Barracuda官方教程阅读笔记（一）

Introduction to CPFD Software and the Barracuda Virtual Reactor

Fluid-Particle flows

Examples

• Fluidized Beds
• Ore Reactors
• Cyclones
• Risers
• Deep Beds

What is different than single phase flows?

Particles are NOT fluids:

• Particles are discrete entities (cannot be subdivided like a fluid)
• Particles have a size distribution
• Particle cannot completely fill a space
• Particles occupy a physical volume (and displace fluid)
• Particles CAN support a shear stress (while fluids CANNOT support a shear stress)

Other considerations:

• Coupling between particles and fluids
• Wall treatments
• Boundary treatment
• Thermal, chemistry…

Modeling approaches

To accurately simulate fluid-particle flows, one must model the effects of:

• Drag and coupling
  • Dilute flows (<1% by volume)
  • Dense flows (up to close pack)
• Many particle sizes or size distribution
• Multiple types of particles (size, density, composition)
• Particle interactions (walls, other particles)
• Heat transfer
• Chemical reactions
  • Gas-phase (homogeneous)
  • Gas + particles (heterogeneous)
  • Changing particle composition

There are different approaches to modeling particle flows

Modeling Approachs

Single Phase

Multi-Phase

Eulerian

Lagrangian

Eulerian/Eulerian

Eulerian/Lagrangian

Unidirectional Coupling

Bi-directional Coupling: Barracuda VR

The CPFD? modeling approach

Overview

1. What about the large number of particles?
   • Lesser number of computational particles
   • The particle field is resolved by using a reasonable number of computational particles
   • Each computational particle represents one or more actual particle(s) with identical physical properties
   • The physics are computed on the individual particle (e.g. drag based on size, chemistry, etc.)
   • All changes experienced by the computational particle are applied to all actual particles represented by that computational particle (proper fluid displacement)
   • Many CPFD calculations utilize between 500,000 and 5,000,000 computational particles
2. What about particle contact and collision?
   • Modeled, rather than directly computed
   • Collision detection can be prohibitive with millions of computational particles
   • Rather than computing which particle a given computational particle will impact, the CPFD method is more concerned with the question “is a collision likely to occur?”
   • The collisions are then subjected to various models
     • Enduring contact at close-pack handled via a non-linear stress tensor
     • BGK-type collisional damping
3. What about inter-phase coupling?
   • Inter-phase interpolation operators, and tight, bi-directional coupling
   • Different particles experience different motion, even though both are in the same cell
   • All sub-grid particle motion is coupled back to the fluid phase momentum equation

Advantages and disadvantages

Advantages:

• PSD
• Erosion
• Number of particles

Disadvantages:

• Direct particle contact
• Multiple particles must fit in cell

Validation

• $U_{mf}$
• dP/dz
• 2D Bed
• PSRI Jet Cup

Commercial examples and case studies

Biomass CFB combustor

FCC regenerator