Don't know your school or company used schlieren apparatus, you tell you whether the practice experience of schlieren instrument works, do not use it, only know and not know it, now I'll use a simple words to tell you, how schlieren apparatus works.Schlieren instrument is a kind of using the index of refraction of light in different medium is different, the principle of the on the condition of airflow optical transpose.By optical flow, already use in modern aviation engineering.Joe burea aperture method is used in the schlieren apparatus operating principle.Don't know if this make you understand the working principle of schlieren apparatus.
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