LML boundary layer wind tunnel

• High Reynolds number turbulent boundary layer at large scale;
• Flow resolvable over all scales by current measurement technology;
• Advanced Stereo and Tomo PIV expertise of the operating team;
• Both flat plate, favorable and adverse pressure gradient boundary layer available;
• Study of boundary layer separation possible.

The facility is unique in Europe in terms of size and Reynolds number and in terms of the optical measurement technology developed around it.

The LML boundary layer wind tunnel was built in 1993. The aim was to build a modern world class facility to enable the study of turbulent boundary layers at high Reynolds number with the most advanced measurement techniques. For that purpose, the wind tunnel had a unique 20 m long test section, to allow thick boundary layers to develop (boundary layer thickness is about 30 cm at the end of the test section, compared to a few mm on an aircraft). This allows of course very detailed near wall measurements. Both velocity (±1%) and temperature (±0.2C) are regulated to allow extensive and precise hot wire measurements. It is also made fully transparent in the last 5 m of the test section, to allow easy setting of any kind of optical measurement.

The present characteristics of the facility are:

• Free stream velocity 3 to 10 m/s
• Maximum boundary layer thickness 30 cm
• Reynolds number range 8 000 to 20 000 based on momentum thickness.

Different models are available to allow studies on boundary layers under pressure gradient (fig. 2). Multiple hot wire anemometry, hot wire rakes, stereo and Tomo PIV, standard and high repetition PIV have been used extensively in this facility thanks to its unique optical accessibility.

The facility provides the following measurement equipment for use with the facility:

• Single and x wire anemometry with traversing system, fully automatized and coupled to the regulation of the velocity and temperature of the wind tunnel to ensure accurate measurement;
• Three high sensitivity microphones from B&K, conditioning electronics and data acquisition system;
• Six unsteady pressure transducers from Endevco, conditioning electronics and data acquisition system;
• Two stereoscopic PIV systems based on 2k x 2K Hamamatsu cameras at 4Hz;
• One tomo PIV system based on 2k x 2K Hamamatsu cameras at 4Hz;
• One high repetition Stereo PIV system based on 2 Phantom V9 cameras allowing 1000x1000  stereo PIV records at 1kHz with a field of view of 10x10 cm².