At the turbine department of the Institute of Propulsion Technology at DLR in Göttingen a turbine test facility is currently in operation, which was originally designed and built in 1971 for the investigation of the flow through rotating annular cascades, the so called Wind Tunnel for Rotating Cascades (RGG). Due to its unique features this facility was up to now well utilized by turbine stage investigations for industrial, national and international research projects.
Because of the rapid turbine development in recent years, the RGG does not cover all requirements from turbo machine industry and topics for future research projects. Measurements with modern single-stage high pressure turbines have shown, that important key and off-design operating points were close to the limitations of this test facility, some points could be set up only with compromises. As a result there is a need for a new test rig that is both capable of simulating the main flow parameters of future high-performance turbines (e.g. higher pressure ratios, more stages, extension to low pressure turbines etc.) and enough size to enable more detailed measurements during the experiments.
The Institute of Propulsion Technology will design and build up the new turbine test facility at DLR in Göttingen. This facility will be build up in two subsequent stages and starting its operation in 2013. The new rig, called Next Generation Turbine Test Facility (NG-Turb), will operate as a closed circuit with dry air as flow medium, allowing the independent setting of Mach- and Reynolds numbers. Reynolds numbers can be adjusted by varying the overall pressure or temperature level in the circuit. The flow medium is driven by a four stage radial gear compressor with a high pressure ratio and a broad performance map for small to very high volume flow, designed and manufactured by MAN Diesel & Turbo SE in Oberhausen.
Compressor performance data:
Compressor performance map
Turbine test section, 1st stage of completion
Turbine test section, 2nd stage of completion
Gear compressor (4 stages, radial)
Maximum pressure ratio
60 ÷ 230.000
Characteristic parameters of the turbine test section:
Number of stages
100.000 ÷ 1.000.000
Total inlet pressure
≈ 10 ÷ 200
≈ 300 ÷ 700
≈ 10 ÷ 12
Maximum mass flow
Minimum hub radius
Maximum casing radius (HPT)
Maximum casing radius (LPT)
Shaft power (HPT)
Shaft power (LPT)
A main feature of the NG-Turb will be the application of a combustor simulator in combination with a high pressure turbine. For such investigations the compressor air of the NG-Turb can be split into a cooled and an additional electrically heated line. Hot and cold air flow are then fed and mixed into combustion chamber like inserts in the test section in order to generate temperature profiles similar to the ones in the exit of combustors in real gas turbines.
In order to avoid major reconstruction times between individual experiments, the new turbine rig will have a very modular build up of the test section. The stators (vanes) of the turbine stages and the combustor simulator are installed rotatable so that "clocking" effects can be studied. Auxiliary compressors provide enough pressurized air to simulate coolant flow ejection at the turbine blades and the hub and casing wall of the annulus. A good spatial and optical accessibility allows the installation of extensive measurement techniques. In addition to standard techniques such as pneumatic probes, steady and unsteady pressures, thermocouples, etc., following techniques will be particularly employed:
Determination of steady and unsteady surface pressures by applying the Pressure Sensitive Paint
Heat transfer and cooling film effectiveness measurement techniques, in which surface temperatures are detected by infrared image cameras or the Temperature Sensitive Paint (TSP) Method
Data from measurements in rotating systems (e.g. steady and unsteady surface pressures on rotor blades) will be transmitted into the laboratory frame of reference applying a suitable telemetry system.
Turbine test rig, meridional section, 2nd stage of completion
Reynolds- and Mach number range of EGG when operated in a closed circuit
In future a much higher loading with transonic flow through the blade rows for low-pressure turbines in a jet engine is expected. In order to make the Wind Tunnel for Linear Cascades (EGG) furthermore applicable for the support of design processes for turbine blade profiles and detailed studies of simple models for high and low pressure turbines, its test section will additionally be connected to the new compressor unit. Due to the high compressor pressure ratio in combination with a closed circuit experiments with higher Mach numbers (e.g. for tip section blade profiles from steam turbines) and the independent variation of Mach and Reynolds number can then be performed at the EGG. In particular cascades with blade profiles from low pressure turbines can be studied under realistic engine conditions.