In fluid dynamics and aerodynamics, a characteristic line is a curve that represents the path along which disturbances in a fluid flow propagate. The average slope of a characteristic line between two points, such as points nine and twelve, typically refers to the average rate of change of a certain property or variable along this curve as you move from point nine to point twelve. The specific property or variable being considered depends on the context and the problem at hand.
NOTE: No right-running waves cross the characteristic line between points 9 and 12. As a result, the characteristic line between points 9 and 12 is a straight line, along which 𝜃 is constant, that is, 𝜃12 = 𝜃8. The section of the wall contour between points 8 and 12 is approximated by a straight line with an average slope of,
- Average slope of characteristic line between points nine and twelve
- Angle between velocity to the below velocity at point eight (𝜃8) in rad
- Angle between velocity to the below velocity at point twelve (𝜃12) in rad