Stereoscopic PIV measurements and numerical simulation of turbulent flow of liquid passing through rectangular apertures in a narrow annulus: influence of aperture shape on velocity field

摘要

Experimental and numerical studies were carried out to investigate the development of confined turbulent vortical flow of liquid passing through four identical rectangular apertures, which are equally spaced on the periphery of the intermediate wall dividing two annuli. Two different designs of apertures were analyzed using numerical simulations. Stereoscopic Particle Image Velocimetry system was used to measure the velocity field of the initial design. Measurement results were used to validate the use of selected numerical model and computational grids. It was found that Realizable K-£ model provides qualitatively predictable flow field as compared to experiments of initial design of the aperture. In order to obtain satisfactory measurements of liquid flow in given geometry, a number of improvements were developed for the PIV system. Laser sheet alignment (with respect to required measurement position) was assured using specially designed calibration system assembly. Macro lenses were used to provide the necessary field of view in order to take measurements. The entire PIV system was repositioned vertically using translation stages to obtain measurements at various locations of the test section. A polyurethane based coating was developed to mitigate the effects of wall reflections by shifting the wavelength of laser light reemitted by the walls. Both the experiments and measurements show that vortices are formed as the fluid is bypassing the longitudinal edges of the aperture. Aperture shape can be modified to reduce velocity and vorticity magnitudes as the fluid is exiting the apertures. This would reduce erosion rates experienced by the outer wall, if particle-laden liquid was pumped through investigated apparatus.