On flowfield periodicity in the NASA transonic flutter cascade

A combined experimental and numerical program was carried out to improve th e flow uniformity and periodicity in the NASA transonic flutter cascade. Th e objectives of the program were to improve the periodicity of the cascade and to resolve discrepancies between measured and computed flow incidence a ngles and exit pressures. Previous experimental data and some of the discre pancies with computations are discussed. In the present work surface pressu re taps, boundary layer probes, shadowgraphs, and pressure-sensitive paints were used to measure the effects of boundary layer bleed and tailboard set tings on flowfield periodicity. These measurements are described in detail. Two numerical methods were used to analyze the cascade. A multibody panel code was used to analyze the entire cascade and a quasi-three-dimensional v iscous code was used to analyze the isolated blades. The codes are describe d and the results are compared to the measurements. The measurements and co mputations both showed that the operation of the cascade was heavily depend ent on the endwall configuration. The endwalls were redesigned to approxima te the midpassage streamlines predicted using the viscous code, and the mea surements were repeated. The results of the program were that: (1) Boundary layer bleed does not improve the cascade flow periodicity. (2) Tunnel endw alls must be shaped like predicted cascade streamlines. (3) The actual flow , incidence must be measured for each cascade configuration rather than usi ng the tunnel geometry. (4) The redesigned cascade exhibits excellent perio dicity over six of the nine blades.