| Turbomachinery rotors are often operated in flow fields that contain convecting turbulent eddies. This situation results in a broadband spectrum of unsteady forces and sound. The spectrum is generally important over the same frequency range as the first few blade passing harmonics, and can often contain spectral features (“humps”) associated with multiple blades chopping a region of correlated turbulent fluid. Extensive prior research has been conducted in this area, leading to estimates of the spectra when the turbulence is both homogeneous and isotropic.; The present research extends those prior works by addressing the forces and sound that are generated when the inflow turbulence is both inhomogeneous and anisotropic. A boundary layer inflow is used for motivation and for development of a suitable empirical turbulence model.; As developed by the prior research, a two-point space-time correlation function is useful for representing the statistical behavior of the turbulent velocity fluctuations. Therefore, an extensive measurement database was acquired (Re&thetas; ≈ 10,000 at multiple reference locations within a suitable boundary layer, and that database was used to develop and calibrate an empirical turbulence model. The turbulence model reproduces many of the expected features that have been previously reported from flow visualization and particle image velocimetry. Specifically, the modeled regions of correlated fluid display elliptical iso-contours of the two-point correlation coefficients. These iso-contours are elongated in the downstream direction and their major axes are inclined towards the wall. The region of correlated fluid converts downstream at a fraction of the local free stream velocity.; The new turbulence model has been incorporated, along with other minor updates, into a new tool for prediction of unsteady forces and sound. Parametric studies reveal the effects of anisotropy and inhomogeneity, which tend mainly to enhance some of the spectral humps. Careful experiments will be required in the future in order to fully verify these developments. |
