A new test facility for probe calibration offering independent variation of Mach and Reynolds number

Kurzfassung

At DLR, Göttingen, a new facility for probe calibration was built where dried air is driven by two compressors forming a closed circuit system with a free jet test section. Mach number and Reynolds number are the parameters to be varied while the total temperature is kept constant at T0 = 298K (25°C). The Mach number covers the range from Ma = 0.3 to 1.6 and will be extended down to Ma = 0.2 and up to 1.8 when the some modifications in the circuit will be installed. Variation of the Reynolds number is possible via the total pressure which can range from p0 = 30kPa up to 300kPa. There are different axisymmetric nozzles with an exit diameter up to 50 mm to achieve different Mach numbers. First a convergent nozzle covers the subsonic range, second a slotted nozzle is used within the transonic range and third three Laval nozzles are available for supersonic Mach numbers (Ma = 1.4, 1.5 and 1.6). The orientation of the probe head positioned downstream of the exit plane on the centre line of the nozzle flow can be varied from -22° up to +22° for both the angle of attack and the yaw angle using stepping motors. Data acquisition is done by means of a PSI-module (for the most important pressures) and a SIMATIC operating system from Siemens, while the automatic data collection and a first evaluation is done using a software based on LabVIEW. First measurements of the jet quality at different distances from the nozzle exit plane showed that the flow field is well suited for probe calibrations. Then two probes, a pyramid probe to be used in 3D flow fields and a wedge type probe to be used in 2D flow fields were calibrated. These results were already applied when wake traverses were performed in the Wind Tunnel for Straight Cascades (EGG) at DLR, Göttingen. The technical set up of the wind tunnel, first measurements concerning the flow quality and some results of probe calibration will be presented.