In this paper, a colorful schlieren system without any protecting windows was introduced which results in that the 1.2m primary mirror would directly be confronted with the pressure and temperature variation from the wind tunnel test. To achieve a good schlieren image under the wind tunnel test working condition of a wide temperature fluctuation range (-10° to 50°) as well as a pressure (2kPa), a new flexible support method of the primary mirror was strategically designed. A finite element model of the primary mirror combined with its supporting structures was built up to approach the surface figure of the primary mirror under the complex working conditions as gravity, temperature variation, and pressure. The schlieren images due to the change of the primary mirror surface figure were simulated by Light-tools software. It was found that the temperature changing and pressure would lead to the variation of the surface figure of the primary mirror surface figure and therefore, results in the changing of the quality of simulated schlieren images.
Schlieren photography is a visual process to display the flow of fluids of varying density. It is widely used in wind tunnel tests to photograph the flow of air around objects. To achieve schlieren images with high sensitivity and high resolution, and satisfy the requirements of the large-scale wind tunnel tests, it is urgent to develop schlieren photographers with large aperture primary mirrors. However, the application of large aperture primary mirrors may bring many challenges in the design of the schlieren system. First, the surface figure of large aperture primary mirrors is difficult to control so that the support structure may need more strategical design. Second, because the schlieren system works under some severe environments of the wind tunnel test including the air disturbance, wind-induced ground vibration and high ambient pressure, it has to withstand serious instability risks to ensure a good schlieren image quality. In this work, the current status of the development in the large aperture schlieren systems is reviewed. Several advanced methods, for example, active damping control technique, focal spot monitoring technique, 18-points whilffletree support technique, etc.., are introduced to deal with the challenges of the large aperture schlieren system. This work aims at improving the technical development of large aperture schlieren photographer, which may contribute to the acquisition of the high sensitive and high resolution schlieren images and the improvement of the testing capability in wind tunnel experiments.