Abstract
In modelling of elastic objects immersed in a fluid, very important part of the model is the interaction between objects and fluid. In models based on immersed boundary method and lattice-Boltzmann method, this interaction is mediated by friction coefficient between fluid and particles. The friction coefficient is phenomenological and needs to be properly calibrated. In this work we design an experiment, the results of which can be predicted by theoretical computations. Based on the theory, we calibrate friction coefficient to properly describe the interaction between fluid and objects. The simulation experiments are performed in Object-in-fluid framework. We calibrate it for objects immersed in flow with low Reynolds number to model flow of cells inside microfluidic devices. We analyze dependence of interaction method on number of nodes and size of spherical object.
Highlights
We consider model of elastic objects immersed in a fluid based on the lattice-Boltzmann (LB) method coupled with the immersed boundary (IB) method
Current implementation of the Object-in-fluid framework distributed as a part of ESPResSo [?] requires to set the friction coefficient
The initial speed of the sphere was set to the IB points only and the inner fluid of the sphere was initiated with zero speed. This way, the whole movement had to be mediated by the IB points only, while we argue that the inner fluid should have been initiated with the same initial speed as the IB points
Summary
We consider model of elastic objects immersed in a fluid based on the lattice-Boltzmann (LB) method coupled with the immersed boundary (IB) method. The discretization mesh contains boundary points linked together by elastic forces along the edges and faces of the mesh These forces move the IB points in the space according to Newton equation of motion. This equations include the mass of individual IB points This way, the object’s boundary may change the shape according to the elastic forces. Basic principle for objects immersed in a fluid is the so called no-slip boundary condition The aim of this method is to keep the zero difference between the fluid velocity and the velocity of IB points on the surface of the objects. Current implementation of the Object-in-fluid framework distributed as a part of ESPResSo [?] requires to set the friction coefficient This phenomenological constant was previously calibrated by the following experiment: A rigid ball with the same density as surrounding fluid was put into a static fluid. We present new experiment with physically correct assumption in Section ??
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