Application of the Rainbow Schlieren Method in Free Underexpanded Jets

An experimental investigation into free underexpanded jets is described. In this paper the experiment took the axis-symmetry unexpended jets as the object, used the typical "Z" schlieren system and replaced the edge with rainbow filter.The rainbow schlieren method is used to obtain measurements in underexpanded jets with nozzle pressure ratios ranging from 2.97 to 19.80. Obtaining the result of that the influence of pressure ratio on jet structure. This paper provides an operation method in the concrete and some useful reference for the rainbow schlieren technique.