모델 볼 밸브의 질식 유동 예측 연구

김철규(Chul-Kyu Kim),이상문(Sang-Moon Lee),전석윤(Seok-Yun Jeon),장춘만(Choon-Man Jang) 대한설비공학회 2016 대한설비공학회 학술발표대회논문집 Vol.2016 No.6

This study focuses on the prediction of a choked flow using a model ball valve, which has similar characteristics with a 42-inch ball valve. The gas transported through pipeline system needs to be avoided a choked flow to ensure safety and reliability of the system. The model ball valve having a diameter of 1-inch has been introduced to evaluate the performance test while the rotational speed of a blower keeps constant. The valve opening rates were controlled from 10% to 100% as the interval of 10%. The pressure, temperature and volumetric flow rate were measured using each transmitter and were stored using a data acquisition system. The prediction of choked flow was estimated using the conditions of pressure drop, volumetric flowrate, Mach number and valve flow coefficient obtained by the experimental data. In the choked and subsonic flow condition, flow characteristics were different in comparison with the incompressible flow. In conclusion, the prediction of choked flow can be determined a system operating condition through the limitation range of working fluid, and can be determined the size of the ball valve when designs the gas pipeline.

Two-Phase Choked Flows of Gas and Particle in a Convergent-Divergent Nozzle

Guang Zhang,Yingzi Jin,Heuy Dong Kim 한국가시화정보학회 2016 한국가시화정보학회 학술발표대회 논문집 Vol.2016 No.12

Particle-gas two-phase flows show significantly different behaviors compared to single gas flow through convergent-divergent nozzles. Non-equilibrium effects, thermal and velocity lags lead to the inefficiency of nozzle performance. In the present studies, theoretical analysis and numerical simulations were carried out to study particle-gas flows through a C-D nozzle. Homogeneous equilibrium model that no lag in velocity and temperature happen between particles and gas phase was considered to derive choked mass flow rate and sound speed of multiphase flows. Two-phase flows are regarded as isentropic flows that isentropic relations can be used for homogeneous equilibrium model. Discrete phase model (DPM) where interaction with continuous phase and two-way turbulence coupling model were considered was used to simulate particle-gas flows. Particle mass loading (PML) was varied to investigate its effect on choking phenomena for particle-gas flows. Particle volume fraction, specific heat ratio, velocity slip ratio and sound speed of mixture flows were theoretically calculated by homogeneous equilibrium model and compared with numerical results.

Unstart phenomena induced by flow choking in scramjet inlet-isolators

Im, Seong-kyun,Do, Hyungrok Elsevier 2018 Progress in aerospace sciences Vol.97 No.-

<P><B>Abstract</B></P> <P>A review of recent research outcomes in downstream flow choking-driven unstart is presented. Unstart is a flow phenomenon at the inlet that severely reduces the air mass flow rate through the engine, causing a loss of thrust and considerable transient mechanical loading. Therefore, unstart in a scramjet engine crucially affects the design and the operation range of hypersonic vehicles. Downstream flow choking is known to be one of the major mechanisms inducing inlet unstart, as confirmed by recent scramjet-powered flight tests. The current paper examines recent research progress in identifying flow choking mechanisms that trigger unstart. Three different flow choking mechanisms are discussed: flow blockage, mass addition, and heat release from combustion reactions. Current research outcomes on the characteristic of unstarting flows, such as transient and quasi-steady motions, are reviewed for each flow choking mechanism. The characteristics of unstarted flows are described including Buzzing phenomena and oscillatory motions of unstarted shockwaves. Then, the state-of-the-art methods to predict, detect, and control unstart are presented. The review suggests that further investigations with high-enthalpy ground facilities will aid understanding of heat release-driven unstart.</P>

압축성 스월유동에 관한 이론적 및 수치 해석적 연구

이재혁(Jaehyeok Lee),조양명(Yangmyeong Jo),Fanshi Kong,김희동(Heuydong Kim) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11

