Analysis of a Turbulent Boundary Layer Subjected to a Strong Adverse Pressure Gradient


Gungor A. G. , Maciel Y., SIMENS M. P. , Soria J.

1st Multiflow Summer Workshop on Turbulence, Madrid, İspanya, 10 Haziran - 12 Temmuz 2013, cilt.506 identifier identifier

Özet

A strongly decelerated turbulent boundary layer is investigated by direct numerical simulation. Transition to turbulence is triggered by a trip wire which is modelled using the immersed boundary method. The Reynolds number close to the exit of the numerical domain is Re-theta = 2175 and the shape-factor is H = 2.5. The analysis focuses on the latter portion of the flow with large velocity defect, at higher Reynolds numbers and further from the transition region. Mean velocity profiles do not reveal a logarithmic law. Departure from the law of the wall occurs throughout the inner region. The production and Reynolds stress peaks move to roughly the middle of the boundary layer. The profiles of the uv correlation factor reveal that u and v become less correlated throughout the boundary layer as the mean velocity defect increases, especially near the wall. The structure parameter is low in the present How, similar to equilibrium APG flows and mixing layers, and decreases as the mean velocity defect increases. The statistics of the upper half of the boundary layer resemble those of a mixing layer. Furthermore, various two-dimensional two-point correlation maps are obtained. The C-vv and C-ww correlations obtained far from the transition region at Re-theta = 2175 and at y/delta = 0.4 coincide with results obtained for a ZPG boundary layer, implying that the structure of the v, w fluctuations is the same as in ZPG. However, C-uu indicates that the structure of the u fluctuation in this APG boundary layer is almost twice as short as the ZPG one. The APG structures are also less correlated with the flow at the wall. The near-wall structures are different from ZPG flow ones in that streaks are much shorter or absent.