Oil and smoke flow visualization on airfoils at low Reynolds number:
- E387 with oil flow viz at a Reynolds number of 350,000 and angle of attack of 2 deg in the UIUC tunnel: We start by spraying an oil mix onto the model (see Vol 3 above for more details). Under a black light the sprayed-on oil has an orange-peel textured look. Once in the tunnel for ~15 mins, the laminar flow smoothly streaks the oil, until point A where laminar separation starts. Beyond this point and inside the bubble, there is very little flow and the oil does not change; it keeps the orange-peel textured look. At reattachment (point B) which is quite unsteady and vigorous, the flow impinges on the surface and creates high shear stress that scours away the oil. It moves some oil upstream and some oil downstream as the downflow "splashes" onto the surface effectively creating a "continental divide" defined by a very fine dividing line. The oil moving upstream pools into what we call the "oil accumulation line," while the oil going downstream moves towards the trailing edge.
- Smoke flow visualization of a laminar separation bubble on the Eppler 387 airfoil at a chord Reynolds number of 100,000 and 2 deg angle of attack. Only a section of the airfoil is shown. Photo courtesy of Greg Cole and Prof. Mueller, University of Notre Dame. If you use this photo, please acknowledge Greg Cole and Prof. Mueller as the source.
- Low Reynolds number oil flow visualization on a Formula 1 chassis.