A Spectral Study of a Moderately Loaded Low-Pressure Turbine Airfoil—Part I: Identifying Frequencies Affecting Bypass Transition

Abstract

A single wire, hot-wire, probe is used to examine the airflow in, and in close vicinity to, the shear layer of a low-pressure turbine (LPT) airfoil. A spectral analysis of the data identifies two sets of wide peaks of turbulent kinetic energy, one near 200 Hz and a second near 1 kHz. A method is developed to identify these peaks based on a combination of empirical relations between the airflow velocity and boundary layer thickness and on the location of the frequency peaks relative to the state of the free shear layer as it transitioned from laminar to turbulent. The method suggests the presence of Tollmien–Schlichting waves and Kelvin–Helmholtz instabilities. The Kelvin–Helmholtz instabilities are shown to pair.