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In summer, the high ambient air temperatures and increased solar radiation cause rises in rail temperatures, and rails can experience the buckling. In this study, a thermofluidic analysis was conducted to predict the temperature of a rail. Numerical simulations were performed by changing the orientation of the rails. The south-north rail and the east-west rail was named “0° rail” and “90° rail”, respectively. The numerical results from the 0° and 90° rails were validated by comparing them with measured values. Based on this validation, the temperature distribution of a 45° rail was analyzed. The total amount of energies received by the rail were in the order of 0° > 45° > 90°. The results of this study showed that the temperature of a rail can be sufficiently predicted through numerical simulation, and this approach can be used in a forecast to predict a time when buckling might occur.

Recently, electrically driven pump-fed cycle rocket engines (i.e., ElecPump engines) have received considerable attention. ElecPump engines are superior to pressure-fed engines and will likely replace gas generator cycle engines under a 100 kN thrust level. This study focuses on LOX/methane ElecPump engines with a low-thrust level and estimates the nominal operation point of the engine. The objective variable was set to the maximum velocity increment of the stage. The mixture ratio and combustion pressure were explored as the design variables. Thus, the optimal mixture ratio was proposed as the design variable, considering not only the engine weight but also the structural weight.

Monitoring rail temperature is very important for determining the safe running speed of trains and to prevent buckling. In general, the maximum variation of the internal rail temperature can be >7 ℃ depending on the point of measurement. However, there is as yet no sufficient information about how to predict the measurement point to represent the thermal deformation due to temperature distribution. In this study, the authors report a new point, called the representative measurement point, at which the rail temperature can be measured. This point considers the average deformation of the rail through structural analysis by adopting experimental and actual rail temperature data. The authors designed and installed a measurement system similar to an actual rail environment. Using the system, various data were acquired (internal/surface rail temperature and weather data) for 10 months. On the basis of these data, an analysis was done to calculate the average deformation point through thermal analysis. Finally, the representative measurement point was proposed as the position at which the average deformation point converges regardless of weather or seasons. The authors believe that the method described herein is advantageous in that it could be used in a high-accuracy temperature-monitoring system and for predicting thermal deformation and buckling.

The objective of present study is to assess the performance of the first stage compressor in a total 3-stage 5000 HP-level turbo compressor. CFD commercial code, CFX has been used to predict three-dimensional flow characteristics inside of the impeller. Shear Stress Transport (SST) model has been used to simulate turbulent flows through Reynolds-averaged Navier-Stokes (RANS) equations. Grid dependency has been also checked to get optimal grid distribution. Numerical results have been compared with the experimental test results to elucidate performance characteristics of the present compressor. In addition, flow characteristics of the impeller only have been studied for various blade configurations. Angular offset in leading edge of the blade has been selected for the optimal blade design. Performance characteristics in region of low mass flow rate and high pressure ratio between the impeller entrance and exit have been investigated for the selection of optimal blade design. Also, flow instability such as stall phenomena has been studied and anti-stall characteristics have been checked for various blade configurations in the operational window.

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)

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.

The effect of baffle gaps on the damping enhancement of a liquid rocket engine combustor has been elucidated through a series of tests, which include cold acoustic tests under both atmospheric and simulated viscous conditions and simulated combustion tests. The injector-formed baffles, which consist of an array of protruded coaxial injectors, were found to have a much greater acoustic damping effect than conventional planar baffles. For several axial baffle lengths, an optimal acoustic damping capacitance has been achieved at a 0.1 ∼ 0.2 mm baffle gap. The reason there exists an optimal baffle gap is thought to be mainly due to the viscous dissipation at the surface of the injector-formed baffles. Consequently, the axial baffle length can be reduced by taking advantage of the optimal baffle gap, providing a possible solution to the thermal cooling problem persistent with the baffle. Moreover, these optimum characteristics can provide some guidelines for manufacturing and assembling of the baffled injectors in 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.

