• Title, Summary, Keyword: Reynold's number

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The Characteristics of Dye Jet and Dye Laser Output Depending on the Reynold's Number (레이놀드 수에 따른 색소 젯트의 특성 및 색소레이저의 출력변화)

  • Kim, Sung Ho;Ko, Do-Kyeong;Lee, Jong-Min;Lim, Gwon;Jo, Jae-Heung;Chang, Soo
    • Korean Journal of Optics and Photonics
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    • v.5 no.4
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    • pp.461-465
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    • 1994
  • The spatial flatness of dye jet depending on the Reynold's number has analyzed by using a Michelson interferometer. When the Reynold's number of dye jet was 600, the flatness of the flow was the best. Under this condition, the dye laser with Littman-type configuration has been operated in a single longitudinal mode at the pumping energy of 0.5~1.0 mJ/pulse. The conversion efficiency and beam divergence were 4.7% and 3 mrad, respectively. ively.

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Cavitation Test at High Reynolds Number Using a Partial Propeller Blade Model (부분 프로펠러 날개 모형을 이용한 높은 레이놀즈 수에서의 공동시험)

  • Choi, Gil-Hwan;Chang, Bong-Jun;Cho, Dae-Seung
    • Journal of the Society of Naval Architects of Korea
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    • v.46 no.6
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    • pp.569-577
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    • 2009
  • As the scale factor of model propellers utilized in cavitation test is about 40, it is difficult to find out practical countermeasures against the small area erosions on the blade tip region throughout model erosion tests. In this study, a partial propeller blade model was used for the observation of cavitation pattern for the eroded propeller. A partial propeller blade model was manufactured from 0.7R to tip with expanded profile and with adjustable device of angle of attack. Reynold's number of a partial propeller blade model is 7 times larger than that of a model propeller. Also, anti-singing edge and application of countermeasures to partial propeller blade model which produced in large scale can be more practical than a model propeller. For the observation of cavitation at high Reynold's number, high speed cavitation tunnel was used. To find out the most severe erosive blade position during a revolution, cavitation observation tests were carried out at 5 blade angle positions.

CONVERGENCE OF THE NEWTON'S METHOD FOR AN OPTIMAL CONTROL PROBLEMS FOR NAVIER-STOKES EQUATIONS

  • Choi, Young-Mi;Kim, Sang-Dong;Lee, Hyung-Chun
    • Bulletin of the Korean Mathematical Society
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    • v.48 no.5
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    • pp.1079-1092
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    • 2011
  • We consider the Newton's method for an direct solver of the optimal control problems of the Navier-Stokes equations. We show that the finite element solutions of the optimal control problem for Stoke equations may be chosen as the initial guess for the quadratic convergence of Newton's algorithm applied to the optimal control problem for the Navier-Stokes equations provided there are sufficiently small mesh size h and the moderate Reynold's number.

Effect of suction on flow of dusty fluid along exponentially stretching cylinder

  • Iqbal, Waheed;Jalil, Mudassar;Qazaq, Amjad;Khadimallah, Mohamed A.;Naeem, Muhammad N.;Hussain, Muzamal;Mahmoud, S.R.;Ghandourah, E.;Tounsi, Abdelouahed
    • Advances in nano research
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    • v.10 no.3
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    • pp.263-270
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    • 2021
  • The present manuscript focuses the effects of suction on the flow of the dusty fluid along permeable exponentially stretching cylinder. Derived PDEs for this work are changed into ODEs by adopting right transformations. Numerical procedure is carried out for the obtained resultant equations by Shooting Technique in accordance with Runge-Kutta (RK-6) technique. Obtained results for the parameters namely, particle interaction parameter, suction parameter and Reynold number parameters are probed thoroughly. Some salient points are: (a) Fluid velocity decreases and the dust phase velocity rises for the higher values of particle interaction parameter; (b) more suction produces retarding velocities for both the phases; (c) high Reynold number slows down the fluid velocity while the speed of dust phase and (d) skin friction coefficient goes high for all these parameters.

