• 한국가시화정보학회지
• /
• 제15권1호
• /
• pp.53-63
• /
• 2017

Sonic and supersonic jets include many complicated flow physics associated with shock waves, shear layers, vortices as well as strong interactions among them, and have a variety of engineering applications. Much has been learned from the previous researches on the sonic and supersonic jets but quantitative assessment of these jets is still uneasy due to the high velocity of flow, compressibility effects, and sometimes flow unsteadiness. In the present study, the sonic jets issuing from a convergent nozzle were measured by PIV and Schlieren optical techniques. Particle Image Velocimetry (PIV) with Olive oil particles of $1{\mu}m$ was employed to obtain the velocity field of the jets, and the black-white and color Schlieren images were obtained using Xe ramp. A color filter of Blue-Green-Red has been designed for the color Schlieren and obtained from an Ink jet printer. In experiments, two types of sonic nozzles were used at different operating pressure ratios(NPR). The obtained images clearly showed the major features of the jets such as Mach disk, barrel shock waves, jet boundaries, etc.

• 한국분무공학회지
• /
• 제4권3호
• /
• pp.32-41
• /
• 1999

In this research, internal-mixing twin-fluid atomizer using sonic energy is designed and manufactured. We are trying to intimate high efficiency twin-fluid atomizer to obtain good liquid atomization in the low pressure region. Define of geometric form of atomizer, characteristics of spray is influenced by position, depth and height variation of cavity resonator, variation of sound intensity and resonant sound frequency with liquid flow rate. The liquid atomization is promoted by multi-stage disintegration of mixing flow of gas with liquid and the optimum condition of position and depth of cavity resonator according to sonic energy is obtained from the condition at a=2.5mm and L=2mm. The velocity distribution of droplets shows negative value due to recirculation region at the center of axial, and as the radial direction distance is far, the velocity distribution of droplets decrease slowly after having a maximum value. However velocity and SMD show nearly uniform distribution at the down stream and as result compared to Nukiyama and Tanasawa's equation. atomization of mixing flow with air and liquid dispersing from the outlet of the nozzle is promoted by the effect of collision at the cavity resonator.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2003년도 추계학술대회
• /
• pp.580-585
• /
• 2003

The present study addresses experimental results to investigate the details of the near field flow structures produced in the under-expanded, dual, coaxial, swirling, jet. The sonic/supersonic swirling jets are emitted from the sonic inner nozzle and the outer annular nozzle produce the co-swirling and counter swirling against the primary swirling jet, respectively. The interactions between both the secondary annular swirling and primary inner supersonic swirling jets are quantified by the pitot impact and static pressure measurements and visualized by using the Schliern optical method. The experiment is performed for different swirl intensity and pressure ratio. The results obtained show that the secondary co-swirling jet significantly changes the inner under-expanded swirling jet, such as the recirculation zone, pressure distribution, through strong interactions between both the swirling jets and the effects of the secondary counter-swirling jet is similar to the secondary co-swirl jet case.

• 대한기계학회논문집B
• /
• 제33권2호
• /
• pp.93-100
• /
• 2009

Characteristics of micro-sonic/supersonic axi-symmetric jet impinging on a flat plate with a pre-drilled hole were both experimentally and numerically studied, to observe the role of assist-gas jet to eject melted materials from the cut zone in the laser machining. For various Mach numbers of the nozzle and the total pressures of the assist gas, detailed impinging jet flow structures over the plate and the variations of mass flux through the pre-drilled hole were observed. It was found that the present experimental and numerical results show a good agreement, which proves the accountability of the present work. From the present study, it was also observed that the mass flow rate through the hole was closely related with the total pressure loss caused by the Mach disc on the work piece, and that supersonic nozzle could perform more efficient roles as blowing the assist-gas jet in the laser machining, as compared to sonic nozzles.

• 한국추진공학회지
• /
• 제5권4호
• /
• pp.50-56
• /
• 2001

본 연구는 음속/초음속 공기이젝터 시스템을 통하는 유동을 실험적으로 조사한 것으로, 이젝터 시스템의 2차정체실 압력-시간의 의존성을 조사하였다. 본 실험에서 적용된 1차구동 노즐은 총 6가지 형태로, 두 개의 음속노즐과 두 개의 초음속 노즐 그리고 페탈노즐 및 로브형 노즐이 사용되었다. 실험에서는 이젝터-디퓨저 벽면에서 압력을 측정하였으며, 2차 정실실의 체적이 이젝터 내부에 미치는 영향을 조사하기 위하여, 2차 정체실의 체적을 변화시켰다. 그 결과 2차정체실의 체적은 이젝터 시스템의 정상 작동에는 영향을 미치지 않았지만, 2차정체실에서의 압력-시간 의존성은 2차정체실의 체적에 큰 영향을 받는다는 것을 알았다.

