Improved PIV Algorithm For Flow Around Arbitrarily Moving And Deforming Boundary

The interaction between arbitrarily moving boundary and fluid is atypical Fluid-Structure Interaction (FSI) phenomenon, which is inevitable indaily life and engineering practice. However, due to its complexity, theexperimental study of strong nonlinear coupling of fluid-structure interactionis still lacking. The use of advanced data post-processing methodologies inPIV has made it possible to accurately determine the flow field neararbitrarily moving and deforming boundary, which is vital to thecharacterization of our knowledge of FSI.In the present work, a state-of-the-art algorithm of the Particle ImageVelocimetry (PIV) is proposed to accurately extract the location of theinterface and the flow field near arbitrarily moving and deforming boundary,which is usually associated with strong nonlinear coupling of fluid-structureinteraction. A smart algorithm based on Radon transformation is employed tofaithfully track the fluid-structure interface with large deformation. Particleimages of different signal to noise ratio (SNR) are synthetically generated totest the algorithm. The smart algorithm can accurately recognize the interfacefrom synthetically generated particle images with SNR range from-11.70dBto-17.62dB. The reliability of the interface tracking mothed is verified bypractical application, flexible film in bluff body wakes is measured byTR-PIV system. The time-displacement curve of film is obtained by thisinterface detection algorithm, providing a solid basis for vortex induced vibration mechanism analysis and validation of numerical calculations.The approach to accurately determine flow field near arbitrarily movinginterface is also discussed in the present work. A body-fitted arrangement ofinterrogation windows is made based on detected boundary information, andthe standard cross-correlation PIV algorithm is applied to get reliable flowfield information near the boundary. The proposed algorithm go throughbench-mark tests by using synthetically generated image pairs, showing thegreat potential for measuring the fluid flow around arbitrarily moving anddeforming interface. Finally, the fluid flow of fluid-structure interactionassociated with a flexible membrane, which is placed behind a squarecylinder, is measured by PIV; the instantaneous flow fields near the violentlymoving and deforming membrane are determined.