Spectral Analysis of Measurements of Separated Flow Transition on a Turbine Airfoil
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Bibliographic record
Abstract
†This paper describes spectral analyses of simultaneous surface hot-film (quasi-wallshear-stress) and hot-wire (velocity) measurements over the suction surface of a moderatelyloaded turbine blade at low Reynolds numbers. Under the conditions of the measurements, the flow on the aft portion of the suction surface experiences laminar separation and transition in a separated shear-layer. As the free shear layer becomes turbulent, the increased entrainment results in reattachment of the boundary layer. This paper evaluates the ability of spectral analysis (in this case digital fast Fourier analyses) to give insights into the transition process and the flow characteristics within the separation bubble, and to provide benchmark data for Large-Eddy Simulations (LES). The findings regarding the transition process show that the method is capable of defining an inertial range of turbulence where there are low levels of turbulent energy present, including at the fluctuation levels that are present in the nominally laminar regions. The results suggest that it may be useful to apply the concept of Kolmogorov-type turbulence dissipation in much earlier stages of transition than is normally considered appropriate. The shear layer that forms the outer edge of the separation bubble was found to contain two superimposed spectra. This is a phenomenon that cannot readily be captured by LES unless the filter size is much smaller than the spectrum with the highest frequency. The spectra of the turbulentkinetic-energy (hot-wire data) and of the quasi-wall-shear-stress fluctuations (hot-film data) were used to define the location in spectral space of the inertial range of the turbulence decay. In particular, it was possible to define the location of the inertial range close to the surface and at set intervals away across the bubble. It was found that for small distances they match very well, but as distance from the surface of the airfoil increases, the match degrades. Thus, the present results indicate that the spectral content from the surface signals, obtained beneath the separation bubble, only provide limited information about the spectral content of the turbulence in the adjacent free shear layer.
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Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
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