High-Enthalpy Flow Investigations by UV Laser-Induced Fluorescence

Abstract

A dual-dye-laser Laser-induced Fluorescence (LIF) system is established for flow field investigations in JF-10, a H 2 /O 2 -detonation-driven shock tunnel. The shock tunnel generates 400 mm-wide hypersonic flow with total enthalpy of 16.1 MJ/kg and static pressure at only105Pa, where LIF measurement is extremely challenging. In this LIF system, the laser sheet of a conventional planar LIF is rotated 90 degrees along its propagation direction, so that the fluorescence signal collected by the camera concentrates on a sharp line. The S/N ratio is increased, thus single-shot measurements are achievable. The rotational temperature of the flow measured by two-line thermometry (TLT) with simultaneous excitation of two $\gamma$ (0,0) transitions of NO at distinct rotational levels. Compared with single-dye-laser set-up, the current system is less affected by the fluctuation of the flow field from each facility operation, thus capable of reflect the dramatic temperature change across the shock layer. With precise control of the proper of the laser, and through evaluation of the error of the data, the temperature measurement and numerical simulation in the flow is consistent. Meanwhile, the velocity of the flow is measured by molecular tagging velocimetry (MTV) with a long-life fluorescence excitation, and the result agrees with the expected value. The UV LIF technique is proven useful in flow diagnostics in high-enthalpy regime.