Flow Visualisation

Of extreme importance before attempting to analyse an aerodynamic flow is to understand the behaviour of the flow. This can be done by making the flow visible. The introduction of smoke lines to follow the airflow, the addition of surface tufts, oils or sensitive pigments are all methods to allow the investigator to "see" what is happening.

These visualisations can then be used to infer the nature of the flow in terms of circulation, vortex effects, flow separations and turbulence. This allows appropriate choices or simplifications of the equations used to solve the flow. Without such visualisation, incorrect assumptions will lead to the solution of flow cases that may not be directly relevant to the problem being considered and hence may lead to large errors.

Some examples of flow visualisation are shown below.

1. Aerofoil section flow.

Smoke visualistion of flow around two dimensional aerofoil section. Note: change in smokeline curvature and spacing as the angle increases. slight turbulence on upper surface even at low angles when flow is attached. total separation of flow from upper surface at 15 degrees angle of attack, indicating stall.

2. Vortex Wing Tip Flow.

Smoke visualistion of flow around three dimensional wing showing tip formation of trailing vortex flow. Note: Smoke lines spiral around wing tip forming large trailing vortex. Vortex size increases as angle of attack is increased.

3. Delta Wing Vortex Pair.

Smoke visualistion of flow around three dimensional delta wing showing surface vorticies formed from leading edge separation. Note: Smoke lines spiral from leading edge into a large pair of vorticies sitting over top surface. Location of vortex core running over surface behind leading edge.

4. Aerodynamically Designed Car.

Smoke visualistion of flow around three dimensional sports car showing centerline flow. Note: Position of leading stagnation point. Position of trailing separation point. Size of separated wake region.

5. Square Edged Truck.

Smoke visualistion of flow around three dimensional truck showing centerline flow. Note: Position ofleading stagnation point. Second stagnation point on windscreen. Position of trailing separation point. Size of separated wake region.

6. Car, Caravan Combination.

Smoke visualistion of flow around three dimensional car and caravan model showing centerline flow. Note: Position ofleading stagnation point. Second stagnation point on caravan. Position of trailing separation point. Size of separated wake region.