Institute of Particle Science and Engineering, University of Leeds, LS2 9JT, UK 2

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1 INFLUENCES OF PARTICLE-SCALE PROPERTIES ON THE FLOW PROPERTIES OF POWDER MEDIA IN LOW GRAVITY ENVIRONMENTS: COMPUTATIONAL ANALYSIS S. Joseph Antony, T. Amanbayev 2, B. Arowosola and L. Richter 3 Institute of Particle Science and Engineering, University of Leeds, LS2 9JT, UK 2 Department of Mathematical Methods and simulation, Southern-Kazakh State University, Shimkent,62, Kazakhstan 3 Kayser-Threde GmbH, Wolfratshauser Straße 48, 8379 Munich, Germany GOLD PEAK CENTRE OF EXCELLENCE Dr S Joseph Antony Associate Professor S.J.Antony@leeds.ac.uk Institute of Particle Science and Engineering (IPSE) School of Process, Environmental and Materials Eng. (SPEME) University of Leeds Leeds LS2 9JT, England, U.K. Dust and Grains in Low Gravity and Space Environment 2-4 April 22, ESA/ESTEC, The Netherlands

2 Flow behaviour of powders and grains through confined geometries under low gravity environments Exceedingly complex and not yet well established, but much needed in the design of operating capabilities of space explorers such as EXOMARS EXOMARS-SPDS (Schulte et al. 28) Low gravity experiments such as using parabolic flights are expensive, yet low gravity levels are available only for a short duration (~ few minutes) Alternatives: Virtual experiments using Theoretical/Modelling approaches, but they are not yet well studied for low gravitational granular flows Continuum theories: mostly do not account inherent discrete nature of grains, but probably less expensive Discrete element modelling(dem): discreteness accounted, but could be computationally extensive and expensive

3 Aim: To develop fundamental understandings on the influence of particle-scale properties on the flow behaviour of grains through SPDS chambers under Lunar, Martian and Earth gravities Computational Analysis (free flowing grains) Discrete Element Modelling Continuum Analysis Discrete Layer Approach (h-lagrange) KIRYA Structural Continuum Model Imposed boundary stresses & servo control FORCE CONTACT LAW DISPLACEMENT Imposed boundary strain rule Comparison with experiments Conclusions Gravity forces LAW OF MOTION Integrate Accelerations DEM Basic concept Cundall and Strack (979)

4 CONTINUUM APPROACH MODELS DL A KIRYA STRUCTURE MODEL Zones of flow out of granular particles Q=f(f)

5 KEY RESULTS I. DLA ANALYSIS x, m Effect of flow rate on the position of particle layer and emptying time.35 2 Q=. Q= Q=.2 2 Q=.25 Q=.3.2 Q=.35 Q=.4.5 Q=.45 Q=.5. Tempty, s ξ=.2 ξ= Q, m 2 /s t, s Results Increase in flow rate implies decrease in completion time Completion time increases rapidly for flow rate less than about.3m 2 /s

6 Effect of slit opening variation a =.5m 2 2 T empty, s 2 4 a=.5 35 a=. 3 8 a= a, m Q, m 2 /s T empty, s 2 ξ=.2 ξ=.3 Result: Increase in slit size leads to increase in completion time

7 Effect of velocity with x Result: As the particle exits with the maximum velocity Effect of internal angle with flow rate x, m t, s Result: π/2 π/3 π/4 π/5 π/6 - Time to empty varying with internal angle. Increase in internal angle (α) leads to increase in completion time

8 II. KIRYA Structural Continuum Model (non-cohesive flow) Effect of gravity with flow rate Effect of gravity on varying friction a=.m; K2 = ; k = ; d = µm; f =.3 (typical) Effect of gravity on varying particle diameter. a=.m; K2 = ; k = ; g = 9.8; l = hc; d = E-6m Results: flow rate varies non-linearly with g Increase in friction coefficient leads to decrease in flow rate Particle diameter in the range - micron seems not to affect the flow (non-cohesive) a=.m; K2 = ; k = ; f =.3(typical) [The effect of the particle diameter was thus tested for different friction coefficients in which results had similar trend]

