Three-dimensional (3D) experimental realization and observation of a granular gas in microgravity

Harth, Kirsten; Trittel, Torsten; May, Kathrin; Wegner, Sandra; Stannarius, Ralf

doi:10.1016/j.asr.2015.01.027

Cited by 23 publications

(21 citation statements)

References 28 publications

(26 reference statements)

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“…In regions where the particle velocities are correlated the temperature drops, which, in turn, creates a region of low pressure. These are the seeds for a second instability if the system size is larger than k * −1 [13,15,17].Experimental studies [18][19][20][21][22] of granular gases are rather scarce because of formidable challenges in preparing a system free of external forces. Microgravity experiments on parabolic flights or drop towers potentially offer good conditions, but it is very difficult to remove the influence of confining potentials or surrounding walls on the granular system.…”

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confidence: 99%

“…Experimental studies [18][19][20][21][22] of granular gases are rather scarce because of formidable challenges in preparing a system free of external forces. Microgravity experiments on parabolic flights or drop towers potentially offer good conditions, but it is very difficult to remove the influence of confining potentials or surrounding walls on the granular system.…”

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confidence: 99%

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A universal scaling law for the evolution of granular gases

Hummel

Clewett

Mazza

2016

EPL

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Dry, freely evolving granular materials in a dilute gaseous state coalesce into dense clusters only due to dissipative interactions. This clustering transition is important for a number of problems ranging from geophysics to cosmology. Here we show that the evolution of a dilute, freely cooling granular gas is determined in a universal way by the ratio of inertial flow and thermal velocities, that is, the Mach number. Theoretical calculations and direct numerical simulations of the granular Navier-Stokes equations show that irrespective of the coefficient of restitution, density or initial velocity distribution, the density fluctuations follow a universal quadratic dependence on the system's Mach number. We find that the clustering exhibits a scale-free dynamics but the clustered state becomes observable when the Mach number is approximately of O(1). Our results provide a method to determine the age of a granular gas and predict the macroscopic appearance of clusters.Geophysical processes [1], the solar corona [2], the asteroid belt between Mars and Jupiter, planetary rings [3,4], protoplanetary disks [5], and the formation of cosmological structures [6] are systems where granular clustering processes are at play. Even a small degree of dissipation in the kinetics of granular particles produces spatial correlations and structures in a dilute, homogeneous gas [7]. Hydrodynamic treatments suggest that a shear instability initiates this transition [7]. However, what exactly initiates this process is not known. The equations of granular hydrodynamics [8] predict a linear instability of the transverse mode [9] when the wavevectorand ε is the coefficient of restitution. This instability leads to the formation of vortices. In regions where the particle velocities are correlated the temperature drops, which, in turn, creates a region of low pressure. These are the seeds for a second instability if the system size is larger than k * −1 [13,15,17].Experimental studies [18][19][20][21][22] of granular gases are rather scarce because of formidable challenges in preparing a system free of external forces. Microgravity experiments on parabolic flights or drop towers potentially offer good conditions, but it is very difficult to remove the influence of confining potentials or surrounding walls on the granular system. The necessity of studying large system sizes and of characterizing fluctuations in regions of sharp gradients in temperature and density, developing into supersonic flow, without ambiguities motivates us to tackle the continuous hydrodynamic equations beyond perturbative schemes. Hydrodynamic fields can be rigorously defined in a manner similar to molecular fluids by means of a coarse-graining of the microscopic kinetic equations. First, one considers the one-particle distribution function f ( r, w, t), which obeys the Boltzmann equation and represents the number of particles within a volume d r centered at r and with velocity w within the interval d w. Then, the transport equations for inelastic systems are deri...

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confidence: 99%

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confidence: 99%

A universal scaling law for the evolution of granular gases

Hummel

Clewett

Mazza

2016

EPL

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“…This allows 3D experiments using drop tower shots at the ZARM Bremen [24], offering ≈ 9 s of excellent micro-gravity. Parabolic flight experiments are inappropriate for low-excitation experiments in general [24] due to the g-jitter, but may be applied for investigation at strong excitation [18] or of dense granular systems [25]. This presentation will provide the first detailed experimental study of free homogeneous cooling of a 3D granular gas.…”

Section: Velocity Distributions In the Coordinatesmentioning

confidence: 99%

“…Our setup is similar to that of Refs. [22,24]: It consists of a cuboid container of ≈ 11 × 8 × 8 cm 3 with two movable side walls. Front and top walls are made of ITO coated acrylic glass, other walls are flat white painted aluminum.…”

Section: Velocity Distributions In the Coordinatesmentioning

confidence: 99%

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Cooling of 3D granular gases in microgravity experiments

et al. 2017

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Granular gases are a most peculiar state, superficially similar to molecular gases: They are loose ensembles of moving grains, rarely interacting with each other and with container walls. The most investigated scenario is the "granular cooling", the collective loss of energy from an initially excited state. We present an experimental study of the cooling of a 3D granular gas of rodlike grains in micro-gravity. Driven steady states of non-spherical grains are characterized by a lack of energy equipartition between the degrees of freedom of translation and rotation. Excitation by vibrating walls additionally introduces strong gradients in the direction and magnitude of translational velocities. We show that the degrees of freedom equilibrate during granular cooling in the homogeneous cooling state. The energy loss follows a t −2 scaling. In addition, the alignment of the rod axes with the excitation direction and with the instantaneous velocities are altered during this process.

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Driven and undriven states of multicomponent granular gases of inelastic and rough hard disks or spheres

Megías

Santos

2019

Granular Matter

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Starting from a recent derivation of the energy production rates in terms of the number of translational and rotational degrees of freedom, a comparative study on different granular temperatures in gas mixtures of inelastic and rough disks or spheres is carried out. Both the homogeneous freely cooling state and the state driven by a stochastic thermostat are considered. It is found that the relaxation number of collisions per particle is generally smaller for disks than for spheres, the mean angular velocity relaxing more rapidly than the temperature ratios. In the asymptotic regime of the undriven system, the rotational-translational nonequipartition is stronger in disks than in spheres, while it is hardly dependent on the class of particles in the driven system. On the other hand, the degree of component-component nonequipartition is higher for spheres than for disks, both for driven and undriven systems. A study of the mimicry effect (whereby a multicomponent gas mimics the rotational-translational temperature ratio of a monocomponent gas) is also undertaken.

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Three-dimensional (3D) experimental realization and observation of a granular gas in microgravity

Cited by 23 publications

References 28 publications

A universal scaling law for the evolution of granular gases

A universal scaling law for the evolution of granular gases

Cooling of 3D granular gases in microgravity experiments

Driven and undriven states of multicomponent granular gases of inelastic and rough hard disks or spheres

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