Pressure distribution on the sidewall at zero leakage . Heat transfer distribution on the sidewall at zero leakageAerothermal Investigations on Turbine Endwalls and Blades
In the context of work package 3 of the framework V project AITEB-1 intensive studies of the flow field and heat transfer at the end wall region of a nozzle guide vane with additional presence of leakage effects were performed. Due to the necessity of a working clearance between the shroud of a rotor and the turbine casing, fluid is leaking through this clearance and affects the flow field in the downstream stator.
The accurate prediction of the distribution of leakage air as well as its influence on the surface heat transfer at the sidewall and blade is therefore important for the understanding of this flow region and the resulting losses. The tasks to be done at DLR Göttingen were: The investigation of the 3D-flow field and heat transfer in the endwall region of a turbine blade with different kinds of leakage air in front of the blade and with realistic (elevated) turbulence intensities.
The experiments were performed in the Low Speed Cascade Tunnel (NGG). which was recently dedicated to that task only. Three blades with a chord length of 200mm are arranged as a straight cascade, whereby the middle blade was investigated, only. Blades and endwall are smoothly connected by a fillet. The meridional flow path is diverging from inlet to exit.
All investigations were performed at a downstream Mach number of 0.523. The measurements were carried out with and without a turbulence generator, whereby inlet turbulence levels higher than 10% were achieved. The turbulence generator consists of a grid of perforated rectangular rods with the possibility of up- and downstream ejection of compressed air. The influence of the leakage was simulated with the help of a leakage gap which is placed in the edge of a 4mm backward facing step 20mm upstream of the cascade. Four leakage gap geometries with different blowing angles can be assembled in the test section.
The test surface (blade up to half height, fillet radius and endwall) are covered with electrically heated foils which generate a constant heat flux. Thermographic images were taken by an infrared camera. Additional thermocouples were used to determine a possible offset of the camera, whereas conduction losses to the rear side of the endwall were measured by heat flux sensors.
Test schedule:
The obtained experimental data are used as a data base for CFD calculations to improve the numerical procedures for future developments of turbo machines.
Results of investigations at DLR in the course of the AITEB-1-task can be found in following publication: Rehder, H.-J., Dannhauer, A.:Experimental Investigation of Turbine Leakage Flows on the 3D Flow Field and End Wall Heat Transfer ASME Technical paper GT2006-90173, 2006
The intention of the AITEB-1 project and a description of the work packages are to be found on following Web page: http://www.aiteb.tu-berlin.de
Authors: Fritz Kost, Hans-Jürgen Rehder, Axel Dannhauer