• lattice Boltzmann;
  • bounce back;
  • fluid solid interaction;
  • external boundary force;
  • no-slip condition;
  • lattice spring;
  • red blood cell


A method for direct numerical analysis of three-dimensional deformable particles suspended in fluid is presented. The flow is computed on a fixed regular ‘lattice’ using the lattice Boltzmann method (LBM), where each solid particle is mapped onto a Lagrangian frame moving continuously through the domain. Instead of the bounce-back method, an external boundary force (EBF) is used to impose the no-slip boundary condition at the fluid–solid interface for stationary or moving boundaries. The EBF is added directly to the lattice Boltzmann equation. The motion and orientation of the particles are obtained from Newtonian dynamics equations. The advantage of this approach is outlined in comparison with the standard and higher-order interpolated bounce-back methods as well as the LBM immersed-boundary and the volume-of-fluid methods. Although the EBF method is general, in this application, it is used in conjunction with the lattice–spring model for deformable particles. The methodology is validated by comparing with experimental and theoretical results. Copyright © 2009 John Wiley & Sons, Ltd.