• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2008.11a
• /
• pp.11-14
• /
• 2008

Acoustic design parameters of a half-wave resonator are studied experimentally for acoustic stability in a model acoustic tube. According to standard acoustic-test procedures, acoustic-pressure signals are measured. Quantitative acoustic properties of sound absorption coefficient are evaluated and thereby, the acoustic damping capacity of the resonator is characterized. The diameter and the number of a half-wave resonator and the diameter of the tube are selected as design parameters for optimal tuning of the resonator. Optimum acoustic damping capacity is observed at smaller open area ratio as the resonator diameter increases.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.26 no.4
• /
• pp.1-9
• /
• 2022

In the current study, in order to understand the dynamic response characteristics of the system according to the external acoustic forcing, a numerical approach was developed by adding an sign-sweep forcing function to the existing network model. Through this model, the sensitivity of frequency and pressure amplitude changes according to system parameters such as the physical dimensions and boundary conditions of the target combustor was analyzed in a wide frequency range. Analysis results of dynamic response characteristics of the target combustor are shown that the frequency regime with high dynamic pressure response was similar to the instability frequency range measured in the same combustor, and in particular, the response of the system depends greatly on the location of the acoustic forcing source term.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2002.10a
• /
• pp.33-33
• /
• 2002

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.38 no.5
• /
• pp.445-455
• /
• 2010

In order to effectively predict thermo-acoustic instability within real combustors of rocket engines and gas turbines, in the present study, the Helmholtz equation in conjunction with the time lag hypothesis is discretized by the finite element method on three-dimensional hybrid unstructured mesh. Numerical nonlinearity caused by the combustion response term is linearized by an iterative method, and the large-scale eigenvalue problem is solved by the Arnoldi method available in the ARPACK. As a consequence, the final solution of complex valued eigenfrequency and acoustic pressure field can be interpreted as resonant frequency, growth rate, and modal shape for acoustic modes of interest. The predictive capabilities of the present method have been validated against two academic problems with complex impedance boundary and premixed flame, as well as an ambient acoustic test for liquid rocket combustion chamber with/without baffle.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.22 no.3
• /
• pp.46-52
• /
• 2018

A simple Crocco's $n-{\tau}$ time delay model and linear analysis of fluid flow coupled with acoustics are combined to investigate the high frequency combustion instability in the combustion chamber of LOX/hydrocarbon engines. The partial differential equation of the velocity potential is separated into ordinary differential equations, and eigenvalues that correspond to tangential resonance modes in the cylindrical chamber are determined. A general solution is obtained by solving the differential equation in the axial direction, and boundary conditions at the injector face and nozzle entrance are applied in order to calculate the chamber admittance. Frequency analysis of the transfer function is used to evaluate the stability of system. Stability margin is determined from the system gain and phase angle for the desired frequency range of 1T mode. The chamber model with variable baffle length and configurations are also considered in order to enhance the 1T mode stability of the combustion chamber.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• v.y2005m4
• /
• pp.364-367
• /
• 2005

A series of computational simulations have been carried out for non-reacting and reacting flows in channel-type and divergent scramjet combustor configurations with and without a cavity. Transverse injection of hydrogen is considered with the injection pressure varying from 0.5 to 1.5 MPa. The detailed resolution of the oscillatory flow and flame dynamics are captured at sufficient scale to identify the underlying physical mechanisms, and the role of combustor configuration, cavity and amount of heat addition could be understood.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2002.04a
• /
• pp.4-5
• /
• 2002

로켓 엔진의 개발에 있어 성능과 수명(life time)에 가장 문제가 되는 것은 연소 안정성에 있다. 일반적으로 연소 불안정을 야기시키는 것은 3가지로서 축방향(longitudinal), 반경방향(radial)과 접선방향(longitudinal) 모드(mode)가 있다. 이와 같은 모드를 제어하는 방법에는 수동적 제어방법으로 음향공(acoustic cavity)과 배플(baffle)이 있으며, 음향공은 모드에 관계없이 특정한 주파수에 맞추어 체적을 조절하여 음향파(acoustic wave)를 감쇄시키는 것이고 배플은 주파수에 관계없이 접선방향 모드를 제어하는 것이 기본 목적이나 허브(hub)를 설치하여 반경방향 모드까지 제어할 수 있다. 음향공은 엔진의 성능 또는 연소장에는 영향을 주지 않고 작동하는 반면, 배플은 초기 엔진설계를 할 때 고려하지 않으면 후에 배플을 장착하였을 때는 초기 설계의 제한 때문에 장착의 어려움과 성능 및 연소장에 영향을 미쳐 원하지 않는 엔진의 시험 결과를 야기할 수 있다. 본 연구에서는 KSR-III와 동일한 조건의 연소기에서 다양한 배플을 장착하였을 경우에 대하여 성능과 연소장에 대하여 예측하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.38 no.5
• /
• pp.456-466
• /
• 2010

Typical combustion instability such as DC-Shift found in the hybrid rocket motor is characterized by non-linearity. DC-Shift can occur in two different realizations. One is so-called a positive shift of measured DC voltage where the pressure increase suddenly. The other is a negative shift where the pressure drops abruptly. In the present work, specifically the negative DC-Shift was investigated to analyze the effect of oxidizer flow condition and the resonance between fundamental frequency and other ones, such as Helmholtz frequency, and acoustic frequency. Results show a peak frequency of several hundreds HZ shifts as combustion proceeds. A negative DC-shift was found as the result of phase cancellation between two dominant frequency, combustion frequency and flow related frequency. Still is it required to study further to identify the change of dominance of frequency during the combustion.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.32 no.6
• /
• pp.110-116
• /
• 2004

In this study, a three-dimensional finite-element analysis code has been developed to predict acoustic behaviors in rocket combustion chambers and to quantitatively evaluate acoustic stability margins for various designs with passive stabilization devices such as baffle and acoustic resonators. As a validation case, computations are made for combustion chambers with/without a hub-and-six-blade baffle which are developed in the KSR-III Development Program. Compared with experimental results from ambient acoustic test, the numerical approach reasonably well predicts acoustic pressure responses to acoustic oscillation excitation for both unbaffled and baffled combustion chambers and yields quantitatively good agreement for acoustic damping effects of baffle installation in terms of damping factor ratio and resonant frequency shift.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.11 no.4
• /
• pp.52-58
• /
• 2007

The irregular fuel surface was observed by the visualization of hybrid rocket combustion. Even though the test condition maintained oxidizer rich environment, the irregular dark fuel surface was formed as the result of incomplete combustion. In order to investigate the correlation of the characteristics of oxidizer flow and the irregular fuel surface, various flow conditions were imposed such as swirl flow, induced swirl flow by helical fuel configuration and straight flow. Test results revealed no correlation was found between oxidizer flow condition and irregular fuel surface. And this can be a commonly observed phenomena in the tests with different fuel/oxidizer combination. Thus, the irregular fuel surface can be a result of the interaction of blowing flow of vaporized fuel and the boundary layer of oxidizer flow. A further study will be required to confirm the assumption for the formation of irregular fuel surface.