Direct numerical simulations (DNS) were used to study the effects of periodic incoming wakes on the flow near the endwall in a linear turbine cascade T106. The moving cylindrical bars generating the wakes in the experiment were represented by means of appropriate unsteady turbulent inflow conditions. In the simulations, two cases, with and without incoming wakes, were conducted at a Reynolds number of 90,000 based on chord length and outlet velocity. The results were validated with experimental data. Due to constructive limitations of the experimental setup, the incoming boundary layer is very thin, so that some features of the secondary flow are absent or small. Employing phase-averaging, however, the periodic formation of vortical structures caused by the wakes can be identified in the vicinity of the endwall.
The paper presents numerical investigations of a model setup conceived to investigate the influence of the Coriolis force on the secondary flow in a low pressure turbine cascade. It addresses the question in which sense and by how much results in a linear cascade may differ from the situation in a rotating cascade. For this purpose highly resolved Direct Numerical Simulations of the flow within a T106A passage close to the endwall were conducted for two cases with and without rotation and hence with and without Coriolis force at a Reynolds number of 20,000. Comparing non-rotating and rotating turbine passage, several effects are detected: First, the Coriolis force causes transition of the horseshoe vortices, so that the region between the blades becomes much more turbulent and an explanation for the destabilization is provided. Second, the strong radial flow caused by the Coriolis force suppresses the laminar separation of the boundary flow at the suction side. Third, in the case with rotation, the large-scale secondary motion creates higher stagnation pressure loss than in the reference case and is responsible for a complete redistribution of the flow field in the passage. An additional test case with opposite rotation was computed for completeness.
In the present work, direct numerical simulations (DNS) of the flow through a low-pressure linear turbine cascade T106 with parallel endwalls were conducted to investigate the effects of unsteady passing wakes of the upstream blade row on the secondary flow in the endwall region of the passage. The impact of the wakes on the secondary flow is discussed by means of the time-averaged values. Furthermore, the results of DNS are compared with experimental data.
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