The Influence of Tailboards on Unsteady Measurements in a Linear Cascade

The present paper shows the comparison between steady-state and unsteady results from two versions of a flow solver and measurements in a linear cascade at transonic flow conditions for forced vibration of a single blade. Experiments have been conducted in a linear test facility with a cascade composed of five turbine blades. The center blade was forced to oscillate in a pure bending mode with a frequency of 160 Hz. Tailboards are fixed in this test facility at the trailing edges of the border blades to create a periodic flow at the outlet of the cascade. A 2D inviscid flow solver for unsteady flows through vibrating blade rows was adapted to simulate the flow conditions in the linear cascade. The initial adaptation of the flow solver was the limitation to only one vibrating blade. Comparisons with measurements showed discrepancies which were hypothesized to be due to the presence of the tailboards which can create reflections of pressure waves and shocks. Therefore, as a second modification of the program, the periodic boundaries downstream of the blades were replaced by solid walls. Based on these computations it can be concluded that for transonic flows the tailboards have a significant influence on both the steady-state and unsteady flow in the outlet region as well as on the blade in the shock region. In particular, the unsteady data measured in a linear cascade has to be analyzed very carefully to estimate the influence of the tailboards. NOMENCLATURE