• 오토저널
• /
• 제15권2호
• /
• pp.92-104
• /
• 1993

In the present study, the velocity profiles and entrance length of developing transitional pulsating flows are investigated both analytically and experimentally in the entrance region of a square duct. The systems of conservation equations for transitional pulsating flows in a square duct are solved analytically by linearizing the non-linear convective terms. Analytical solutions are obtained in the form of infinite series for velocity pofiles. The experimental study for the air flow in a square duct(40mm*40mm*4000mm) is carried out to measure velocity profiles and other parameters by using a hot-wire anemometer with a data acquisition and processing system. The distribution of velocity profiles( $u_{ps}$ / $u_{m,ta}$) in the decelerating period is higher than in the accelerating period. The distribution of the axial component of the axial component of velocity in the transitional flow is nearly uniform in the central region of the duct, and decrease rapidly near the wall. The entrance length correlation of the transitional pulsating flows in a square duct is obtained to be $L_{e}$/ $D_{h}$=0.83 $A_{1}$R $e_{ta}$ /(.omega. sup+1)$^{2}$TEX>

• 한국농업기계학회:학술대회논문집
• /
• 한국농업기계학회 2005년도 동계 학술대회 논문집
• /
• pp.76-82
• /
• 2005

This paper presents the combustion characteristics of hydrocarbon fuel from a conventional pressureswirl nozzle of a small-scale burner. The nozzle has orifice diameters of 0.256 mm and liquid flow rates raging from 50 to 64 mL/min were selected for the experiments. The furnace temperature distribution along the axial distance, the gas emission such as CO, $CO_2,\;NOx,\;S0_2,$ flue gas temperature, and combustion efficiency were studied. The local furnace and flue gas temperatures decreased with an increase in air velocity. At injection pressures of 1.1 and 1.3 MPa the maximum furnace temperatures occurred closer to the burner exit, at an axial distance of 242 mm from the diffuser tip. The CO and $CO_2$ concentrations decreased with an increase in air velocity, but they increased with an increase in injection pressure. The effect of air velocity on NOx was not clearly seen at low injection pressures, but at injection pressure of 1.3 MPa it decreased with an increase in air velocity. The effect of air velocity $SO_2$ concentration level is not well understood. The combustion efficiency decreased with an increase in air velocity but it increased with an increase in injection pressure. It is recommended that injection pressure less than 0.9 MPa with air velocity not above 8.0 m/s would be suitable for this burner.

• Steel and Composite Structures
• /
• 제49권3호
• /
• pp.325-335
• /
• 2023

The missile is affected by both spinning and axial motion during its movement, which will have a very adverse impact on the stability and reliability of the missile. This paper regards missiles as cylindrical shell structures with spinning and axial motion. In this article, the forced vibration of carbon nanotube-reinforced composites (CNTRCs) cylindrical shells with spinning motion and axial motion is investigated, in which the clamped-clamped and simply-simply supported boundary conditions are considered. The displacement field is described by the first-order shear theory, and the vibration equation is deduced by using the Euler-Lagrange equation, after dimensionless processing, the dimensionless equation of motion is obtained. The correctness of this paper is verified by comparing with the results of the existing literature, in which the simply-simply supported ends are taken into account. In the end, the effects of different parameters such as spinning velocity, axial velocity, carbon nanotube volume fraction, length thickness ratio and load position on the resonance behavior of cylindrical shells are given. It can be found that these parameters can significantly change the resonance of axially moving and rotating moving CNTRCs cylindrical shells.

• 지구물리와물리탐사
• /
• 제14권4호
• /
• pp.305-315
• /
• 2011

암석시료에 대한 음파 속도측정의 정확성을 검증하고 정밀한 측정을 위한 기초적인 실험의 일환으로 아크릴과 스테인리스강 재질의 시료에 대하여 길이와 축하중을 달리하여 각각에 대해 3회씩 측정한 총 864 경우에 대하여, 시험편을 통과한 초동 주시를 측정하고 분석하였다. 축하중이 가해진 상태에서의 S-파 측정은 P-파에 비해 측정에 어려움이 있었으며 이에 따라 반복측정, 길이, 축하중에 의한 편차도 S-파가 훨씬 크게 나타났다. 또한, 재질에 따라서는 스테인레스강 시편보다는 아크릴 시편의 초동주시 편차가 약 2배 정도 양호하게 나타났으며 이는 아크릴 시험편의 경우가 트랜스 듀서와 시험편 간의 접촉 coupling이 안정적이며 또한 동일한 시간 분해능이나 유사한 전기적 잡음에 비하여 초동 주시가 길기 때문으로 판단된다. 실험결과, 아크릴 시험편과 스테인리스강 시험편의 탄성파 속도를 측정할 때는 60 ~ 90 mm 정도의 길이를 갖는 시험편을 20 kg (27.7 $N/cm^2$) ~ 30 kg (41.6 $N/cm^2$) 내외의 축하중 하에서 측정하는 것이 가장 좋으며, 스테인리스강 시험편의 S-파 속도는 길이 50 mm 이하의 시험편을 사용하여 측정해야 한다. 이러한 실험 결과는 암석 코어의 속도 측정시 시스템 지연의 측정 및 보정에 활용될 수 있을 것이다.