Simulating combustion tests have been performed to elucidate the effect of baffle gaps on the optimal damping characteristics in liquid rocket combustors where coaxial injectors are installed. Amplitude of pressure oscillation in model combustion chamber and the combustion stability margin are used to quantify the damping capacitance of baffles. Satisfactory agreement has been achieved with the results of cold acoustic tests. Present results have shown that the optimal gap for high acoustic damping capacity has also the large combustion stability margin in simulating combustion tests. Therefore, the present results can be utilized to determine the baffle length and optimal gap in full-scaled 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.

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.

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.

To optimize and limit the axial length of the baffle of the KSR-III engine, stability rating tests using pulse gun as one of artificial disturbance devices have been done. Generally a rocket engine can be considered to be dynamically stable if a certain imposed external perturbation or pressure oscillation in rocket combustion chamber could be suppressed within a short time period. Decay time and other parameters for the evaluation of stabilization ability of an engine to external perturbation have been analyzed to quantify stabilization capacity of engine, in other words, dynamic stability margin. Baffle not covering flame zone enough which can be considered as collision region of injector wasn`t be able to suppress external perturbation sufficiently. The limit of combustion stability margin of engine is assumed to be 50 mm length baffle of the KSR-III engine.

Cold acoustic tests have been performed to elucidate the efiect of ba†e gaps on the damping characteristics of the flrst-tangential acoustic mode in a liquid rocket engine where coaxial injectors are installed. Injector-forming ba†es have much more advantage in acoustic damping than typical straight conflgurations. For several axial ba†e lengths, an optimal acoustic damping capacitance has been achieved in 0.1»0.2mm gap. These characteristics can be re∞ected by the acoustic intensity of 1T mode. The main reason of optimal gap is that the absorption and the feasibility of the vortex formation may increase damping capacity at the surface of the injector-forming ba†es. Resonant frequency shift becomes smaller as the axial ba†e length decreases. Therefore, axial ba†e length can be reduced by using the optimal ba†e 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 engines.

In this study, a numerical methodology has been developed to predict acoustic behaviors in liquid propellant rocket combustion chambers and to quantitatively evaluate acoustic stability margins for various designs with passive stabilization devices such as ba†e and acoustic resonators. For this purpose, linear harmonic analysis for convected Helmholtz equation is employed by utilizing the flnite element method on arbitrary three-dimensional grids. As a validation case, computations are made for combustion chambers with/without a hub-and-six-blade ba†e which are developed during the KSR(Korea Sounding Rocket)-III Development Program. Compared to experimental results from ambient acoustic test, the numerical approach reasonably well predicts acoustic pressure responses to acoustic oscillation excitation and yields quantitatively good agreement for acoustic damping efiects of ba†e installation in terms of damping factor ratio and resonant frequency shift. Next, a conceptual design process of ba†e conflguration through the numerical approach has been carried out by varying geometrical parameters. Consequently, as more efiective and economical design tool, the present numerical method proposed in this work is expected to supplement and replace experimental procedures based on acoustic test under ambient condition.

Characteristics of quenching meshes for control of hydrogen combustion in severe accident in nuclear power plant are experimentally investigated. Quenching distances of hydrogen-air mixtures without steam over a range of initial pressure are measured. Those of stoichiometric hydrogen-air mixtures with steam with respect to initial pressure are also measured. In addition, parameters that should be considered to ensure the performance and validity of the installation of quenching meshes for the control of hydrogen combustion in closed compartments are obtained from a simplified phenomenological analysis and experimentally investigated.Copyright © 2002 by ASME

To measure the displacement of a shape memory alloy (SMA) coil spring actuator for feedback control, displacement sensors larger than the actuator are normally required. In this study, a novel method for estimating the displacement of an SMA coil spring actuator without a sensor is proposed. Instead of a sensor, coil inductance is used for estimating the displacement. Coil inductance is estimated by measuring the voltage and the transient response of the current. It has a one-to-one relationship with the displacement of the coil and is not affected by load. Previous methods for estimating displacement using resistance measurements are heavily affected by load variations. The experimental results herein show that displacement is estimated with reasonable accuracy under varying loads using coil inductance. This sensorless method of estimating the displacement of an SMA coil spring actuator can be used to build a compact feedback controller because there is no need for a bulky displacement sensor.