풍동시험과 CFD 해석 결과를 반영한 유도무기 조종날개 공력계수 모델링 기법 연구

임경진 한국군사과학기술학회 2019 한국군사과학기술학회지 Vol.22 No.3

A study on aerodynamic modeling was performed to predict the hinge moments required for initial design of missile. Fin aerodynamic coefficients were modeled using the equivalent angle of attack method based on the wind tunnel test. In addition, CFD analysis was performed to calculate the dynamic pressure around the body and improve the accuracy of aerodynamic coefficients. The aerodynamic coefficient accuracy was verified by comparisons of the coefficient acquired from wind tunnel test and prediction of flow conditions, not involved in the model built-up. It was confirmed that fin aerodynamic coefficients can be predicted effectively by using the proposed method.

다충실도 모형화를 통한 공기로 모사된 측방제트가 유도무기의 공력특성에 미치는 영향 연구

강신성(Shinseong Kang),강다영(Dayoung Kang),이경훈(Kyunghoon Lee) 한국항공우주학회 2021 韓國航空宇宙學會誌 Vol.49 No.2

측방제트는 조종면에 비해 즉각적인 유도무기 기동이 가능하지만 자유류를 간섭하여 공력계수에 영향을 줄 수 있다. 공력계수에 대한 측방제트의 영향을 파악하기 위해 측방제트를 공기로 모사한 후 측방제트 유무에 따른 공력계수 차이를 다충실도 모형을 사용하여 살펴본다. 측방제트 유무에 따라 공력계수 예측 모형으로 추정된 공력계수 간 차이를 계산하여 측방제트의 영향을 마하수, 뱅크각, 받음각의 변화에 따라 조사한다. 분석 결과, 종방향 힘 및 모멘트 계수는 비대칭적으로 발달한 측방제트에 큰 영향을 받았으며, 횡방향 힘 및 모멘트 계수는 -30°와 +30° 사이 뱅크각에서 최대로 변동하였다. 이에 반해 축방향 힘 계수는 측방제트에 영향을 받지 않았으며, 축방향 모멘트 계수는 마하수 변화에 대한 표본 부족으로 측방제트의 영향을 판단하기 어려웠다. 종합하면 측방제트가 종방향 및 횡방향 공력계수에 주요한 영향을 주어 유도무기 자세 변화를 일으킨다는 것을 확인하였다. Side-jets enable the immediate maneuver of a missile compared to control surfaces; however, they may cause adverse effects on aerodynamic coefficients, for they interfere with freestream. To find out the impact of side-jets on aerodynamic coefficients, we simulate side-jets as air gas and utilize multi-fidelity models to evaluate differences between aerodynamic coefficients obtained with and without side-jets. We computed differences in aerodynamic coefficients to investigate side-jet effects for the changes of a Mach number, a bank angle, and an angle of attack. As a result, asymmetrically developed side-jets affect the longitudinal force and moment coefficients, and the lateral force and moment coefficients drastically change in-between -30 and 30 degrees of bank angles. In contrast, side-jets hardly influence the axial force coefficients. As for the axial moment coefficient, we could not determine the side-jet effect due to a lack of aerodynamic coefficient samples in the Mach number. All in all, we confirm that side-jets lead to the change of a missile attitude as they considerably vary the longitudinal and lateral aerodynamic coefficients.

Computation of aerodynamic coefficients of a re-entry vehicle at Mach 6

R.C. Mehta,E. Rathakrishnan Techno-Press 2023 Advances in aircraft and spacecraft science Vol.10 No.5

The paper evaluates the aerodynamic coefficients on a blunt-nose re-entry capsule with a conical cross-section followed by a cone-flare body. A computer code is developed to solve three-dimensional compressible inviscid equationsfor flow over a Space Recovery Experiment (SRE) configuration at different flare-cone half-angle at Mach 6 and angle of attack up to 5°, at 1° interval. The surface pressure variation is numerically integrated to obtain the aerodynamic forces and pitching moment. The numerical analysis reveals the influence of flare-cone geometry on the flow characteristics and aerodynamic coefficients. The numerical results agree with wind tunnel results. Increase of cone-flare angle from 25° to 35° results in increase of normal force slope, axial forebody drag, base drag and location of centre of pressure by 62.5%, 56.2% and 33.13%, respectively, from the basic configuration ofthe SRE of 25°.

