Benchmarking and Validation of a Combined CFD-Optics Solver for Micro-Scale Problems

Abstract

In this work we present a new approach for coupled CFD-Optics problems that consists of a combination of a Finite Element Method (FEM) based flow solver with a ray tracing based tool for optic forces that are induced by a laser. This is a setup that is mainly encountered in the field of optical traps. We combined the open-source computational fluid dynamics (CFD) package FEATFLOW with the raytracing software of the LAT-RUB with this task in mind. We benchmark and analyze the solver first based on a configuration with a single spherical particle that is subjected to the laser forces of an optical trap. The setup is based on an experiment which is then compared to the results of our combined CFD-Optics solver. As an extension of the standard procedure to simulate such problems we present a method with a time-stepping scheme that contains a macro step approach. The results showthat this macro time-stepping scheme provides a significant acceleration of the standard procedure while still maintaining good accuracy. A second configuration is analyzed that involves non-spherical geometries such as micro rotors. We describe a procedure that is able to efficiently and accurately calculate optical forces with surface triangulations as input geometries. Then we proceed to compare simulation results of the final angular velocity of the micro rotor with experimental measurements.