Refractive Index Matched Tunnel

• Index matched tunnel operated with cosmetic white oil (with almost the same kinematic viscosity of air at the operating temperature);
• Dimensions of test-section: 0.6 m x 0.45 m x 2.5 m (w x h x l), Flow speed: 0 - 4.8 m/s, Turbulence intensity: < 0.1 %;
• Measurement systems: 3 component LDA, PIV, Stereo PIV, hot-film sensors;
• Test objects made of quartz glass, to resolve internal & near wall;
• Broad variety of application areas, especially flow with complex geometries

The Institute of Fluid Mechanics at FAU Erlangen-Nuernberg possesses a novel test facility which enables various measurements that were previously impossible. The special feature of the new test facility is the use of cosmetic white oil as the working fluid, which has an optical refractive index identical to that of quartz glass. This prevents refraction at the surface of any quarz object inserted into the flow. As a result, investigations of the flow in the immediate vicinity of the surface of complex objects by optical measurement techniques become feasible.

Major foci of the research conducted in this facility are turbulence and transition. Due to the relatively large dimensions of the tunnel and the achieved high flow rates, the applications range from basic research to practice-relevant model tests.

The first studies conducted in this facility (for AIRBUS) were on the transition between laminar and turbulent flow on a flat plate. The obtained data are used for validating DNS on the same problem. Furthermore, many other types of boundary layer flows at high Reynolds numbers can be studied.  Thereby, the main focus lies on flows through complex structures, like heat exchangers or nuclear fuel rods. Already, the facility has been a part of collaborative activities on the development of surface sensors.