Determination of the NTS-factor for the DNW-NWB

Kurzfassung

The Low-Speed Wind Tunnel NWB operated by the foundation German-Dutch Wind Tunnels (DNW) offers as laminar wind tunnel with low turbulence level excellent options to verify the performance parameters of specifically developed laminar airfoils. These airfoils are applied to light weight aircrafts respectively gliders, wind power facilities, etc. After the refurbishment of the NWB to an aero-acoustic wind tunnel in 2009/2010 the commissioning tests turned out that the excellent aerodynamic characteristics of DNW-NWB were kept. Within this framework turbulence levels were checked and a calibration of the wind tunnel concerning the limit-N-factors NTS for Tollmien-Schlichting waves and NQS for crossflow vortices was conducted. To determine the limit-NTS-factor wind tunnel tests with a two-dimensional laminar airfoil were performed. The flow conditions of the boundary layers on the upper and lower side of the airfoil were observed with infrared cameras, so that the location of transition from laminar to turbulent boundary layer could be determined. Additionally the pressure distribution was measured at an intersection line on the surface of the airfoil. The resulting limit-NTS-factor of the wind tunnel was compared with data from free flight tests to get a statement about the validation to transmit measured lift-drag-polars at DNW-NWB to free flight conditions and that the excellent flow quality as laminar wind tunnel was retained over the refurbishment to an aero-acoustic wind tunnel.