Study of rate of dust build up on optical windows

Abstract

The work presented in thesis is part of the DANIELA project which aims to replace the current air data system on civil aircrafts with a flush mounted Air Data System (ADS) built around a 3 axis Doppler LIDAR function as the primary data channel. This thesis is focused on the comparison of different window materials and their optical clarity by means of theoretical and experimental analysis. Four different window materials including BK7, Sapphire, Germanium and ZnS are placed in a wind tunnel. The samples are each exposed to flows of air and water for specific periods of time during which temperature, pressure and air speed are recorded. Subsequently, each sample is carefully observed under the microscope. This is followed by the measurement of the amount of back scatter via detecting the change in the voltage once it is placed in the optical station. The optical tests reveal the amount of dust adhered to the samples which results in increased voltage. Review of these samples under the microscope matches the results obtained from the optical test. The two sets of data obtained from the two tests determined that some samples collected more dust in comparison to others. It was established that under identical test conditions i.e. flow, temperature and moisture, BK7 and Sapphire collect considerably less dust compared to ZnS. Moreover it was impossible to test Germanium sample optically, under a microscope as it is a dark opaque glass.