Chae Hoon Sohn

Acoustic Stability Analysis of Liquid Propellant Rocket Combustion Chambers

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.

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...

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.

Experimental Study of Performance and Bubble Pattern of Air-Lift Pumps with Various Tube Diameters and Submergence Ratios

An airlift pump can be used to pump liquids and sediments within itself, which cannot easily be pumped up by a conventional method, by using the airlift effect. This characteristic of the airlift pump can be exploited in a DCFC (Direct Carbon Fuel Cell) so that molten fuel with high temperature may be carried or transported. The basic characteristics of airlift are investigated. A simple system is constructed, where the reservoir is filled with water, a tube is inserted, and air is supplied from the bottom of the tube. Then, water is lifted and its flow rate is measured. Bubble patterns in the tube are observed in a range of air flow rates with the parameters of the tube diameter and submergence ratio, leading to four distinct regimes. The pumping performance is predicted, and the correlation between the supplied gas flow rate and the induced flow rate of water is found.

A Numerical Study on Combustion Characteristics of Coaxial-Jet Injectors Using Scaling Techniques in a Subscale Chamber

Numerical analyses are conducted with scaling techniques to predict combustion instability in actual fullscale combustion chamber of rocket engines. From the simulation with a subscale chamber, flame patterns are investigated as a function of the recess length and spreading angle of fuel jet is focused on. For stability rating, damping factors have been obtained as a function of hydraulic parameter and the data give us information on relatively stable and unstable zones. From the numerical results, the stable zone can be identified in a quantitative manner.