Mobile digital speckle pattern interferometer for studying resonant vibrations in rotor system structures

Subject of study. This study examined the process of recording speckle interferograms in the optical system of a digital speckle pattern interferometer operating under external mechanical disturbances without vibration isolation. Aim of study. The aim of this study was to develop a mobile speckle pattern interferometer equipped with a continuous-wave laser and diffusely scattering element (DSE) for registering the natural vibration modes of the bladed wheels of a gas-turbine engine. Method. A newly developed algorithm was used for statistical processing and the accumulation of residual images formed from video stream frames to obtain high-contrast speckle interferograms recorded by the time-averaging method under the random mechanical excitation of the speckle interferometer. Main results. The experimental results confirmed that the developed speckle interferometer can operate without the vibrational isolation of the optical system. The feasibility of using polymer adhesive films as a diffusely scattering coating on the optical surface of the scattering element was investigated. The optimal transparency of the polymer light-scattering film that ensured the registration of high-contrast speckle interferograms was experimentally determined. The influence of broadband mechanical disturbances in the form of white and pink noise on the formation and recording of interference patterns was determined both with and without a polymer film or paint layer deposited on the surface of the DSE. The results demonstrate that a polymer coating on the surface of the DSE can be used to reduce the vibration level of its surface under impact loads. Practical significance. The obtained results can be applied in the development of mobile digital speckle pattern interferometers for integration into the test systems of aerospace industry companies.