• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1482-1487
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• 2004

In general the swirl jet is generated by the injected flow that is forced to the tangential direction. A spiral nozzle which is composed of an annular slit and a convergent nozzle, is released the spiral jet that is generated by the radial flow injection through an annular slit. The objective of the present study is to investigate the additional study that is studied a changed the convergent nozzle angle and nozzle length. In the present computation, a finite volume scheme is used to solve three dimensional Navier-Stokes equations with RNG $k-{\varepsilon}$ turbulent model. The convergent nozzle angle and the nozzle length of the spiral nozzle are varied to obtain different spiral flows inside the conical convergent nozzle. The present computational results are compared with the previous experimental data. The results obtained show that the convergent nozzle angle and the nozzle length of the spiral jet strongly influence the characteristics of the spiral jets, such as a tangential and a jet width.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.131-134
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• 2002

Compressible gas flow through a convergent-divergent nozzle is choked at the nozzle throat under a certain critical pressure ratio, and then being no longer dependent on the pressure change in the downstream flow field. In practical, the flow field at the divergent part of the critical nozzle can affect the effective critical pressure ratio. In order to investigate details of flow field through a critical nozzle, the present study solves the axisymmetric, compressible, Wavier-Stokes equations. The diameter of the nozzle throat is D=8.26mm and the half angle of the diffuser is changed between $2^{\circ}\;and\;10^{\circ}$ Computational results are compared with the previous experimental ones. The results obtained show that the divergence angle is significantly influences the critical pressure ratio and the present computations predict the experimented discharge coefficient and critical pressure ratio with a good accuracy. It is also found that a nozzle with the half angle of $4^{\circ}$ nearly predicts the theoretical critical pressure ratio.

• 한국자동차공학회논문집
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• 제7권6호
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• pp.49-56
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• 1999

The effects of the internal flow in a D.I. Diesel injection nozzle on the atomization of a spray were analyzed experimentally. Flow visualization studies were made using a transparent acrylic model nozzle as a diesel nozzle . Water instead of disel fuel was used as the injection liquid. The geometry of the model nozzle was scaled up 10 times of the actual nozzle and the injection pressure for the model nozzle was adjusted so as to achieve a Reynolds number at the discharge hole that was the same as the actual nozzle. Experimental results show that when the needle lift was small, the high turbulence in the sac chamber generated by the high velocity seat flow made the spread angle of the spray plume large. Cavitation, which arose from the sac chamber, makes the spread angle of the spray plume large but the discharge coefficient small.

• 대한기계학회논문집B
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• 제21권8호
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• pp.1077-1085
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• 1997

The use of "clean fuels" such as butane, propane, and mixtures of these (LPG) is an attractive way to reduce exhaust emissions. In this study internal flow of the pintle type injector for LPG engine is studied. The breakup of liquid jet is the result of competing, unstable hydrodynamic forces acting on the liquid jet as it exits the nozzle. The nozzle geometry and up-stream injection conditions affect the characteristics of flow inside the nozzle, such as turbulence and cavitation bubbles. A set of calculations of the internal flow in a pintle type nozzle were performed using a two dimensional flow simulation under different nozzle geometry and upstream flow conditions. The calculation showed that the turbulent intensity and discharge coefficient are related to needle leading angle(.alpha.) and needle lift.edle lift.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.426-431
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• 2001

This paper experimentally investigates the characteristics of dual coaxial jet issuing from inner supersonic nozzle and four kinds of outer converging nozzle of 40, 50, $60^{\circ}$ and $70^{\circ}$ in outer ejection angle. The pressure ratio of the stagnation to the exit ambient pressures in the inner supersonic nozzle of constant expansion rate is 7.5, which is corresponded to the condition of a slightly underexpanded, and that of outer nozzle is 4.0. Flow visualizations by using of shadowgraph method, impact pressure and centerline static pressure measurements are presented. It is found that the jet structure is changed significantly by the variation of outer nozzle ejection angle. Impact pressure level is lower and undulation of static pressure is higher, as the injection angle of outer jet increases.

