Shear lift forces on convex non-spherical particles in the free molecular regime

For the theoretical description of the lift forces on particle suspended in a gas, a real particle is usually simplified as a sphere. However, most real particles are non-spherical particles. The influence of the geometric shape and orientation on the transport of the suspended particle is unambiguously non-negligible. In the present paper, the shear lift forces exerted on non-spherical particles are studied in the free molecular regime. Based on the gas kinetic theory, the expressions for effective forces are obtained by integrating the forces on the surface element over the whole particle surface. It is theoretically found that the effective forces are proportional to the surface area of the particle, and the proportion coefficient is independent of the particle size or shape, providing that the particle orientation distribution is uniform. These findings in the present paper has been verified by direct simulation Monte Carlo and can simplify the calculation of the shear lift forces on non-spherical particles in the free molecular regime with a wider range of practical applications.