Abstract: Under the condition that the incident shock Mach number is fixed , the variation of the transition Reynolds number of boundary layer on the shock tube walls only as a function of the free-stream unit Reynolds number is investigated in this paper. The test section of the shock tube is 1.7 metres in length and its cross-section is a square with side length of 94 mm. Moreover, an elaborate analog circuit which can directly show the complete transition process from laminar to turbulent boundary layers has been made. From the measured values, an empirical formula to predict boundary layer transition Reynolds number for a flat plate or shock tube wall at varying free-stream unit Reynolds number has been obtained.

Key words: boundary layer transition, unit Reynolds number, analog circuit, shock tube