Dong Joo Song

An optimum design study of the yarn-channel shape of the air-interlacing nozzle by analysis of fluid flow

The air-interlacing process provides assurance in the downstream performance in weaving and knitting without changing the properties of the synthetic yarn. The air-interlacing nozzle is an important component for improving the performance in the air-interlacing process. The airflow inside the air-interlacing nozzle is investigated to design an optimum yarn-channel shape of the nozzle. The width and height of the yarn-channel and inlet pressure are the design variables of the air-interlacing nozzle. The design variables are evaluated by the vorticity. The design of experiments (DOE) approach is utilized to study the influence of the nozzle configuration. Minitab is used as a practical and effective tool in optimizing the nozzle geometry to improve performance. Computational simulations of the impinging airflow inside the nozzle are undertaken using ANSYS CFX. The airflow characteristics such as the vorticity, shock wave, and velocity distributions were discussed. Various cross-sectional shapes of the yarn-channel are investigated with the same inlet pressure. The cross-sectional shape of Shape 6 which has high vorticity is observed to find optimal configurations for the nozzle of the air-interlacing process. The design variables of the nozzle are the width and the height of the yarn-channel and the inlet pressure. The reason for the evaluation of the performance of the nozzle is the maximization of the vorticity. The response surface method (RSM) is applied for the shape optimization. The vorticity cannot increase at the high inlet pressure due to the shock wave. The air-interlacing nozzle, with optimum configurations, is verified numerically and experimentally.

A Computational Study on the Efficiency of Boundary Layer Bleeding for the Supersonic Bump Type Inlet

A Computational Fluid Dynamic investigation was conducted on a variable geometry supersonic/subsonic compression inlet. The concept of three-dimensional surface to control the boundary layer in supersonic inlet flow has been used Simon et al. According to previous researches, a three-dimensional bump installed in the supersonic inlet may play an important role as an effective compression surface and also an upstream boundary layers removal system that prevents the low-energy airflow from entering the inlet instead of complex and active heavy mechanical bleeding systems. Therefore, it is of interest to study the effectiveness of the compression systems using a bump on shock/boundary-layer interactions in high-speed inlet flow. This research would show efficient bump shape and the performance of the bump-type inlet with bleeding by changing bleeding condition.

A Design Study of an Air-twist Nozzle by Analysis of Fluid Flow

The efficiency of the air-twist nozzle has a direct effect on the uniform tension of spandex yarn during the winding and unwinding process. The different geometries of the air-twist nozzle were studied as a reference. Compressed air coming out of the air orifice flows through the wall of the yarn channel in a twisting motion. The purpose of this research is to develop an air-twist nozzle geometry which has well-twisted motion, with reasonable vorticity strength and velocity. The paper presents investigations of the effects of the inlet pressure and the yarn channel shape of the air-twist nozzle. The Ansys CFX was used to perform steady simulations of jet flow inside the air-twist nozzles. Results of computational simulations for the two most promising cases were confirmed by experimental tests. The twist and flow patterns, specifically vorticity and velocity inside the air twist nozzles, are discussed in this paper. As a result of this research, an air-twist nozzle of improved design is now being produced for commercial use.

Internet-Based Graphic User Interface for Postprocessor of Computational Fluid Dynamics

The program developed during this research includes postprocessor, Navier-Stokes solver with remote server. Postprocessor of computational fluid dynamics (CFD) takes data from solver and shows results graphically. Flow visualization graphic user interface with Visual C#.NET is easily possible to find the input data error and observe interactive computational results while the Navier-Stokes solver code is running, so that there is no need to wait and store all data files until the program completes. The Solver is based on a combination of the Visual C#.NET application and FORTRAN 77 code. The program developed is interactive plotting program for visualizing and analyzing engineering and scientific data from the Navier-Stokes solver code. It is necessary to use network access and powerful solver computer (server) to extend accessibility of the present program. The postprocessor program can take data file from the solver or remote solver. The program introduces XY plot, mesh plot, boundary plot, vector plot, and contour plot with different options. Residual plot shows (root-mean-square) RMS error history graphically and takes data from solver or remote solver. The results obtained by using the program developed were compared

Improving airflow loss through the yarn-loading slit of the air-interlacing nozzle using TRIZ

The air-interlacing nozzle has a yarn channel, an air inlet and a yarn-loading slit. The previously investigated optimum air-interlacing nozzle was analyzed to improve the airflow loss through the slit by reducing the width of the slit and by applying TRIZ tool. TRIZ, the theory of inventive problem solving, was applied to find a solution for the airflow loss through the yarn-loading slit. The airflow inside the air-interlacing nozzle was computed using ANSYS CFX software. The computational results of the air-interlacing nozzle were evaluated by the vorticity, velocity and the airflow loss. The vorticity was increased and the airflow loss was improved slightly when the width of the slit was reduced. The yarn-loading slit is for the yarn loading into the yarn channel before the air-interlacing process. The technical contradiction of the air-interlacing nozzle was that reducing the width of the yarn-loading slit makes it difficult to load the yarn into the yarn channel. Principles 10 and 31 of TRIZ were obtained through the contradiction matrix and were applied to the nozzle. The computational results showed that the vorticity and velocity were increased and the airflow loss through the slit was improved. The air-interlacing nozzle after applying principles of TRIZ showed better results when compared numerically and experimentally with other existing nozzles.

