Question 1

What is dye flow visualization and how does it work?

Accepted Answer

Dye flow visualization coats a body with a semi-viscous mixture of fluorescent dye particles and mineral oil to observe surface flow patterns. The highly viscous oil maintains flow patterns on the body surface, while fluorescent dye becomes visible under UV light. This cost-effective technique provides qualitative images of surface flow, including laminar bubbles, boundary layer transitions, and flow separation.

Question 2

What is a streakline and what does it reveal about flow?

Accepted Answer

A streakline is the line joining all dyed particles passing through a point or area, visible when images are captured with prolonged exposure. In supersonic flow, streaklines identify flow separation points, shock formation, and flow movement across surfaces. Smooth streaklines indicate attached flow, while clumped, brighter dye regions reveal flow separation zones.

Question 3

How does Mach number affect flow separation on a sphere?

Accepted Answer

As Mach number increases in supersonic flow, the separation point moves toward the aft of the sphere, showing decreasing flow separation. Higher velocity flows have greater momentum, helping fluid overcome adverse pressure gradients and achieve higher flow attachment. This effect demonstrates how increased speed enhances flow stability on curved surfaces.

Question 4

What flow features can be identified using streakline patterns?

Accepted Answer

Streakline patterns reveal multiple flow features including attached flow regions shown as smooth streaklines, flow separation indicated by coalesced dye, shock waves marked by thin bright curves, and surface deformities causing streakline disturbance. These patterns help researchers understand complex aerodynamic behavior around bodies in supersonic conditions.

Question 5

How does angle of attack influence streakline patterns on a wedge?

Accepted Answer

At zero angle of attack, wedge streaklines show uniform flow except at surface deformities. At positive angles, flow deflects upward along the surface, while negative angles produce downward deflection. These directional changes in streaklines reveal how angle of attack alters pressure distribution and flow direction on aerodynamic surfaces.

Question 6

What are the differences between surface and off-the-surface flow visualization?

Accepted Answer

Surface flow visualization coats the body with dye to study surface flow, making it invasive but simple and cost-effective. Off-the-surface techniques like schlieren imaging and particle image velocimetry determine flow characteristics around the body without contact, providing quantitative data but requiring expensive, complex equipment setup.

Question 7

How do shock waves appear in dye flow visualization on missile fins?

Accepted Answer

Shock waves appear as thin bright curves on the body surface, visible through coalesced dye patterns. On missile fins, a bow shock forms at the leading edge of the central fin, marked by the dye shape. The shock location and intensity change with angle of attack, revealing how supersonic flow compresses and deflects around the fin geometry.

Modello	Impostazione angolo di attacco (q) o numero di Mach (M)
Cuneo 2D 10°	θ = 0, 12 e -12°
Cuneo 3D 10°	θ = 0, 12 e -12°
Cono	θ = 0, 13 e -13°
Corpo del naso smussato	θ = 0, 11 e -11°
Missile	θ = 0 e 11°
Sfera	M = 2, 2,5 e 3

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