The half-model measuring section is a half-model channel which works according to the so-called "suck down" principle.
In this operating mode, dried air is sucked from a reservoir into a vacuum system. The strong reduction in temperature as a result of the expansion into vacuum makes it necessary to dry the air. The dried air is accelerated to supersonic speeds by means of a fast-expanding "short expansion" corner laval nozzle with a fixed nozzle contour corresponding to the respective nominal power number.
For variation of the number of flow machines, interchangeable nozzles from M = 1.5 - 3.0 with DM = 0.25 are available. According to the design of the duct as a half model measuring section, the duct bottom lies exactly in the plane of symmetry of the nozzle, resulting in a measuring chamber cross-section of 200 x 150 mm. As a result, a very long, turbulent flat-plate boundary layer is formed from the narrowest cross-section of the nozzle, which is perfectly suitable for the investigation of impact-interface interaction problems.
In addition, the wind tunnel is equipped with a holder for inserting full models into the free flow. Optical accessibility is provided by windows in the channel side walls. The optical windows with a diameter of ø = 200 mm are installed in such a way that the centre of the window falls exactly onto the end of the nozzle. As a result of the way the duct works, the reservoir state is determined by the atmospheric state in the air reservoir, therefore the unit Reynolds number R/m and Mach number M can only be varied in a coupled manner.