• 한국전산유체공학회지
• /
• 제5권3호
• /
• pp.8-15
• /
• 2000

This research is aimed to find out how the inlet angle of secondary air affects the uniformity of temperature distribution inside a small incinerator. A commercial code, PHOENICS, is used to simulate the thermal-flow field of an incinerator. The computational grid system is constructed by Multi-Block technique provided by PHOENICS. Numerical experiments are done with the five different angles of secondary air inlet. The uniformity of temperature distribution is evaluated by checking the standard deviation of temperature distribution in an incinerator. The computational results show that there is the minimum value of standard deviation at the certain angle of secondary air inlet, which means that there is an optimum angle of secondary air inlet that could improve the uniformity of temperature distribution in an incinerator. The optimum angle of secondary air inlet is between 30 degree and 45 degree in this particular case.

• International Journal of Aeronautical and Space Sciences
• /
• 제16권1호
• /
• pp.8-18
• /
• 2015

A numerical simulation for a nonslender BWB UCAV configuration with a rounded leading edge and span of 1.0 m was performed to analyze its aerodynamic characteristics. Numerical results were compared with experimental data obtained at a free stream velocity of 50 m/s and at angles of attack from -4 to $26^{\circ}$. The Reynolds number, based on the mean chord length, is $1.25{\times}106$. 3D multi-block hexahedral grids are used to guarantee good grid quality and to efficiently resolve the boundary layer. Menter's shear stress transport model and two transition models (${\gamma}-Re_{\theta}$ model and ${\gamma}$ model) were used to assess the effect of the laminar/turbulent transition on the flow characteristics. Aerodynamic coefficients, such as drag, lift, and the pitching moment, were compared with experimental data. Drag and lift coefficients of the UCAV were predicted well while the pitching moment coefficient was underpredicted at high angles of attack and influenced strongly by the selected turbulent models. After assessing the pressure distribution, skin friction lines and velocity field around UCAV configuration, it was found that the transition effect should be considered in the prediction of aerodynamic characteristics of vortical flow fields.

• 한국항공우주학회지
• /
• 제42권7호
• /
• pp.535-543
• /
• 2014

비세장형, 둥근 앞전을 가지고 스팬이 1.0m로 축소된 BWB형 UCAV에 대해 완전난류, 천이 모델을 사용하여 전산해석을 수행하였다. 자유류는 받음각 -4도부터 26도까지 50m/s이며, 평균 시위 기준 레이놀즈수는 $1.25{\times}10^6$이다. 멀티블록 6면체 격자와 함께 완전난류 모델과 천이 모델의 결과를 비교하여 천이효과가 공력 특성에 미치는 영향을 살펴보았다. 풍동 실험과 비교한 결과 양/항력 계수는 해석범위 내에서 잘 일치하였으며, 피칭 모멘트는 높은 받음각에서 작게 예측됨과 동시에 난류모델에 따라 결과가 크게 달라졌다. 압력분포와 skin friction line, 축 방향 속도장을 이용하여 와류구조의 거동과 천이현상이 미치는 영향을 살펴본 결과, 천이효과를 고려하는 것이 UCAV의 정확한 와류 구조와 공력특성 예측에 필요한 것으로 확인하였다.

• Journal of Ship and Ocean Technology
• /
• 제10권4호
• /
• pp.12-23
• /
• 2006

In this paper, a numerical study is carried out to investigate the turbulent flow around a twin-skeg container ship model with rudders including propeller effects. A commercial CFD code, FLUENT is used with body forces distributed on the propeller disk to simulate the ship stem and wake flows with the propeller in operation. A multi-block, matching, structured grid system has been generated for the container ship hull with twin-skegs in consideration of rudders and body-force propeller disks. The RANS equations for incompressible fluid flows are solved numerically by using a finite volume method. For the turbulence closure, a Reynolds stress model is used in conjunction with a wall function. Computations are carried out for the bare hull as well as the hull with appendages of a twin-skeg container ship model. For the bare hull, the computational results are compared with experimental data and show generally a good agreement. For the hull with appendages, the changes of the stem flow by the rudders and the propellers have been analyzed based on the computed result since there is no experimental data available for comparison. It is found the flow incoming to the rudders has an angle of attack due to the influence of the skegs and thereby the hull surface pressure and the limiting streamlines are changed slightly by the rudders. The axial velocity of the propeller disk is found to be accelerated overall by about 35% due to the propeller operation with the rudders. The area and the magnitude of low pressure on the hull surface enlarge with the flow acceleration caused by the propeller. The propellers are found to have an effect on up to the position where the skeg begins. The propeller slipstream is disturbed strongly by the rudders and the flow is accelerated further and the transverse velocity vectors are weakened due to the flow rectifying effect of the rudder.