Abstract
The present study investigates wake-induced bypass transition of boundary layers on a flat plate subjected to favorable and adverse pressure gradients. The aim is to exploit unsteady effects in order to design an aft-loaded turbine blade without increasing the profile loss, as has been achieved for low pressure turbine blades. First of all, this fundamental study is to reveal the effect of the Strouhal number, which changed by using different numbers of wake generating bars. Detailed boundary layer measurements were conducted using two hot-wire probes. A passage-contouring device was employed to generate a pressure gradient on the test model, which was typical to that generated by an aft-loaded turbine blade. A spoked-wheel-type wake generator was used to create periodic wakes in front of the flat plate. It was found that the wake passage induces a significant change in the flow structure downstream of the flow acceleration region.
Highlights
The flow field in turbomachines is characterized by complicated flow that has three dimensional effects from unsteady flow
The present study investigates wake-induced bypass transition of boundary layers on a flat plate subjected to favorable and adverse pressure gradients
This study investigates the effect of the Strouhal number of wake on the transition onset of the boundary layer on a flat plate, which is subjected to favorable and adverse pressure gradients
Summary
The flow field in turbomachines is characterized by complicated flow that has three dimensional effects from unsteady flow. Many researchers have been studying the transition process of the boundary layer on turbomachinery blades in a flow that is periodically disturbed by the rotor wakes [1,2,3,4,5,6,7,8]. The initial two-dimensional instability phase of a natural transition is bypassed in this case. A natural transition is a classical process that arises from the appearance of the two-dimensional Tollmien-Schlichting instability waves in the laminar boundary layer. A spoked-wheel-type wake generator is used to simulate the unsteady flow field over the suction surface of a turbine rotor
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