Investigations on Vortex-Induced Vibration of the Wind Turbine Airfoil at Standstill

ABSTRACT

The wind turbines, which are in extreme wind conditions or during scheduled maintenance, would have to be cut off. In this standstill or parked condition, the wind turbine blades may vibrate and eventually fail due to unsteady aerodynamic loads at very high angles of attack. Vortex-induced vibration of the wind turbine airfoil at standstill is investigated with the fluid-structure coupling simulation. The nonlinear aeroelastic phenomena like frequency lock-in, bifurcation, limit cycle oscillation and beating are analyzed through constructing the “aero-damping map” based on prescribed vibration simulations. The “aero-damping map” can also be used to predict the vibration responses in the lock-in regime. The dominant flow modes in the lock-in condition and unlock-in condition are extracted with the dynamic mode decomposition method. The effective added mass coefficient is solved to evaluate the influence of fluid-solid interaction on the frequency response. Effects of inflow turbulence on vortex-induced vibration are also explored based on the identified Van der Pol oscillator model. Besides, the simulation of 3D detached eddy simulation (DES) represents more flow details compared to 2D k-ω SST turbulence model, while show strong 2D flow characteristics during vortex-induced vibration.

Lian Bo is a visiting PhD student from Shanghai Jiao Tong University, China, under guidance of Prof. Khoo Boo Cheong and Dr. Cui Yongdong in NUS. He majors in power engineering and engineering thermophysics. His PhD thesis is Effects of inflow turbulence on flow-induced vibration of the wind turbine blade at standstill. His main research interests are in turbomachinery aeroelasticity including vortex-induced vibration of the wind turbine blade and flutter of the aero-engine compressor blade. Lian Bo has published three journal papers and four conference papers as of now.

Experimental Studies of Continuous Detonation in a Linearized Combustor: Shuttling Transverse Combustion

ABSTRACT

A novel continuous detonation phenomenon, named shuttling transverse combustion (STC), has been experimentally investigated by fast-response wall pressure measurements, high-speed flame luminosity imaging, fast-shutter OH* chemiluminescence imaging, and schlieren imaging. STC is found to be a branch of pressure gain combustion (PGC), in which steep-fronted combustion-supported pressure waves continuously propagate near the region of the reactant injection. Different from conventional PGC, the STC waves are sustained via repeatedly reflection instead of rotation. During the experiments, STC was developed under a critical oxygen flow rate, which was just able to establish the continuous STC process. Three different wave modes, which are longitudinal pulsed, single wave, and double wave modes, have been observed by progressively increasing the equivalence ratio for different runs of experiments. Similar to conventional PGC, wave velocity deficits relative to the Chapman-Jouguet detonation wave velocities have been observed in STC, which implies that the unique characteristics of the STC waves differ from the classical detonation waves. The results indicate the analogous nature between STC and conventional PGC with regard to the reacting flow structures and the wave mode dynamics. Considering the simple quasi two-dimensional combustor geometry of the STC, the STC would have both practical and fundamental importance to be further studied.

Dr. Huang Xin is presently working in TL@NUS. He received his B.S. in Applied Physics from Nanyang Technological University in 2014, and Ph.D. in Mechanical Engineering from National University of Singapore in 2018. His research interests include experimental fluid mechanics, optical-based flow diagnostic techniques, chemically reacting flow, and continuous detonation.