공동현상 가시화 실험을 통한 절환밸브 바텀플러그 형상 최적화

김태안(Tae An Kim),이명곤(Myeong Gon Lee),한승호(Seung Ho Han) 대한기계학회 2016 大韓機械學會論文集A Vol.40 No.11

자동차 엔진과 변속기 블록 등의 가공과정에서 잔류하는 기름때를 제거하기 위한 부품 세척장비는 정교한 제어장치 없이도 정확한 수류방향 절환이 원활히 이루지는 3 방향 절환밸브를 사용한다. 그러나, 밸브의 복잡한 유로 및 바텀플러그 형상으로 인해 유속변화가 심하게 발생하여 공동현상이 나타날 수 있다. 본 연구에서는 3 방향 절환밸브 내의 유동특성을 해석적으로 평가하였으며, 바텀플러그 하부에서 나타나는 공동현상을 공동화지표와 POC(Percent of cavitation)를 도입하여 정량화하였다. 공동현상의 저감을 위해 바텀플러그 형상을 매개변수화하고, 해석의 수렴성 개선과 해석시간을 단축시킬 수 있는 단순 유한요소모델을 이용하여 유동해석을 통한 형상최적설계를 실시하였다. 또한, 연구팀에서 보유하고 있는 유동시험설비와 ISA-RP75.23 규격에 맞게 제작된 시편을 이용하여 공동현상 가시화 실험을 실시하여 해석결과를 검증하였다. A three-way reversing valve, which provides rapid and accurate changes in the water flow direction without requiring any precise control device, is used in automotive washing machines to remove oil and dirt that remain on the machined engine and transmission blocks. Because of the complicated shape of the bottom-plug, however, cavitation occurs in the plug. In this study, the cavitation index and POC (percent of cavitation) were used to quantitatively evaluate the cavitation effect occurring in the bottom-plug on the downstream side. An optimal shape design was conducted via parametric study with a simple CAE model to avoid time-consuming CFD analysis and hard-to-achieve convergence. To verify the results of the numerical analysis, a flow visualization test was conducted using a specimen prepared according to ISA-RP75.23. In this test, the flow characteristics, such as cavitation occurring on the downstream side, were investigated using flow test equipment that included a valve, pump, flow control system, and high-speed camera.

3 방향 절환밸브의 공동현상 저감을 위한 형상최적화

이명곤(Myeong Gon Lee),임채석(Cha Suk Lim),한승호(Seung Ho Han) 대한기계학회 2015 大韓機械學會論文集A Vol.39 No.11

