The paper presents experimental and numerical investigations of the two most relevant turbulent quantities, turbulence intensity and integral length scale, within a 1.5 stage axial flow turbine, with emphasis on the flow through the first stator row. The experimental data has been recorded using a miniature hot wire probe, equipped with three 9µm platinized tungsten wires, allowing the determination of the kinetic energy in all three spatial directions. By means of turbulent grids, a total of three different inlet turbulence levels, varying from 0.4 to 4.5%, was created. Extensive field traverses up- and downstream of the first stator have been conducted, covering more than one stator pitch and including both the free stream and the wake. Three axial positions between the stator and the rotor have been measured.&nbsp;After the first flow acceleration, the free stream measurements show a clear convergence of the three variants with respect to turbulent energy. While the highest inlet value significantly decreases, the middle one does not change considerably, and the lowest inlet turbulence level even increases along the first stator. Detailed investigation of all three fluctuation components reveal that, depending on the anisotropy level and the distribution of energy along the three spatial directions at the stator’s inlet, the velocity gradients within the first stator either trigger a production or destruction of turbulent kinetic energy. As a consequence, the distribution of turbulent energy along the three spatial directions is at the stator’s outlet almost identical for the three configurations. Supplemental explanation of turbulence development mechanisms was gained by RANS simulations with the k-w turbulence model, together with appropriate modifications for accurate reproduction of the turbulence development.&nbsp;Further, the diffusion behavior of the suction and pressure side boundary layer into the free stream is analyzed. For the first time, a new evaluation method, the cumulative turbulent kinetic energy, is introduced as a new post processing method improving the analysis of time resolved measurement data. The experimental data shows that, in contrast to the suction side boundary layer, the pressure side one diffuses strongly into the free stream, reducing continuously the lateral extension of the free stream. By means of the new evaluation method, the different diffusion behavior was linked to the different integral length scales, present within the boundary layers.&nbsp;

Development of Turbulent Quantities Inside an Axial Turbine Vane

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2021/volume/84898

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