• Advances in aircraft and spacecraft science
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• v.6 no.6
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• pp.515-528
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• 2019

The structural vibrations of a flat plate induced by fluctuating wall pressures within wall-bounded transonic jet flow downstream of a high-aspect ratio rectangular nozzle are simulated. The wall pressures are calculated using Hybrid RANS/LES CFD, where LES models the large-scale turbulence in the shear layers downstream of the nozzle. The structural vibrations are computed using modes from a finite element model and a time-domain forced response calculation methodology. At low flow speeds, the convecting turbulence in the shear layers loads the plate in a manner similar to that of turbulent boundary layer flow. However, at high nozzle pressure ratio discharge conditions the flow over the panel becomes transonic, and the shear layer turbulence scatters from shock cells just downstream of the nozzle, generating backward traveling low frequency surface pressure loads that also drive the plate. The structural mode shapes and subsonic and transonic surface pressure fields are transformed to wavenumber space to better understand the nature of the loading distributions and individual modal responses. Modes with wavenumber distributions which align well with those of the pressure field respond strongly. Negative wavenumber loading components are clearly visible in the transforms of the supersonic flow wall pressures near the nozzle, indicating backward propagating pressure fields. In those cases the modal joint acceptances include significant contributions from negative wavenumber terms.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.12
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• pp.4036-4043
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• 1996

When a high-speed railway train enters a tunnel, a compression wave is generated ahead of the train and propagates along the tunnel, compressing and accelerating the rest air in front of the wave. At the exit of the tunnel, an impulsive wave is emitted outward toward the surrounding, which causes a positive impulsive noise like a kind of sonic boom produced by a supersonic aircraft. With the advent of high-speed train, such an impulsive noise can be large enough to cause the noise problem, unless some attempts are made to alleviate its pressure levels. In the purpose of the impulsive noise reduction, the present study tested the effect of porous walls on the compression wave propagating into a model tunnel. Experimental results were obtained using a shock tube with an open end. The results showed that the cavity/porous wall is very effective for the compression wave with a large nonlinear effect. The porosity of 30% is most effective for attenuation and pressure gradient reduction of the compression wave front. Also the impulsive noise reduction increases with increasing the length and height of the cavity, compared with the tunnel equivalent diameter.

• Journal of Institute of Control, Robotics and Systems
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• v.6 no.9
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• pp.758-767
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• 2000

The properties of linear time-varying(LTV) systems vary because of the time-varying property of plant parameters. The generalized controller design method for linear time-varying systems does not exit because the analytic soultion of dynamic equation has not been found yet. Hence, to design a controller for LTV systems, the robust control methods for uncertain LTI systems which are the approximation of LTV systems have been generally ised omstead. However, these methods are not sufficient to reflect the fast dynamics of the original time-varying systems such as missiles and supersonic aircraft. In general, both the performance and the robustness of the control system which is designed with these are not satisfactory. In addition, since a better model will give the more robustness to the controlled system, a gain scheduling technique based on LTI controller design methods has been uesd to solve time problem. Therefore, we propose a new gain scheduled QFT method for LTV systems based on neural networks in this paper. The gain scheduled QFT involves gain dcheduling procedured which are the first trial for QFT and are well suited consideration of the properties of the existing QFT method. The proposed method is illustrated by a numerical example.

• Industrial Engineering and Management Systems
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• v.11 no.4
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• pp.346-352
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• 2012

While systems engineering has been widely applied to complex system development, some evidences are reported about major budget and schedule overruns in systems engineering applied. On the other hand, many organizations have been deploying Design for Six Sigma (DFSS) to build Six Sigma momentums in the area of design and development for their products and processes. To explore the possibility of having a DFSS complement systems engineering process, this process reviews the systems engineering with their categories of effort and DFSS with its methodologies. A comparison of the systems engineering process and DFSS indicates that DFSS can be a complement to systems engineering for delivering higher quality products to customers faster at a lower cost. We suggest a simplified framework of systems engineering process, that is, PADOV which was derived from the generic systems engineering process which has been applied to the development of T-50 advanced supersonic trainer aircraft by Korea Aerospace Industries (KAI) with technical assistance of Lockheed Martin. We demonstrated that each phase of PADOV framework is comprehensively matched to the pertinent categories of systems engineering effort from various standards.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.2
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• pp.84-93
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• 2013

Stealthy, high maneuverability and super cruise abilities are required for the next generation fighter and unmanned aircraft. Thrust vector control technique currently come into use to meet these requirements. In this experimental study, axial and pitch thrust were measured and Schlieren visualization were carried out using the scaled two dimensional thrust vector nozzles under various pitch deflection angle, pitch flap length and height. From the study, we could get the supersonic flow characteristics and draw an optimum geometric configuration of the two dimensional thrust vector nozzle.

