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Analysis of Shear Stresses on Surface of Micro Particle in Turbulece through Direct Numerical Simulation Method with Relevance for Bireactors

Mortazavi, Mohammad Sadegh | 2025

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 58724 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Saeedi, Mohammad Saeed; Moosavi, Ali
  7. Abstract:
  8. We investigate the shear stresses imposed on a SPHerical particle floating in a turbulent flow using particle-resolved direct numerical simulation. A dilute turbulent flow is considered with Re_λ~50 and Kolmogorov’s length scale η and particles with diameter d_p in viscous sub-range, d_p/η<7. This allows the simulation of the non-uniform and time-varying shear stresses on the surface of a microparticle as it moves through the turbulent flow field. Also, it extends a multiscale numerical framework to investigate the interaction of particles and turbulence in the viscous subrange. We analyze the results of different numerical tests and show that the size ratio, d_p/η, and the density ratio of the particles to the fluid, ρ_p/ρ_f, are the main effective parameters on these stresses, except for the sub-range of d_p/η<2 in which surface stresses are independent of the particle size. Due to the statistical nature of these stresses, new equations are introduced to calculate the statistical characteristics of the stresses experienced by the particles in the viscous subrange. The newly introduced equations give a more realistic estimate of the surface stresses and can replace existing equations which are based on several simplifying assumptions. The results are presented in the form of relationships, tables, and charts usable for a more precise assessment of particle damage in turbulent flows. A comparison of the findings from this research with experimentally reported results in the scientific literature demonstrates a strong agreement between the simulations and experimental data
  9. Keywords:
  10. Direct Numerical Simulation (DNS) ; Surface Stress ; Particle Surface Stress ; Particle-Turbulence Interaction ; Turbulent Multiphase Flow ; Stress Analysis

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