The effects of emotion and COVID-19 context priming on the size and color of drawings: based on human figure drawings and tree drawings.

Introduction: This study aimed to investigate the effects of emotional themes and the COVID-19 pandemic context priming on the size and color of drawings. Methods: A 3 (emotion: peacefulness, gratitude, loneliness) × 2 (context: pandemic, regular) mixed design was used and 113 university students in Shanghai were recruited to draw human figures and trees using 10 marker colors. Results: The size of the drawings depicting loneliness was smaller than that of the those depicting peacefulness and gratitude. Drawings depicting loneliness used more cool and non-preferred colors; drawings depicting gratitude used more warm and preferred colors. Drawings in the pandemic context were larger, which may reflect the more significant threat perceived by individuals. Drawings in the pandemic context used more red colors, showing symbolic meanings such as danger. Discussion: The drawing size and drawing color are influenced by emotional themes and the pandemic context priming.

An experimental investigation of aerodynamic and aeroacoustic performance of a wind turbine airfoil with trailing edge serrations.

Trailing edge (TE) serrations are widely used as an effective passive control method to reduce the turbulent TE noise from wind turbine blades. Other than the acoustic effects, the aerodynamic performance of serrations is also an important issue that should be considered, since it determines the power output of the blade. To this end, the far-field sound pressure level, flow field, and aerodynamic force of the serrated airfoil were measured in an anechoic wind tunnel, and the lift increase and noise reduction effects of the TE serrations were comprehensively evaluated. The result showed that the presence of TE serrations could achieve noise reduction by about 2 dB at the low-to-moderate frequency range at small angles of attack, and meanwhile it could suppress the fluctuation of aerodynamic forces. In addition, the proper orthogonal decomposition method was deployed to decompose the wake flow into various vortex structures with different portions of turbulent kinetic energy so as to reveal the noise reduction mechanism of the serrated TE. The result suggested that TE serrations could effectively inhibit large-scale vortex structures that shed from the boundary layer on the suction side, thereby achieving noise reduction around the vortex shedding frequency.

Optimal design of aeroacoustic airfoils with owl-inspired trailing-edge serrations.

The trailing-edge serration that imitates the silent owl wing is used as a flow control method to suppress the aerodynamic noise generated from the rotating wind turbine blade. Recent studies have found that the addition of serrations could degrade the overall aerodynamic performance of the airfoil. To this end, an optimal design method for airfoils with the trailing-edge serration is developed. Combined with the modeling methods of aerodynamics for serrations, the fundamental parameters of serrations are integrated into the optimal design of wind turbine airfoils. Specifically, based on the existing multidisciplinary optimization method for airfoils, the aerodynamic prediction and evaluation module for the serrated airfoil was introduced to develop an aerodynamic-structural optimal design platform. In this way, a novel serrated airfoil equipped with high aerodynamic performance can be designed. Compared with the reference airfoil, the maximum lift-to-drag ratio and lift coefficient of the optimal serrated airfoil at the design point have been increased by 1.9% and 32.5%, while the aerodynamic noise could also be reduced. Finally, experiments were conducted in an anechoic chamber to verify the noise-reduction level of the optimal serrated airfoil, which sufficiently demonstrate the capability to improve the comprehensive performance of the airfoil using such a developed optimal scheme.