• Advances in aircraft and spacecraft science
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• v.10 no.3
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• pp.203-222
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• 2023

The detonation combustion is a supersonic combustion process follows on shock wave oscillations in detonation tube. In this paper numerical studies are carried out combined effect of blockage ratio and spacing of obstacle on detonation wave propagation of hydrogen-air mixture in pulse detonation combustor. The deflagration to detonation transition of stoichiometric (ϕ=1)fuel-air mixture in channel has been analyzed for effect of blockage ratio (BR)=0.39, 0.51, 0.59, 0.71 with spacing of 2D and 3D. The reactive Navier-Stokes equation is used to solve the detonation wave propagation mechanism in Ansys Fluent platform. The result shows that fully developed detonation wave initiation regime is observed near smaller vortex generator ratio of BR=0.39 inside the combustor. The turbulent rate of reaction has also a great significance role for shock wave structure. However, vortices of rapid detonation wave are appears near thin boundary layer of each obstacle. Finally, detonation combustor demonstrates the superiority of pressure gain combustor with turbulent rate of reaction of 0.6 kg mol/m3 -s inside the detonation tube with obstacle spacing of 12 cm, this blockage enhanced the turbulence intensity and propulsive thrust. The successful detonation wave propagation speed is achieved in shortest possible time of 0.031s with a significance magnitude of 2349 m/s, which is higher than Chapman-Jouguet (C-J) velocity of 1848 m/s. Furthermore, stronger propulsive thrust force of 36.82 N is generated in pulse time of 0.031s.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.6
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• pp.102-109
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• 2003

The number of engines for fighters has been decided by thrust required and available engines at the time since the beginning of the jet age. However, many factors such as combat effectiveness, survivability, performance, and cost were considered as engine technology has been progressed. From the vietnam war and desert storm, a twin engine fighter was shown slight superiority to a single engine one in an vulnerability，but single engine fighters were a little predominant in susceptibility This paper includes the trade-off study results on the number of engines for the supersonic light attack aircraft with single and twin engines. Twin engine configuration is 8%, 26%, and 13% higher than single engine one in MTOGW, Flyaway Cost, and LCC respectively. Little difference has been found in RM&S, Maneuver and field performance. According to the factors above, single engine fighter is profitable for low class and twin engine one for medium and higher class.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.2
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• pp.94-104
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• 2013

A numerical analysis has been conducted to determine the pitch thrust vectoring characteristics of a two-dimensional convergent divergent exhaust nozzle for supersonic aircraft application. The numerical analysis was done by using Fluent and verified by the experimental test results. Analysis was performed with pitch angle of $0^{\circ}$ and $20^{\circ}$ each at the ambient temperature condition. To see the effect of a ratio of pitch flap length and pitch flap height, the ratio was varied from 0.5 to 2.5. The numerical analysis shows that pitch thrust is changed greatly with pitch flap length. The big difference of the pitch thrust with pitch flap length is due to the shock interactions in the nozzle.

• Journal of the Korea Institute of Military Science and Technology
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• v.24 no.1
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• pp.1-11
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• 2021

Thermal protection system structures such as double-panel structures are used on the skin of the fuselage and wings to prevent the transfer of high heat into the interior of an high supersonic/hypersonic aircraft. The thin-walled double-panel skin can be exposed to acoustic loads by high power engine noise and jet flow noise, which can cause sonic fatigue damage. In order to predict the fatigue life of the skin, the octave bandwidth SPL should be calculated as narrow bandwidth PSD or acoustic load history using interpolation method. In this paper, a method of converting the octave bandwidth SPL acoustic load into a narrow bandwidth PSD and reconstructed acoustic load history was investigated. The octave bandwidth SPL was converted to the narrow bandwidth PSD using various interpolation methods such as flat, log and linear scale, and the probabilistic characteristics and fatigue damage results were compared. It was found that average error of fatigue damage index by the log scale interpolation method was relatively small among three methods.