The drag force acting on a cylinder or a flat plate exposed to a plasma flow for great Knudsen numbers

As a continuation of previous papers, analytical expressions for the drag and/or lift forces acting on two typical non-spherical objects (a cylinder and a flat plate) exposed to a plasma flow are presented for the extreme case of great Knudsen numbers and a thin plasma sheath. Combined specular and diffuse reflection at the object's surface is included in the analysis. It is shown that the drag and/or lift coefficients are independent of the object's size and not influenced much by the plasma's temperature. The drag or lift force increases with increasing specular-reflection fraction of gas particles at the object's surface, but the rate of increase for the drag or lift force on a flat plate is appreciably greater than that for the drag force on a cylinder. Some suggestions concerning how to check the present kinetic-theory analysis and to determine the values of the specular-reflection fraction of gas particles at the object's surface through the drag or lift force measurements are proposed.