Influence of thermalization protocol on Poiseuille flow of confined soft glass

A short poster talk presented at CompFlu-2021

Associated video on YouTube: https://youtu.be/3p9yh4VIbIo

Related publication:
https://doi.org/10.1063/5.0045302

Transcript

1. Imposed Stress Field Expected Velocity X Z Flow Direction Con fi nement Influence of thermalization protocol on Poiseuille flow of confined soft glass Vinay Vaibhav The Institute of Mathematical Sciences, Chennai Homi Bhabha National Institute, Mumbai Pinaki Chaudhuri
2. Imposed Stress Field Expected Velocity X Z Flow Direction Con fi nement Influence of thermalization protocol on Poiseuille flow of confined soft glass Vinay Vaibhav The Institute of Mathematical Sciences, Chennai Homi Bhabha National Institute, Mumbai Pinaki Chaudhuri
3. Poiseuille fl ow of glassy binary mixture Imposed Stress Field Expected Velocity X Z Flow Direction Con fi nement Poiseuille fl ow: pressure induced fl ow through a con fi ned channel or pipe Molecular dynamics simulation Model: 80-20 Lennard-Jones binary mixture at temperature T=0.4 (below TMCT) con fi ned via rough walls Control parameter: Applied different forcing strengths to cause the fl ow 114 480 particles wall wall Channel width = 100 Flow
4. Temperature pro fi le Nonuniform temperature variation in the channel Uniform temperature in the channel Atoms making the walls are vibrating and their temperature is maintained; such thermal wall control fl uid temperature; close to many experiments and applications Two different thermalization protocols °40 °20 0 20 40 z 0.40 0.42 0.44 0.46 0.48 T(z) °40 °20 0 20 40 z 0.0 0.1 0.2 0.3 0.4 0.006 0.007 0.008 0.009 0.010 0.011 Walls are rigid and fl uid temperature is controlled via direct thermostatting Wall thermostat DPD thermostat forcing strength Thermostat removes the excess heat produced due to fl ow Wall thermostat: simultaneous presence of local stress gradient and temperature gradient
5. Temperature pro fi le Nonuniform temperature variation in the channel Uniform temperature in the channel Atoms making the walls are vibrating and their temperature is maintained; such thermal wall control fl uid temperature; close to many experiments and applications Two different thermalization protocols °40 °20 0 20 40 z 0.40 0.42 0.44 0.46 0.48 T(z) °40 °20 0 20 40 z 0.0 0.1 0.2 0.3 0.4 0.006 0.007 0.008 0.009 0.010 0.011 Walls are rigid and fl uid temperature is controlled via direct thermostatting Wall thermostat DPD thermostat forcing strength Thermostat removes the excess heat produced due to fl ow Wall thermostat: simultaneous presence of local stress gradient and temperature gradient Goal How the two thermalisation protocols affect the fl
6. Steady state response 1.150 1.175 1.200 1.225 1.250 r(z) 0.006 0.007 0.008 0.009 0.010 0.011 °40 °20 0 20 40 z °0.6 °0.3 0.0 0.3 0.6 sxz(z) °40 °20 0 20 40 z # no fl ow: similar thermal and structural behaviour # wall thermostat: hydrodynamic prediction of temperature for Newtonian liquids don’t match # identical density and shear-stress pro fi les # different thermal conditions but similar structural properties Wall thermostat DPD thermostat forcing strength °40 °20 0 20 40 z 0.0 0.1 0.2 0.3 0.4 T(z) Wall thermostat DPD thermostat °40 °20 0 20 40 z 1.16 1.18 1.20 1.22 1.24 r(z) In the absence of fl ow °40 °20 0 20 40 z 0.40 0.42 0.44 0.46 0.48 T(z) °40 °20 0 20 40 z 0.0 0.1 0.2 0.3 0.4 0.006 0.007 0.008 0.009 0.010 0.011 In the presence of fl ow forcing strength Density Stress Temperature
7. Steady state response 0.00 0.04 0.08 0.12 vx(z) °40 °20 0 20 40 z 10°5 10°4 10°3 10°2 abs( ˙ g(z)) °40 °20 0 20 40 z 0.006 0.007 0.008 0.009 0.010 0.011 10°5 10°4 10°3 10°2 ˙ g 10°2 10°1 100 sxz 10°5 10°4 10°3 10°2 ˙ g 0.006 0.007 0.008 0.009 0.010 0.011 # Blunted velocity pro fi les # Wall thermostat: higher central velocity and narrower blunted region # Nonlinear shear-rate pro fi les # Difference in fl ow curves: different branches for wall thermostat case; collapse on a master curve for DPD case ( fi tted with Herschel– Bulkley form) # Comparison with Couette fl ow measurements Wall thermostat DPD thermostat forcing strength velocity pro fi le shear-rate pro fi le fl ow-curves stress vs shear-rate
8. Transient behaviour 20000 60000 t 10°4 10°3 10°2 10°1 Vcmx(t) 0.006 0.007 0.008 0.009 0.010 0.011 20000 60000 t 0.4 0.6 sw 103 104 to Wall thermostat DPD thermostat 0.40 0.41 0.42 0.43 0.44 T(z) 0.0 0.1 0.2 0.3 0.4 tw=750 tw=1250 tw=2250 tw=4250 0.00 0.02 0.04 0.06 0.08 vx(z) °40 °20 0 20 40 z 10°5 10°4 10°3 10°2 abs( ˙ g(z)) °40 °20 0 20 40 z # For a given forcing, fl ow is faster in wall thermostated system # Timescale for the onset of steady fl ow is larger in the presence of DPD thermostat Wall thermostat DPD thermostat Wall thermostat DPD thermostat Onset timescale waiting time temperature velocity shear-rate Flow-velocity Flow-velocity forcing strength forcing strength = 0.01
9. # Thermalization via wall and direct thermalization of fl uid # Steady and transient response # Impact on rheology: presence of temperature gradient in wall thermostat case # Compared with Couette fl ow (uniform shear-rate) response (not shown here) # Changing channel width (not shown here) Summary
10. # Thermalization via wall and direct thermalization of fl uid # Steady and transient response # Impact on rheology: presence of temperature gradient in wall thermostat case # Compared with Couette fl ow (uniform shear-rate) response (not shown here) # Changing channel width (not shown here) ThankYou Summary