular and diffuse reflection off particles with spherical, cylindrical, and cuboidal shape, and show that the theory describes thermalization, photophoresis, and the inverse Magnus effect in the free molecular regime.

High-Speed Rarefied Flow Past a Rotating Cylinder: The Inverse Magnus Effect

In the present study, we investigate flow past a rotating cylinder over a wide range of flow rarefaction from the early slip through to the free-molecular regime using the direct simulation Monte Carlo method. We focus specifically on high-speed flow conditions and consider a wide range of Mach numbers near the high subsonic, transonic, and supersonic regimes. Various flow parameters such as the coefficients of lift and drag as well as the coefficients of pressure, skin friction, and wall heat transfer have been investigated as a function of both the Mach number and the Knudsen number to gain insight into the flow physics in the different regimes. The flow characteristics in the transonic regime have been found to be substantially different from those in the supersonic regime. In particular, an inverse Magnus effect involving a change in the direction of the lift force occurs in the supersonic regime. In contrast, subsonic flows in the early slip-flow regime experience the conventional direction for the Magnus lift force. This paper demonstrates that there is a subtle interplay between the Mach number and Knudsen number for the occurrence of the inverse Magnus effect.

Complex motions of grains in dusty plasma with nonuniform magnetic field

We have studied various complex motions of the irregular dust grains immersed in non-uniformly magnetized plasma. The cylindrical magnet that we used for experiments significantly alters the radial distribution of the sheath potential which confines the negatively charged grains. Grains are horizontally illuminated by a 50 mW, 532 nm laser sheet and imaged by a CCD camera from the upper transparent electrode. Hypocycloid and epicycloid motions of grains are observed for the first time as far as we know. Cuspate cycloid motions, circle motion, wave motion, and stationary grains are also observed. Their trajectories can be obtained by using long-time exposure, and the characteristic parameters of the grain movement are measured by using the image processing with MATLAB. Though the dust grains can move around the magnet steadily in various trajectories, the induced magnetic field is too weak to give rise to cycloid motions of grains. Then we propose a new mechanism that an inverse Magnus force induced by the spin of the irregular grains plays an important role in their cycloid motions. The pollen pini we used for experiment is not a regular microsphere, there is a symmetry in the shape. On the basis of Bernoulli principle, the pressure difference between the left and right side of the forward moving grains produces the inverse Magnus effect. Additional comparison experiments with regular microspheres are also performed to confirm that the cycloid motions are distinctive features of an irregular dust grain immersed in the plasma. The periodical change of the cyclotron radius as the grain travels would result in the (cuspate) cycloid motions, and the maximal value of angular velocity of spin is about 105 rad/s. Our experimental observations can be well explained based on the force analysis in 2D horizontal plane.

Inverse Magnus effect on a rotating sphere: when and why

AbstractIn some specific conditions, a flying spinning ball deflects in a direction opposite to that predicted by the Magnus effect, which is known as the inverse Magnus effect. To elucidate when and why this effect occurs, we measure the variations of the drag and lift forces on a rotating sphere and the corresponding flow field with the spin ratio (the ratio of the rotational velocity to the translational one). This counterintuitive phenomenon occurs because the boundary layer flow moving against the surface of a rotating sphere undergoes a transition to turbulence, whereas that moving with the rotating surface remains laminar. The turbulence energizes the flow and thus the main separation occurs farther downstream, inducing faster flow velocity there and generating negative lift force. Empirical formulae are derived to predict the location where the flow separates as a function of the Reynolds number and the spin ratio. Using the formulae derived, the condition for the onset of the inverse Magnus effect is suggested based on the negative lift generation mechanism.

Response to “Comment on ‘Force on a spinning sphere moving in a rarefied gas’ and ‘On the inverse Magnus effect in free molecular flow’” [Phys. Fluids 16, 3832 (2004)

Response to Comment on 'Force on a spinning sphere moving in a rarefied gas' and 'On the inverse Magnus effect in free molecular flow' [Phys. Fluids 16, 3832 (2004)]

Comment on “Force on a spinning sphere moving in a rarefied gas” [Phys. Fluids 15, 736 (2003)] and “On the inverse Magnus effect in free molecular flow” [Phys. Fluids 16, L9 (2004)

Comment on “Force on a spinning sphere moving in a rarefied gas” [Phys. Fluids <b>15</b>, 736 (2003)] and “On the inverse Magnus effect in free molecular flow” [Phys. Fluids <b>16</b>, L9 (2004)

Response to “Comment on ‘Force on a spinning sphere moving in a rarefied gas’ and ‘On the inverse Magnus effect in free molecular flow’” [Phys. Fluids 16, 3832 (2004)

Response to “Comment on ‘Force on a spinning sphere moving in a rarefied gas’ and ‘On the inverse Magnus effect in free molecular flow’” [Phys. Fluids <b>16</b>, 3832 (2004)

On the inverse Magnus effect in free molecular flow

A Newton-inspired particle interaction model is introduced to compute the sideways force on spinning projectiles translating through a rarefied gas. The simple model reproduces the inverse Magnus force on a sphere reported by Borg, Söderholm and Essén [Phys. Fluids 15, 736 (2003)] using probability theory. Further analyses given for cylinders and parallelepipeds of rectangular and regular polygon section point to a universal law for this class of geometric shapes: when the inverse Magnus force is steady, it is proportional to one-half the mass M of gas displaced by the body.

The backward jump of a box moss mite

Indotritia cf. heterotrichia, a box moss mite 800 μm in length, combines the abilities to curl up and to jump. Despite the lack of specialized legs and of extensor muscles in its knee joints, the backward leap is characterized by a short take-off time (ca. 0.5 ms). This is apparently facilitated by a catch mechanism made up of a small hook on each forefemur that hitches on the rim of the anterior shield of the body and maintains the forelegs in a flexed position during a prejump phase. While the animal is propelled backwards, its body simultaneously spins in a forward direction: it is supposed that, at take-off, the hindlegs initiate a forward rolling of the body, which is powered by internal hydraulic pressure, before the hook disengages from the shield rim and triggers a sudden backward impulse. The non-parabolic trajectory of the flight can be described with a model where the air resistance due to the spin (Magnus effect) and to the translatory motion is taken into account.