9 III. DEM Analysis First objective is to find out how far the results obtained from discrete element modelling agree (or disagree) with continuum analysis for flow properties Typical geometry of a hopper Material properties Wall normal stiffness (wn) = e8pa Wall shear stiffness (ws) = e8pa Wall friction coefficient =.7 Ball shear stiffness (bs) = e8pa Ball normal stiffness = e8pa Ball density = 6kg/m3 Ball contact normal strength (bcn) = e8pa Ball contact shear strength (bcs) = e8pa Ball contact friction coefficient =.7 Radius multiplier (puff) =.6 Desired final porosity (poros) =.36 Number of balls = varies

10 Effect of gravity on Average Volumetric flow rate Effect of gravity on emptying time Emptying time Vs gravity (DEM) Cont.6 DEM.4 t/to Ave. Q/Qo (m3/s) g/go g/go.8 In comparing the gravity effect with continuum analysis, Results: Comparison of DEM simulated gravity effect with continuum analysis gives similar trend A decrease in gravity leads to a decrease in discharge rate which in turns increase the emptying time.2

11 Second objective is to find out how far the macroscopic measure such as angle of repose is affected by gravity and to compare with experimental results DEM Simulation Results Gravity 2.8, Angle = 3.6degrees Gravity 4.8, Angle = 3.6degrees Gravity 6.8, Angle = 3.8degrees Gravity 9.8, Angle = 32.4degrees

12 Results: The result obtained is typical to a recent study done by (Nakashima et al., 2) based on experiments and 2d DEM simulations. * Nakashima et al, 2 showed that at all gravity levels examined using both dense and loose sand does not affect the angle of repose and the shape of the pile formed (angle of repose obtained during the experiments were close to 3.degrees) Our 3-d simulations: angle of repose : degrees (/6 G 2 G) But, we have shown earlier that other flow characteristics can be significantly affected by gravity though angle of repose measure could be insensitive to gravity!

13 Third objective is to compare some observations from experimental flight test results with DEM results Experiments: Material type: Sandstone, Hopper material: Steel Key observation: Though the flow of grains was complete under Martian gravity, for the same material under lunar gravity left over materials were recorded in the flow chambers, which subsequently emptied under 2G gravity. Such behaviours could cross-contaminate samples and more understanding is needed to eliminate them. Experiments Conducted by Kayser-Threde (22) DEM Results: Influence of gravity level on mass flow rate of sandstone grains.2 Earth.2 Earth M/Mo.8 M/Mo.8.6 Mars.6 Mars Lunar Lunar g/go g/go 3

14 .6E+5.4E+5 Mass flow (g).2e+5 2go gravity level Lunar 2g.E+5 8.E+4 6.E+4 4.E+4 2.E+4.E+.E+.E+2 2.E+2 3.E+2 4.E+2 5.E+2 6.E+2 7.E+2 8.E+2 Accum time (secs) Results: Flow was observed to be difficult at Lunar gravity levels and after long simulation run time, particles were still found in the hopper not flowing out. Remaining particles were taken to 2go levels and all particles dropped out of the hopper within very little time as observed also in parabolic flight tests Materials that can be processed under Martian gravity can still be difficult to process at Lunar gravity level

15 Ongoing: Investigations on what happens inside the flow chambers under Earth, Martian and Lunar (EML) gravities Contact force profile Velocity profile Contact force profile (Arch formation) Particle flow profile (Arch formation)

16 Videos: Evolution of force distribution and particle profile inside flow geometries under EML gravities

17 Conclusions From the theoretical/simulation results in comparison with experimental data, it can be deduced that gravity has a very real impact and considerable influence on the functioning (and cross-contamination levels) of SPDS station Conventional measures such as angle of repose in itself could be less sensitive to gravity same angle of repose for different cases does not mean that flow behaviours inside different chambers are identical DEM simulations can be applied to space applications, but with caution Future works Including strong cohesivity of grains and long-range forces Geometrical effects etc...

18 Acknowledgement Kayser-Threde