137

20/6.1 x 105/12.0%

at this condition is 6.2 x 105. The boundary layer characteristics, including velocity distribution, velocity profile in the wall coordinates, and the wake characteristics, are measured at three different locations on the planel (X/Cx = —1.6) at a distance of half pitch from each other on the tip-endwall, as displayed in fig. 3.2.

In fig. 3.2 it shows that the velocity profile near the wall is very steep and assumes the power law with an index of 5.7, while the profile in the wall coordinates follows the log law of the wall. The boundary layer shape factor is 1.38 with a displacement thickness of 0.17cm. The solid line of turbulence intensity is used as an inlet condition in the numerical simulation.

In summary, the data shows that at normal condition, the boundary layer flow on the tip-endwall is uniform and turbulent, following the log law of the wall and the law of the wake, and the displacement thickness is typical of that in a gas turbine engine (1% of chord, Hodson and Dominy (1986)). Although the boundary layer thickness may have influence on the heat/mass transfer on the blade surface as suggested by Graziani et al. (1980), the experiment from Chan et al. (1994) showed that the inlet boundary layer thickness may not have significant effects on tip leakage flow and vortex. Therefore, the effects of inlet boundary layer thickness are not considered further in this study.

0 0

Post a comment