A transition detection study at Mach 1.5, 2.0, and 2.5 using a micro-thin hot-film system

A boundary-layer transition detection study was conducted in the NASA Langley unitary plan wind tunnel with an array of microthin hot films on a flat plate at Mach numbers 1.5, 2.0, and 2.5 and Reynolds numbers (1.0-4.5) x 10 to the 6th/ft. Transition locations were obtained online from the variation of normalized rms voltages from an array of hot-film sensors for both natural transition and a grit-induced wedge of turbulence. The effects of Mach number and Reynolds number on the location and length of the transition region for the two types of transition are presented from the online data. Also shown are the unit Reynolds number effects on transition Reynolds number, voltage-versus-time traces, spectra, and the data-acquisition system.