I think it might be this one:

http://web.archive.org/web/200006091.../aleg2a_hq.mov

It's not a glider, it's an ATL (Avion Très Léger), a light French two-seater single engine aircraft with V-tail. Probably filmed at Lille (France) where there is a vertical wind tunnel.

This video used to be op the ONERA (French aerodynamics laboratory) website, but I had to look it up on the internet archive.