In-Hyun Cho

Modeling the Prediction of Helium Mass Requirement for Propellant Tank Pressurization

DOI: 10.2514/1.A32073 A numerical model that predicts the helium mass required for propellant tank pressurization during propellant outflow was developed. The model has the feature of including the effects of the internal hardware of the propellant tanksuchasbaffles,pressurantstoragetanks,andotherinstrumentation.Ituseda finitevolumemethodthatdivides the ullage and tank wall one-dimensionally along the propellant tank axis. A series of cryogenic propellant drainage testswerecarriedouttoverifythedevelopednumericalmodel.Therequiredamountofheliummasspredictedbythe model showed very good agreement with test data within an accuracy of 2:27% under the operating conditions. The developed model was applied to the pressurization system of Korea Sounding Rocket-III, and the results were compared withthe flight-test data.The comparisonresults showedthatthe developed modelwassatisfactory for the prediction of the required helium mass during flight. Additionally, a parametric study was performed to test the sensitivity of the developed model, and the results showed that the heat transfer coefficient between the ullage and the tank wall was the key factor in the accuracy of the model.

Flow Rate Control Characteristics of a Cavitating Venturi in a Liquid Rocket Propellant Feed System

Characteristics of flow rate control has been studied for a cavitating venturi adopted in a liquid rocket propellant feed system. Both experiment and numerical simulation have been performed to give about 10% discrepancy of mass flow rate for cavitating flow regime. Mass flow rate is confirmed to be saturated for pressure difference higher than pa when the upstream pressure is fixed to pa and the downstream pressure is varied. The evaporation amount depends substantially to non-condensable gas concentration. However the mass flow rate characteristics is relatively insensitive to the mass fraction of non-condensable gas. So it reduces by only 2% when the non-condensable gas concentration is increased from 1.5PPM to 150PPM. From the previous comparison the expansion of the non-condensable gas and the evaporation of liquid are verified to gave same effect to the pressure recovery pattern.

The Rubber Performance Evaluation for Kick Motor Flexible Seal

A Kick Motor, KSLV-I second stage propulsion system, utilizes a flexible seal for pitch and yaw axis controls during combustion. A flexible seal consists of the alternate laminate of rubber and composite reinforcement between forward and aft rings. A Kick Motor nozzle is rotated by the shear deformation of rubber layers. Consequently, the development of rubber, which is appropriate to the usage condition of flexible seal, is very important. A tensile test, QLS test (shear modulus and failure shear stress), and aging test have been carried out to confirm the performance of rubber developed. Test results show that the shear modulus of rubber are 0.4310 ~ 0.4997MPa and the failure shear stress is more than 2.5MPa.

Required Pressurant Mass for Cryogenic Propellant Tank with Pressurant Temperature Variation

The prediction of the required pressurant mass for maintaining the pressure of propellant tanks during propellant feeding is an important issue in designing pressurization system. The temperature of pressurant fed into propellant tank is the critical factor in the required pressurant mass and is one of the most crucial design parameters in the development of pressurization system including designing the weight of pressurant tanks and the size of heat exchanger. Hence a series of propellant drainage tests by pressurizing propellant stored in a cryogenic propellant tank have been performed with measuring the temperature distribution inside ullage and the required pressurant mass according to the temperature condition of pressurant. Results shows that the required pressurant mass decreases as the temperature of pressurant increases. However, the rate of the actual pressurant mass to the ideal required pressurant mass increases.

Determination of Cyclogram for Liquid-Propellant Rocket Engine

A vertical test stand based on launcher propulsion system was constructed and several tests for the determination of cyclogram were carried out. To make an accurate estimation, static and dynamic pressures were measured and analyzed. Especially, static pressure measurements using fast response sensors without extension tubes were used to determine operation sequence more evidently. The standard operation times of final valves were determined in cold flow tests with an engine head, and fire formation time in combustion chamber was checked in an ignition test with an ignitor only. On the basis of these tests, ignition sequence was established and combustion test cyclogram was finally determined. According to combustion test, test results were well matched with the determined cyclogram within 0.05 sec.