Jeonggyu Bak

Effects of Inlet Turbulence Conditions and Near-wall Treatment Methods on Heat Transfer Prediction over Gas Turbine Vanes

This paper investigates the effects of inlet turbulence conditions and near-wall treatment methods on the heat transfer prediction of gas turbine vanes within the range of engine relevant turbulence conditions. The two near-wall treatment methods, the wall-function and low-Reynolds number method, were combined with the SST and ωRSM turbulence model. Additionally, the RNG k-e, SSG RSM, and SST+γ-Reθ transition model were adopted for the purpose of comparison. All computations were conducted using a commercial CFD code, CFX, considering a three-dimensional, steady, compressible flow. The conjugate heat transfer method was applied to all simulation cases with internally cooled NASA turbine vanes. The CFD results at mid-span were compared with the measured data under different inlet turbulence conditions. In the SST solutions, on the pressure side, both the wall-function and low-Reynolds number method exhibited a reasonable agreement with the measured data. On the suction side, however, both wall-function and low-Reynolds number method failed to predict the variations of heat transfer coefficient and temperature caused by boundary layer flow transition. In the ωRSM results, the wall-function showed reasonable predictions for both the heat transfer coefficient and temperature variations including flow transition onset on suction side, but, low-Reynolds methods did not properly capture the variation of the heat transfer coefficient. The SST+γ-Reθ transition model showed variation of the heat transfer coefficient on the transition regions, but did not capture the proper transition onset location, and was found to be much more sensitive to the inlet turbulence length scale. Overall, the Reynolds stress model and wall function configuration showed the reasonable predictions in presented cases.

PMSG design for usage of VTOL UAV in consideration of occurrence of heat according to the change of input current

This paper presents the characteristics of heat through the input current of PMSG used in Vertical Take-Off and Landing (VTOL) hybrid-electric propulsion Unmanned Aerial Vehicles (UAV). This UAV requires 10 times more output power than horizontal flight in case of vertical takeoff. So, PMSG which is the fundamental role of providing prime power of flight vehicle also needs to respond to this momentary requirement of high output power. Generally, PMSG performance is dominated by electromagnetic field and thermal design, and these two factors are closely related to each other. In the case of high input current, heat value affects the performance of PMSG, but the research on this field is yet to be flourished. Thus, this paper analyzes the thermal characteristics of PMSG in case of high input current in comparison with rated output, and designed the PMSG based on above implication.

Comparative Study of Near-Wall Treatment Methods for Prediction of Heat Transfer over Gas Turbine Nozzle Guide Vane

* Dept. of Mechanical Engineering, Hanyang Univ., ** Dept. of Mechanical Design and Production, Konkuk Univ.,*** Korea Aerospace Research Institute, **** Dept. of Mechanical Systems Engineering, Hansung Univ., (Received January 3, 2014 ; Revised May 19, 2014 ; Accepted May 19, 2014)Key Words: Gas Turbine Nozzle Guide Vane(가스터빈 노즐 가이드 베인), Near-Wall Treatment Method(벽면처리 방법), Transition Model(천이모델), Conjugate Heat Transfer(복합열전달) 초록: 난류모델에서 벽면처리법이 터빈 노즐 베인의 열전달 예측에 미치는 영향을 비교·분석하였다. 본 연구를 위해 NASA의 C3X 터빈 노즐 베인을 사용하였다. 벽함수 방법, 저레이놀즈수 방법, 천이모델을 사용하여 베인 표면에서의 압력 및 온도를 해석하였다. 해석 결과 터빈 노즐 베인의 중간 압력분포는 각 벽면처리법에 따른 차이 없이 실험값과 잘 일치하였다. 그러나 터빈 노즐 베인의 온도와 열전달 계수는 각 벽면처리법에 따라 큰 차이를 보였다. 전반적으로 저레이놀즈수 방법과 천이모델은 벽함수 방법에 비해 온도 및 열전달 계수 예측에 특별한 이점을 보이지 않았으며, 벽함수 방법을 적용한 레이놀즈응력 난류모델이 터빈 노즐 베인 표면의 온도 및 열전달 계수를 비교적 잘 예측하였다.Abstract: The comparative analysis of near-wall treatment methods that affect the prediction of heat transfer over the gas turbine nozzle guide vane were presented. To achieve this objective, wall-function and low Reynolds number methods, and the transition model were applied and simulated using NASA´s C3X turbine vane. The predicted turbine vane surface pressure distribution data using the near-wall treatment methods were found to be in close agreement with experimental data. However, the predicted vane metal temperature and heat transfer coefficient displayed significant differences. Overall, the low Reynolds method and transition model did not offer specific advantages in the prediction of temperature and heat transfer than did the wall-function method. The Reynolds stress model used along with the wall-function method resulted in a relatively high accuracy of prediction of the vane metal temperature and heat transfer coefficient.