Model Tests for the Detailed Investigation of the Trailing Edge Flow in Convergent Transonic Turbine Cascades

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Abstract
The paper presents some experiments concerning the trailing edge flow of transonic turbine bladings. The experiments are conducted on a model simulating very closely the flow in the overhang section of convergent turbine cascades. The first test series simulates cascade flow conditions with shock free flow in the overhang section (limit load conditions), while the second test series simulates cascade flow conditions characterized by trailing edge shock interferences with the flow in the overhang section. Particular attention is given to the trailing edge separation shock and the length of the isobaric trailing edge base region. The test results indicate that the strength of the separation shock for the rounded trailing edge is of the same order as the strength of the lip shock found by Merzkirch for sharp-edged wedges. The length of the isobaric base region is only 60 to 80 percent of the trailing edge thickness, while the pressure recovery region is about twice as long as the constant pressure region. From an analysis of the flow parameters influencing the base pressure, it is concluded that the boundary-layer shape factor plays a significant role in establishing the base pressure.

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