Technological Development On Smoke Visualization And PIV And Its Application In Bridge Wind Tunnel Test

Flow visualization is the art of making flow patterns directly visible, combined with the PIV algorithm, it can also quantitatively analyze the distribution of flow field. It is an important tool for experimental fluid mechanics. Powell lens can transform laser beam into a uniform light sheet for the illumination of the particles in the fluid. By using titanium tetrachloride as smoke agent, the phenomena of the flow around the object in the wind tunnel is qualitatively shown. Meanwhile, the visualization images of the flow around a cylinder and the flow around a box girder during vortex-induced vibration are recorded with this technique. And the images are compared with the numerical simulation results. By using polystyrene as tracer particles and self-designed simplified PIV system, the particle image of channel flow are acquired. And an improved PIV algorithm is used to quantitatively analyze the flow field distribution. Moreover the possibility of the use of the system in biomedicine and river hydrology is discussed. The primary reasearch of this thesis are as follows:1. By using light sheet and smoke agent, a sequence of photographs of the flow around a cylinder are obtained. And experiments also show that an instability develops in the shear layer separating from the cylinder, where the shear layer rolls into small vortices. The instability waves corresponding to the these small-scale vortices are often called transition waves. Three different turbulence models are used to simulate the flow around a cylinder, and the results are compared with the flow visualization images. Meanwhile the advantages and disadvantages of three kinds of turbulence models for simulating the flow around a cylinder are discussed.2. By using Runge-Kutta method, the structural vibration response was numerically solved. And the differences of the Runge-Kutta method’s results and the mesh update results in Fluent is corrected. Meanwhile The reliability of the algorithm is verified by the Anagnostopoulos and Bearman parameters. The two dimensional vortex-induced vibration responses of box girder is simulated successfully by using the method. The wind tunnel experiment of the segmental model of the free suspension system was carried out. And the visualiztion images of the flow around the box girder during torsional vortex-induced vibration and the flow around a stationary box under the same wind speed. Some similarities and differences between the numerical simulations and the flow visualization images have been obtained. The effect of fluid structure interaction of flow around a box girder is also discussed.3. An improved method of PIV evaluation based on FFT correlation is proposed. It improves the accuracy of particle image at large displacement by increasing the search radius. And the reliability of the algorithm is verified by using the standard PIV particle image. Furthermore using a self-designed simplified PIV system and polystyrene, the particle images of channel flow by using the consumer-grade video camera are acquired. Through the analysis of a variety of image resolutions and frame-rates, it obtained some possible resons of causing evaluation error, and explored the possibility of the use of the system in the biomedical field and river hydrology.