Gujeong Park

Surface Instability on Cryogenic Swirl Flow at Sub- to Supercritical Conditions

An experimental investigation was conducted to discover the characteristics of a cryogenic swirl flow at subcritical to supercritical conditions. In the experiment, liquid nitrogen was injected into a high-pressure chamber through an open-type simplex swirl injector. The flow was imaged by high-speed photography, and the instability frequency was measured by the laser beam diagnostics of the flow. Comparing the flow images of the cryogenic and conventional swirl flows, different behaviors were noted, and it was hypothesized that the instability of the cryogenic swirl flow was dominated by the precessing vortex core in the central toroidal recirculation zone. When the ambient condition of the flow was changed from subcritical to supercritical, the phase change and subsequent density change of the injectant differed, and flow actions, such as the behavior of the downstream flow, the spray angle, the wavelength, and the propagation velocity, changed drastically. When measuring the frequency of the flow insta...

A Study on Dynamic Characteristics of Gas Centered Swirl Coaxial Injector with Acoustic Excitation by Varying Momentum Flux Ratio

Abstract Combustion instability is critical problem in developing liquid rocket engine. There have been many efforts to solve thisproblem. In this study, the method was sought through the injector as part of these efforts to suppress combustion instability.If the injector can suppress the disturbance coming from the supply line as a kind of buffer it will serve to reduce combus-tion instability. Especially we target at gas propellant oscillation in gas-centered swirl coaxial injector. The phenomenon issimulated with acoustic excitation of speaker. The film thickness response at injector exit was measured by using a liquidfilm electrode. Also the response of spray to the disturbance was observed by high-speed photography. Gas-liquid momentumflux ratio and the frequency of feeding gas oscillation were changed to investigate the effect of these experimental parame-ters. The trend of response by varying these parameters and the cause of weak points was studied to suggest the better designof injector for suppressing combustion instability.

Experimental Study on the Spray Characteristics of a Dual-Manifold Liquid-Centered Swirl Coaxial Injector

A throttleable rocket engine enables operational possibilities such as the docking of spacecraft, maneuvering in a certain orbit and landing on a planet’s surface, altitude control, and entrance to atmosphere-less planets. Thus, throttling methods have long been researched. However, dual-manifold injectors, which represent one throttling method, have been investigated less than others. In this study, dual-manifold and single-manifold injectors were compared to determine the characteristics of dual manifold injectors. Also, the effects of gas injection were investigated with various F/O ratios. To investigate the characteristics, mass flow rate, spray pattern, spray angle, and droplet size were measured. The spray angle and droplet size were captured by indirect photography. About 30 images were taken to assess the spray patterns and spray angle. Also, 700 images were analyzed to understand the droplet distribution and targeting area, moving to the right from the centerline with 1.11-㎝ intervals. The droplet size was obtained from an image processing procedure. From the results, the spray angle showed two transition regions, due to swirl momentum in the swirl chamber regardless of the F/O ratio. The droplet size showed similar trends in both dual-manifold and single-manifold injectors except in the low mass flow rate region. In the case of the dual- manifold injector, the spray cone was not fully developed in the low mass flow rate region due to low angular momentum in the swirl chamber.

Dense Spray Patternation using Optical Tomography

Optical tomography was used to measure the pattern of spray cross-section. The maximum-likelihood estimation (MLE) algorithm was used to reconstruct the spray cross-section from the measured transmission rate of the spray. A swirl-type injector was used to form an optically dense spray, and the test was carried out in a high-pressure chamber, to control the pressure condition of the test site. Before the experiment, the reliability of the MLE-based reconstruction algorithm was verified, by comparing it with a conventional filtered back projection reconstruction (FBP) method. The MLE algorithm showed superior reconstruction of the image. In the spray patternation experiment, the results of the optical tomography and optical line patternator, which uses Mie scattering signal information, were compared. While measuring the cross-section of optically dense spray, the intensity of the scattering signal had attenuated to an uncorrectable level, which led to incorrect spray pattern measurement by the optical line patternator. However, reliable results were obtained by optical tomography, under the same condition. Finally, the pattern of the optically dense spray was measured at various chamber pressures, of up to 3 MPa. As the chamber pressure increased, the hollow cone-shaped swirl spray shrank, and the attenuation coefficient value of the inner region increased.

Spray Patterns and Injection Characteristics of Gas-Centered Swirl Coaxial Injectors

AbstractSpray characteristics of gas-centered swirl coaxial injectors, which are commonly used in staged combustion cycle engines, are investigated numerically and experimentally. The spray angle a...

Effect of excitation on gas centered swirl coaxial injectors

This work was supported by the Advanced Research Centre Program (NRF-2013R1A5A1073861) through a National Research Foundation of Korea (NRF) grant, funded by the Korean government (MSIP), and contracted through the Advanced Space Propulsion Research Centre at Seoul National University and was supported by an NRF (National Research Foundation of Korea) Grant funded by the Korean Government (NRF-2016-Fostering Core Leaders of the Future Basic Science Program/Global Ph.D. Fellowship Program).

Characteristics of Gas-Centered Swirl Coaxial Injector with Acoustic Excitation of Gas Flow

Various research activities on combustion instability that significantly influences engine efficiency have been conducted. The instability of liquid fuel flow by perturbation of gas oxidizer flow in gas-centered swirl coaxial injectors is investigated using air and water. Gas perturbation is generated by a speaker, and variation in the film thickness at the end of the injector is measured. The spray patterns have different shapes, depending on the excitation frequency. The excitation effect is enhanced by the increment of the momentum flux ratio. Different gain values are achieved according to the input frequency, and a high value is realized in both low and high frequencies. The high- and low-frequency peaks are due to the resonant frequency of the gas feeding line and gas–liquid interface instability, respectively. The high-gain frequency can possibly cause combustion instability.

Effect of Injector Geometry on Cryogenic Jet Flow

Characteristics of cryogenic single jet flow were investigated. Liquid nitrogen was injected into a high-pressure chamber and formed single jet. Ambient condition around jet was changed from subcritical to superctirical condition of nitrogen. Injector geometries also were changed. A shape of the jet and core diameter were measured by flow visualization technique, and core spreading angle was calculated. Flow instability was found at atmospheric pressure condition. As ambient pressure increased, core spreading angle was increased and maintained after certain pressure.