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We investigated the mechanism of hysteresis and uncontrolled deflection in jet vectoring control based on the Coanda effect. Thrust vectoring control based on the Coanda effect is highly applicable in the field of fluid dynamics because they can achieve jet deflection control with a simple geometric structure and low energy consumption. However, the hysteresis and uncontrolled deflection phenomena considerably hinder the practical application of these technologies. We designed a new passive fluidic thrust vectoring control model to analyze the mechanism of these disadvantages. We developed a synchronous pressure, force, and flow field measurement system to investigate the evolutions of flow structures and their effects on wall pressure distribution and vectoring force. The characteristics of the key flow structures, including the separation bubble, the secondary flow, and the backflow, were investigated. The transient features of jet attachment and jet detachment were researched to identify the transition of near-wall flow structures and wall pressure distribution during jet uncontrolled deflection. The mechanism of uncontrolled deflection is that the formation/breakdown of the separation bubble changes the flow state of the backflow, and the near-wall mass flux balance is collapsed. This causes a dramatic change in the jet vectoring angle, which is out of the valve's control. During attachment, the shear layer first touches the wall and forms a separation bubble, and then, the bubble shrinks. During detachment, the bubble first enlarges and then breaks down. Therefore, the formation and breakdown of the separation bubble correspond to different valve positions, which is the mechanism of hysteresis. [ABSTRACT FROM AUTHOR]

Compared with highly efficient green, red, and near-infrared perovskite light-emitting diodes (PeLEDs), the performance of blue PeLEDs is still unsatisfactory due to the serious spectral instability issue at high working voltages. In this work, a multidentate amine-based ligand with four amino groups is utilized to achieve spectral stable blue quasi-2D PeLEDs. As a result, the optimized quasi-2D perovskite films exhibit stable photoluminescence spectra under continuous UV illumination and heating. Finally, the blue quasi-2D PeLEDs emitting at 478 nm with the peak external quantum efficiency up to 4.8% are achieved. Meanwhile, there is no obvious peak shift of the electroluminescence spectral under high external working voltages, exhibiting excellent spectral stability. The findings in this work confirm the validity of this strategy, providing a strategy to achieve steady blue PeLEDs. [ABSTRACT FROM AUTHOR]