Hong-Jip Kim

Structural Analysis of Gas Generator Regenerative Cooling Chamber

Elastic-plastic structural analysis for regenerative cooling chamber of gas generator was performed. Uniaxial tension test was conducted for STS316L at room and high temperature conditions to get the material data necessary for the structural analysis of the chamber which was operated under thermal load and high internal pressure. Physical properties including thermal conductivity, specific heat and thermal expansion were also measured. The structural analysis for four different types of regenerative cooling chamber of gas generator revealed that increased cooling performance decreased the thermal load and strain of the cooling channel structure. The results propose that in order for the regenerative cooling gas generator chamber to have high structural stability with endurance to high mechanical and thermal loads, it is important for the chamber to be designed to have high cooling performance.

A Study on Quantification of Damping Efficiency of Acoustic Cavities by Absorption Coefficient

A Helmholtz resonator as a stabilization device to control high-frequency combustion instabilities in liquid rocket engine is adopted and its damping capacity is verified by linear acoustic analysis and atmospheric acoustic tests. To compare the results of acoustic attenuation effect in accordance with uni-resonator`s geometry, quantitative analyses were made in the cases of various orifice diameters and lengths. Next, in the experiments to compare the results of acoustic attenuation effect by a difference in the number of resonators, damping capacity of harmful resonant frequency was improved by the increase of the number of resonators. On the other hand, attenuation efficiency of the frequency tended rather to lower due to over damping from the point of view of absorption coefficient. As the result, tuning the suitable geometry for the resonator to the resonant frequency is required for the control using the resonator. Also, the design of resonator`s geometry and the choice of its number are important to put up the optimal efficiency in consideration of restriction of its volume.

Flow Control Characteristics of Cavitating Venturi in a Liquid Rocket Engine Test Facility

The flow rate control of a cavitating venturi has been investigated with downstream pressure variation. A set of cavitating venturies for a liquid rocket engine thrust chamber firing test facility have been designed and manufactured. The flow characteristics of the cavitating venturies have been analyzed by experimental and computational methods. Results showed that constant mass flow rate condition was established by the cavitation inside the venturi. However, upstream pressure less than the actual design pressure of the cavitating venturi could not supply a constant flow rate.

Hydraulic Characteristics of Branching and Merging of Channels in Regenerative Cooling Passage in Liquid Rocket Combustors

Regenerative cooling passage to guarantee the thermal survivability in high performance rocket engine combustors could have complex configurations of the branching/merging of channels and flow turning, etc. By applying the classical hydraulic coefficients which can be found in the literature according to the flow conditions, hydraulic characteristics in regenerative cooling passages can be obtained effectively through dividing the pressure loss into friction loss and local resistance loss. Satisfactory agreement has been obtained by comparing the present results with experimental measurement of water flow test. In addition, the present results were in good agreement with CFD results when the actual coolant, kerosene was used. Therefore, the application of the present method is expected to be useful to design regeneratively cooled combustors.

An Experimental Study on Pressure Loss in Straight Cooling Channels

A regeneratively-cooled channel in a liquid rocket engine is used to effectively cool a combustion chamber inner wall from hot combustion gas, and the heat transfer/pressure loss characteristics should be predicted in advance to design cooling channels. In the present research, five cooling channels with different geometric dimensions were designed and the channels were respectively manufactured using cutter and endmill. By changing coolant velocity and downstream pressure, the effects of manufacturing method, channel shape, and flow condition on pressure losses were experimentally investigated and the results were compared with the analytical results. At same channel shape and flow condition, the pressure loss in the channel machined by the cutter was lower than that by the endmill. It was also found that the pressure loss ratio between the experimental result and the analytical data changed with the channel shape and flow condition.

A Numerical Study on Flow and Heat Transfer Characteristics of Supersonic Second Throat Exhaust Diffuser for High Altitude Simulation

ABSTRACT A numerical study has been conducted to investigate flow and heat transfer characteristics of supersonic second throat exhaust diffusers for high altitude si mulation. By changing pressure and configuration, flow and cooling characteristics of the diffuser have been studied. At the normal operation of the diffuser, there were high temperature regions over 3,000 K without cooling, especially near wall and in subsonic diffuser part. If the cooling system of the diffuser is added, flow velocity is increased due to the cooled wall temperature. 초 록 고고도 모사를 위한 초음속 이차목 디퓨저의 유동 및 열전달 특성에 대한 수치적 연구를 수행하였다. 디퓨저의 유동 특성에 영향을 주는 작동압력과 형상을 변화시켜 유동 특성과 냉각 특성을 파악하였다. 냉각이 없는 경우 디퓨저가 시동 된 후, 디퓨저 벽과 아음속 구간에서 3,000 K 이상의 고온 구간이 나타났다. 디퓨저에 냉각 시스템을 추가하면 벽면 근처가 냉각되면서 유속이 빨라져 유동 길이가 길어지고 유동 박리와 함께 압력 회복이 급격해진다. 디퓨저 내부에 압력 변화를 가져오는 유동 현상과 함께 heat flux의 경향도 유사하게 나타났다. Key Words: High-altitude Simulation(고고도 모사), STED(Second Throat Exhaust Diffuser)(이차목 디퓨저), Plume(플룸), Normal Shock(수직 충격파), Burnt Gas(연소가스)

Cold Acoustic Tests for the Elucidation of the Gap of Optimal Damping Capacity of Baffled Injectors in Liquid Rocket Combustors

Cold acoustic tests have been performed to elucidate the effect of baffle gaps on the optimal damping characteristics in a liquid rocket combustor where coaxial injectors are installed. For several axial baffle lengths, an optimal acoustic damping capacitance has been achieved in a certain gap range. Cold acoustic tests for simulating fluid viscosity by changing the pressure in a model chamber have been done to study the main mechanism of optimal damping. Experimental data have shown that the optimal gap for high damping capacity exists mainly due to the viscosity near the gap of baffles. Therefore, axial baffle length can be reduced by using the optimal baffle gap, providing a possible solution of thermal cooling problems. Also, these optimum characteristics can be some guidelines for manufacturing and assembling injectors in full-scaled rocket combustors.

Effects of Finite-Rate Chemistry and Film Cooling on Linear Combustion-Stability Limit in Liquid Rocket Engine

Thermal effect of finite-rate chemistry on linear combustion stability and film-cooling effect are investigated in sample rocket engines. The flow variables required to evaluate stability limits are obtained from CFD data with finite-rate chemistry adopted in three dimensional chamber. Major flow variables are affected appreciably by finite--rate chemistry and thereby, the calculated stability limits are modified. It is found that finite-rate chemistry contributes to stability enhancement in thermal point of view. And film cooling also has the effect of combustion stabilization.ࠀȀ耀

A Study on the Combustion Stability Evaluation of Double Swirl Coaxial Injector

A liquid rocket thrust chamber should have a high confidence in its combustion performance and combustion stability. Expecially, the injector of which function is spraying and mixing propellants plays an important role in getting the confidence. This study was carried out to evaluate combustion stability of a double swirl coaxial injector by using the model similarity method. Besides, in case of a baffle which was used to improve combustion stability, the length and gap effects of the baffle were investigated.