Flow Instability In Rotor Spinning Conical Chamber

As an important rotating component for rotor spinning machine, the shape, size, speed of the rotorhave significant impacts on the quality of the yarn product. From previous studies, it is suggested that theflow structure in rotating container changes significantly with the increase of speed, especially the shapeand size of the zone of low pressure near the center axis. However, the study on the swirl flow in spinningrotor received little attention so that the flow behavior is not well understood. In this paper, the flowparameters are obtained by numerical simulation on the swirl flow in the spinning rotor, and the energygradient theory is applied on the numerical simulation results for further analysis of the stability of flow.At the same time, it can be verified the rationality of energy gradient method used to analyze the flow inthe spinning rotor.First of all, to verify the applicability of the energy gradient theory on flow instability of complexflow, steady three-dimensional Navier-Stokes equations are used to study the instability of flow in180°curved duct with rectangular cross-section. Based on the assumption that the curved duct size is samewith duct in the experiment of Gauthier, three-dimensional flow field is obtained by three-dimensionalnumerical simulation under different Reynolds numbers. The distribution of the energy gradient functionK is calculated by the energy gradient theory. Compared with experimental results under the sameconditions, it is found that the position of the maximum of K is the first place where fluid flow is easy tolose its stability, then forming vortices. The distribution characteristics of K calculated by numericalsimulation are in agreement with the instability zones implied by experimental data. Thus, it is verifiedthat the applicability of energy gradient method on the flow instability in the curved duct.Secondly, unsteady three-dimensional Navier-Stokes equations are used to study vortex breakdownof swirl flow in an enclosed spinning rotor conical chamber with a rotating top wall by numericalsimulation and analyze the vortex breakdown in spinning rotor conical chamber. The distribution of theenergy gradient function K is calculated by the energy gradient theory using the whole parameters in flowfield and study the physical mechanism of vortex breakdown. Three types of chambers are studied,conical chamber with slip angle, common conical chamber, and cylindrical chmber. It is found from thestudy of conical chamber with slip angle that the region of vortex breakdown where the velocity is lowwould appear near the axis of the conical chamber when the Reynolds number reaches a critical value. Asthe Reynolds number increases further, the size of vortex breakdown bubble grows and it moves away from the driving surface within the parameter range studied. However, the position where the vortexbreakdown first occurs doesn’t change with the variation of the slip angle of the conical chamber.Compared with common conical chamber, conical chamber with the slip angle promotes the generation ofvortex breakdown and it suppresses the generation of vortex breakdown compared with cylindricalchambers. The research shows that the position of the maximum of the energy gradient function K is thefirst place where the flow loses its stability. The distribution characteristic of K calculated by numericalsimulation is in agreement with locations of the instability zones.Finally, steady three-dimensional Navier-Stokes equations and k-ε turbulence model are used tosimulate numerically the flow in rotor spinning channel applied in industry and study the effect of rotorspeed and geometric parameters on the flow characteristics in the spinning rotor. Finite volume methodand SIMPLE algorithm are used as numerical method, and the unstructured grid is applied to divide thecalculated area. The flow characteristics in spinning channel drawn from the simulation results obtainedare as follows: the air is accelerated in the fiber tube and the speed reaches maximum in the export offiber tube. Due to the asymmetry of the fiber tube in the spinning rotor, the airflow from fiber duct splitinto two airstreams of different sizes in the two opposite directions after hitting the wall. The flowrotating along the clockwise is more than that along counterclockwise, and they flow out of the spinningrotor after the collision between two airstreams when the clockwise stream flowing through270°. Fiberin the condensation tank rotates clockwise with air flow and the counterclockwise rotor is good for fibretwisting and increasing the strength of the yarn. Therefor, the rotor speed should be as large as possible inthe premise of constant airflow collision location. Flow structure in meridional plane of spinning rotorchanges significantly with the increase of rotor speed. With the increase of rotor speed, the low-pressurezone located in center of rotor first moved to the center axis, and then away from the central axis. This isdue to the balance of low pressure zone caused by rotational rotor and the high speed in the export offiber tube. It is found from the study the main low-pressure zone is located at axis of the rotor when therotor speed is2000r/s. In this case, the axial symmetry of flow in the rotor is the best, and the pulsationand vibration is the smallest. It is found that the effect of increasing slip angle is similar to the increasingrotor speed on flow behavior. The results provide reference to chose rotor speed and geometries for therotor spinning machine.