Jungkun Jin

Chugging Instability of H2O2 Monopropellant Thrusters with Reactor Aspect Ratio and Pressures

Among the three types of instabilities, the low-frequency instability (chugging instability) was experimentally investigated with respect to the chamber pressure and aspect ratio (L=D) of catalytic reactors in a monopropellant thruster. ThreeH2O2 thrusterswere used, and two parameters were found to be the dominant factors that generated a chugging instability of the order of several tens of hertz. Ahigh chamber pressure and lowL=D values (lowpressure drop across the catalyst bed) were preferable for reducing pressure oscillation inside the reaction chamber. In addition, it was found that these two parameters were not independent but coupled; therefore, the point where chugging instability occurred varied slightly depending on the interaction between these parameters.

Development of a rational design procedure for a pressure recovery system for HPCL

From the geometric parameter study, an optimal ejector design procedure of pressure recovery system for chemical lasers was acquired. For given primary flow reservoir conditions, an up-scaled ejector was designed and manufactured. In the performance test, secondary mass flow rate of 200g/s air was entrained satisfying the design secondary pressure, 40 ~ 50torr. Performance validation of a supersonic ejector system along with an investigation of effects of supersonic diffuser was conducted. Placement of the diffuser at the secondary inlet further reduced diffuser upstream pressure to 7torr. Lastly, the duplicate of apparatus (air 100 g/s secondary mass flow rate each) was built and connected in parallel to assess proportionality behavior on a system to handle larger mass flow rate. Test and comparison of the parallel unit demonstrated the secondary mass flow rate was proportional to the number of individual units that were brought together maintaining the lasing pressure.

Development of an Ejector System for Operation of Chemical Lasers (II) - Optimal Design of the Second-Throat Type Annular Supersonic Ejector -

Determination of geometric design parameters of a second-throat type annual supersonic ejector is described. Tested geometric parameters were primary nozzle area ratio, cross-sectional area of second-throat, L/D ratio of second-throat and primary flow injection angle. Varying these four geometric parameters, we build a test matrix made of 81 test conditions, and experimental apparatus was fabricated to accommodate them. For each test condition, the stagnation pressure of primary flow and the static pressure of the secondary flow were measured simultaneously along with their transition to steady operation and finally to unstarting condition. Comparing the performance curve of every case focused on starting pressure, the unstarting pressure and the minimum secondary pressure, we could derive correlations that the parameters have on the performance of the ejector and presented the optimal design method of the ejector. Additional experiments were carried out to find effects of temperature and mass flow rate of the secondary flow.

The Affects of Molecular Properties of Motive Gas on Supersonic Ejection

The motive gas of a supersonic ejector is supplied from different sources depending on the application. The performance of an ejector that is represented by the secondary flow pressure, starting and unstarting pressures heavily depends on the molecular properties of the motive gas. The effects of specific heat ratio of the motive gas were investigated experimentally for an axi-symmetric annular injection type supersonic ejector. Both the starting pressure and unstarting pressure, however, decreased with the increase of the specific heat ratio of the motive gas. It was discovered that the secondary flow pressure increased as the specific heat ratio of the motive gas decreased even if the stagnation pressure of the motive flow was invariant. However, when the motive gas flow nozzle area ratio is large enough for the motive gas to be condensed, different tendency was observed.

The effects of motive gas physical properties on the performance of ejector for chemical lasers

Axi-symmetric annular type ejector has been developed as a pressure recovery system for HF/DF chemical laser. Ejector was tested using air as operating gases and low-pressure entrained flow was obtained. In this paper, we changed motive gas since operating gases for chemical laser system are products of chemical reaction. By selection of motive gas, physical properties of operating gas changes, therefore the performance of ejector is different for each motive gas, i.e., specific heat at constant pressure (CP) and average molecular weight (MW) on the effectiveness of ejection. The research was carried out by both numerical analysis using commercial CFD code, FLUENT and experiments.

Development of an Ejector System for Operating of Chemical Lasers (III) - Development and Performance Validation of a Full-Scale Ejector System for High Power Chemical Lasers -

From the geometric parameter study, an optimal ejector design procedure of pressure recovery system for chemical lasers was acquired. For given primary flow reservoir conditions, an up-scaled ejector was designed and manufactured. In the performance test, secondary mass flow rate of 100g/s air was entrained satisfying the design secondary pressure, . Performance validation of a supersonic ejector system along with an investigation of effects of supersonic diffuser was conducted. Placement of the diffuser at the secondary inlet further reduced diffuser upstream pressure to 7torr. Lastly, the duplicate of apparatus (air 500g/s secondary mass flow rate each) was built and connected in parallel to assess proportionality behavior on a system to handle larger mass flow rate. Test and comparison of the parallel unit demonstrated the secondary mass flow rate was proportional to the number of individual units that were brought together maintaining the lasing pressure.

The effects of primary gas physical properties on the performance of annular injection type supersonic ejector

The effects of the physical properties of primary flow on the performance of a supersonic ejector were investigated. Axisymmetric annular injection type supersonic ejector was used for the study of the effects of molecular weight and the specific heat at constant pressure on the ejection performance. Test gases include; air, CO2, Ar, C3H8, and CCl2F2 for different values of gas properties. As the molecular weight and CP of the primary gas increase, the secondary flow pressure increases at the same primary stagnation pressure and this behavior results from the combined effects of molar specific heat or specific heat ratio.᠊缀Ѐ㘰〻਀呥捨湯汯杹