The Große Wasserkanal Braunschweig (Large Watertunnel Braunschweig) is a joint project of the ISM and the Institute of Jet Propulsion and Turbomachinery. Designed as a closed-circuit tunnel it will be used for research on high-lift configurations, fan-intakes, aircraft configurations (incl. wake vortices) and interior fan flows. The dimensions of the tunnel are ca. 14'000mm x 6000mm x 4000 mm, the calculated weigth is 120 tons including 60 tons of water. The test section has a cross-section of 1000mm by 1000mm with a working length of 6000mm. The maximum flow velocity in the test section is 6m/s. In combination with the low viscosity of water (factor 15 in comparison to air), which can be further controlled by heating, Reynolds-numbers of up to 2.5x10e6 on typical airfoils(c=0.4m) are possible. To avoid cavitation on tested models and in the pump the tunnel can be pressurized to twice the atmospheric pressure.
The low flow velocity is a major advantage for precise time-resolved field-measuring techniques (especially PIV) at these high Reynolds numbers.
- closed circuit, pressurized, heated
- contraction 5.3:1
- test section 1000mm x 1000mm x 6000mm
- max. velocity in test section: 6 m/s
- Re up to 2.5x10e6 on 2D-airfoils
- motor power: 160 kW
- blade wheel diameter of axial pump: 1.52m
- turbulence (design) < 0.2 %
- max. pressure against atmosphere: 2bar
- max. temperature: 40°C
- 2 screens in wide-angle diffusor, 2 turbulence screens, flow straightener, all stainless steel
The welded construction of the tunnel contains steel of sheet thickness ranging from 10mm to 15mm. A lot of stiffeners help to stand the loads in pressurized operation. The turning vanes are made from cast iron and installed in the corner frames. The wetted surfaces of all 16 modules of the tunnel are coated with a durable two-component epoxy-resin to avoid corrosion. The outside of the tunnel is covered with elastomeric insulation to minimize heat loss. The complete fluidmechanical design and large parts of the construction including preliminary design for strength were carried out at the ISM.
The test section is completely made from stainless steel. The main frame contains several different wall segments, all interchangeable. In the basic layout one third of the segments is made of security glass to allow the use of optical measurement techniques, especially PIV. One sidewindow is designed as door for easy access to the testsection.
The axial pump has a blade wheel diameter of 1.52m. A 4-pole three phase motor with frequency control and an output of 160kW drives the pump via a reduction gear unit. Since motor and gear are located outside the tunnel, the pump shaft connects the blade wheel with the drivetrain trough the second turning corner, where also the shaft-sealing is located.
The basic instrumentation of the tunnel contains sensors to measure the flow velocity in the test section, several temperature sensors to detect layering and fill level detectors to control filling and dumping. The tunnel will be prepared for automated speed and Reynolds number control. A modular pressurelogger with 64 channels has been built for scanning pressure distributions of airfoil models. Further extensions of the measuring equipment will be installed according to planned projects. For easy visualization of the flow a constant laser is available.
The tunnel was completed in October 2010. Following the acceptance procedure and the validation, the tunnel has been used extensively within the collaborative research program SFB880, researching a high-lift configuration with blown flap.