Origins of radiometric forces on a circular vane with a temperature gradient

Radiometric force on a 0.12 m circular vane is studied experimentally and numerically over a wide range of pressures that cover the flow regimes from near free molecular to near continuum. In the experiment, the vane is resistively heated to about 419 K on one side and 394 K on the other side, and immersed in a rarefied argon gas. The radiometric force is then measured on a nano-Newton thrust stand in a 3 m vacuum chamber and compared with the present numerical predictions and analytical predictions proposed by various authors. The computational modelling is conducted with a kinetic approach based on the solution of ellipsoidal statistical Bhatnagar–Gross–Krook (ES-BGK) equation. Numerical modelling showed the importance of regions with elevated pressure observed near the edges of the vane for the radiometric force production. A simple empirical expression is proposed for the radiometric force as a function of pressure that is found to be in good agreement with the experimental data. The shear force on the lateral side of the vane was found to decrease the total radiometric force.