Visualization of Hysteresis Phenomenon of Shock Waves in Supersonic Internal Flow

Suryan, Abhilash,Shin, Choon-Sik,Setoguchi, Toshiaki,Kim, Heuy-Dong The Korean Society of Visualization 2010 한국가시화정보학회지 Vol.8 No.2

Hysteresis is an effect by which the order of previous events influences the order of subsequent events. Hysteresis phenomenon of supersonic internal flows with shock waves has not yet been clarified satisfactorily. In the present study, experiments are carried out on internal flow in a supersonic nozzle to clarify the hysteresis phenomena for the shock waves. Flow visualization is carried out separately on the straight and divergent channels downstream of the nozzle throat section. Results obtained were compared with numerically simulated data. The results confirmed hysteresis phenomenon for shock wave in the Laval nozzle at a certain specific condition. The relationship between hysteresis phenomenon and the range of the rate of change of pressure ratio with time was shown experimentally. The existence of hysteretic behavior in the formation, both the location and strength, of shock wave in the straight part of the supersonic nozzle with a range of pressure ratio has also been confirmed numerically.

Hydrodynamic Analysis of Rectangular Sieve Tray under Weeping Conditions

호산나 우위톤즈,이인원,Uwitonze, Hosanna,Lee, Inwon The Korean Society of Visualization 2017 한국가시화정보학회지 Vol.15 No.3

Within fractionating devices existing in separation and purification industries, sieve trays are widely used as tower internals and their choice is due to economical attractiveness. While operating a trayed distillation tower weeping phenomenon has a critical effect on the efficiency, in this case study a weeping phenomenon was undertaken by means of numerical model in a rectangular sieve tray. Eulerian-Eulerian Computational Fluid Dynamics (CFD) method was used and the obtained CFD results are in a good agreement with the experimental data in terms of weeping rate and pressure drop.

A Study on the Flow Characteristics of the Spiral Flow Nozzle with the Width Change of Annular Slit

Kim, T.H.,Setoguchi, T.,Lee, Y.W. The Korean Society of Visualization 2009 한국가시화정보학회지 Vol.7 No.1

In comparison with previous researches fur swirling flow, the spiral flow self-generated in the spiral flow nozzle has some different characteristics. It is not needed a compulsive tangential momentum to get its velocity component and has long potential core, relatively low swirl ratio, and high focusing ability. In this study, the self-generated mechanism of the spiral flow was clarified and the effect on the width of annular slit on spiral flow characteristics was investigated experimentally and numerically. As a result, the existence of tangential velocity component regardless of a compulsive angular momentum is clarified and the results obtained by experiment have a satisfactory agreement with those by numerical method, quantitatively and qualitatively.

Review of Experimental Studies on Swirling Flow in the Circular Tube using PIV Technique

Chang, Tae-Hyun,Nah, Do-Baek,Kim, Sang-Woo The Korean Society of Visualization 2009 한국가시화정보학회지 Vol.7 No.1

The study of swirling flow is of technical and scientific interest because it has an internal recirculation field, and its tangential velocity is related to the curvature of streamline. The fluid flow for tubes and elbow of heat exchangers has been studied largely through experiments and numerical methods, but studies about swirling flow have been insufficient. Using the particle image velocimetry(PTV) method, this study found the time averaged velocity distribution with swirl and without swirl along longitude sections and the results appear to be physically reasonable. In addition, streamwise mean velocity distribution was compares with that of other. Furthermore, other experimental investigation was performed to study the characteristics of turbulent water flow in a horizontal circular tube by using liquid crystal. 2D PIV technique is employed for velocity measurement and liquid crystal is used for heat transfer experiments in water. Temperature visualization was made quantitatively by calibrating the colour of the liquid crystal versus temperature using various approaches.

Three-dimensional vortex structure near a corner of a translating plate

김대겸,Kim, Daegyoum The Korean Society of Visualization 2015 한국가시화정보학회지 Vol.13 No.1

Three-dimensional vortex structures in the corner region of translating normal plates are visualized experimentally with defocusing digital particle image velocimetry. Vortex formation processes for three plates with corner angle $60^{\circ}$, $90^{\circ}$, and $120^{\circ}$ are compared in order to study the effect of corner shape on vortex formation. In all cases, the self-induction of the starting vortex and its interaction with the potential flow induced by the moving plate cause the vortex to change its form dynamically after the plate starts to translate. While the vortex near a corner follows the plate in the low corner angle of $60^{\circ}$, the vortex separates early from the plate and its forward motion becomes slow in the high corner angle of $120^{\circ}$. It is also found that the starting vortex can transport inward at the corner, which depends on the corner angle.

