Surface Heat Transfer Measurements Inside a Supersonic Combustor by Laser-Induced Fluorescence

A study has been conducted to measure surface temperatures inside a model rectangular supersonic combustor by the use of a nonintrusive thermal imaging system, based on the fluorescence properties of a dysprosium doped yttrium-aluminum-garnet (Dy3+:YAG) thermographic phosphor. In this system, the phosphor coating on the test surface is excited by a pulsed Nd:YAG laser. The resulting fluorescent emission of the temperature-sensitive 456-nm transition and that of the temperature-independent 496-nm transition are acquired by the use of a pair of image-intensified charge-coupled device cameras. The ratio of the acquired emissions is then correlated to temperature. The wind tunnel was a blowdown type that used vitiated air with nominal conditions at the entrance of the test section: M∞ = 2.5, P0 = 5 × 105 N/m2, T0 = 800 K, and Re∞/m = 9.6 × 106. The fuel was hydrogen gas at room temperature, injected parallel to the tunnel through a fuel-injector slit located along the backward surface of a step. The results under hot flow conditions were compared with numerical simulations performed using a two-dimensional Navier-Stokes code with full chemistry. Temperature measurements demonstrate the feasibility of laser-induced fluorescence for surface heat transfer studies in reactive flows involving significant unsteadiness and transient phenomena.