New experimental techniques for probing gun barrel boundary layers

A laser Doppler velocimeter measures velocity histories of the propellant gas flow inside a gun barrel. Two coupled velocimeters measure velocity reductions near the tube wall at distances of 1 mm. A shaped window to measure propellant gas luminances under observation angles of 90 and 27 deg is designed, and used to measure the transmittance of propellant gas residues deposited on its inner surface. To measure surface temperature at the inner side of the window, a sensor based on the temperature dependence of the reflectivity of silver coatings in the UV is designed. Using the optical probes effective absorption thickness of the thermal boundary layer in the 0.5 mm range is detected.