Numerical Study on Blood Flow Dynamics and Wall Mechanics in a Compliant Carotid Bifurcation Model

웬민투안,이상욱,Nguyen, Minh Tuan,Lee, Sang-Wook The Korean Society of Visualization 2015 한국가시화정보학회지 Vol.13 No.2

Blood flow simulations in an realistic carotid bifurcation model with considering wall compliance were carried out to investigate the effect of wall elasticity on the wall shear stress and wall solid stress. Canonical waveforms of flow rates and pressure in carotid arteries were imposed for boundary conditions. Compared to a rigid wall model, we found an increased recirculation region at the carotid bulb and an overall reduction of wall shear stress in a compliant model. Additionally, there was appreciable change of flow rate and pressure wave in longitudinal direction. Both solid and wall shear stress concentration occur at the bifurcation apex.

A Numerical Study of the Performance of a Contoured Shock Tube for Needle-free Drug Delivery

Rasel, Md. Alim Iftekhar,Kim, Heuy Dong The Korean Society of Visualization 2012 한국가시화정보학회지 Vol.10 No.2

In recent years a unique drug delivery system named as the transdermal drug delivery system has been developed which can deliver drug particles to the human skin without using any external needle. The solid drug particles are accelerated by means of high speed gas flow through a shock tube imparting enough momentum so that particles can penetrate through the outer layer of the skin. Different systems have been tried and tested in order to make it more convenient for clinical use. One of them is the contoured shock tube system (CST). The contoured shock tube consists of a classical shock tube connected with a correctly expanded supersonic nozzle. A set of bursting membrane are placed upstream of the nozzle section which retains the drug particle as well as initiates the gas flow (act as a diaphragm in a shock tube). The key feature of the CST system is it can deliver particles with a controllable velocity and spatial distribution. The flow dynamics of the contoured shock tube is analyzed numerically using computational fluid dynamics (CFD). To validate the numerical approach pressure histories in different sections on the CST are compared with the experimental results. The key features of the flow field have been studied and analyzed in details. To investigate the performance of the CST system flow behavior through the shock tube under different operating conditions are also observed.

Measurement of Turbulent Intensity Distributions of a Cylinder Wake

Doh, Deog Hee,Cho, Gyeong Rae,Moon, Kyeong Rok,Cho, Yong Beom The Korean Society of Visualization 2013 한국가시화정보학회지 Vol.11 No.1

Turbulence properties of a cylinder wake (d=10 mm) have been investigated with a new volume PTV algorithm. The measurement system consists of two-high-cameras(1 $k{\times}1$ k), a Nd-Yag laser and a host computer. A fitness function representing three-dimensional coherency has been adopted to sort out spurious vectors. A hybrid fitness function representing the relations between the fitness and the three-dimensional shortest distances constructed by the two collinears of the two cameras has been also adopted. The constructed algorithm has been employed for the measurements of the cylinder wakes. The Reynolds numbers tested in this paper are 360, 540, 720, 900, 1080 and 1260. More than 10,000 instantaneous 3D vectors have been obtained by the constructed system. The volumetric distributions of the turbulence intensities (for u', v', w') indicate that clearly different patterns for all Reynolds numbers and imply that a regular pattern (like a similarity rule) for the turbulent properties exists.

PIV Measurement of Velocity Profile in the 1/8 Scale CANDU6 Moderator Circulation Test

김형태,서한,차재은,방인철,Kim, Hyoung Tae,Seo, Han,Chan, Jae Eun,Bang, In Cheol The Korean Society of Visualization 2014 한국가시화정보학회지 Vol.12 No.1

The Korea Atomic Energy Research Institute (KAERI) has a scaled-down moderator test program to simulate the CANDU6 moderator circulation phenomena during steady state operation and accident conditions. In the present work a preliminary experiment using a 1/8 scaled-down moderator tank has been performed to identify the potential problems of the flow visualization and measurement in the scaled-down moderator test facility. With a transparent moderator tank model, a velocity field is measured with a Particle Image Velocimetry (PIV) technique under an isothermal state. The flow patterns from the inlet nozzles to the top region of the tank are investigated using PIV for a 1/8 scale moderator tank.

Numerical visualization of mixing in a circular chamber by two opposite impinging jets

하미드 카바시안,김영우,이인범,한범정,정용채,김경천,Karbasian, Hamidreza,Kim, Youngwoo,Lee, In Bum,Han, Beom Jeong,Jeong, Yong Chai,Kim, Kyung Chun The Korean Society of Visualization 2016 한국가시화정보학회지 Vol.14 No.3

In this study, the mixing process of two distinct flow is numerically investigated. Two flow with different physical properties (resin and hardener) are mixed through the opposing mixing jets. At a high pressure mixing process, the high speed flow is provided by two in-line nozzles. In the case of numerical modeling, Reynolds-Averaged Navier-Stokes Equations (RANS) is conducted to model the flow pattern inside the chamber. Additionally, SST k-omega turbulence model is selected to predict the kinetic energy of flow in impingement zone. The results show that mixing of two distinct flows would be efficient if the velocity of jet is high enough and nozzle diameter is a predominant parameter. Also, this velocity would create higher shear stress between two distinct flows which increases the mixing quality as well as strength of formed vortices. Eventually, the histogram of concentration fraction of resin is examined in order to show the quality of mixing and the range of concentration fractions in the output of chamber.