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항공기 착빙 해석자에 대한 물리적 표면조도 모델의 적용
민승인(S. Min),손찬규(C. Son),이관중(K. Yee) 한국전산유체공학회 2018 한국전산유체공학회지 Vol.23 No.2
Surface roughness should be taken into account when numerically predicting the aircraft icing shape since it affects the underlying physics of the frozen surface. Empirical correlation equation which introduces the uniform value of roughness based on experimental results has been widely used due to its simplicity and limitations of numerical methods for applying the physical model. Through this paper, the physical roughness models that present the roughness height varying depending on the state of the surface is introduced. Also, the differences between each model are compared, and the physical roughness model applicable to RANS based aircraft icing code is proposed. When applying the model, the analytical solution for the film thickness is derived based on the modified governing equation. Then, through the force equilibrium equation, the maximum bead height and minimum film height are computed. Subsequently, surface roughness and surface state are determined by comparing with the film thickness. For the validation of the model, the roughness, heat convection and shapes were compared with numerical results with empirical correlation and experimental results. The changes in roughness height and heat convection were evident, but the shape was not significantly different from the numerical correlation results. Specifically, the reason for the change in roughness and heat convection is discussed. Finally, the qualitative discussion is made for the little change in shape, and the necessity of the model was presented compared with the result of empirical correlation.
표면 조도를 고려한 난류 천이 모델의 항공기 결빙 해석자에 대한 적용 연구
민승인(Seungin Min),이관중(Kwanjung Yee) 한국항공우주학회 2020 韓國航空宇宙學會誌 Vol.48 No.1
본 연구에서는 표면 조도 분포가 항공기 결빙 수치 해석에 미치는 영향성에 대한 연구를 수행하였다. 기존의 항공기 결빙 해석 연구에서는 표면 조도의 크기에 초점이 맞춰져 있었으며, 표면조도의 효과 측면에서는 완전 난류 가정을 적용하여 난류 천이를 고려하지 못하고 있다. 또한 일부 연구에서, 표면 조도가 천이 과정에 미치는 영향이 선험적인 수식으로 나타났으나, 이러한 기법은 항공기 결빙 해석의 정확도를 낮추는 요인으로 여겨졌다. 따라서 본 연구에서는 표면 조도가 난류 천이 및 열 경계층에 미치는 영향을 모두 고려할 수 있도록, 2-방정식 난류 모델을 기반으로 하는 난류 천이 모델을 적용하였다. 표면 조도의 효과를 고려할 수 있도록 표면 조도 증폭 파라미터를 수송 방정식 형태로 적용하였으며, 물리적인 특성을 고려하기 위해서 표면 조도 분포 모델을 적용하였다. 이를 검증하기 위하여 2차원 익형의 표면 조도, 대류 열전달 계수 및 결빙 형상을 획득하였으며, 실험 결과와 기존 기법들을 사용한 수치 해석 연구결과를 비교하였다. 그 결과, 앞전에서의 열전달 계수의 과도한 예측과 그에 따른 익형 아랫면에서의 얼음뿔 형상이 개선되는 것을 확인할 수 있었다. In this study, the effect of surface roughness distribution and its influence on the inflight icing code was investigated. Previous numerical studies focused on the magnitude of surface roughness, and the effects were only addressed in terms of changes in thermal boundary layers with fully turbulent assumption. In addition, the empirical formula was used to take account the turbulent transition due to surface roughness, which was regarded as reducing the accuracy of ice shape prediction. Therefore, in this study, the turbulent transition model based on the two-equation turbulence model was applied to consider the effects of surface roughness. In order to consider the effect of surface roughness, the transport equation for roughness amplification parameter was applied, and the surface roughness distribution model was implemented to consider the physical properties. For validation, the surface roughness, convective heat transfer coefficient, and ice shape were compared with experimental results and other numerical methodology. As a result, it was confirmed that the excessive prediction of the heat transfer coefficient at the leading edge and the ice horn shape at the bottom of the airfoil were improved accordingly.