321 Surface flow visualization

For surface flow visualization, a mixture of paint powder and oil is applied to blade surfaces near the tip, the tip surface, and the tip-endwall covered by a piece of tightly fitted white sheet, respectively, at different tip clearances to visualize the surface flow pattern in the linear turbine cascade.

Viscosity of the mixture is adjusted by trial and error to allow the powder particles to follow the direction of shear stresses and to display the shear force pattern on the wall. Patterns on the sheet are photographed using a Richon camera immediately after wind tunnel test at inlet mainstream speed of about 20m/s (Reex = 6.0 x 106) to avoid fading of the pattern.

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