Computational analysis of air orifice to enhance air twist formation in twisting nozzles

An air twisting nozzle was investigated by modifying the horizontal connection angle (α) and vertical connection angle (β) of the air orifice relative to the yarn channel, using computational fluid dynamics. Here, α represents the horizontal (rotational) connection angle of the air orifice relative to the yarn channel axis, while β denotes the vertical inclination angle between the air orifice and the yarn channel. A yarn channel with double air orifices was also analyzed under different connection angles. Airflow vorticity and velocity within the air twisting nozzle were evaluated to assess the influence of these connection angles. The connection angles were set at α=30° and α=90°, while β was fixed at 40°. At α=30°, the velocity decreased by approximately 8%, and vorticity dropped by about 12%, which disrupted the air twisting process. Next, β was varied (25°,30°,35°,40°,45°) while α was fixed at 90°. The velocity and vorticity reached their highest values when α=90° and β ranged between 30° and 40°, with the maximum vorticity recorded at 1.58x106 1/s for β=30°, an 18% increase compared to β=25° (1.34x106 1/s). The diameter of the yarn channel and the air orifice geometry remained constant throughout these computations. These connection angles were optimized to enhance airflow velocity and vorticity, with highest values were observed near the air orifice. Connecting the air orifice to the yarn channel at these optimized angles significantly increased both velocity and vorticity. The addition of double air orifices further improved flow dynamics, increasing average channel vorticity by approximately 20% compared to single air orifice designs. The developed air twisting nozzle with double air orifices was fabricated as a prototype and tested on a spandex winder at 900 m/min and 10 kPa inlet pressure. Compared with an existing single air orifice nozzle, the developed design achieved a 30% increase in twist number, reduced running tension by 14%, and improved flux uniformity, resulting in more stable yarn processing. These results demonstrate that the developed nozzle can significantly enhance twisting efficiency and yarn quality in industrial applications.