Characterization of Laminar Separation Bubbles Using Infrared Thermography

Abstract

An experimental investigation is conducted to develop and validate a quantitative methodology for identification and characterization of a laminar separation bubble based on infrared thermography measurements. All experiments are performed on a NACA 0018 airfoil at chord-based Reynolds numbers of 80,000 and 120,000 and a range of angles of attack. A comparative analysis of near-wall flow development captured with planar, two-component PIV and surface temperature characteristics is used to establish a methodology for surface temperature-based diagnostics of laminar separation bubbles. For convection-dominated surface cooling, streamwise gradients of surface temperature are shown to mark mean separation and transition, occurring at the maximum and minimum values, respectively. The location of mean reattachment aligns with the location of minimum surface temperature. The obtained estimates are shown to agree well with those from PIV measurements. Transient surface cooling is also considered to estimate the local convective heat transfer coefficient, supporting the results obtained based on quasi-steady temperature measurements.