Although compressible swirling flows are often encountered in many diverse engineering applications, the related flow physics is seldom known. Thus, almost all of fluid machinery with the swirling flow are so far designed neglecting the compressibility effects that can lead to mal-operation or performance deterioration of the device. In the present study, theoretical and computational analyses have been carried out to investigate the planar, isentropic, axisymmetric compressible swirling flow. A series of governing equations have derived to disclose the compressibility effects in the swirling flow. The present theoretical results show the choking phenomena which are discussed in terms with the swirl angle and pressure ratio. A computational work has been performed to reveal the complicated flow involved in the compressible swirl flow. It is expected that the present results would be very helpful in designing the flow devices operated at high pressure ratios.

Influence of Gas Desorption in a Safety Relief Valve Undergoing Cavitation

Marcos Lema,Anne Gosset,Fernando López Peña 한국유체기계학회 2019 International journal of fluid machinery and syste Vol.12 No.4

In this study, the characterization of the flow through a safety relief valve (SRV) is performed in presence of cavitation and gas desorption. For this purpose, a transparent safety relief valve model is used on an experimental facility in which the flow conditions (mass flow rate, fluid temperature, and pressure upstream and downstream the valve) are accurately monitored. For six different valve openings, the characteristic curves of the valve are measured while flow visualization is performed on the transparent model. The results show that choked flow conditions are reached for the six valve openings used in this study, and with a remarkable repeatability. In order to take into consideration the gas saturation level of the working fluid, the vacuum system used to adjust the pressure downstream the valve is also used for gas desorption by storing the liquid under vacuum conditions, a process known as vacuum degasification. In saturated liquids the evolved gas bubbles modify the flow properties, such as the speed of sound, and this may have an influence in the cavitation inception and the occurrence of choked flow. This study proves that gas saturated water in standard conditions (atmospheric pressure and 293 K) has the same behavior that fully deaerated water, both under the same cavitating conditions. It is thus not necessary to take the saturation level of the liquid into account when in standard conditions.

Transient Aspects of Rayleigh Flow at Transonic Speeds

Rajarshi Das,Heuy-Dong Kim 한국추진공학회 2015 한국추진공학회 학술대회논문집 Vol.2015 No.11

Development of high speed combustors requires extensive investigation into transonic and supersonic flow under conditions of heat addition. Conventional Rayleigh theory covers this phenomenon but is limited to steady state conditions. In addition, Rayleigh theory falls short of explaining the effects of heat addition at sonic conditions. In this work, effects of heat addition at choking conditions for Rayleigh flow is investigated treating the flow as unsteady and modifying the governing equations suitably. During the study it was observed that, at sonic conditions, the mass flow unexpectedly changes thereby necessitating an overall change in the flow parameters. Taking this anomaly into account, an analytical solution is proposed in the paper for investigating such flows. The primary observations of this analysis are the unsteady fluctuation of the flow properties at sonic conditions.

Analytical Study on the Gas-Solid Suspension Flows through Sonic and Supersonic Nozzles

JianGuo Sun,G.Rajesh,Heuydong Kim(김희동) 한국추진공학회 2013 한국추진공학회지 Vol.17 No.1

A considerable deal of work has been carried out to get an insight into the gas-solid suspension flows and to specify the particle motion and its influence on the gas flow field. In this paper an attempt is made to develop an analytical model to study the effect of nozzle inlet/exit pressure ratio, particle/gas loading and the particle diameter effect on gas-solid suspension flow. The effect of the particle/gas loading on the mass flow, Mach number, thrust coefficient and static pressure variation through the nozzle is analyzed. The results obtained show that the presence of particles seems to reduce the strength of the shock wave. It is also found that smaller the particle diameter is, bigger will be the velocity as bigger particle will have larger slip velocity. The suspension flow of smaller diameter particles has almost same trend as that of single phase flow with ideal gas as working fluid. Depending on the ambient pressure, the thrust coefficient is found to be higher for larger particle/gas loading or back pressure ratio.

