Self-excited oscillations of stalled turbomachine blades at low Reynolds numbers

What is it about?

The propensity of a turbomachine blade, kept at a high angle to an incident flow, to undergo self-excited oscillations (stall flutter) is investigated experimentally. The simultaneous measurements of forces and flow field show the dependence of the excitation with the phase of oscillations of the separated shear layer at the leading edge of the blade. Various flow conditions have been studied to demarcate the stall-flutter boundaries.

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Why is it important?

The flow through gas turbines of the unmanned air vehicles and that through small and micro turbines is typically at low Reynolds numbers. Although, the viscous effects are important at those Reynolds number, the present study shows that the separated flow at the leading edge of a blade (at high angles of attack) also oscillates. At certain flow conditions, these oscillations produce pressure fluctuations around the blade so as to excite the blade to cause the stall flutter. To avoid the blade weakening and damage, it is important to avoid this phenomenon in turbomachines. The present work demarcates flutter boundaries showing the conditions under which the stall flutter is possible.