Colour Schlieren Visualisation

This technique using the light beam deflection by density gradients is a standard technique in flow visualisation used already since the mid of the 19^th century. We use a slight modification proposed in 1970 by G.S.Settles "A Four Colour Schlieren Technique with sensitivity in all directions", Tennessee Engineer, pp 4,5,7-9 (reprint in SPIE Milestone Series MS61, Selected papers on Schlieren optics, pp125-129). This approach combines the high sensitivity of a knife edge technique with a directional colour encoding.

GIF picture (260 KB)

This picture shows the principle setup used in the linear cascade at the Institute for Thermal Turbomachinery and Machine Dynamics. This type of Schlieren visualisation is used for all flow investigations in the transonic test rig. Here you see the Mach 1.2 flow through a VKI-LS59 profile (Projekt S6801)

MPEG video (126 KB)

This movie was recorded in a specially designed Mach 2 nozzle (flow from the right). Under continuos operation small sized particles can be fed into the flow to study material erosion and compare flow measurements (LDA, PIV) with numerical results for two phase flows (Project S6807). You see a truncated wedge with a fully developed shock system. Green: Positive density gradient from right to left (red opposite); Blue: positive density gradient from the upper part to the lower one (yellow opposite).