• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.6
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• pp.29-35
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• 2020

Transition Nozzles are used in industrial air-cooled heat exchangers and widely used in industrial sites as an important component in the heat energy transfer between a heat source and an actuating fluid. There is a worldwide demand for transition nozzles with various materials and shapes, depending on the use environment. This paper aims to improve the transition nozzle forging process suitable for the production of many varieties using Steps 1 to 6 of the TRIZ Methodology for Problem Solving. By utilizing the TRIZ Methodology, this study derives a method to design a variable mold, which is more efficient and can reduce costs compared with having to use several molds. To verify the suitability of the methods derived using the TRIZ technique, a forging analysis is performed on a transition nozzle using DEFORMⓇ, a commercial program for plasticity analysis, and the nozzle material is evaluated for damage as a result of deformation of the transition nozzle thickness. The derived methods can be applied to transition nozzle formation equipment to improve the efficiency of the formation process.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.3
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• pp.68-75
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• 2017

Dual bell nozzle is a type of altitude compensation nozzle, which is a nozzle that minimize the losses of the specific impulse at the off-design point of a typical bell nozzle. In this paper, numerical computations are performed to understand the transition characteristics of dual bell nozzles with fixed expansion ratios. The major design variables are the length of extension and the angle of inflection. As the length of the extension increased, the transition altitude and transition duration increased and the reduction of the thrust coefficient decreased. As the angle of inflection increased, the transition altitude and transition duration decreased and the reduction of the thrust coefficient increased.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.3
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• pp.207-215
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• 2020

Design of a shape transition nozzle is carried out as a part of building a lab-scale supersonic combustion experimental equipment. In order to connect directly the circular shaped vitiation air heater to the square shaped scramjet combustor, area change is evaluated by using the method of characteristics. Shape transition function is introduced to control the transition rate. Boundary layer correction was made through the three-dimensional computational fluid dynamics with the assessment on the several shape transition functions. The shape transition nozzle is proved minimizing the growth of boundary layer at the center of the rectangular nozzle surfaces that caused by the pressure gradient at the corners of the rectangular nozzle and the following recirculation regions.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.679-681
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• 2017

Numerical analysis was carried out by applying the concept of E-D(expansion-deflection) nozzle to dual bell nozzle. We used the CEA code to calculate the chemical composition of the nozzle and to analyze the freezing flow of 8 species. The turbulence model was chosen as the $k-{\omega}$ SST. We applied the concept of E-D nozzle to the dual bell nozzle and performed the calculated transition altitude and performance. As a result of the interpretation, the application of the E-D nozzle concept led to the formation of over-expansion conditions, which resulted in an increase in the transition altitude.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.324-330
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• 2012

Dual bell nozzle is one of the most promising choices among the altitude adaptation nozzles. This facilitates having a forced, steady and symmetrical separation at lower altitudes and a controlled flow separation at the wall inflection point which prevents the generation of dangerous side loads. In order to ensure the attached flow in the second bell, a clear understanding of the flow transition is required. Hence the motivation of our study is to arrive at an optimum profile for the second bell, which allows a sudden and controlled transition. In this work, we designed the first bell using the conventional MoC and the second bell using an inverse MoC, imposing a pressure gradient constraint. A CFD analysis is also carried out. It is found that the separation point is near the inflection point within one fourth of the extension length or it is near the exit.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.379-382
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• 2017

Flow characteristics of dual bell nozzle with pintle were investigated. Thrust and thrust coefficient were compared with the pintle-bell nozzle of the same condition, and difference according to the pintle stroke was investigated. At stroke 0 mm, the thrust of the dual bell nozzle was about 13.18% higher than the bell nozzle, and when the pintle was backward, it was similar to the bell nozzle. The change in expansion ratio with stroke was considered to be more advantageous for a dual bell nozzle that performs altitude compensation through separation and transition.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.10
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• pp.844-854
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• 2017

The Expansion-Deflection(E-D) nozzle is a nozzle that has a performance gain through the altitude compensation effect by changing the effective area within the nozzle according to the altitude. An E-D nozzle has been known to reduce the length of the nozzle and achieve the payload gain of the launch vehicle. Due to the potential advantages of an E-D nozzle, related research has been carried out in the United Kingdom, Germany, Australia and Europe etc. In the UK, the flow characteristics of the E-D nozzle and the performance comparison with the dual-bell nozzle which is altitude compensation nozzle were studied. In order to understand the transition characteristics of the E-D nozzle in DLR, the transition characteristics according to the nozzle pressure ratio change were analyzed. In Europe, numerical study using the E-D nozzle concept on upper stage of the launch vehicle Ariane 5 ESC-B was carried out to confirm the possibility of payload gain according to the nozzle length reduction. In this paper, research trends of an E-D nozzle performed outside the country are classified and analyzed according to their characteristics and utilized as basic data of E-D nozzle research in the future.

• Journal of Mechanical Science and Technology
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• v.15 no.12
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• pp.1816-1821
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• 2001

Two-dimensional blow-down type supersonic wind tunnel was designed and built to investigate the transient behavior of the startup of a supersonic flow from rest. The contour of the divergent part of the nozzle was determined by the MOC calculation. The converging part of the nozzle, upstream of fille throat was contoured to make the flow uniform at the throat. The flow characteristics of the steady supersonic condition were visualized using the high-speed schlieren photography. The Mach number was evaluated from the oblique shock wave angle on a sharp wedge with halt angle of 5 degree. The measured Mach number was 2.4 and was slightly less than the value predicted by the design calculation. The initial transient behavior of the nozzle was recorded by a high-speed digital video camera with schlieren technique. The measured transition time from standstill to a steady supersonic flow was estimated by analyzing the serial images. Typical transition time was approximately 0.1sec.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.14 no.2
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• pp.87-97
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• 1985

Experimental measurements of the heat flux to a upward impinging water jet on high heated test surface were obtained in the transition and film boiling regimes. Test variables were nozzle outlet velocity, subcooled water temperature and height of supplementary water. Boiling curve of this investigation is similar to a pool boiling curve, but it has one or two cap-shaped peaks in the transition regime. In the film boiling regime, the heat transfer rates are increased along with the increment of nozzle outlet velocity and subcooled temperature. There is optimum height of supplementary water for the augmentation of heat transfer Generalized correlations of boiling heat transfer are presented for maximum heat flux, minimum heat flux and $q_c$ at each supplementary height.

• Journal of the Korean Society of Visualization
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• v.8 no.3
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• pp.56-62
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• 2010

The interaction patterns between shock wave and boundary layer in a rocket nozzle are mainly classified into two categories, FSS(Free Shock Separation) and RSS(Restricted Shock Separation), both of which are associated with the thrust characteristics as well as side loads of the engine. According to the previous investigations, strong side loads of the engine are produced during the period of transition from FSS to RSS or vice versa. The present work aims at investigating the unsteady behavior of the separation shock waves in a two-dimensional supersonic nozzle, using experimental method and CFD. Schlieren optical method was employed to visualize the time-mean and time-dependent shock motions in the nozzle. The unsteady, compressible N-S equations with SST K-$\omega$ turbulence closure were solved using a fully implicit finite volume scheme. The results obtained show the separation shock motions during the transition of the interaction pattern.