An Improved Schlieren Apparatus

This paper describes an improved schlieren apparatus that forms two separate images of the test section simultaneously. One image indicates vertical density gradients; the other, horizontal density gradients. The determination of transient density fields is more accurate with this modified schlieren system than with the ordinary schlieren system taking two successive pictures. At present, this apparatus is being used to study the interaction between shock waves and boundary layers. the flow is not steady and schlieren pictures corresponding to two different knife edge orientations are desired, such pictures should be taken simultaneously to obtain comparable pictures. A device has been developed a t the Gas Turbine Laboratory of the Massachusetts Ins t i tu te of Technology for this purpose. Two pictures are taken simultaneously on a single negative. One of these