Abstract

A boundary layer on the surface of a turbine blade can be significantly affected by the presence of periodic wake-passing from upstream blade rows, leading to a special form of transition mode from the high turbulence in the periodic wakes. In an effort to predict the evolution of wake-induced transition, time-resolved calculations were carried out using an unsteady two-dimensional boundary layer code and a newly developed transition model. The model is based on the theory of turbulent spot propagation and its subsequent growth. As a benchmark for the model, a single turbulent spot was simulated and compared with measurements. The results yielded the two-dimensional characteristics of the turbulent spot, as well as the becalmed region behind the spot. By imposing successive turbulent strips and freestream velocity defects in the time-space domain, the process of wake-induced transition was predicted for several test cases. The results showed good agreement on both the time-resolved and time-averaged measurements for the boundary layer quantities. In addition, predictions reproduced many details of the flow structure of wake-disturbed boundary layers and transition process.

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