자동차부품 세척장비는 엔진과 변속기 블록 등의 가공과정에서 잔류하는 기름때를 제거하며, 잦은 수류방향 전환과 고압수의 분사를 위해 한 쌍의 2 방향 밸브를 사용한다. 그러나 정교한 밸브제어장치 없이 2 방향 밸브를 사용하는 경우 급격한 수류방향 전환에 따른 맥동현상이 발생하여 사용에 어려움이 따른다. 대안으로 하나의 3 방향 절환밸브를 사용하는 방법은 정교한 제어장치 없이도 정확한 수류방향 절환이 원활히 이루어져 이러한 문제점을 해결할 수 있다. 그러나 복잡한 유로 및 바텀플러그 형상으로 인해 유속변화가 심하게 발생하여 공동현상이 나타날 수 있다. 본 연구에서는 3 방향 절환밸브 내의 유동특성을 해석적으로 평가하였으며, 바텀플러그 하부에서 나타나는 공동현상을 공동화지표와 POC(Percent of cavitation)를 도입하여 정량화하였다. 공동현상의 저감을 위해 바텀플러그 형상을 매개변수화하고, 해석의 수렴성 개선과 해석시간을 단축시킬 수 있는 단순 유한요소모델을 이용하여 유동해석을 통한 형상최적설계를 실시하였다. 완전요인배치법을 통한 실험계획법과 인공신경망 기반 반응표면모델을 적용하여 공동현상이 발생하지 않는 POC 가 30% 미만인 바텀플러그의 형상을 제시하였다. 얻어진 최적해는 POC 27%에 대하여 바텀플러그의 허리길이와 꼬리길이가 각각 6.42mm 및 6.96mm 이다. A pair of two-way valves typically is used in automotive washing machines, where the water flow direction is frequently reversed and highly pressurized clean water is sprayed to remove the oil and dirt remaining on machined engine and transmission blocks. Although this valve system has been widely used because of its competitive price, its application is sometimes restricted by surging effects, such as pressure ripples occurring in rapid changes in water flow caused by inaccurate valve control. As an alternative, one three-way reversing valve can replace the valve system because it provides rapid and accurate changes to the water flow direction without any precise control device. However, a cavitation effect occurs because of the complicated bottom plug shape of the valve. In this study, the cavitation index and percent of cavitation (POC) were introduced to numerically evaluate fluid flows via computational fluid dynamics (CFD) analysis. To reduce the cavitation effect generated by the bottom plug, the optimal shape design was carried out through a parametric study, in which a simple computer-aided engineering (CAE) model was applied to avoid timeconsuming CFD analysis and difficulties in achieving convergence. The optimal shape design process using full factorial design of experiments (DOEs) and an artificial neural network meta-model yielded the optimal waist and tail length of the bottom plug with a POC value of less than 30%, which meets the requirement of no cavitation occurrence. The optimal waist length, tail length and POC value were found to 6.42 mm, 6.96 mm and 27%, respectively.

오리피스를 통과하는 극저온 유체 공동 현상 해석

이세영(Seyoung Lee),이창진(Changjin Lee) 한국항공우주학회 2008 韓國航空宇宙學會誌 Vol.36 No.3

액체 로켓의 주 추진제로 사용되는 극저온 유체의 공동발생은 온도 변화에 매우 민감하다. 이것은 공동발생이 증발 냉각현상에 따른 ‘열역학적 효과’와 매우 밀접한 관계가 있기 때문이며 수치 해석의 계산에서는 반드시 이런 관계를 고려하여야 한다. 본 연구에서는 에너지 방정식과 상 수송 방정식을 사용하여 이러한 열역학적 효과를 적용하고 등온 유체에 적용하던 공동 현상 모델을 수정하여 극저온 유체의 공동현상을 해석하였다. 연구 방법의 검증을 위해 축대칭 형상의 ogive 형상에 관한 해석을 실시하여 실험 결과 및 다른 연구 결과와 비교해보았다. 그리고 2차원 오리피스 내부에서 발생하는 공동 현상에 대한 수치해석을 실시하여 공동의 생성과 소멸에 따른 압력 변화를 살펴보았다. 또한 공동 현상이 발생했을 때와 발생하지 않았을 때의 오리피스 통과 유량의 차이를 계산하였다. The generation of cavitation in cryogenic propellant used in the liquid rocket engine is very sensitive to the temperature variation. The sensitivity causes the numerical calculation more difficult due to so called “thermal effect” of cryogenic fluid caused by the vaporization-cooling mechanism The numerical calculations have been conducted to investigate the cavitation characteristics of cryogenic fluid by implementing thermal effect and properly modified cavitation model. The validation was also checked by the comparison of calculation results with experimental data and other results for spherical and ogive bodies. And the calculation revealed that the generation and depletion of cavitation could produce the pressure oscillation in the downstream of orifices. Also the mass flow rate through the orifice can be underestimated by the inception of cavitation, which leads to the mismatch between the prediction and thrust generation.

