Plane Cascade Schlieren Image Processing And Measurement Systems Development

Experimental research of two-dimensional (2-D) cascade flow field plays an important role in aero engine blade design. The data reduction procedure of schlieren image is one of the key tasks of the testing. The image characteristic parameters were distinguished by experience traditionally. To obtain the accurate testing results, the quantitative analysis and measurement methods were presented depend on image processing, and the schlieren image processing system was designed and developed.The project of schlieren image parameters measurement and analysis system was presented, based on an integrated analysis of (2-D) cascade shock wave phenomena and their distributions under variety experimental conditions. First, the appropriate preprocessing algorithms were chosen to improve the image quality. The legible outlines of the shock waves were given by using the edge detection algorithm. An optimal algorithm combined the threshold with the morphologic algorithm was proposed to separate the figures of blades and shock waves, and the binary images of the blades and shock waves were obtained separately. The refined cavity method by image moments was presented to acquire the individual figures. Then, the geometric projection method was used to measure the characteristic parameters of the images. Furthermore, a semi-automatic shock wave quantitative measurement method for the angle, length and position parameters was given to meet the practical needs, and theinteractive interface was designed.Finally, the schlieren image processing system software and the 2~D cascade test database were developed. The system was tested and applied on SB302 wind tunnel and its practicability was proved.