Visualization of Transonic Nozzle Flow by Laser-induced Fluorescence Method

In the large-scale gas or stream turbine, the flow around the blade tip becomes transonic, and the shock waves are generated in the blade passage. These shock waves induce the boundary layer separation and the vibrations of blades, which degrade the efficiency. This unstable flow phenomenon is closely related to the secondary flow associated with the large change in flow direction in the blade passage. To measure the secondary flow, the nonintrusive diagnostic technique is desirable, and the laser-induced fluorescence (LIF) method offers one of the best tools for this purpose. To prove the validity of LIF method in determining the temperature of the transonic flow field, the transonic nozzle with rectangular cross-section was made. The temperature calculated from the measured LIF intensity in the nozzle was shown to agree very well with that obtained from the static pressure measurement.