Aerodynamics Lecture 2 Notes

Introduction

• Focus of Last Lecture: Differences in the study of aerodynamics vs. fluid mechanics.
• Today's Topic: In-depth examination of flow variables and their force generation on objects.

Key Flow Variables in Aerodynamics

• Flow Variables: Found in conservation equations; contribute to object forcing.
• Main Variables:
  • Velocity
  • Pressure
  • Viscosity
  • Density
  • Temperature
• Variable Use Cases:
  • Incompressible & inviscid flow: Velocity and pressure are predominant.
  • Incompressible but viscous flow: Viscosity important in boundary layers (Navier-Stokes equations).
  • Compressible & viscous flow: Complex, requires simulations and measurements.

Detailed Examination of Variables

Velocity

• Representation: u, v, w for x, y, z directions.
• Units: Distance/time.
• Perspective: Eulerian (fixed observation point).
• Nature: Macroscopic, statistical average of molecule movement.

Pressure

• Representation: Capital P.
• Units: Force/area.
• Explanation: Force from fluid molecules striking a surface.
• Pressure Difference: Causes net force, appears in momentum equations.

Density

• Representation: Greek letter ρ.
• Units: Mass/volume.
• Concept: Number of molecules in a volume.
• Density Gradient: Leads to forces due to molecular collisions.

Temperature

• Representation: T or sometimes theta.
• Nature: Dimensionless, in Kelvin or Celsius.
• Relationship to Kinetic Energy: Average kinetic energy of molecules.
• Influence on Force: Changes across surfaces can result in force differences.
• Ideal Gas Law: Relates pressure, density, and temperature.

Viscosity

• Dynamic Viscosity: Greek letter μ, units of force*time/area.
• Kinematic Viscosity: ν, dynamic viscosity/density.
• Role: Fluid friction, important in flows with velocity gradients.

Conclusion

• Summary:
  • Reviewed five main variables and their role in force generation.
  • Importance of both macroscopic and microscopic perspectives.
• Next Lecture Preview: Understanding body forces from these variables in aerodynamics.