• 한국연소학회지
• /
• 제11권3호
• /
• pp.36-43
• /
• 2006

The modulated LII technique has been suggested for the measurement of axial velocity profiles of laminar diffusion flames. The theoretical background is explained based on the blackbody radiation and LII signal. Experimentally, soot particles in ethylene diffusion flames are heated by a modulated Ar-ion laser beam. LII signals and their phase angles are measured using a lock-in amplifier at the different flame heights and the axial flow velocities are obtained from the measured phase angle delay informations. The measured velocities are similar to those from LDV measurements under the same operating conditions. The effects of laser power, LII signal wavelength, and modulation frequencies are not sensitive to the velocity measurement. However, the choice of an optical chopper blade type could affect the measurement result. The use of a 6/5 chopper blade showed the better result that is. possibly due to the square shape of modulated laser beam. This study successfully demonstrated that axial flow velocities of laminar diffusion flames can be measured by a new technique utilizing LII signal, which does not need particle seeding unlikely to LDV or PIV techniques.

• 대한기계학회논문집B
• /
• 제25권12호
• /
• pp.1813-1820
• /
• 2001

The purpose of this study was to investigate the significant characteristics in atomization process of industrial etching spray fur the design or Precise pressure-swirl nozzles. The experiment was carried out with different viscosities and densities of the liquid. The macro characteristics of liquid spray, such as the spray angle and breakup process were captured by PMAS and the micro characteristics of liquid spray. such as droplet size and velocity measurements were obtained by PDA. The droplet axial and radial velocity and SMD were measured along axial and radial direction. The RMS of two velocities was measured along radial direction. It was found that the fluid with higher kinematic viscosity resulted in the larger SMD and the lower mean droplet velocity. And we could divide breakup processes into three regions that is atomization, non-dilution and dilution one in spray of pressure-swirl nozzle. The radial as well as axial velocity of droplet played an important role in the atomization process of higher kinematic viscosity fluid.

• 한국가시화정보학회지
• /
• 제8권1호
• /
• pp.53-60
• /
• 2010

Experimental investigations were conducted to study the characteristics of turbulent swirling flow in an axisymmetric annuli. Swirl angle measurements were performed using a flow visualization technique using smoke and dye liquid for Re=60,00080,000. Using the two-dimensional particle image velocimetry method, we found the time-mean velocity distribution and turbulent intensities in water with swirl for Re=20,000, 30,000, and 40,000 along longitudinal sections. Neutral points occurred for equal axial velocity at y/(R-r)=0.70.75, and the highest axial velocity was recorded near y/(R-r)=0.9. Negative axial velocity was observed near the convex tube along X/(D-d)=3~23. Another experimental study was performed to investigate heat transfer characteristics of turbulent swirling flow in an axisymmetric annuli. Static pressure, and local flow temperature were measured using tangential inlet condition and the friction factors and Nusselt number were calculated for several Reynolds numbers.

• 한국유체기계학회 논문집
• /
• 제14권4호
• /
• pp.19-24
• /
• 2011

An experimental study was conducted to examine the effectiveness of a suction-blowing fan that could not only remove polluted air by suction but also create the air-curtain by blowing. In order to create the air-curtain, rotors were installed on the surface of the shroud. These blows fresh air into the polluted region. The fresh air is spouted backward 45o on the basis of the axial direction using a double-ducted bellmouth. In the same suction operating condition, the suction region was extended by increasing the blowing velocity. However, the increasing rate of suction region was reduced when the blowing velocity was increased steadily. Thus, an efficient blowing velocity should be determined depending on the suction operating condition. In addition, the blowing requires additional input power. In a fixed suction operating condition, the input power was linearly increased in proportion to the blowing flowrate. When the suction-blowing fan was operated in the same input power as the suction fan, the suction region was increased more than 30% based on the 0.6m/sec velocity.

• 대한조선학회지
• /
• 제25권2호
• /
• pp.1-10
• /
• 1988

An axially marching numerical method is developed for the simulation of the internal waves produced by translation of a submersed vehicle in a density-stratified ocean. The method provides for the direct solution of the primitive variables [$\upsilon,\;p,\;\rho$] for the nonlinear and steady state three-dimensional Euler's equation with a non-constant density term in the vehicle-fixed cartesian co-ordinate system. By utilizing a known potential flow around the vehicle for an estimate of the axial velocity gradient, the present parabolic algorithm local upstreamwise disturbances and axial velocity variation.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2000년도 추계학술대회논문집B
• /
• pp.397-403
• /
• 2000

In the present study, flow characteristics of turbulent pulsating flow in a square-sectional $180^{\circ}$ curved duct were experimentally investigated. Experimental studies for air flows were conducted to measure axial velocity and wall shear stress distributions and entrance length in a square-sectional $180^{\circ}$ curved duct by using the LDV with the data acquisition and the processing system. The experiment was conducted in seven sections from the inlet (${\phi}=0^{\circ}$) to the outlet (${\phi}=180^{\circ}$) at $30^{\circ}$ intervals of the duct. The results obtained from the experimentation were summarized as follows ; (1) When the ratio of velocity amplitude ($A_1$) was less than one, there was hardly any velocity change in the section except near the wall and any change in axial velocity distributions along the phase. When the ratio of velocity amplitude ($A_1$) was 0.6, the change rate of velocity was slow. (2) Wall shear stress distributions of turbulent pulsating flow were similar to those of turbulent steady flow. The value of the wall shear stress became minimum in the inner wall aid gradually increased toward the outer wall where it became maximum. (3) The entrance length of turbulent pulsating flow reached near the region of bend angle of $90^{\circ}$, like that of turbulent steady flow. The entrance length was changed by the dimensionless angular frequency (${\omega}^+$).