Large Eddy Simulations in Turbines: Influence of Roughness and Free-Stream Turbulence

Free-stream turbulence effects on the boundary layer of a high-lift low-pressure-turbine blade

“…In this case the boundary layer is characterized by almost the same shear layer thickness of the low FSTI condition, but it appears closer to the wall. Similar results have been observed in the recent LES numerical simulations of Rao et al [39], showing that the higher the FSTI the closer to the wall the shear layer. At high FSTI the best fitting with the Pohlhausen's profile is obtained with Λ  0.5.…”

Numerical observations of turbulence structure modification in channel flow over 2D and 3D rough walls

“…Looking at the kurtosis parameter, it can be observed that in all cases the roughness disagrees from the normal distribution. The achieved values are consistent with those observed over irregular rough walls derived by degraded turbine Flack and Schultz (2010), Yuan and Piomelli (2014), Mejia-Alvarez and Christensen (2013), and Nagabhushana Rao et al (2014). 2D roughness are characterised by K u < 3, Table 1 Domain size, number of cells, mesh resolution.…”

“…1, it can be observed that the proposed mesh is fine enough to capture even the small scales of the irregularities. Even though it is reproduced through the superimposition of sinusoidal functions, the 3D shape is clearly similar to those investigated by Yuan and Piomelli (2014) and Nagabhushana Rao et al (2014), where degraded turbine blades are reproduced. Nevertheless the proposed shape is slightly smoothed with respect to the real roughness.…”

“…The mean value of the oscillations is usually adopted as the representative geometrical parameter, but it has been deeply demonstrated that the mean roughness height cannot be considered representative of the roughness effect, whereas the shape (or texture) of the roughness must be taken into account. Following recent researches Schultz and Flack (2009), Wu and Christensen (2007), Flack and Schultz (2010), Wu and Christensen (2010), Yuan and Piomelli (2014), Mejia-Alvarez and Christensen (2013), and Nagabhushana Rao et al (2014), the rough wall has been analysed in the light of statistical moments up to fourth order. In the present research, due to the nature of the sinusoidal functions the centerline of the roughness vanishes and cannot be considered a real metric for the roughness characterisation.…”

“…The authors focused also the attention on roughness parametrisation, finding new insight in the critical effective slope ES, defined by Napoli et al (2008) and later analysed by Schultz and Flack (2009). The effects of irregular rough surfaces, derived by topographical shape of real turbine blade damaged by spallation, was studied by Nagabhushana Rao et al (2014) applying Large Eddy Simulation technique. Single and coupled effects of incoming free stream turbulence and surface roughness were systematically studied.…”