• Journal of Mechanical Science and Technology
• /
• 제17권12호
• /
• pp.2107-2115
• /
• 2003

A supersonic dual coaxial jet has been employed popularly for various industrial purposes, such as gasdynamic laser, supersonic ejector, noise control and enhancement of mixing. Detailed characteristics of supersonic dual coaxial jets issuing from an inner supersonic nozzle and outer sonic nozzles with various ejection angles are experimentally investigated. Three important parameters, such as pressure ratios of the inner and outer nozzles, and outer nozzle ejection angle, are chosen for a better understanding of jet structures in the present study. The results obtained from the present experimental study show that the Mach disk diameter becomes smaller, and the Mach disk moves toward the nozzle exit, and the length of the first shock cell decreases with the pressure ratio of the outer nozzle. It was also found that the highly underexpanded outer jet produces a new oblique shock wave, which makes jet structure much more complicated. On the other hand the outer jet ejection angle affects the structure of the inner jet structure less than the pressure ratio of the outer nozzle, relatively.

• 한국신재생에너지학회:학술대회논문집
• /
• 한국신재생에너지학회 2007년도 추계학술대회 논문집
• /
• pp.156-160
• /
• 2007

Ejector system is a device to transport a low-pressure secondary flow by using a high-pressure primary flow. Ejector system is, in general, composed of a primary nozzle, a mixing section, a casing part for suction of secondary flow and a diffuser. It can induce the secondary flow or affect the secondary chamber pressure by both shear stress and pressure drop which are generated in the primary jet boundary. Ejector system is simple in construction and has no moving parts, so it can not only compress and transport a massive capacity of fluid without trouble, but also has little need for maintenance. Ejectors are widely used in a range of applications such as a turbine-based combined-cycle propulsion system and a high altitude test facility for rocket engine, pressure recovery system, desalination plant and ejector ramjet etc. The primary interest of this study is to set up an applicable model and operating conditions for an ejector in the condition of sonic and subsonic, which can be extended to the hydrogen fuel cell vehicle. Experimental and theoretical investigation on the sonic and subsonic ejectors with a converging-diverging diffuser was carried out. Optimization technique and numerical simulation was adopted for an optimal geometry design and satisfying the required performance at design point of ejector for hydrogen recirculation. Also, some sonic and subsonic ejectors with the function of changing nozzle position were manufactured precisely and tested for the comparison with the calculation results.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2005년도 제24회 춘계학술대회논문집
• /
• pp.409-412
• /
• 2005

본 논문에서는 Pressure Sensitive Paint(이하 PSP)를 이용한 M=2.5 초음속 풍동의 노즐 벽면 압력 측정 과정을 보여주고, NASA Lewis Research Center에서 유사한 조건에서 수행한 실험결과와 비교하였다.

• 대한기계학회논문집B
• /
• 제29권12호
• /
• pp.1329-1334
• /
• 2005

Synthesis of silver nanoparticles by the supersonic nozzle expansion method with corona discharge ions was investigated. Corona discharge ions functioned as seeds for heterogeneous nucleation in the silver nanoparticles formation process and provided silver nanoparticles with electronic repulsive force that prevents aggregation of the particles. For ion ejecting, we used sonic-jet corona discharger. Upon application of the corona discharge ions, the mean diameter of the produced particles was decreased from 12.54 to 6.22nm and the standard deviation was decreased from 5.02 to 3.34nm. In addition, the agglomeration of silver nanoparticles was reduced.

• 한국항공우주학회지
• /
• 제32권10호
• /
• pp.112-117
• /
• 2004

본 연구는 공기역학적 운동에너지를 이용하여 점화장치를 구성하는데 따른 해석과 실험에 관한 연구로써 공기역학 점화기는 크게 노즐과 공명관으로 구성되어 있다. 압축가스가 노즐을 통과하여 공명관으로 유입되며, 이때 노즐과 공명관사이에 압력맥동이 발생한다. 이러한 압력맥동에 의한 운동에너지는 일정한 조건하에 공명관 내부에서 열에너지로 변화하게 된다. 본 연구에서는 음속노즐과 초음속 노즐을 두개의 각기 다른 공명관에서 실험과 수치해석을 실시하였으며, 노즐표면의 마찰손실과 공기역학 손실을 최소화하는 초음속 노즐의 최적형상을 제시하였다.