Wind Tunnel

  • Used to study the aerodynamic properties of an object in a stationary manner
  • Motion is simulated by moving air (fluid) around the object of interest
  • Properties measure in wind tunnel include pressures, forces, velocities, and vibrations
  • Wind tunnel studies are not 100% accurate
  • Wind tunnel pictorials:



Types of Wind Tunnels

  • A basic wind tunnel (open-circuit)
  • General Motors’ wind tunnel (close-circuit)

·  Open-circuit wind tunnels

  • Less expensive
  • Subject to ambient conditions
  • Require more power



·  Close-circuit wind tunnels

  • Avoids loss of return air’s momentum
  • Constant ambient conditions
  • Expensive



·  A wind tunnel can not always simulate road conditions, e.g.,

  • Ground effect
  • Tire rotation
  • Reynolds number (scale corrections)
  • Wall interference
  • Natural variations in ambient conditions


  • Challenges
    • Model size
      • The larger, the greater the wall effect
      • The smaller, the less accurate
    • Simulation of the moving road
    • Mounting of model and rotating wheels


  • Wall effect
  • Examples of wall effect corrections
  • Simulation of moving ground


Important issue about wind tunnel studies
  • Understanding the aerodynamic problem is more critical than sensitive instrumentation
  • Whatever works satisfactorily in the wind tunnel, will usually work well on the road
  • Scale model studies are usually too conservative, and the vehicle can be further optimized