| Popis: |
Flow in turbomachines is generally highly turbulent. The boundary layers, however, often exhibit laminar-to-turbulent transition. But also relaminarization of the turbulent flow may occur. It is therefore important for the designer to understand the process of boundary layer transition in both directions and to determine the position of transition onset and the length of the transitional region. In the last decades several transition models have been developed to enable modern CFD codes to predict the transition and relaminarization processes. This has the advantage that the boundary layer behavior can be analyzed in advance, which enables the design of blades which trigger a ”suitable” boundary layer. But in order to use CFD for designing tasks, the code must predict accurately and reliably the transition and relaminarization processes within the boundary layer. Therefore in this work, the γ-ReΘ transition model is tested regarding relaminarization prediction. An in-house flat plate test case is analyzed where extensive measurement results are available. Since the test case shows flow pulsations caused by a separation bubble, different cases are investigated where either the full range of the measured velocity fluctuations or only the fluctuations above the integral subscale are prescribed as boundary conditions. Both boundary conditions are combined with either a steady or unsteady simulation where the latter allows to consider the velocity fluctuations additionally. Aim of this variation is to understand the influence of inlet turbulence boundary condition of the predictions of the transition model regarding relaminarization. |
