Influence of Chord Length and Inlet Boundary Layer on the Secondary Losses of Turbine Blades
Helmut Sauer, Robin Schmidt, Konrad Vogeler
abstract:
In the present paper results concerning the influence of chord length and inlet boundary layer thickness on the endwall loss of a linear turbine cascade are discussed. The investigations were performed in a low speed cascade tunnel using the turbine profile T40. The turning of 90 and 70 deg, the velocity ratio in the cascade from 1.0 to 3.5 as well as the chord length of 100, 200 and 300 mm were specified. In a measurement distance of one chord behind the cascade in mainflow direction, an approximate proportionality of endwall loss and chord was observed in a wide range of velocity ratios. At small measurement distances (e.g. s2/l= 0.4), this proportionality does not exist. If a part of the flow path within the cascade is approximately incorporated, a proportionality to the chord at small measurement distances can be obtained, too. Then the magnitude of the endwall loss mainly depends on the distance in main flow direction. At velocity ratios near 1.0, the influence of the chord decreases rapidly, while at a velocity ratio of 1.0, the endwall loss is independent of the chord. By varying the inlet boundary layer thickness no correlation of displacement thickness and endwall loss was achieved. A calculation method according to the modified integral equation by van Driest delivers the wall shear stress. Its influence on the endwall loss was analyzed.
reference:
Sauer, H., Schmidt, R., Vogeler, K., 2011:
"Influence of Chord Length and Inlet Boundary Layer on the Secondary Losses of Turbine Blades",
ASME Journal of Turbomachinery, Vol. 134, Issue 1, pp. 011015-1 - 011015-10.