Structural Analysis And Design Of Φ800mm Aperture Schlieren System

Schlieren technique is a classical optical method on display and measurement of the flow fields, which is widely used to observe the phenomenons of boundary layer in the flow, combustion, shock wave, heat convection in gases and so on. Nowadays, as an optical testing method frequently used in wind tunnels, large aperture schlieren systems are needed along with the developing of large scale flow field devices. Meanwhile, a high performance structure to support the primary mirror and an accurate adjustability of the optical system are required. The surface figure and optical adjustability affect the system's imaging quality directly.At first, the development of techniques to support the large aperture mirror was summarized in this article.The supporting structures generally used were listed. The applications of the computer aided design technique and the finite element method were summed up. Computational algorithms were introduced to process datas of the surface deformation.According to the design scheme of the system, technical requirements of the primary mirror were given, which is the key part in the testing system. The size of the mirror, material, lightweight processing and supporting method were studied considering the requirements. Finally, K9 glass was selected as the mirror's material. Its size isΦ840 mm×110 mm, no lightweight holes inside, and steel belt supporting structure was adopted to mount the mirror.Stress and deformation of the mirror on the steel belt were analyzed by means of finite element method. According to the stress result, the value of the mirror's maximum concentrated stress didn't reach 1 MPa, far less than the ultimate tensile strength of K9 glass (σs,load=38.4 MPa, calculated by the theory of fracture probability prediction under actual load).With the spherical surface fitting algorithm, the optimized root mean square (RMS) value of the mirror's deformed surface was 1.4 nm, which was lower than one tenth of the permissible value. So the design requirements of supporting the primary mirror were met in this large aperture schlieren system.At last, the structural schemes of primary mirror, minor mirror, source and imaging system, optical window, appearance structure and mobile platform were analyzed. Concrete structural design and product's types are given. By means of the computer aided design technique, engineering drawings and stereograms of the device are given. A high performance schlieren system is obtained which meets the requirements of opto-mechanic design, beauty and operability.