Quasi-Steady-State Scheme and Application on Prewhirl Flow and Heat Transfer in Aeroengine

Hong Xiao,Zhe-Zhu Xu,류성기 한국정밀공학회 2015 International Journal of Precision Engineering and Vol.16 No.2

For solving three-dimensional complex unsteady flow to predict aerodynamic characteristics of turbine disc cavity in aeroengine, aquasi-steady-state scheme is proposed. To validate and get reliable turbulence model, three-dimensional numerical studies, of turbinedisc cavity prewhirl flow and heat transfer, are conducted. For comparison, unsteady state computational fluid dynamics simulationsof prewhirl flow are also performed. Five turbulence models, including standard k-å model, RNG k-å model, Realizable k-å model,SST k-ù model and RSM model, are applied both quasi-steady-state scheme and unsteady CFD. Then, reliable quasi-steady-statescheme is obtained and the feasibility, instead of unsteady-state CFD simulation for reducing time resource, is verified. Furthermore,investigations of prewhirl flow and heat transfer in turbine disc cavity of aeroengine are conducted by the proposed quasi-steady-statescheme. It was found that the rotation Reynolds number should be increased to strengthen the blade cooling and weaken the heattransfer in turbine disc cavity. All the results are applied in the design of aeroengine. Also, it proves that quasi-steady-state schemeis effective in the prediction of aerodynamic characteristics in aeroengine.

종이내 수분확산 (제4보) - 종이의 비정상상태 수분확산 모델과 섬유상 수분확산 계수 -

윤성훈,박종문,이병철 한국펄프종이공학회 2002 펄프.종이기술 Vol.34 No.3

An unsteady-state moisture diffusion through cellulosic fibers in paper was characterized from the moisture sorption experiment and the mathematical modeling. The sorption experiment was conducted by exposing thin dry paper specimens to a constant temperature-humidity environment. Oven dried blotting papers and filter papers were used as test samples and the gains of their weights were constantly monitored and recorded as a function of sorption time. For a mathematical approach, the moisture transport was assumed to be an one-dimensional diffusion in thickness direction through the geometrically symmetric structure of paper. The model was asymptotically simplified with a short-term approximation. It gave us a new insight into the moisture uptake phenomena as a function of square root of sorption time. The fiber-phase moisture diffusivities(FPMD) of paper samples were then determined by correlating the experimental data with the unsteady-state diffusion model obtained. Their values were found to be on the order of magnitude of $10^{-6}-10^{-7}cm^2$/min., which were equivalent to the hypothetical effective diffusion coefficients at the limit of zero porosity. The moisture sorption curve predicted from the model fairly agreed with that obtained from the experiment at some limited initial stages of the moisture uptake process. The FPMD value of paper significantly varied depending upon the current moisture content of paper. The mean FPMD was about 0.7-0.8 times as large as the short-term approximated FPMD.

핀틀 구동속도에 따른 핀틀 추력기의 비정상상태 특성에 대한 실험적 연구

황희성(Heuiseong Hwang),허환일(Hwanil Huh) 한국항공우주학회 2016 韓國航空宇宙學會誌 Vol.44 No.3

본 논문에서는 핀틀 추력기의 비정상상태 특성을 파악하기 위하여 구동기의 속도를 측정하였으며, 정상상태 실험을 통해 비정상상태 실험 시스템을 구성하였다. 비정상상태 실험은 총 3 가지의 구동 속도(3.01 mm/s, 5.65 mm/s, 10.83 mm/s)를 이용하여 진행하였다. 그 결과 핀틀이 후진하는 경우가 전진하는 경우보다 더 빨리 명령 압력 값에 수렴하였으며, 이는 핀틀이 후진하는 경우가 연소실의 압력이 높은 상태로 형성되어 있기 때문이다. 핀틀이 전 · 후진하는 경우에 추력 곡선에 특이점들이 나타났으며, 이는 연소실 압력과 노즐 목 면적 변화에 기인하여 나타난 질유량 변화로 인한 것이다. 구동 속도가 빠를수록 이러한 현상이 뚜렷하게 나타났다. The purpose of this study is to investigate unsteady-state characteristics of a pintle thruster with various pintle speed. Based on steady state experimental results, non-linear pintle stroke equation is obtained and applied to the unsteady state experimental system. For the unsteady state experiments, three different pintle speeds are used: 3.10 mm/s, 5.65 mm/s, 10.83 mm/s, respectively. Results show that backward pintle stroke results in faster convergence time because of high chamber pressure during backward pintle stroke sequence. During the forward and backward process, thrust curve shows singular points. These phenomenons is caused by variation of mass flow rate, which is mainly due to changes of both chamber pressures and nozzle throat area. This behavior becomes distinctive for a faster pintle speed case.

MPGA-Based Indoor Localization for Non Steady-State Gas Source

Qiuming Li,Zhigang Liu,Jinkuan Wang,Kai Cheng 보안공학연구지원센터 2016 International Journal of Signal Processing, Image Vol.9 No.11

Traditional gas source localization algorithms are usually based on gas steady-state diffusion model which ignores the factor of the time, it is difficult to meet the practical application conditions. In order to solve this problem, we propose an effective gas source localization method based multiple population genetic algorithm(MPGA) to estimate the location of gas-leakage source via wireless sensor network. In this paper, we first build a gas unsteady-state diffusion model without wind based on the gas diffusion theory, and then we transfer the gas source location problem into a global optimization problem with the measured information of sensor nodes. Finally, we use MPGA to solve the optimization problem and obtain the location of the gas source. The simulation results show that the proposed method can quickly obtain the location of the gas source, and has the higher positioning accuracy as compared with tradition localization algorithms.

