Flow Visualisation

Oil Flows

One of the most powerful and successful flow visualisation techniques available today is the oil flow.

The model is coated with coloured oils which flow under friction with the air flow when the wind is turned on.

High quality photographic stills and videos of the model from multiple view points are recorded during the test for subsequent analysis.

The animation shows the development of a shockwave over the ARA in-house reference model which is used to perform regular checks on the tunnel.

Shockwaves are clearly visible for two reasons – first, the direction of the pattern changes sharply across a shock – and second, oil collects underneath shockwaves making the line of the shock even clearer.

Wool Tufts

A simple yet very useful technique is to attach wool tufts to the surface of the model in regions where flow quality needs to be investigated. Regions of separated (or disturbed) flow can be readily distinguished by how the wool tufts move. Photographic stills and videos of the model are recorded during the test for subsequent analysis.

Sublimation

Performance testing usually requires transition bands to be applied to the model to force the boundary layer to transition from laminar to turbulent as it would at full scale.

A sublimation test is used to ensure that the transition bands are working properly. The sublimate Acenaphthene is applied to the model. With the wind turned on, the turbulent regions of the boundary layer will remove the sublimate much faster than the laminar regions. After a few minutes, the difference between the two regions is clearly visible.