Andreas Heselhaus

A New Test Rig for Film Cooling Experiments on Turbine Endwalls

Endwall film cooling has been subject to many investigations over the past years. Since the coolant is injected into the wall boundary layer, it is primarily affected by the complex three-dimensional flow structure which is developed near the endwall inside turbine bladings. Little information can be found in the literature about how load variation affects endwall film cooling. As the secondary flow, driven by the circumferential and radial pressure gradient, is intensified with higher cascade load, strong interaction of the coolant injected in the near-wall cross flow is expected. Therefore, an airfoil cascade rig has been designed with an endwall cooling configuration containing multiple rows of expanded film holes. The film rows are combined to groups which can be supplied with different types of coolant gas through individual plenum cavities. Additionally, basic film cooling experiments have been conducted on a flat surface to validate the temperature measurement technique on results available in the literature. Film cooling injection is established through a row of 7 cylindrical holes inclined streamwise at 35° for a blowing rate ranging from 0.35 to 1.5. Experiments are conducted at constant main flow conditions at ReD = 4200 and at low turbulence level Tu = 1.5% with CO2 (DR = 1.37) and Air (DR = 0.9) used as coolant gas. Centerline effectiveness for selected blowing rates is compared to results available from previous literature.Copyright

Investigations at the Over-Tip Casing of a High Pressure Turbine Including Off-Design Conditions and Heat Transfer Correlations

Turbine inlet temperature is reaching values far above acceptable material temperatures. Thus the thermally highly loaded components have to be cooled intensively. One of the most thermally loaded components is the over-tip casing. In recent years research on heat transfer at the over-tip casing received a big boost by availability of faster and more accurate measurement techniques. So far the investigations are limited to design condition, no information is available at off-design conditions. This paper aims to contribute to a better understanding of the major phenomena governing heat transfer in the over-tip casing region, including the influence of different operating conditions. Using an HP-turbine at different flow conditions, extended measurements were performed at DLR’s wind tunnel for Rotating Cascades (RGG), Gottingen, including the flow field in the tip gap and close to the over-tip casing. The Nusselt correlation for a flat plate was investigated for it’s applicability to the over-tip casing. The influence of the incidence angle on the heat transfer levels at the upstream part of the over-tip casing is investigated. Also the influence of the rotational speed on tip-leakage flow and casing heat transfer will be discussed. These results are compared to flat plate heat transfer correlations for design and off-design conditions.Copyright