연비향상을 위해 최적화된 opening을 이용한 aerodynamic front end styling

이규익(Kyuik Lee),송봉하(Bongha Song),하종백(Jonpaek Ha),이태원(Taewon Lee) 한국자동차공학회 2010 한국자동차공학회 부문종합 학술대회 Vol.2010 No.5

As the environmental disruption caused by the vehicle is emerged, new vehicles with high fuel efficiency are needed. To improve fuel efficiency, vehicles have certainly the low aerodynamic drag coefficient. This paper is mainly purposed to reduce aerodynamic drag coefficient using the optimized opening for fuel efficiency front end styling by using CFD analysis. There are two ways to reduce aerodynamic drag coefficient in this paper. First one is to lower air leakage from front opening to CRFM module. Second one is to have the optimized opening. As a result, this paper showed that aerodynamic drag coefficient was reduced by lowering leakage and front opening. Also engine cooling performance was increased with aero-friendly styling.

Experimental investigation of surface roughness effect on a free-flight sphere in a Ludwieg tube

Seong-Hyeon Park,Eunju Kim,Min Hyun Han,Soo Hyung Park,Yung Hwan Byun,Ikhyun Kim 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.7

Understanding the aerodynamic coefficients of meteoroid fragments, deorbiting space debris, or launch vehicle stages through atmospheric reentry is essential for ground risk assessments. In high enthalpy flow, surface roughness is a crucial factor affecting the aerodynamic coefficient. In this work, the effect of surface roughness on drag coefficient is investigated experimentally within a Ludwieg tube at a Mach 4 test condition. The test model is a sphere with a 5 mm diameter. Three different types of surface roughness are considered using a pre-heating process. Shadowgraph technique was used to visualize the flow features and model behavior. Based on the acquired high-speed images, the drag coefficients were obtained using an image tracking technique. Results show that the drag coefficient decreases with corresponding increases in surface roughness for the given flow condition, implying the importance of surface roughness effect in ground risk assessments.

단면형상변화에 따른 박스거더단면의 정적 공기력에 관한 실험적 연구

김희덕,곽태화 한국풍공학회 2009 한국풍공학회지 Vol.13 No.2

본 연구는 박스거더단면을 대상으로 정적공기력특성에 미치는 단면형상의 영향을 파악하기 위하여 변장비 B/D=2.5∼15범위에서 6종류의 기본단면을 채택하고 하부거더의 개수 및 브래킷 길이를 변화시킨 총 47개 단면에 대하여 영각 -8°∼+8° 범위에서 풍동실험을 통하여 정적공기력을 측정하였다. 그 결과를 요약하면, 전연박리류의 재부착여부에 따라 정적공기력계수는 확연한 차이를 나타냈으며, 브래킷부의 유무에 따라서도 공기력계수의 변화특성이 달라졌으며, 하부거더수의 변화는 공기력계수의 변화에 크게 영향을 미치지 않았다. 또, 영각 -5°~+5°범위에서 최대 항력계수는 1.5정도로 현행 기준치에 약간 밑도는 값으로 나타났으나, 양력계수는 최대값이 =0.95, 최소값은 -0.6 정도로 무시할 만큼 작은 값은 아니므로 향후 설계기준개정시 반영되어야 될 것으로 판단된다. 모멘트계수은 최대값 0.05, 최소값은 -0.29로서 의 타 계수에 비하여 미소한 값으로 나타났다. In this study, the aerodynamic force coefficients are investigated for box-girder sections with various sectional shapes through wind tunnel tests. As the experimental models, three types of box-girder section are selected such as single, two and three girder-sections. The aspect ratios of models are in the range of 2.5 to 15, where bracket length is changed. As the results of experiments, the reattachment of separating flow from leading edge is strongly affects on the characteristics of aerodynamic force coefficients. The maximum drag coefficient in the range of =-5°∼+5° is =1.5, which is lower than the reference value from Korean Bridge Design Specification. The maximum and minimum lift coefficient is appeared as 0.95 and -0.6, respectively. It is noted that the lift force is not so small to disregard. The gradients of aerodynamic force coefficients at attack angle =0° are also investigated for aeroelasticity analysis.

플레이트거더의 정적 공기력계수에 미치는 단면형상의 영향에 관한 연구

김희덕,허수영 한국풍공학회 2008 한국풍공학회지 Vol.12 No.3

In this study, the effects of sectional shape on aerodynamic force coefficients of plate girder are investigated through wind-tunnel tests. As the experimental models, 36 types of sections are employed where the range of aspect ratio is 2.5 to 15 and bracket length and number of main girder are changed. As the results of experiments, the reattachment of separating flow form leading edge is strongly affects on the characteristics of aerodynamic force coefficients. The maximum drag coefficient in the range of α=-5°∼+5° exceeds the reference value from Korean Bridge Design Specification. The maximum and minimum lift coefficient is appeared as 1.0 and -0.7, respectively. Basing on results of the study, the drag and lift coefficients are suggested as the design wind loads for plate girder sections. The gradients of aerodynamic force coefficients at attack angle α=0° are also investigated for aeroelasticity analysis of plate girder.

