Windtunnel

 

 

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