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Donghyuk Kang,Daichi Nakai,Yuka Iga 한국유체기계학회 2019 International journal of fluid machinery and syste Vol.12 No.4
Investigation of the thermodynamic effect of tip-leakage-vortex cavitation on a two-dimensional hydrofoil designed with a tip clearance for hot water is reported herein. During unsteady cavitation of water maintained at 90 °C (hereinafter referred to as hot water), the observed decrease in temperature in the tip-leakage region was greater compared to that in the mid-span region. In contrast, during supercavitation of hot water, the situation was reversed (i.e., the temperature decrease in the tip-leakage region was smaller than that in the mid-span region). The cavitation-pattern map for hot water was observed to be largely similar to that for water maintained at 30 °C (hereinafter referred to as tepid water). On the other hand, the amplitude of the dominant frequencies of unsteady cavitation of the hot water was observed to be greater than that of the cavitation of tepid water owing to the sudden collapse of cloud cavitation.
Three-Dimensional Theoretical Study on Flow Characteristics of a Spiral-Channel Viscous Micropump
Donghyuk Kang,Koichi Nishibe,Kotaro Sato,Kazuhiko Yokota 한국유체기계학회 2019 International journal of fluid machinery and syste Vol.12 No.2
Technological developments have led to micropumps playing an ever-greater role at the heart of micro total analysis systems. Spiral-channel viscous micropumps have been studied theoretically, numerically, and experimentally. However, high-accuracy performance predictions have not been achieved over a wide range of operating conditions. The present study proposes three-dimensional and quasi-three-dimensional theoretical expressions for predicting the pressure performance of spiral-channel viscous micropumps in low-Reynolds-number environments. The theoretical analysis is validated through a series of comparisons with numerical simulation results for the pressure performance curves, velocity distributions, velocity gradient distributions, and channel internal pressure distributions. Furthermore, the influence of the channel aspect ratio on the performance characteristics is investigated.
Two-Dimensional Theoretical Study on Flow Characteristics of a Spiral-Channel Viscous Micropump
Donghyuk Kang,Koichi Nishibe,Kotaro Sato,Kazuhiko Yokota 한국유체기계학회 2018 International journal of fluid machinery and syste Vol.11 No.4
This study investigates the flow characteristics of a spiral-channel viscous micropump using two-dimensional theoretical analysis. The obtained results are compared to the results obtained from experiments, numerical simulations, and the theoretical analysis of Kilani et al., and the similarities and differences between these approaches are discussed. The present two-dimensional theoretical approach is validated. Its accuracy is improved as compared to previous work by setting the spiral-channel axis as the spiral-channel length from the pump inlet to the outlet and by considering the moving wall as a component in the spiral-channel direction of the circumferential velocity of the rotating disk. Furthermore, the present two-dimensional analysis can accurately predict pump performance, even though the actual flow in the micropump is three dimensional.
Donghyuk Kang,Satoshi Yamazaki,Shusaku Kagawa,Byungjin An,Motohiko Nohmi,Kazuhiko Yokota 한국유체기계학회 2019 International journal of fluid machinery and syste Vol.12 No.1
The present study investigated flow characteristics in the V-shaped region of the suction performance curve for a double-suction centrifugal pump based on the computational fluid dynamics (CFD). The V-shaped region in the time-averaged suction performance curve was simulated well. The CFD simulated the fluid oscillations due to cavitation surge and rotating cavitation well. The V-shaped region was observed in the absolute total pressure difference between the impeller inlet and outlet. The time histories showed that the cavity produced vorticity, resulting in an increase in a pressure loss, and a decrease in an impeller torque and an angular momentum flow rate. The time-averaged cavity volume, pressure loss between the impeller inlet and outlet, vorticity in the blade passage and impeller torque were examined. A Λ shape of a cavity volume curve caused a Λ shape of a vorticity curve, resulting in a Λ shape of a pressure loss curve and a V shape of an impeller torque curve. The Λ shape of the pressure loss curve and the V shape of the impeller torque curve caused the V shape of the suction performance curve.
