• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2011.11a
• /
• pp.641-644
• /
• 2011

The performance tests of secondary throat supersonic exhaust diffusers were carried out by using scaled down model and gas nitrogen. It was performed to find the performance characteristics according to diffuser inlet length(Ld), secondary throat length(Lst), divergence length(Ls). There was few change by diffuser inlet length(Ld), but starting pressures of the diffusers were effected by secondary throat length(Lst), divergence length(Ls). It was confirmed that starting pressure was not changed over 8 Lst/Dst.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.38 no.4
• /
• pp.279-288
• /
• 2014

Second throat supersonic exhaust diffusers (STEDs) were designed to simulate high-altitude conditions according to the normal-shock model. Experimental studies were performed on the STEDs to investigate how performance characteristics varied with the length and diameter of the STED using high-pressure nitrogen gas. The variation in performance due to length indicated that the performance of the STED could be very slightly improved by adjusting the diffuser inlet length ($L_d$), and it could be significantly improved by optimizing the second throat length ratio ($L_{st}/D_{st}$) and the divergence length ($L_s$). The starting and vacuum chamber pressures exhibited the highest level of performance near ($A_d/A_{st}$) of the design point.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2008.05a
• /
• pp.321-327
• /
• 2008

Performance characteristics of the axi-symmetric supersonic exhaust diffuser (SED) with a second throat are numerically investigated. Computational strategy repeats those for a straight exhaust diffuser with zero-secondary flows. Renolds-Average Navier-Stokes equations with a standard ${\kappa}-{\varepsilon}$ turbulence model incorporated with standard wall function are solved to simulate the diffusing evolutions of the nozzle plume. The methodology is validated with accuracy. To predict the improvement of starting performance by second throat diffuser, diffuser characteristic curve due to the SED equipped with the second throat is speculated with respect to that of a straight area type as a function of nozzle stagnation pressure. Principal physics caused by the of the second throst is also addressed in terms of a second throat area ratio.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2011.11a
• /
• pp.970-972
• /
• 2011

The vacuum chamber pressure was investigated according to the second throat exhaust diffuser entrance diameter. The sizes of diffuser entrance were changed three cases, and each case was computed by using CFD. Also in order to relatively compare the vacuum chamber pressure the Euler equation was adopted. According to the results, as the size of diffuser entrance was increased it was observed that the vacuum chamber pressure was decreased.

• Journal of the Korean Wood Science and Technology
• /
• v.34 no.6
• /
• pp.1-11
• /
• 2006

Grafted tissues were investigated using various microscopic techniques. Pinus thunbergii was used as stock and scion and autografted by cleft graft method. Histochemically, grafting processes can be proceeded by four stages: 1) formation of necrotic layer, 2) proliferation of callus, 3) development of neo-cambium from callus, and 4) restoration of new vascular xylem. Necrotic la yer composed of pectin and lignin was gradually degraded during grafting process and disappeared when new union was formed between stock and scion. A large number of starch and lipid bodies in the cytoplasm were also gradually degraded during grafting process and disappeared at the grafting interface. Nucleus and plasmodesmata were not changed. Bubble-like callus was generated from all living parenchyma cells and from the callus. The tracheary elements differentiated from the callus had either reticulate or pit-like thickenings in the secondary walls with bordered pits. Secondary cell wall thickening occurred toward filing to the void parts between reticulated secondary wall. Tracheids formed in the secondary xylem were short with irregular wall thickness. New secondary xylem cells with swirled shapes, which developed in graft union were oriented horizontally and obliquely to axis of the stem.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2011.11a
• /
• pp.968-969
• /
• 2011

The characteristics of second throat exhaust diffuser were investigated by using CFD. Because the second throat exhaust diffuser(STED) is known as the effective device for simulating high-altitude circumstance more than a cylindrical supersonic diffuser STED was analyzed. The back pressure around nozzle was reduced by entrance size of STED and it was observed that the initial strong shock was the weak oblique shock along the diffuser. Therefore the static pressure at nozzle exit was recovered as the ambient pressure and the STED worked well.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2011.11a
• /
• pp.881-884
• /
• 2011

Secondary throat supersonic exhaust diffusers were designed by Normal-shock theory and manufactured. Experimental studies of the diffusers were performed using nitrogen gas of room temperature. It showed a difference about 18% between the experimental and theoretical results. The difference was shown by friction loss at the wall of the diffuers.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.38 no.4
• /
• pp.321-328
• /
• 2014

The performance characteristics of a subscale diffuser under non-reacting conditions for high-altitude simulation were numerically investigated with respect to different lengths of the secondary throat diffuser. The ratio of the length of the diffuser entrance to the nozzle exit diameter was set to 0, 50, and 100%. In addition, flow characteristics were studied for a range of length-to-diameter ratios of the secondary throat diffuser. An insufficient diffuser entrance length caused contraction of the plume immediately after the nozzle exit. When the length-to-diameter ratio was less than 8, a strong Mach disk was formed inside the diffuser, resulting in a sharp increase in pressure. In addition, flow characteristics in the diverging part of the diffuser were investigated for a range of diverging part lengths. A short diverging part may lead to abrupt pressure recovery, resulting in the possible application of mechanical load to the diffuser.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.24 no.8
• /
• pp.1128-1138
• /
• 2000

Pumping action in ejector systems is generally achieved through the mixing of a high-velocity and high-energy stream with a lower-velocity and lower-energy stream within a duct. The design and performance evaluation of the ejector systems has developed as a combination of scale-model experiments, empiricism and theoretical analyses applicable only to very simplified configurations, because of the generic complexity of the flow phenomena. In order to predict the detailed performance characteristics of such systems, the flow phenomena throughout the operating regimes of the ejector system should be fully understood. This paper presents the computational results for the two-dimensional supersonic ejector system with a second throat. The numerical simulations are based on a fully implicit finite volume scheme of the compressible Reynolds-averaged Navier-Stokes equation in a domain that extends from the stagnation chamber to the diffuser exit. For a wide range of the operating pressure ratio the flow field inside the ejector system is investigated in detail. The results show that the supersonic ejector systems have an optimal throat area for the operating pressure ratio to be minimized.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.3 no.4
• /
• pp.58-66
• /
• 1999

The flow characteristics of supersonic ejectors is often subject to compressibility, unsteadiness and shock wave systems. The numerical works carried out thus far have been of one-dimensional analyses or some Computational Fluid Dynamics(CFD) which has been applied to only a very simplified configuration. For the design of effective ejector-pump systems the effects of secondary mass flow on the supersonic ejector flow should be fully understood. In the present work the supersonic ejector-pump flows with a secondary mass flow were simulated using CFD. A fully implicit finite volume scheme was applied to axisymmetric compressible Navier-Stokes equations. The standard two-equation turbulence model was employed to predict turbulent stresses. The results obtained showed that the flow characteristics of constant area mixing tube types were nearly independent of the secondary flow rate, but the flow fields of ejector system with the second-throat were strongly dependent on the secondary flow rate due to the effect of the back pressure near the primary nozzle exit.