Determination of Yarn Interlacing Frequency of Triangular Interlacing Nozzles through a Compressible Flow Simulation

A numerical approach to predict the yarn interlacing frequency of triangular interlacing nozzle is discussed in this paper. The inviscid, compressible flow field inside air nozzles is computed through solving the steady continuity, momentum and energy equations with a finite volume method. A mathematical model for the prediction of yarn interlacing frequency of air nozzle is proposed, which is determined by the vorticity strength, air density, yarn density and yarn feed speed. The influences of inlet size, inlet pressure and inlet angle on the yarn interlacing frequency of an air nozzle series are studied. The numerical results are validated by experimental measurements and show good prediction accuracy for yarn interlacing frequency. The shock interaction inside the expansion chamber explains the nonlinear behavior of the yarn interlacing frequency curve under various operation conditions. For air nozzles only differing in their inlet diameter, an optimal size of inlet diameter can be attained for a given pressure. Insufficient or excessive size of inlet opening leads to a weak interaction of shock surface inside the expansion chamber, and results in a lower number of knots per unit length. For a given nozzle, an optimal inlet pressure can be obtained, which yields the largest yarn interlacing frequency per unit pressure. A minor increase in the yarn interlacing frequency is achieved for the inlet pressure greater than the critical pressure because the upper-lower shock surface has been completely developed. For air nozzles only differing in their inlet angle, an optimal inlet angle can be found at a given pressure, which seems insensitive to the inlet pressure. The proposed approach is proven to be effective and accurate in predicting the yarn interlacing frequency of air-jet nozzles, and also very promising for the design of air-jet interlacing nozzles to evaluate yarn interlacing frequency under different working conditions.