Unsteadytransitional mass transfer from blade surfaces

To study the effect of unsteady flow near the mid-span on the pressure side caused by the Taylor-Gortler vortices, the local standard deviation of Sherwood numbers along the pressure surface are plotted for different cases in fig. 4.3(a). We can find high variations in Sh after reattachment at Sp/C = 0.2 for the cases at different mainstream Reynolds numbers, showing that the flows are rather unstable due to the Taylor-Gortler vortices. For the high mainstream turbulence intensity case, the Sh' variation dies down from the leading edge and remains low afterwards, which indicates the flow becomes perhaps laminar near the leading edge and after separation and reattachment the Taylor-Gortler vortices do not appear in this case.

The effects of mainstream Reynolds number and turbulence intensity on the unsteady flow on the pressure surface can also be observed in fig. 4.4, where local Sh near the mid-span are plotted. The local distributions of Sh for the high mainstream turbulence case are alway smooth until close to the trailing edge (Sp/C > 1.0). For other cases with low mainstream turbulence intensity but different Reynolds numbers, the fluctuations of local Sh numbers are apparent, and the higher the mainstream Reynolds number, the earlier occurrence of the fluctuation, and the more irregular the fluctuations become further downstream.

On the suction side, Sh' are shown in fig. 4.3(b) along the blade surface in the curvilinear coordinate. For different mainstream Reynolds numbers, the variation becomes much higher near and after the transition (Ss/C ps 1.2). However, it seems the high mainstream turbulence intensity does not have an obvious effect on the variation Sh number until very near the trailing edge. Local fluctuations near the mid-span on the suction surface are displayed in fig. 4.5. For the higher mainstream Reynolds number cases, the fluctuation in Sh starts earlier and becomes more irregular downstream. For all cases, similar results can also be found in Wang (1997).

0 0

Post a comment