Determination of roughness parameters of the surface interacting with rarefied gas flow

Abstract

Numerical algorithm is proposed to determine the real values of surface roughness parameter σ1 from aerodynamic measurements in rarefied gas flow. This algorithm is based on the solution of the inverse problem because the main input into the influence of surface roughness on aerodynamic values is contributed by the roughness of smaller scale. This roughness is usually negligible on the profile diagram, even if the roughness parameter σ1 is measured in the experiment from the profile diagram. Moreover, the parameter σ1 is not included in technical standard of surface quality: the main parameter defining surface roughness according to usual standard procedures is not σ1, but the square mean deviation σ of the height of the surface. To solve the inverse problem we apply the simulation of surface roughness on micro-level by Gaussian or poly-Gaussian random field and the expansion of the scattering function on rough surface which has been applied earlier to solve the direct problem of studying the effect of surface roughness in rarefied gas flow. The value of roughness parameter σ1 obtained from the solution of inverse problem is substantially higher than the value of σ1 from the profile diagram measurements.