2차원 쐐기 형상의 자연 및 분사 공동의 비정상 유동 해석 연구

김진하(J.H. Kim),최요한(Y.H. Choi),김종암(C.A. Kim),정소원(S.W. Jeong),안병권(B.K. Ahn) 한국전산유체공학회 2017 한국전산유체공학회지 Vol.22 No.2

In this paper, the natural and ventilated cavitating flows behind a two-dimensional wedge is numerically investigated. In order to simulate the cavitation, we use multi-phase RANS flow solver with a homogeneous mixture model and a preconditioning technique. Good agreements are obtained between the present numerical results and the experiment for cavitating flow patterns, cavity length, and cavity pressure. Both cavitating flows show the characteristic of unsteady periodic vortical flow above certain cavitation number. The change of drag coefficients of a wedge by cavitation is also analyzed. Drag coefficients along with cavitation numbers change more by ventilated cavitation than natural cavitation. Compared to drag coefficients with no cavitation, drag coefficients are decreased by natural and ventilated cavitation. Ventilated cavitation can significantly decrease drag coefficients by changing pressure behind a wedge.

2차원 및 축대칭 운동체 주위의 초공동 현상에 대한 수치해석

박선호(Sunho Park),이신형(Shin Hyung Rhee) 한국전산유체공학회 2011 한국전산유체공학회지 Vol.16 No.1

Super-cavitating flows around under-water bodies are being studied for drag reduction and dramatic speed increase. In this paper, high speed super-cavitating flow around a two-dimensional symmetric wedge-shaped body were studied using an unsteady Reynolds-averaged Navier-Stokes equations solver based on a cell-centered finite volume method. To verify the computational method, flow over a hemispherical head-form body was simulated and validated against existing experimental data. Various computational conditions, such as different wedge angles and caviation numbers, were considered for the super-cavitating flow around the wedge-shaped body. Super-cavity begins to form in the low pressure region and propagates along the wedge body. The computed cavity lengths and velocities on the cavity boundary with varying cavitation number were validated by comparing with analytic solution.

2차원 및 축대칭 운동체 주위의 초공동 현상에 대한 수치해석

박선호(S. Park),이신형(S. H. Rhee) 한국전산유체공학회 2010 한국전산유체공학회 학술대회논문집 Vol.2010 No.11

Super-cavitating flows around under-water bodies are being studied for drag reduction and dramatic speed increase. In this paper, high speed super-cavitating flow around a two-dimensional symmetric wedge-shaped body were studied using an unsteady Reynolds-averaged Navier-Stokes equations solver based on a cell-centered finite volume method. To verify the computational method, flow over a hemispherical head-form body was simulated and validated against existing experimental data. Various computational conditions, such as different wedge angles and caviation numbers, were considered for the super-cavitating flow around the wedge-shaped body. Super-cavity begins to from in the low pressure region and propagates along the wedge body. The computed cavity lenths and velocities on the cavity boundary with varying cavitation number were validated by comparing with analytic solution.

단일 거칠기 요소가 벤투리 캐비테이션에 미치는 영향

황종빈,신이수,김주하 한국가시화정보학회 2023 한국가시화정보학회지 Vol.21 No.1

In this study, we investigate the effects of a single roughness element on Venturi cavitation. The single roughness element of hemispherical shape is installed at the throat inlet of a Venturi tube. Since the wake behind the roughness element induces an additional pressure drop, cavitation inception occurs at a higher Cavitation number for the Venturi model with the single roughness element than for the Venturi model with no roughness. Cavitation bubbles form along the wake of the roughness element and lengthen in the streamwise direction as the Cavitation number decreases, forming a longitudinal cavitation. With a further decrease in the Cavitation number, the longitudinal cavitation bubble merges with the sheet cavitation initiated from the exit edge of the Venturi tube throat, followed by the shedding of cloud cavitation. The merging of the longitudinal cavitation and sheet cavitation is accompanied by a sudden decrease in the discharge coefficient and an increase in the pressure loss coefficient as it chokes the flow inside the Venturi tube.

