Holography as a Tool in the Gas Turbine Industry

Abstract

Jet aircraft engines comprise what is probably the most important segment of the gas turbine industry, and it is because these engines are critical to aircraft safety and performance that holographic techniques of measurement and inspection have found cost effective applications. The three major ones are vibration analysis, nondestructive bonding inspection, and flow visualization. Vibration analysis usually consists of recording time-average holograms of an object under vibration and observing Bessel-function fringes in the reconstructions. Bonding inspection is usually done by recording either time-average holograms with the object excited by high frecquency vibration or double-exposure holograms of the object before and after some form of stress. The hologram reconstructions show the differential movement of the regions of the object that are poorly bonded and allow identification of bonding flaws. Flow visualization usually involves recording double-exposure holograms of diffusely reflecting or transmitting objects through the gas flow. The fringes in the reconstruction allow determination of shock waves and gas density.