Multisensor Hot-Wire Probe for High-Speed Aerodynamics

A multisensor hot-wire probe consisting of three hot-wire sensors staggered in the streamwise and spanwise directions was developed to study radiated fluctuations from high-speed boundary layers. This probe was designed to make measurements outside the boundary layer and capture the spectral phase difference from the three sensors to determine plane wave characteristics such as streamwise and spanwise wavenumber, phase velocity, and group velocity associated with different frequencies of boundary-layer fluctuations. The capabilities of this probe were demonstrated by performing measurements of radiated fluctuations outside a laminar boundary layer on a flat plate at Mach 1.65. This flow phenomenon has been widely studied in literature, providing a rich database for validating the measurements of this new probe. Experiments using this multisensor probe were complemented by single-sensor hot-wire measurements detailing the amplitude and frequency evolution. The measurements revealed the modal growth mechanisms of the primary instability, also known as oblique modes, and were subsequently followed by the presence of its subharmonics. Measurements made outside the boundary layer using the multisensor hot-wire probe provided evidence for a phase synchronization between the subharmonics and the oblique modes of the transitional laminar boundary layer.