• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.145-148
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• 2009

Combustion tests of a fuel-rich gas generator had been conducted using the assembly of a powerpack. A gas generator is prone to longitudinal modes of combustion instabilities in a powerpack due to the increase of a characteristic length. It has been observed that the orifice inserted at the exit of the gas generator suppresses a longitudinal combustion instability. The intensities of pressure fluctuations in the manifolds and the chamber increase quadratically with a chamber pressure. Pressure fluctuations in the fuel manifold reveal two-fold strength greater than those in the oxygen manifold and the chamber. Frequency analysis indicates nonlinear characteristics inherent in the pressure fluctuations in the fuel manifold.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.05a
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• pp.36-39
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• 2008

Combustion instability is one of the most difficult problems in the development of liquid rocket engines. One of the damping devices for combustion instability is helmholtz resonator. Orifice length is one of factors for designing it. In this study, effects of orifice length are investigated by an experimental tests and a linear acoustic analysis. Damping capacity was improved by the increase of the length of resonator. And the results of an experimental tests and a linear acoustic analysis are showed similar tendency. Also, effects of supplied SPL(sound pressure level) are investigated and the results show that nonlinear effects are increase by the increase of supplied SPL.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.244-248
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• 2012

A series of hybrid rocket combustion experiments were carried out with PMMA/GOx changing diameter and length of the disk installed at pre-chamber. The disk can generate vortex shedding flow and change flow conditions prior to entering the fuel grain which could also alter the combustion characteristics and pressure oscillations. The interaction of vortex shedding in the pre-chamber and small-scale vortices adjacent to burning surfaces by using combustion test.

• Journal of the Korean Society of Propulsion Engineers
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• v.2 no.2
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• pp.30-37
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• 1998

This paper investigates the linear stability of wakes with special emphasis on the effect of chemical reaction. Velocity and density profiles for laminar flows are obtained from analytic profiles as well as from simulation. Wakes have two generalized inflection points and two unstable modes-sinuous and varicose modes. For analytical laminar profiles, sinuous modes are more unstable than varicose modes irrespective of density variation, which shows wakes will be destabilized by sinuous modes. Large velocity difference and density difference lead to more unstable wakes due to large momentum difference. For simulated laminar profiles, chemical reaction with stoichiometric chemistry increases temperature and stabilizes the flow due to increase in compressible reacting wades, flow becomes stable as velocity increases due to viscous dissipation.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.649-652
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• 2011

A series of hybrid rocket combustion experiments were carried out with PMMA/GOx changing diameter and length of the disk installed at pre-chamber. The disk can generate vortex shedding flow and change flow conditions prior to entering the fuel grain which could also alter the combustion characteristics and pressure oscillations. Isolated dimple-like surface roughness patterns distributed all over the fuel surface, which can be thought of as a realization of the inherent flow instability. It is very likely that the formation of cell structures is originated from the modification of boundary layer characteristics of an entering oxidizer flow caused by a blowing effect mainly taking place near the wall. This coincided with our LES results. It would be a meaningful basis to understand combustion instability of hybrid rocket motor.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.9
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• pp.838-844
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• 2015

This paper includes summarization and analysis of previous research results on acoustic attenuation due to particles and flow turning in rocket motors among various damping parameters. Particle damping is the most effective mechanism in suppressing high-frequency combustion instabilities occurring in rocket combustion chambers, which is dependent on the size and the mass fraction of particles. Relatively weak attenuation by flow turning compared to particle damping depends on the geometry of propellant and a combustion chamber. Pumping driving effects need to be taken into account when realizing vorticity generation on the propellant surface. However, its driving effects become cancelled out by flow turning loss when the propellant geometry is cylindrical.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• v.y2005m4
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• pp.291-298
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• 2005

Linear acoustic analysis has been performed to elucidate damping characteristics of acoustic cavities. Results have shown that resonant frequencies of acoustic cavity obtained by classical theoretic approach and present linear analysis are somewhat different from each other. This difference is due to the limitation of classical theory. To quantify the damping characteristics, acoustic impedance has been introduced and resultant absorption and conductance have been evaluated. Satisfactory agreement has been achieved with previous experiment. Finally the design procedure for optimal tuning of acoustic cavity has been established

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.1
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• pp.40-47
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• 2013

The similarity in internal flow of solid and hybrid rocket suggests that hybrid rocket combustion can be susceptible to instability due to vortex sheddings and their interaction. This study focuses on the evolution of interaction of vortex generated in pre-chamber with other types of vortex in the combustor and the change of combustion characteristics. Baseline and other results tested with disks show that there are five different frequency bands appeared in spectral domain. These include a frequency with thermal lag of solid fuel, vortex shedding due to obstacles such as forward, backward facing step and wall vortices near surface. The comparison of frequency behavior in the cases with disk 1 and 3 reveals that vortex shedding generated in pre-chamber can interact with other types of vortex shedding at a certain condition. The frequency of Helmholtz mode is one of candidates resulting to a resonance when it was excited by other types of oscillation even if this mode was not discernable in baseline test. This selective mechanism of resonance may explain the reason why non-linear combustion instability occurs in hybrid rocket combustion.

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

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.05a
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• pp.73-76
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• 2006

Acoustic cavity as a stabilization device to control high-frequency combustion instabilities in liquid rocket engine is adopted and its damping capacity is verified in atmospheric temperature. Geometric effects of acoustic cavity on damping characteristics are analyzed and compared quantitatively. Satisfactory agreements have been achieved with linear acoustic analysis and experimental approach. Results show that the acoustic cavity of the largest orifice area or the shortest orifice length was the most effective in acoustic damping of the harmful resonant frequency finally, it is proved that an optimal design process is indispensable for the effective control of combustion instabilities.