서로 다른 두 개의 공동모델의 모델 상수값이 공동의 길이에 미치는 영향연구

김미선(M. S. Jin),하콩투(C. T. Ha),박원규(W. G. Park),정철민(C. M. Jung) 한국전산유체공학회 2012 한국전산유체공학회지 Vol.17 No.3

This work was devoted to compare two different cavitation models to study the dependency of model constants. The cavitation model of Merkle et al.(2006) and Kunz et al.(2000) were used for the present computational study. The cavitation models were coupled with the incompressible unsteady Reynolds-Averaged Navier-Stokes solver to indicate the vaporization and condensation processes. For this purpose, a preconditioning method was added as the pseudo-time term to solve the unsteady stiffness problems. For the validation of the numerical simulation, the computation was performed for the cavitating flow in a converging-diverging channel. The present results show that Merkle’s cavitation model is independent to the model constants, and the higher numerical accuracy over Kunz’s cavitation model.

공동 분사 조건 및 받음각에 따른 수중 운동체 주위 다상 유동장 해석

김동현(Dong-Hyun Kim),박원규(Warn-Gyu Park) 대한기계학회 2020 大韓機械學會論文集B Vol.44 No.6

초공동 수중 운동체 주위 공동의 크기와 방향 등의 형상적 문제는 매우 중요한 문제이다. 이러한 문제에 대한 다양한 연구가 수행되어왔지만, 실험적으로는 형상적 문제에 대한 해결이 원활하지 않아 수치 해석에 의한 접근으로 연구를 수행하였다. 본 연구에서는 3차원 Navier-Stokes 방정식을 기반으로 한 균일 혼상류 모델을 사용하여 다상 유동장에 대한 전산 해석을 수행하였다. 해석 프로그램과 기법의 검증을 위해서 공동 터널에서 분사량 변화에 의한 공동 형상 변화를 실험과 비교 검증하였으며, 상당히 잘 일치하는 결과를 보이고 있다. 인위적으로 분사하는 공동에 의해서 공동의 전체 길이/크기가 커지는 것을 확인하였으며, 공동 발생기의 받음각 변화에 따라 길이/크기의 방향이 변화하는 것을 확인할 수 있다. The shape, size, and orientation of the cavity are important factors in the case of supercaviting underwater vehicle. In order to overcome experimental limitations for this study, we performed computational analysis approach through the study. In this study, we developed multiphase flow analysis code using a homogeneous mixture model for the 3D Navier-Stokes equation. The experimental results and the computational analysis results of the cavity tunnels were compared and verified. As a result of this comparison process, it showed fairly good agreement under various condition. Computational analysis was carried out on the change of cavity shape and cavity number according to injection flow rate by artificial injection.

공동현상을 고려한 3-방향 절환밸브의 형상설계

이명곤(Myeong Gon Lee),김양균(Yang Gyun Kim),임채석(Cha Suk Lim),한승호(Seung Ho Han) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11

The high-pressure valve uses one set of 2-way valves for the purpose of reversing fluid direction. If there is no accurate control device for the 2-way valves, lots of surging can be generated. The surging is a kind of pressure ripple that occurs in rapid changes of fluid motions under inaccurate valve control. To reduce the surging effect, a 3-way reversing valve can be applied which provides a rapid and precise change of water flow directions without any accurate valve control system. However, a cavitation occurs due to a complicated internal trim shape of the 3-way reversing valve. The cavitation causes not only noise and vibration but also decreasing the efficiency of valve-operation, in which the bubbles generated below the saturated vapor pressure are collapsed rapidly at higher pressure zone. The shape optimization of the 3-way reversing valve to minimize the cavitation effect is necessary. In this study, the cavitation index according to the international standard ISA was introduced to estimate macroscopically the occurrence of the cavitation effect. Computational fluid dynamic analysis was carried out, and the cavitation effect was quantified by means of the percent of cavitation converted from calculated results of vapor volume fraction. In addition, the shape design of the 3-way reversing valve was performed by taking into account of the percent of cavitation.