Schlieren photos of transonic turbine cascade flow(more Schlieren photos)
The straight cascade tunnel at DLR Göttingen is of the blowdown type with atmospheric inlet. A sketch of the main flow path of the windtunnel is shown in the following figure.
The ambient air first enters a silica-gel dryer, passes subsequently two screens and a honeycomb flow straightener and enters the cascade after a contraction. Downstream of the cascade the flow passes an adjustable diffuser and the main butterfly valve and enters at last a huge vacuum vessel (10000 m³). This vessel is evacuated by two sets of sliding-vane vacuum pumps.
The inlet total pressure of the cascade is equal to the ambient pressure. Inlet total pressure and temperature are measured in the settling chamber in front of the contraction. The Reynolds number cannot be varied independently, but is a function of the Mach number. Each cascade is mounted between two circular disks establishing the side walls of the flow channel. The inlet angle is adjusted by turning this assembly. The test section dimensions are 400 mm × 125 mm, allowing the cascades to consist of 8 to 20 blades depending on the upstream flow angle and the blade gap.
The flow downstream of the cascade is not guided. The downstream static pressure and therefore the Mach number is adjusted by the plenum pressure (i.e. setting of the diffuser).
Some wind tunnel performance data are listed below:
The testing capabilities comprise conventional pressure distribution measurements on the blade or endwall surfaces and pressure probe measurements in the wake and profile boundary layer in order to gain information on the characteristic cascade values like flow angles and losses and on the boundary layer characteristics. Furthermore Laser velocimetry (L2F, PIV), measurements with heated thin films and with heat transfer sensors are available as additional measurement tools at the windtunnel. Flow visualization is provided by means of oil flow patterns and the Schlieren technique. To simulate coolant ejection there is an additional supply of air and/or CO2.
Measurements of heat transfer and film cooling effectiveness are done by surface bound foils combining heating and temperature measurement or by using heater foils together with an infrared camera. Some experimental results from investigations at EGG and RGG are contained in the following publication:Kost, F., Gieß, P.-A.: Experimental Turbine Research at DLR Goettingen Journal of the Gas Turbine Society of Japan, Vol. 32, No. 6, Nov. 2004