• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2006년도 제26회 춘계학술대회논문집
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• pp.337-340
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• 2006

본 논문은 초음속 제트에서 발생하는 천음속 공명현상에 대한 실험적 연구를 기술한다. 초음속 노즐이 매우 낮은 압력비에서 작동될 때, 노즐내의 확대부에서 충격파가 발생한다. 천음속 공명현상은 이러한 충격파의 불안정한 진동에 의한 강한 음파의 발생에 기인한다. 제트 유동장은 쉴리렌 광학장치를 이용하여 가시화 하였다. 제트유동의 천음속 공명현상을 조사하기 위하여, 음향측정을 수행하였다. 천음속 공명 현상의 음향특성은 스크리치 톤과 비교하였다. 본 연구에서 얻어진 결과에 의하면, 스크리치 톤의 주파수와는 달리, 천음속 톤의 주파수는 노즐 압력비가 증가할수록 증가한다.

• 한국전산유체공학회지
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• 제8권3호
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• pp.7-11
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• 2003

Accurate assessment of the effect of jet plume on the boattail pressure drag of transonic airbreathing missiles is very important to reduce drag and to satisfy the flight range and the required maneuver. Numerical results of drag analysis for boattail and base pressures due to jet plume are presented considering the turbulence modeling. Drag assessment due to the size of jet plume, the conditions of the exhaust gas, the configurations of the boattail, and transonic mach numbers is included.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 춘계학술대회 논문집
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• pp.299-299
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• 2011

In this study, transonic aeroelastic response analyses have been conducted for the business jet aircraft configuration considering shockwave and flow separation effects. The developed fluid-structure coupled analysis system is applied for aeroelastic computations combining computational structural dynamics(CSD), finite element method(FEM) and computational fluid dynamics(CFD) in the time domain. It can give very accurate and useful engineering data on the structural dynamic design of advanced flight vehicles. For the nonlinear unsteady aerodynamics in high transonic flow region, Navier-Stokes equations using the structured grid system have been applied to wing-body configurations. In transonic flight region, the characteristics of static and dynamic aeroelastic responses have been investigated for a typical wing-body configuration model. Also, it is typically shown that the current computation approach can yield realistic and practical results for aircraft design and test engineers.

• Advances in aircraft and spacecraft science
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• 제6권6호
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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.

• International Journal of Aeronautical and Space Sciences
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• 제14권4호
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• pp.387-397
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• 2013

An assessment of two-equation turbulence models, the low Reynolds k-${\varepsilon}$ and k-${\omega}$ SST models, with the compressibility corrections proposed by Sarkar and Wilcox, has been performed. The compressibility models are evaluated by investigating transonic or supersonic flows, including the arc-bump, transonic diffuser, supersonic jet impingement, and unsteady supersonic diffuser. A unified implicit finite volume scheme, consisting of mass, momentum, and energy conservation equations, is used, and the results are compared with experimental data. The model accuracy is found to depend strongly on the flow separation behavior. An MPI (Message Passing Interface) parallel computing scheme is implemented.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.453-457
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• 2011

In this study, transonic aeroelastic response analyses haw been conducted for the business jet aircraft configuration considering shockwave and flow separation effects. The developed fluid-structure coupled analysis system is applied for aeroelastic computations combining computational structural dynamics(CSD), finite element method(FEM) and computational fluid dynamics(CFD) in the time domain. It can give very accurate and useful engineering data on the structural dynamic design of advanced flight vehicles. For the nonlinear unsteady aerodynamics in high transonic flow region, Navier-Stokes equations using the structured grid system have been applied to wing-body configurations. In transonic flight region, the characteristics of static and dynamic aeroelastic responses have been investigated for a typical wing-body configuration model. Also, it is typically shown that the current computation approach can yield realistic and practical results for aircraft design and test engineers.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2000년도 추계 학술대회논문집
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• pp.170-175
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• 2000

Parametric studies are performed of the factors influencing the afterbody drag. To display the effect of differing afterbody shapes, several ogive boattails with combinations of the base area and the angle of boattail end are computed using axisymmetric Navier-Stokes equations with central differencing and a DADI scheme. And Chien's $\kappa-\epsilon$ model is employed used for computations of turbulent flows around the base region. The effects of base area, boattail angle and jet on/off are illustrated on afterbody drag at transonic speed.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1998년도 춘계 학술대회논문집
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• pp.168-173
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• 1998

A numerical analysis of axisymetric backward facing step main nozzle flow in air jet loom has been accomplished. To obtain basic design data for an optimum main nozzle for an air-jet loom and to predict the transonic/supersonic flow, a characteristic based upwind flux difference splitting compressible Navier-Stokes method has been used. The wall static pressure of the main nozzle and the flow velocity changes in the nozzle tube were analyzed by changing air tank pressures and acceleration tube lengths. The flow inside the nozzle experiences double choking one at the needle tip and the other at the acceleration tube exit at tank pressures over $4kg_f/cm^2$. The tank pressure $P_t$ leading to the critical condition depends on the acceleration tube length; i.e, $P_t$ is higher for longer acceleration tubes. The $P_t$ value required to bring the acceleration tube exit to the critical condition is nearly constant regardless of acceleration tube length. The round needle tip shape might lead to less total pressure loss when compared with step shape.

• Journal of Mechanical Science and Technology
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• 제15권4호
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• pp.522-530
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• 2001

An experimental study of compressible jet flows has been undertaken in a small transonic wind tunnel. The aim of this investigation was to realize a jet simulator in the framework of wing/nacelle integration research and to characterize the jet flow behavior. First, free jet configuration, and subsequently jet flow in co-flowing air stream configuration were analyzed. Flow conditions were those encountered in a typical flight condition of a generic transport aircraft, i.e. fully expanded sonic jet flows interacting with a compressible external flowfield. Conventional experimental techniques were used to investigate the jet flows-Schlieren visualization and two-component Laser Doppler Velocimetry (LDV). The mean and fluctuating properties were measured along the jet centerline and in the symmetric plane at various downstream locations. The results of two configurations show remarkable differences in the mean and fluctuating components and agree well with the trend observed by other investigators. Moreover, these experiments enrich the database for such flow conditions and verify the feasibility of its application in future aerodynamic research of wing/nacelle interactions.

• 한국추진공학회지
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• 제16권2호
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• pp.51-57
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• 2012

고속의 제트에서 기저압력은 유체역학 및 실용적 공학 적용의 관점으로 매우 중요한 분야중의 하나로 다루어져 왔다. 현재까지 비압축성 유동의 기저압력 특성들은 비교적 상세하게 알려져 있다. 하지만 천음속 혹은 초음속에서의 기저압력은 압축성 효과 및 충격파 발생으로 인해 매우 다르게 나타난다. 본 연구에서는 이러한 천음속 혹은 초음속에서의 기저압력특성에 관한 이해를 위해 선행된 실험 연구 결과를 바탕으로 수치해석적 연구를 수행하였다. 간단한 오리피스를 사용하여 기저 압력 조절하는 것에 주안점을 두었다. 기저 압력에 영향을 미치는 유동변수의 적용으로 여러 형태의 초음속 제트 플룸을 분석하였다. 선행된 실험결과를 모사하여 수치해석 기법의 타당성을 조사하였으며, 계산된 기저압력과 오리피스의 유출계수에 관하여 논의하였다.