• 한국분무공학회지
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• 제12권1호
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• pp.11-17
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• 2007

The swirl spray for direct-injection spark-ignition (DISI) engines was investigated using a nozzle whose exit surface shape was cut with a certain tapered angle. The reason for the change in spray's characteristics at various tapered angles was explained by the data correlating the taper and flow angles. The spray tended to shift its characteristics from the symmetric to asymmetric when the tapered angle was increased; furthermore, the spray penetration and spray cone angle were also increased. When the tapered angle was greater than the $90^{\circ}$ minus flow angle, an opened hollow cone spray was formed because of the fuel impingement against the tapered surface area of the nozzle exit. This behavior indicates that the reduction in the air pressure difference between the inner and outer spray of the spray can be achieved. This behavior also promises the potential use of the tapered nozzle for the case where the independence of the spray performance from atmospheric pressure and fuel temperature is desired.

• 한국전산유체공학회지
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• 제21권4호
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• pp.11-18
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• 2016

A numerical study is conducted on the optical fiber coating flow in a primary coating nozzle consisting of three major parts: a resin chamber, a contraction and a coating die of small diameter. The flow is driven by the optical fiber penetrating the center of the nozzle at a high speed. The axisymmetric two-dimensional flow and heat transfer induced by viscous heating are examined based on the laminar flow assumption. Numerical experiments are performed with varying the convergent angle of nozzle contraction and the optical fiber drawing speed. The numerical results show that for high drawing speed greater than 30 m/s, there is a transition in the essential flow features depending on the convergent angle. For a large convergent angle greater than $30^{\circ}$, unfavorable multicellular flow structures are monitored, which could be associated with wall boundary-layer separation. In the regime of small convergent angle, as the angle increases, the highest resin temperature at the exit of die and the coating thickness decrease but the sensitivity of coating thickness on drawing speed and the maximum shear strain of resin on the optical fiber increase. The effects of the convergent angle are discussed in view of compromise searching for an appropriate angle for high-speed optical fiber coating.

• 수산해양기술연구
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• 제56권4호
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• pp.395-406
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• 2020

The objectives of this study were to develop the optimal structures of recirculating aquaculture tank for improving the removal efficiency of solid materials and maintaining water quality conditions. Flow analysis was performed using the CFD (computational fluid dynamics) method to understand the hydrodynamic characteristics of the circular tank according to the angle of inclination in the tank bottom (0°, 1.5° and 3°), circulating water inflow method (underwater, horizontal nozzle, vertical nozzle and combination nozzle) and the number of inlets. As the angle in tank bottom increased, the vortex inside the tank decreased, resulting in a constant flow. In the case of the vertical nozzle type, the eddy flow in the tank was greatly improved. The vertical nozzle type showed excellent flow such as constant flow velocity distribution and uniform streamline. The combination nozzle type also showed an internal spiral flow, but the vortex reduction effect was less than the vertical nozzle type. As the number of inlets in the tank increased, problems such as speed reduction were compensated, resulting in uniform fluid flow.

• 대한기계학회논문집B
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• 제31권12호
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• pp.1024-1032
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• 2007

The flow characteristics with the impinging angles of defrost nozzle jet inside a commercial vehicle passenger compartment were investigated experimentally by using the two-dimensional duct-nozzle model. The shape of the nozzle contraction was designed according to the curved line of cubic equation to the vertical plan of the flow direction. The impinging angles, defined as the angle between nozzle axis and a vertical line to the windshield, were varied from the $0^{\circ}\;to\;80^{\circ}$. The mean velocity distributions, the half-widths, and the momentum distributions with the cases of both the free jet and the impinging jet onto the dummy windshield were measured. The impinging jet flows similarly with wall jet from $X/b_o=20$, and the impinging angle has an effect on the half-width of the impinging jet. The momentum distributions onto the windshield increased with the increase of impinging angle, and then their inflection point was observed around the impinging angle of $60^{\circ}$.

• International Journal of Fluid Machinery and Systems
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• 제9권2호
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• pp.137-142
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• 2016

Variable Geometry System (VGS) is widely applied to the nozzle vane for the radial inflow turbine constituting automotive turbochargers for the purpose of optimizing the power output at each operating condition. In order to improve the performance of radial turbines with VGS, it is necessary to clarify the influences of the setting angle of nozzle vane on the internal flow of radial turbine. However, the experimental measurements are considered to be difficult for the flow in radial turbines because of the small size and the high rotational speed. In the present study, the numerical calculations were carried out for the flow in the radial turbine at three operating conditions by applying the corresponding nozzle vane exit angles, which were set up in the experimental study, as the inlet boundary condition. The numerical results revealed the characteristic flow behaviors at each operating condition.