직선형 핀틀 노즐의 길이비에 따른 정상상태와 비정상상태 특성 연구

정기연(Kiyeon Jeong),강동기(Dong-Gi Kang),정은희(Eunhee Jung),이대연(Daeyeon Lee),김덕현(Dukhyun Kim) 한국추진공학회 2018 한국추진공학회지 Vol.22 No.3

In this study, numerical simulations were performed for steady and unsteady state characteristics of length effects on linear pintle nozzles using the overset grid method. Nozzles and pintles are created separately by an auto grid generation program to use the overset grid method. Appropriate turbulent models and numerical methods are selected for the validation of simulations. Pintle shapes are chosen from five types, with differences in the ratio of length and diameter. The longer the pintle length, the greater the thrust and thrust coefficient. The chamber pressure tendency of steady-state and unsteady-state are different for various pintle velocities. The thrust of the nozzle exit responds to changes in the nozzle throat in the unsteady-state, and the speed of pressure propagation wave generated by movement of the pintle is considered to predict the major factor of performance.

열확산계수가 다른 균일물질에 대한 동적 엑서지 분석법과 비정상상태 엑서지 분석법의 비교

조하빈(Jo, Ha-Bin),최원준(Choi, Wonjun) 대한건축학회 2023 대한건축학회 학술발표대회 논문집 Vol.43 No.1

Small temperature differences between a target system and reference state characterize thermal exergy phenomena in the built environment. Exergy analysis results change significantly with temporal changes in environmental conditions, limiting the applicability of steady-state exergy analyses. Dynamic exergy analyses have been used to mitigate these limitations, but they neglect the effect of heat capacity and only change the boundary condition over time. Recently, an unsteady-state exergy analysis method that does not violate the thermodynamic integrity has been established. In this study, the difference between dynamic and unsteady-state analyses are compared with materials of different thermal diffusivity to clarify the limitation of the dynamic analysis and the necessity of unsteady-state exergy analyses.

위치제어 기법을 이용한 핀틀 추력기의 비정상상태 실험

황희성(Heuiseong Hwang),허환일(Hwanil Huh) 한국추진공학회 2013 한국추진공학회 학술대회논문집 Vol.2013 No.12

위치 제어 기법과 위치 피드백 제어 기법을 활용하여 비정상상태 특성을 파악하였다. 비정상상태 실험을 위해 정상상태 실험을 바탕으로 비선형 방정식을 도출하였으며 이를 활용하여 시스템을 구성하였다. 그 결과 위치 제어 기법은 데이터의 진동이 없지만 수렴성이 좋지 않음을 확인할 수 있었고, 위치 피드백 제어 기법은 수렴 시간이 데이터의 진동으로 인하여 다소 느리지만 수렴성은 뛰어나다. 정상상태 특성은 핀틀이 후진할 때가 전진할 때 보다 압력 및 추력의 변화량이 더 크며 이에 따라 수렴 속도가 더 빠르게 나타남을 보여준다. The purpose of this study is to investigate unsteady-state characteristics of a pintle thruster by applying the pintle stroke control method and the pintle feedback stroke control method. Based on steady state experimental results, stroke equation is obtained and applied. Pintle stroke control method results in no oscillation, but poor convergence. Convergence time of pintle stroke feedback control method is slow, but convergence is good. Backward pintle stroke results in larger pressure/thrust variation and faster convergence time.

Linear driving force formulas for unsteady‐state diffusion and reaction in slab, cylinder and sphere catalyst

Wiley Subscription Services, Inc., A Wiley Company 2009 AIChE Journal Vol.55 No.3

지상 플러터 실험을 위한 시간 영역에서의 비정상 공기력 계산

이주연,김종환,배재성,Lee, Juyeon,Kim, Jonghwan,Bae, Jaesung 항공우주시스템공학회 2016 항공우주시스템공학회지 Vol.10 No.1

Flutter wind-tunnel test is an expensive and complicated process. Also, the test model may has discrepancy in the structural characteristics when compared to those of the real model. "Dry Wind-Tunnel" (DWT) is an innovative testing system which consists of the ground vibration test (GVT) hardware system and software which computationally can be operated and feedback in real-time to yield rapidly the unsteady aerodynamic forces. In this paper, we study on the aerodynamic forces of DWT system to feedback in time domain. The aerodynamic forces in the reduced-frequency domain are approximated by Minimum-state approximation. And we present a state-space equation of the aerodynamic forces. With the two simulation model, we compare the results of the flutter analysis.

Numerical Analysis and Experimental Verification to Predict the Internal Pressure of the Flight Vehicle

이동균(Dong Kyun Lee),김준수(Jun Soo Kim),박성우(Sung Woo Park),강성욱(Sung Wook Kang) Korean Society for Precision Engineering 2017 한국정밀공학회지 Vol.34 No.11

In this study, a numerical analysis for predicting the internal pressure of the flight vehicle system with relief valve and N2-injection type cooler was conducted to operate the system safely in an unsteady-state condition. By adopting an incompressible ideal gas equation to computational domain at each time step, internal pressure was calculated without iteration. To increase the accuracy of the numerical analysis results, numerical model was correlated by modifying the volume of the computational domain. To modify the volume of computational domain, internal pressure along time was compared with experimental results. It showed good agreement within system operating time. Air mass flow rate at the relief valve is calculated by interpolating the performance curve data. For accurate and rapid calculation of the internal pressure in an unsteady-state condition, time step size convergence study was conducted additionally. By using a correlated numerical model, Pcr of the relief valve is conducted to remain the flight vehicle system within an internal pressure range of 0.6-2.0 atm, in each flight profile. Finally, specific Pcr of relief valve was applied to the system and the experimental results showed that the internal pressure remained in a safe range.