• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.7
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• pp.709-715
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• 2011

In order to observe the wake interaction between tip vortices generated by a two-bladed rotor with slightly different pitch angles, the velocity components of the tip vortices were measured by using a two-dimensional LDV system. It was observed that the swirl velocity components of the ensuing blade deviated from the Vatistas' n = 2 vortex model and the axial velocity components of the preceding blade deviated from the Gaussian profile. It was also found that in the wake-age range of $200^{\circ}$ to $240^{\circ}$, the filament of the ensuing blade tip vortex was stretched as result of the closing in of two vortices. The results from these observations suggest the possibility that a similar wake interaction is generated in actual rotor blades, especially, in the ones with articulated hubs.

• Proceeding of EDISON Challenge
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• 2013.04a
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• pp.382-386
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• 2013

본 연구에서는 Main Rotor Blade Tip 형상 변화에 따른 후류해석을 통해 와류 생성 및 주변 유동을 분석하여 블레이드 팁 형상의 변화가 와류 간섭을 감소시키는지의 여부를 확인하였다. EDISON CFD를 이용하여 블레이드 Blade Tip 형상에 따라 유동이 어떻게 나타나며, Blade 후류의 압력과 점성의 변화를 분석하여 와류의 양상을 해석하였다. 비교 Blade 형상은 2세대 긴 직사각형 모형, KUH 수리온의 Blade, 유로콥터사의 'Blue Edge'로 비교적 최근에 개발된 대표적인 Blade Tip 형상 3개로 정하였다. 결과를 토대로 블레이드 뒷전의 와류흐름 양상을 확인하여 블레이드 와류 간섭현상의 감소를 확인하였다.

• 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 for Aeronautical & Space Sciences
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• v.41 no.11
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• pp.849-854
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• 2013

Experimental study was conducted to investigate aerodynamic interference effect of wing tip vortex in formation flight of high speed aircraft. In formation flight, wing tip vortex produced by leading aircraft can affect on the aerodynamic characteristics of trailing aircraft. The interference effect of flow is varied with distances between wing tips of leading and trailing aircraft. It is confirmed, in this study, that the interference of wing tip vortex generated from the leading aircraft makes the aerodynamic forces and moments of the trailing aircraft with the vertical or horizontal positions of the trailing aircraft. Especially, the lift coefficients of trailing aircraft were highly increased at y/b=-0.125, z/b=0.0 or deeply decreased at y/b=-0.5, z/b=0.38. The interfering pattern of wing tip vortices from two aircraft is precisely observed.

• 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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.3
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• pp.211-217
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• 2014

This study analyzes the nonlinear interaction between two different vortex shedding frequencies from a cylinder with two diameters. In particular, two different vortex shedding frequencies are generated by preparing a cylinder having two diameters artificially. Flow velocity fluctuations behind the cylinder are measured three-dimensionally. Additionally, we fabricated a hole and placed a pressure transducer for measuring the pressure on the cylinder surface. The pressure signal from the pressure transducer is used as basic signal. A TSC(Trans Spectrum Coherence) is used for checking the strength of the nonlinear interaction between two different vortex shedding frequencies. As a result, the following are clarified: i) frequency distribution behind the cylinder, ii) three-dimensional flow state behind the cylinder through calculation of ensemble average, and iii) close relationship between the vertical vortex and change of low frequency by nonlinear interaction between two different vortex shedding frequencies from the cylinder with two diameters.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2000.11a
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• pp.41-41
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• 2000

터어빈 블레이드의 경우 제작 또는 설계상의 이유로 뭉툭한 끝단을 가질 수밖에 없게 되는데, 이로 인하여 같은 터보기계인 압축기 블레이드의 경우와는 다르게 블레이드 끝단에서 끝단 와류(Trailing edge vortex)가 발생하게 된다. 이 와류는 블레이드의 손실 증가, 고주파 음파의 생성, 국부적으로 매우 큰 열 전달 및 에너지분산 등 터빈 블레이드의 성능에 좋지 못한 영향을 미치게 된다. 또한 와류와 충격파와의 간섭효과 둥이 존재하는 경우에는 매우 복잡한 유동장을 형성하며 심한 유동 구배가 존재하게 되므로 고해상도의 수치해석 방법이 아니고서는 이를 수치적으로 해석하기가 쉽지 않다.(중략)

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.289-292
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• 2009

Injector dynamics of multi swirl injectors in an annular combustor have been investigated by LES(Large Eddy Simulation) turbulent model with MPI parallel computation technique. The present study employs the LM6000 lean premixed swirl-stabilized annular combustor. Real shape combustor is simulated in order to investigate the detail interaction mechanism among multi-injectors. The strong vortex breakdown occurs at the impinging surface between the adjacent injectors so that the complex and strong oscillatory pressure propagates inside of the combustor. Tangential pressure fluctuation mode was captured by including multi injectors in computational domain.

• Journal of Korean Society of Steel Construction
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• v.20 no.6
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• pp.751-759
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• 2008

In this study, the effect of an unsteady flow field around a body of aerostatic/aerodynamic forces were investigated using rectangular cylinders (B/D = 2, 3, 4, 5). Proper orthogonal decomposition (POD) was introduced to the analysis of the fluctuating pressure field that was measured on the stationary/oscillatory B/D=4 rectangular cylinder, and the characteristics of the proper functions with flow patterns were identified. In addition, the physical decoupling and interactions in the different co-existing flow patterns were investigated through POD. The comparison with the identified proper function associated with a particular flow pattern revealed that the Karman vortex is almost not affected by the separation bubble, but that the Karman vortex considerably interferes in the development of the separation bubble around the trailing edge. It can be considered that the Karman vortex induces the increment of the curvature of the substantial separated flow.

• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.57-70
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• 2008

A high-order accurate Euler flow solver based on a discontinuous Galerkin finite-element method has been developed for the numerical simulations of blade-vortex interaction phenomena on unstructured meshes. A free vortex in freestream was investigated to assess the vortex-preserving property and the accuracy of the present flow solver. Blade-vortex interaction problems in subsonic and transonic freestreams were simulated by adopting a multi-level solution-adaptive dynamic mesh refinement/coarsening technique. The results were compared with those of other numerical and experimental methods. It was shown that the present discontinuous Galerkin flow solver can preserve the vortex structure for significantly longer vortex convection time and can accurately capture the complex unsteady blade-vortex interaction flows, including generation and propagation of acoustic waves.