Recent Experimental and Theoretical Extensions of Nearly Free Molecular Flow

The Transition From Continuum to Molecular Flow

“…Confirming experimental data are available for cylinders (13,50,(98)(99)(100), but only drag data are available for spheres. These were obtained in a cleverly conceived micro-ballistic range (101) which has the sole dis advant ' age of requiring an indirect estimate of the surface temperature of the sphere.…”

“…In the regime of nearly free-molecule flow, a confusing variety of theoreti cal results is available for spheres and cylinders, and it must be confessed that the numerous articles in which an attempt has been made to compare these results with experiment (50,98,99) have compounded the confusion. One difficulty is that the existing theories do not attempt to deal with realis tic variations of collision cross section with relative velocity.…”

“…An attempt to compare the theory with experiment requires a judgment as to the most appropriate or representative choice of the constant. Different choices are suggested in each of references (50,98,99). As is discussed in more detail in (99) , there are additional diffi culties of principle in the process of connecting these parameters of the theory to more familiar parameters such as Mach and Reynolds numbers.…”

The Measurement of Sphere Drag in Rarefield Gas Using a Magnetic Wind Tunnel Balance

“…Maslach et al35 listed these values. Slightly different constants result, depending on the relationship used to relate Kn R and Kn".…”