Unified Performance Model for S-Shaped Characteristics of Pump–Turbines Considering Reverse Flow
Donghyuk Kang,Wakana Tsuru,Ono Koudai,Kazuhiko Yokota 한국유체기계학회 2023 International journal of fluid machinery and syste Vol.16 No.1
This study proposes a new unified performance model for the S-shaped characteristics of pump–turbines considering reverse flow. The turbine and reverse pump characteristic equations were unified using a sigmoid function considering the reverse flow. In the analysis, the torque coefficient is larger for small guide vane angles than for large guide vane angles due to an increase in the turbine Euler head. In the turbine mode, the runner shock loss and the circumferential discharge loss are directly proportional to the shock dynamic pressure and the circumferential dynamic pressure in the discharge section, respectively. In the reverse pump mode, the guide vane shock and friction losses are directly proportional to the shock dynamic pressure and the absolute dynamic pressure, respectively. The S-shaped characteristics of pump–turbines can be completely simulated using the proposed theoretical model
1.5톤급 액체-액체 핀틀 분사기 연소시험에서의 핀틀 팁 열손상 원인 분석
강동혁(Donghyuk Kang),황도근(Dokeun Hwang),유철성(Chulsung Ryu),고영성(Youngsung Ko) 한국추진공학회 2020 한국추진공학회지 Vol.24 No.6
Using kerosene and liquid oxygen, 1.5-tonf class liquid-liquid pintle injector with rectangular two-row orifice was designed and manufactured. The combustion test of the pintle injector was carried out to verify the combustion performance and combustion stability under a supercritical condition which is the actual operation condition of the liquid rocket engine. The combustion test result showed that the pintle tip was damaged by the high temperature combustion gas in the high-mixed ratio recirculation zone of the combustion chamber. To solve this problem, the insert nozzle was installed in the pintle injector to increase cooling performance at the pintle tip. As a result of the hot firing test, installation of the insert nozzle, AR and BF had a great effect on pintle tip cooling performance.
3가지 점화 형식에 의한 액체로켓엔진 연소기의 점화 특성 연구
강동혁(Donghyuk Kang),김종규(Jonggyu Kim),김현준(Hyeon-Jun Kim),임병직(Byoungjik Lim),김문기(Munki Kim),황도근(Dokeun Hwang),주성민(Seongmin Joo),최환석(Hwan-Seok Choi) 한국추진공학회 2018 한국추진공학회 학술대회논문집 Vol.2018 No.5
액체로켓엔진에는 자연발화 점화추진제, 가스토치 점화기, pyrotechnic 점화기와 같은 3가지 종류의 주요 점화 방법이 있다. 본 연구에서는 한국형발사체 3단 엔진용 연소기 개발시험에 3가지 종류의 점화 방식을 적용하여 점화시퀀스를 검증하였다. 점화방식 모두 0.3 sec 이내에 정상 연소압에 도달하였다. 검증된 점화시퀀스를 사용하여 액체로켓엔진 연소기 연소시험을 성공적으로 수행하였다. There are three main types of ignition methods such as hypergolic fuel, gas torch, and pyrotechnic igniter for a liquid rocket engine. In this paper, the ignition sequences for 3<SUP>rd</SUP> Engine Combustor of Korea Space Launch Vehicle using ignition methods were verified. All ignition methods have reached an operating pressure during 0.3 s in the combustion chamber. Hot-firing tests for a liquid rocket engine combustor have been successfully performed using a verified ignition sequence.
강동혁(Donghyuk Kang),주성민(Seongmin Joo),김종규(Jong-gyu Kim),최환석(Hwan-Seok Choi) 한국추진공학회 2017 한국추진공학회 학술대회논문집 Vol.2017 No.5
추력은 연소기 개발시험 시 연소 성능을 확인하기 위한 매우 중요한 항목이다. 따라서 정확한 추력을 측정하는 것은 매우 중요하다. 정확한 추력을 측정하기 위해 추력측정장치 시스템 특성, 저항 및 선형성 등을 파악하기 위해 단계적으로 교정 시험을 수행하였다. 추력 교정식으로 산출된 추력과 이론 추력과 비교하여 약 6.9%~8.6%의 오차를 확인하였고, 연소기의 정확한 추력을 측정하기 위해서는 추진제 배관이 연결된 상태에서의 교정이 필요함을 확인하였다. Thrust is one of the crucial performance parameter of a combustion chamber in the combustion chamber development test. So it is very important to measure an accurate thrust. Thrust calibration test was performed to identify the system characteristics, resistance and linearity of a vertical thrust measurement system(TMS) for accurate thrust measurement. It has been found 6.9% ~ 8.6% errors between the measured thrust by TMS calibration equations and theoretical thrust. It has been confirmed that the TMS calibration is necessary to be performed with the propellant lines connected to the combustion chamber for accurate thrust measurement.