Influences of the air inlet and yarn-loading slit on the performance of an air-twist nozzle

An air-twist nozzle has an air inlet and yarn channel with a yarn-loading slit. The nozzle was investigated by changing the width and length of the air inlet and by modifying the yarn-loading slit using computational fluid dynamics. The airflow vorticity, mass flow rate, and velocities of the air-twist nozzle were evaluated to analyze the influences of the air inlet and yarn-loading slit. The velocity and vorticity were high when the width and length of the air inlet were 0.2 and 0.1 mm, while the diameter and length of the yarn channel were fixed at 1 and 3.5 mm, respectively. The air inlet was divided into two and three small rectangular air inlet holes to increase the velocity and vorticity. The velocity and vorticity were high but not uniform at the yarn channel. Dividing the air inlet increased the velocity but disturbed the air-twisting process; therefore, the air inlet without dividing was selected for further computations. The influence of the yarn-loading slit on the air-twist nozzle flowfield was observed to improve the performance of the nozzle by changing and removing the slit. The velocity, vorticity, and mass flow rate were improved significantly when the yarn-loading slit was removed. The air-twist nozzle with the removed yarn-loading slit was fabricated as a prototype for testing. The air-twist nozzle was compared with the existing air-twist nozzles under identical conditions. The test results showed that the developed air-twist nozzle with removed yarn-loading slit had better performance than the existing nozzles.

Optimum design of the injection nozzle system of a three-drive jigger dyeing machine

A jigger dyeing machine is used to dye fabric across the width, which enables the fabric to be passed back and forth in a perfect dyeing bath. A three-drive jigger dyeing machine contains an injection nozzle system. The flowfield inside the injection nozzle system was computed using ANSYS CFX software and was evaluated by mass flow rate, velocity, and pressure. The injection nozzle system was observed by installing two different division plates and by changing the diameter and distance of the outlet holes to improve dyeing efficiency. The division plates have slits and holes help to distribute the dye liquid evenly over all the holes. The standard deviations of the mass flow rate of the division plates with slits and holes were 0.000551 and 0.000368, respectively. The effects of distance and diameter of the outlet holes were analyzed and evaluated by mass flow rate and standard deviation. The developed injection nozzle system of the jigger machine has more uniform mass flow rate. A diameter of 5 mm for the outlet holes and a distance of 50 mm between them were selected to manufacture a prototype. The prototype of the injection nozzle system of the three-drive jigger machine was manufactured and tested. The test results were compared with the computational results from the developed three-drive jigger dyeing machine, the original three-drive jigger dyeing machine, and a classic jigger dyeing machine.

A Computational Analysis of Flow Field in Twin-Track Subway Tunnel to Improve Air Quality

A computational model of existing Seoul subway tunnelwas analyzed in this research. The computational model was comprised of one natural ventilationshaft, two mechanical ventilationshafts, one mechanical airsupply, a twin-track tunnel, and a train. Understanding the flow pattern of the train-induced airflow in the tunnel was necessary to improve ventilation performance. The research objective wasto improve the air quality in the tunnel by investigating train-induced airflow in the twin-track subway tunnel numerically. The numerical analysis characterized the aerodynamic behavior and performance of the ventilation system by solving three-dimensional turbulent Reynolds-averaged Navier-Stokes equations. ANSYS CFX software was used for the computations. The ventilation and aerodynamic characteristics in the tunnel were investigated by analyzing the mass flowrateat the exits of the ventilation mechanicalshafts. As the train passed the mechanical ventilation shafts, the amount of discharged-air in the ventilationshafts decreased rapidly. The air at the exits of the ventilation shafts was gradually recovered with time, after the train passed the ventilation shafts. The developed mechanical air-supply for discharging dusty air and supplying clean airwas investigated.The computational results showed that the developed mechanical air-supplycould improve the air quality in the tunnel.

A Computational Study on the Effect of Angles of Attack on a Double-Cone Type Supersonic Inlet With Bleeding System

The flow characteristics on a supersonic inlet with bleeding system at various angles of attack are studied by using computational 3D turbulent flow analysis. A turbulent CSCM compressible upwind flux difference splitting Navier-Stokes method with k-w turbulence model is used to compute the inlet flowfields. MPICH-2.0 library and PC-cluster system are used to reduce computational times. Distortion and average of total pressure recovery at the AIP (aerodynamic interface plane) are used as evaluation criteria of inlet performance. The flow characteristics at zero of angle of attack of double-cone type supersonic inlet without and with bleeding system have been compared. Without bleeding system inlet with the strong SBLI (shock/boundary-layer interaction) induces slow flow recovery near the throat and produces very thick boundary layer downstream. But the bleeding system successfully removes the low energy flow from the boundary layer near the throat. As the angle of attack at the AIP because large, we can see more non-uniform flow field, and the non-uniform flow field is the major aggravating factor of inlet performance.Copyright

A Computational Study on The Effect of Chine Nose Shapes on a Slender Body Flight Vehicle at High Angles of Attack

The flow characteristics of asymmetric vortices and the side force of a Slender Body flight vehicle with chine nose at high angles of attack have been studied by using a three- dimensional upwind Navier-Stokes method with the k-ω turbulence model and a simple laminar-turbulent transition model. Asymmetrically changing turbulent viscosities that arise from asymmetric laminar-turbulent transition conditions cause asymmetric crossflow vortex structures and side forces at higher angles of attack. The asymmetric flow control capacity of chine nose shapes at high angles of attack is studied.