Abstract
Dynamic stall is a critical limiting factor for airfoil aerodynamics and a challenging problem for active flow control. In this experimental study, dynamic stall was measured by high-frequency surface pressure tapes and pressure-sensitive paint (PSP). The influence of the oscillation frequency was examined. Dynamic mode decomposition (DMD) with time-delay embedding was proposed to predict the pressure field on the oscillating airfoil based on scattered pressure measurements. DMD with time-delay embedding was able to reconstruct and predict the dynamic stall based on scattered measurements with much higher accuracy than standard DMD. The reconstruction accuracy of this method increased with the number of delay steps, but this also prolonged the computation time. In summary, using the Koopman operator obtained by DMD with time-delay embedding, the future dynamic pressure on an oscillating airfoil can be accurately predicted. This method provides powerful support for active flow control of dynamic stall.
Highlights
Stall is one of the most critical limiting factors for airfoil aerodynamics
To examine the two-dimensional pressure field on the oscillating airfoil, the images from pressure-sensitive paint (PSP) measurement were phase-averaged over 15 periods
It should be noted that these PSP measurements only provided a qualitative visualization because the PSP data was influenced by the temperature of the incoming flow
Summary
Stall is one of the most critical limiting factors for airfoil aerodynamics. Static stall occurs when the airfoil reaches a certain angle of attack. Dynamic stall is a more complicated unsteady phenomenon due to the flow separation caused by the rapid change in the angle of attack and the variable stall frequency It leads to an abrupt decay of aerodynamic forces and a fluctuation of the structural load on the airfoil. It is difficult to predict the evolution of the aerodynamics of dynamic airfoil over time In this regard, the dynamical system concept should be taken into consideration, and dynamic mode decomposition (DMD) can provide some inspiration, which is an equation-free and data-driven method to model dynamical systems. Based on the scattered pressure tape measurements, DMD with time-delay embedding was applied to reconstruct the spatiotemporal pressure distribution on the oscillating airfoil and predict the future data in real-time.
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