Surface Dye Flow Visualization: A Qualitative Method to Observe Streakline Patterns in Supersonic Flow

1. Observing streaklines in supersonic flow
   1. Mix the fluorescent dye powder and mineral oil in a plastic bowl. Add small amounts of mineral oil to the dye in increments, mixing continuously until a semi-viscous mixture is obtained. The mixture should not be runny.
   2. Mount the sting above the supersonic wind tunnel test chamber and lock it into place. A blow-down supersonic wind tunnel with a 6 in x 4 in test section and an operating Mach number range of 1.5 to 4 was used in this demonstration, as shown in Figure 1. The Mach number is varied by adjusting the block setting (changing the area ratio of the test section).
   3. Screw the 2D wedge model onto the sting mount and fix the direction of the wedge such that the wedge surface is facing the transparent sidewalls of the wind tunnel test section. All models are shown in Figure 2.
   4. Use a paintbrush to apply a sufficient amount of the dye mixture onto the model. Ensure that the dye does not drip off of the model. See Figure 3 for reference.
   5. Adjust the block setting for the desired free-stream Mach number.
   6. Close and secure the wind tunnel panels.
   7. Run the wind tunnel for 6 seconds.
   8. After the run is complete, shine a UV light onto the model to illuminate the dye. Capture the streakline image with a camera.
   9. Adjust the angle of attack or Mach number according to the test matrix listed in Table 1 for model and repeat steps 1.4 - 1.9.
   10. Repeat steps 1.3 - 1.9 for all models listed in Table 1.
   11. When all models have been tested, shut down the wind tunnel, and dismantle the set-up.

Figure 1. Blow-down supersonic wind tunnel.

Figure 2. Wind tunnel models (left to right) 2D wedge, 3D wedge, cone, blunt nose body, sphere, and missile.

Table 1. Test Matrix.

Model	Angle of Attack (q) or Mach Number (M) setting
2D 10° Wedge	θ = 0, 12, and -12°
3D 10° Wedge	θ = 0, 12, and -12°
Cone	θ = 0, 13, and -13°
Blunt Nose Body	θ = 0, 11, and -11°
Missile	θ = 0 and 11°
Sphere	M = 2, 2.5, and 3

Figure 3. Representative image of fluorescent dye painted on the 2D wedge.