인공신경망 기반의 유도탄 노즈 공력계수 예측 연구

이정용(Jeongyong Lee),이복직(Bok Jik Lee) 한국항공우주학회 2021 韓國航空宇宙學會誌 Vol.49 No.11

본 연구에서는 다양한 유도탄 노즈 형상과 유동조건에 대한 공력계수를 예측할 수 있는 인공신경망 기반의 공력 산출 기법을 제시한다. Missile DATCOM를 통해 유도탄 노즈 형상, 유동조건, 유도탄 공력계수로 구성된 학습 데이터셋을 구축하였다. 인공신경망의 예측 성능을 향상시키기 위해 데이터 전처리 과정으로 데이터 정규화를 진행하였고, 과대적합을 방지하기 위해 신경망 학습과정 중 드롭아웃 기법을 사용하였다. 신경망을 통해 학습하지 않은 유도탄 노즈 형상과 유동조건에 대한 공력계수를 예측하였고 이를 Missile DATCOM 해석 결과와 비교하여 신경망의 성능을 검증하였다. 그 결과 본 연구에서 구축한 신경망은 학습하지 않은 유도탄 노즈 형상과 유동조건에 대한 유도탄 공력계수를 정확하게 산출할 수 있음을 확인하였다. The present study introduces an artificial neural network (ANN) that can predict the missile aerodynamic coefficients for various missile nose shapes and flow conditions such as Mach number and angle of attack. A semi-empirical missile aerodynamics code is utilized to generate a dataset comprised of the geometric description of the nose section of the missiles, flow conditions, and aerodynamic coefficients. Data normalization is performed during the data preprocessing step to improve the performance of the ANN. Dropout is used during the training phase to prevent overfitting. For the missile nose shape and flow conditions not included in the training dataset, the aerodynamic coefficients are predicted through ANN to verify the performance of the ANN. The result shows that not only the ANN predictions are very similar to the aerodynamic coefficients produced by the semi-empirical missile aerodynamics code, but also ANN can predict missile aerodynamic coefficients for the untrained nose section of the missile and flow conditions.

VEHICLE AERODYNAMIC DRAG FOR TIRE SHAPE PARAMETERS USING NUMERICAL ANALYSIS

김문상,이재학,박성오,김용년,오병근오병근 한국자동차공학회 2022 International journal of automotive technology Vol.23 No.2

Numerical analysis has been performed to understand the effect of tires of various shapes mounted on electric vehicles on the aerodynamic drag of the vehicle. For this study, an electric vehicle produced by General Motors is selected as the baseline model, and the baseline tire is 649.4 mm in diameter and 216.5 mm in width with 4 rain grooves 10 mm wide and 7.5 mm deep. A commercial flow solver, ANSYS Fluent, is used for this study. The driving speed of the vehicle is 110 km/hr, and a rotating wall boundary condition is imposed on the tire surface to reflect the rotation of the tire, and the MRF boundary condition is used to reflect the rotation of the wheel. Three types of tire shape parameters such as tire departure angle at tire outboard point, tire corner radius of curvature, and tire bulge rate of side wall are considered and tire shape change is performed using the morphing technique built in ANSYS Fluent. It is found that these shape parameters have a sensitive effect on the increase or decrease of vehicle\'s aerodynamic drag coefficient.

Moving Mass Actuated Reentry Vehicle Control Based on Trajectory Linearization

Xiao-Long Su,Jian-Qiao Yu,Ya-Fei Wang,Lin-lin Wang 한국항공우주학회 2013 International Journal of Aeronautical and Space Sc Vol.14 No.3

The flight control of re-entry vehicles poses a challenge to conventional gain-scheduled flight controllers due to the widely spread aerodynamic coefficients. In addition, a wide range of uncertainties in disturbances must be accommodated by the control system. This paper presents the design of a roll channel controller for a non-axisymmetric reentry vehicle model using the trajectory linearization control (TLC) method. The dynamic equations of a moving mass system and roll control model are established using the Lagrange method. Nonlinear tracking and decoupling control by trajectory linearization can be viewed as the ideal gain-scheduling controller designed at every point along the flight trajectory. It provides robust stability and performance at all stages of the flight without adjusting controller gains. It is this “plug-and-play” feature that is highly preferred for developing, testing and routine operating of the re-entry vehicles. Although the controller is designed only for nominal aerodynamic coefficients, excellent performance is verified by simulation for wind disturbances and variations from -30% to +30% of the aerodynamic coefficients.