Optical characterization of the transient behaviour in laminar separation bubbles

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Pratt and Whitney Canada (P&WC) is a leading manufacturer of turbofan engines used in business jets. The high efficiency of these engines relies on the use of high-bypass ratio fan blades, for which the blades require the airfoil profile to be slender. Often during operation, the flow over these fan blades leads to the formation of a laminar separation bubble (LSB), and the boundary layer flow becomes transitional. At high altitudes and at low Reynolds numbers (Re), movement of the transition point may create unsteady loadings, which can potentially lead to severe vibration of the blade, known as flutter. The goal of this project is to investigate how the formation of the LSB and its movement can contribute to flutter. A SD7003 airfoil profile will be towed in the newly built optical towing tank at Queen's University to simulate flow over fan blades. The velocity field over the airfoil will be sampled using time-resolved planar Particle Image Velocimetry (PIV). The lift and drag force on the airfoil will be measured by a six-component ATI Gamma force/torque balance. The force histories will be correlated to the flow structures obtained from PIV data, which may provide important information about laminar separation flutter.