Image Measurement Study On The Motion Of Single Bubbles In The Near-Wall Regions Through Stationary Water

Two-phase flow is an important flow phenomenon in nature and engineering field, several key issues are involved about two-phase flow in near-wall region with water conservancy and many industry and engineering field. However, limited by means of measurement, the research on the bubble motion law in near-wall region in stationary water is for from enough. Combined with Research Fund for the Doctoral Program of Higher Education, the interaction with rising bubble and inclined wall is studied by the use of digital image processing technique and analysis, preliminary study on the condition and regularity of bubble deformation,bubble adhesion,sliding and rebound along wall is done. The main contents of the studies and achievements are as follows:(1) The design of experimental system. In order to obtain high quality image, light emitting diode was selected as light source after a lot of analysis and test such as incandescent lamp,light emitting diode,halogen lamp and laser, then the diode array light plate was designed and manufactured .By setting big steady voltage air tire and micro regulation valve, the equal time-interval releasing of uniform bubble was successful.(2) Combined with the characteristics of bubble image ,advantages and disadvantages of a series of digital image processing method was analyzed and compared. The complementary operation of bubble image was applied in order to accord with the custom firstly, Application of static background liberation method was used in Pre-process of image, the complementary operation image is subtracted by the background which was produced by static background liberation method. It is better to use the background which was produced by static background liberation method than the background which was picture by using digital camera when doing image pretreatment; and the existed program is adopted for bubble extracting, maximum between-class variance method was used in algorithm of image segmentation. maximum between-class variance method was not effected by image histogram with double peak. It is called maximum-square-error method. Meanwhile, it has a better effect than other in actual application result. Finally maximum between-class variance method was applied to segment image in this paper.(3) From the test, some parameters such as bubble deformation,bubbles movement tracks,bubble rising velocity slipping along inclined wall tangential and rebounded speed in normal direction were obtained. The condition and regularity of bubble adhesion,sliding and rebound along wall is analyzed.(4) The results showed that: the bubble adhered to the wall when the wall placed horizontally; it began to roll and slide when the wall was inclined, meanwhile, the bubble size and shape changed unceasingly. When the distance of its center to the walls is less than its radius, the deformation reduced with the increasing of inclination angle. The variations of deformation of bubble hitting the same wall with time was first decrease and then increase, then decrease again and recovered to the normal at last; The variations of rising velocity of bubble along inclined wall was increased with the increasing of inclination angle. The variations of rebounded velocity of bubble along inclined wall was increased with the increasing of inclination angle.