Abstract

It is well known that the flow in turbomachinery blade channels is inherently non-stationary. It is especially true for the multistage machines where periodic unsteady wakes generated by the preceding row of blades flow through the blade channels and influence strongly the development of the boundary layer causing premature transition and subsequently increase of the local shear stresses and the convective heat transfer rates. Since many years at the Institute of Fluid-Flow Machinery, Gdańsk, the investigations of laminar-turbulent transition have been carried out. These investigations have been made in the subsonic wind tunnel for the flat plate without and with heat transfer (cold and heated surface of the plate) for the case of natural and induced transition in the boundary layer on the plate (low level of turbulence in the outside flow and with wakes). The local skin friction and local Stanton number for these different flow conditions are determined and the velocity and temperature fluctuations in the boundary layer are measured. The non-stationary characteristics of flow in boundary layer are also determined. On the basis of these measurements the experimental correlation for natural and induced boundary layer transition is proposed and the three parameter Weibull distribution for the intermittency factor put forward. Furthermore, the Reynolds analogy for the induced and natural transition in the laminar and turbulent regions of boundary layer is stated.