Oblique shock wave

Definition

An oblique shock wave is a type of shock wave that occurs when a supersonic flow encounters a surface at an angle, causing a rapid change in flow properties such as pressure, temperature, and density. Unlike normal shock waves, which are perpendicular to the flow direction, oblique shocks are inclined to the flow direction and are often associated with the aerodynamic shapes of objects moving at high speeds.

5 Must Know Facts For Your Next Test

1. Oblique shock waves can only occur in supersonic flows and are typically formed at angles when fluid passes over a wedge or similar aerodynamic shape.
2. The strength of an oblique shock wave depends on the angle of incidence and the Mach number of the incoming flow; sharper angles lead to stronger shocks.
3. Flow behind an oblique shock wave can remain supersonic, unlike behind a normal shock where it becomes subsonic.
4. Oblique shocks are characterized by changes in pressure, temperature, and density, which can be calculated using specific relations involving the upstream Mach number and the shock angle.
5. In supersonic jets, oblique shocks can play a significant role in mixing and affecting performance characteristics of engines and other aerodynamic surfaces.

Review Questions

• How do oblique shock waves differ from normal shock waves in terms of their characteristics and effects on flow?
  • Oblique shock waves differ from normal shock waves primarily in their orientation and the resulting flow behavior. Normal shocks are perpendicular to the flow direction and cause an immediate transition from supersonic to subsonic flow, while oblique shocks are inclined to the flow direction, allowing the downstream flow to potentially remain supersonic. This difference affects how pressure, temperature, and density change across each type of shock.
• Discuss how the angle of an oblique shock wave influences its strength and the conditions of the downstream flow.
  • The angle at which an oblique shock wave forms significantly influences its strength. A larger angle leads to stronger shocks, resulting in greater increases in pressure and temperature across the wave. Additionally, depending on the Mach number of the incoming flow and the angle, the downstream flow can remain supersonic or become subsonic, impacting the overall performance of aerodynamic surfaces.
• Evaluate the implications of oblique shock waves on supersonic aircraft design and performance.
  • Oblique shock waves have critical implications for supersonic aircraft design and performance. Understanding how these shocks interact with various shapes helps engineers optimize designs for reduced drag and enhanced stability at high speeds. The ability to predict how oblique shocks influence flow properties allows for better fuel efficiency and performance management during flight. Moreover, managing these shocks is essential to prevent adverse effects like buffet or loss of control at transonic speeds.

Related terms

Normal shock wave: A normal shock wave is a shock wave that occurs when supersonic flow is suddenly compressed to subsonic speeds, resulting in an increase in pressure and temperature across the wave.

Mach number:

The Mach number is a dimensionless quantity representing the ratio of the speed of an object to the speed of sound in the surrounding medium, which determines whether the flow is subsonic, transonic, or supersonic.

Prandtl-Glauert transformation: The Prandtl-Glauert transformation is a mathematical relationship used to convert between incompressible and compressible flow variables, crucial for analyzing flow behavior near shock waves.