Research On The Drag Force And Its Coefficient Of Yarns During Weft Insertion

Currently, there are many researches about the flow field characteristics of weft insertion of air-jet looms and structural optimization have been published in both domestic and foreign scholars. However, there are a few studies on how to distinguish the performance of the main nozzle, and how to calculate the air drag force which influences fabric quality and weaving efficiency. Meanwhile, researches on the air drag force’s parameters are not deeply and thoroughly, so the results which can’t provide the data to support the uses of the drag coefficient of yarns are not ideal.Regarding the above issue in this paper, the systematic derivation of the theoretical formula of the drag force is carried out on the basis of the previous researches. And a new device for measuring drag force is designed according to the main nozzle in ZAX air-jet looms. In order to derive the drag coefficient between air and yarns, the following steps have been done:(i) the air velocity and density of the flow field centerline are obtained by the numerical simulation of internal flow field;(ii) the tests of the drag force of different yarns with the established experimental platform are carried out to get the drag force of yarns on a short length;(iii) the drag coefficient between air and yarns is derived with calculation and analysis under different conditions.According to the comparison, it is observed that:(1) From the air velocity and density of the flow field in the device by the numerical simulation, the stable velocity and density are obtained in the auxiliary pipe of the device which can measure the drag force. What’s more, this device avoids the mutation area of the air velocity and density. So the design of this device is reasonable and effective.(2) The results of the numerical simulation and experimental measurement are importantly affected by the specification of auxiliary pipes. In particular, the influence of the diameter is greater than the length.(3) The drag force increases with increase of total pressure. The velocity of the air increases faster because of the more hairiness when the total pressure is low. On the contrary, the drag force changes slower when the total pressure is high.(4) The drag coefficient decreases with relative velocity increasing in a certain range of supply pressure. On the basis of it, the relationship curve between the drag force coefficient and relative velocity of yarns is derived.In a word, the above results show that the research on drag coefficient provides theoretical basis for production and guiding significance for the future researches.