2차원 채널 유동에서 발생하는 초크현상에 관한 연구

김재형(Kim Jae-Hyung),강민성(Kang Min-Sung),김희동(Kim Heuy-Dong) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10

The properties of gas flow through the flow passage is influenced by some factors such as area changes, friction and heat transfer. Particularly, the friction force is the most important factor affecting the properties in a channel flow. In real flow situations, where viscous effects are not negligible, a boundary layer develops along the channel wall and it has an applicable effect on the channel flow characteristics. Almost all of the studies have not taken account for the boundary layer thickness and its effect on the chocking condition for various back pressures. The present computational study analyzes these boundary layer effects on the computational chocking phenomenon for various back pressure conditions. The computational results show that the discharge coefficient and critical pressure ratio of the channel flow is expressed as blockage effect depending on Reynolds number and channel length.

천음속 원심압축기 내부 유동해석

성선모(Seon-Mo Seong),강신형(Shin-Hyoung Kang),최재호(Jae-Ho Choi),이진수(Jin-Soo Lee) 한국유체기계학회 2008 유체기계 연구개발 발표회 논문집 Vol.2008 No.-

A computational study was carried out to simulate the flow fields within a transonic centrifugal compressor and focused on the variations in the tip leakage flow structure at three operating conditions- near choke, design point and peak pressure rise. The tip leakage flow shows very complex structures composed of the impingement on the pressure surface of the adjacent splitter blade, the spillage ahead of the adjacent splitter blade and strong radially upward flow near the suction surface. The tip leakage flow mixes with the incoming flow and there is a high entropy gradient in the interface between these two flows. As mass flow rate decreased, the interface becomes more tangential and the position of the minimum pressure moves upstream. Therefore, the peak of the tip leakage velocity appears near the leading edge at low mass flow rate. The profile of the tip leakage velocity shows the core with approximately constant slope at 20~80% height of the distance from the blade tip to the casing.

베르누이 부상유동의 이론해석 및 수치해석 연구

남종순(Jong Soon Nam),김규완(Gyu Wan Kim),김진현(Jin Hyeon Kim),김희동(Heuy Dong Kim) 대한기계학회 2013 大韓機械學會論文集B Vol.37 No.7

공압 부상은 베르누이 원리에 기초한다. 그러나 공압 부상 방법은 제품의 원가 상승의 요인이 되는 대량의 유량을 소모하는 것으로 알려져 있다. 이 논문에서는 베르누이 부상 유동의 통찰력을 얻기위해 수치 해석 연구를 수행하였다. 3차원 압축성 Navier-Stokes 방정식과 SST k-ω 난류모델에 유한 체적법을 적용하여 계산하였다. 기체 유량, 공정 제품의 직경 그리고 원형실린더와 공정 제품사이의 간극을 다양하게 변화하여 공정 제품 주위의 유동 특성을 조사하였다. 그 결과 부상력을 위한 최적의 간극과 공급 기체 유량이 증가하면 큰 부상력이 발생한다는 것을 알았다. Pneumatic levitation is based upon Bernoulli’s principle. However, this method is known to require a large gas flow rate that can lead to an increase in the cost of products. In this case, the gas flow rate should be increased, and the compressible effects of the gas may be of practical importance. In the present study, a computational fluid dynamics method has been used to obtain insights into Bernoulli levitation flows. Three-dimensional compressible Navier-Stokes equations in combination with the SST k-ω turbulence model were solved using a fully implicit finite volume scheme. The gas flow rate, workpiece diameter,and clearance gap between the workpiece and the circular cylinder were varied to investigate the flow characteristics inside. It is known that there is an optimal clearance gap for the lifting force and that increasing the supply gas flow rate results in a larger lifting force.