한국시뮬레이션학회논문지 (Journal of the Korea Society for Simulation)

한국시뮬레이션학회 (The Korea Society for Simulation)
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그리드핀을 적용한 작은 세장비를 갖는 자탄의 천음속 공력특성 전산해석

Numerical simulation of the aerodynamic characteristics on the grid-fin adapted sub-munition with low aspect ratio under transonic condition

  • 투고 : 2019.01.31
  • 심사 : 2019.05.07
  • 발행 : 2019.06.30
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초록

작은 세장비(aspect ratio)를 갖는 형상의 자탄(sub-munition)은 자유낙하 시 비행 자세 안정성이 불량하고 항력조절이 어렵다. 이러한 문제점을 해결하기 위해 일반적인 비행 날개 대신 그리드핀이라고 불리는 핀을 설계하여 자탄에 적용하였다. 우선 자탄의 기본모델을 설정하고, 해당 모델에 대한 자유낙하 하는 천음속(transonic) 조건에서의 전산해석이 수행되었으며 풍동시험을 통해 전산해석 결과를 검증하였다. 기본모델의 경우 요구되는 수준의 높은 항력은 얻었으나 자세 안정성이 확보되지 않았다. 이를 개선하기 위해 그리드핀의 설계변수 중 하나인 웹 두께(web-thickness)를 변경하여 2종의 핀을 추가로 설계하였으며 해당 설계안에 대한 전산해석을 수행하였다. 수행 결과, 웹 두께가 가장 얇은 조건에서 자세 안정성이 가장 우수하게 확보되었으며 항력계수도 큰 값을 유지하였다. 해석 결과를 기반으로 그리드핀 설계를 완료하고, 자탄에 대한 공력자료를 확보하여 이를 토대로 자탄의 탄도를 예측할 수 있는 기반이 마련되었다. 또한, 그리드핀이 다양한 형태의 비행체와 탄에 사용될 수 있을 것으로 기대된다.

A sub-munition which has low aspect ratio does not have flight stability and control of drag force under free-fall condition. In order to satisfy those problems, fin, which is called grid-fin, is designed instead of conventional flight fins and adapted to the sub-munition. The base model of the sub-munition is firstly set and numerical simulation of the model is conducted under transonic condition that is free-fall range of the sub-munition. Wind test is secondly performed to verify the simulation result. The result shows that grid fin adapted sub-munition has high drag force, but the flight stability is still needed. In order to enhance the flight stability, two additional grid-fins are designed which modify web-thickness and numerical simulations of modified models are conducted. As the results, the thinnest web-thickness grid-fin has the highest flight stability and still maintains high drag coefficient. Based on these results, design of grid-fin adapted sub-munition is completed, the path trajectory of the sub-munition can be predicted with acquired aerodynamic datum and it is expected that grid fin can be used to various shape of the flight vehicle and bomb.

키워드

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Fig. 1. Typical grid fin of the missile and rocket system (Weimorts, 2001; Space X, 2015)

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Fig. 2. Flow characteristics of a grid fin

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Fig. 3. Design of the grid-fin adapted sub-munition model (Base model)

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Fig. 4. Mesh configuration of the domain

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Fig. 5. Grid-fin adapted sub-munition model for the wind test

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Fig. 6. Comparison between numerical simulation and wind test result of drag coefficient(Cd)

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Fig. 7. Wind test results (pitching moment coefficient)

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Fig 8. Comparison of pitching moment coefficient between numerical simulation and wind test (M=0.9)

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Fig. 9. Mach contour of the base grid-fin adapted model

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Fig. 10. Candidates of grid fins (3 types)

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Fig. 11. Drag coefficient(Cd) under various web-thickness condition

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Fig. 12. Pitching moment coefficient(Cm) of the grid fin adapted models

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Fig. 13. Mach contour of the 3 types grid-fin adapted model (M=0.7, α=15°)

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Fig. 14. Pressure coefficient contour of the 3 types grid-fin adapted model (M=0.7, α=15°)

Table 1. Required conditions for the performance validation

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Table 2. Critical mach number of the grid-fin adapted model

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참고문헌

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  2. Dikbas, E. (2015) Design of a Grid Fin Aerodynamic Device for Transonic Flight Regime, M.S. Thesis, Middle East Technical University.
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