A Study on the BOD Removal Characteristics of Aerobic Submerged Biofilter (Media를 충전(充塡)한 간접폭기식(間接曝氣式) 침지여상(浸漬濾床)에 의한 BOD제거 특성에 관한 연구)

  • Yang, Sang Hyun;Kwon, Young Ho
    • Journal of The Korean Society of Civil Engineers
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    • v.14 no.3
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    • pp.669-678
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    • 1994
  • The BOD removal characteristics of submerged biofilters filled with three kinds of filter media respectively were experimentally examined with constant temperature, pH value and variable BOD loading and recirculation ratio. Obtained results are as follows; 1. The BOD removal ratio decreases with the increasing $BOD_5$ volumetric loading rate, and the loading rate for the BOD removal over 90% is lower thean $1.6kg{\cdot}BOD_5/m^3{\cdot}d$ for the plastic media of Netring and cubic wire meshes. This is a much large value than $0.3{\sim}0.8kg{\cdot}BOD_5/m^3{\cdot}d$ for conventional activated sludge process. The required submerged biofilter volume is found to be much samller than that of conventional activated sludge process. 2. The decreasing order of BOD removal is Netring (random plastic media), cubic wire meshes (plastic module), and then gravel (stone media). This is mainly due to the media characteristics such as void ratio, specific surface area and media shapes. 3. The $BOD_5$ removal rate increases with the recircuration ration, but the rate of increases becomes samaller as the recirculation ratio increases over 20. When $BOD_5$ loading is $1.8kg{\cdot}BOD_5/m^3{\cdot}d$, the required recirculation rationto obtain 90% $BOD_5$ removal is about 20 for Netring and it was about 30 for cubic wire meshes. 4. Reynold's Number increases with recirculation ratio, and the Reynold's Numbers corresponding to the recircuration ratio of 10~50 are less than 52, showing laminar up flows in the filter. The settled and effluent sludges increase with increase of Reynol's Number, and there are the definite Reynold's Numbers at which the settling sludge concentrations become nearly constant respectively in each filters. 5. In this submerged biofilter system, small volume of sludge hopper can be substituted for a separated settling tank.

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Numerical Analysis of Unsteady Flow around a Transversely Oscillating Circular Cylinder

  • Moon, Ji-Soo;Kim, Jae-Soo
    • International Journal of Aeronautical and Space Sciences
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    • v.13 no.1
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    • pp.27-33
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    • 2012
  • The relationship between the excitation frequency and the vortex shedding frequency is analyzed during the oscillation of the circular cylinder. Two-dimension unsteady Navier-Stoke's equation is calculated by using the Optimized High Order Compact (OHOC) scheme. The flow condition is Mach number 0.3 and Reynold's number 1000. From the results acquired by calculation, it can be inferred that, when the excitation frequency is near the vortex shedding frequency at the fixed cylinder wake, the oscillation frequency of lift and drag coefficients appears to lock-on. The lock-on refers to a phenomenon in which the aerodynamic coefficient appears as one primary oscillation frequency through excitation and its amplitude is amplified. In the non-lock-on zone, the excitation frequency is not in the lock-on mode anymore and beat is formed in which two or more primary oscillation frequencies of the aerodynamic coefficient are mixed together.

Study on Correlation of Droplet Flow Rate and Film Boiling Heat Transfer in Spray Cooling (액적 유량과 분무냉각 막비등 열전달의 상관관계에 관한 연구)

  • Yun, Seung-Min;Kim, Yeung-Chan
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.31 no.4
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    • pp.335-340
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    • 2007
  • A new correlation between the Nusselt number based on modified heat transfer coefficient and Reynold number based on droplet-flow-rate was developed for the experimental data. The modified heat transfer coefficient was defined as ratio of wall heat flux to droplet subcooling. In the previous reports, the local heat flux of spray cooling in the film boiling region was experimentally investigated for the water spray region of $D_{max} = 0.0007{\sim}0.03m^3/(m^2s)$ . In the region near the stagnation point of spray flow, a new heat transfer correlation is recommended which shows good predictions for the water spray region of $D_x{\le}0.01m^3/(m^2s)$.

Effects of Number of Heating Walls on Heat Transfer in the Rough Square Channel with Twisted Tape (테이프가 있는 거친 사각채널에서 가열벽면의 수가 열전달에 미치는 효과)

  • Ahn, S.W.;Kim, M.H.;Bae, S.T.;Kang, H.K.
    • Journal of Power System Engineering
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    • v.10 no.3
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    • pp.17-22
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    • 2006
  • Surface modifications like rib-roughening and displaced insert devices like the twisted tape are commonly used in applications such as compact heat exchangers and cooling systems. In this paper, regionally averaged heat transfer distributions in square channels with twisted tape inserts and with twisted tape inserts plus interrupted ribs are respectively investigated. The square ribs are arranged to follow the trace of the twisted tape and along the flow direction defined as axial interrupted ribs. Each wall of the square channel is composed of isolated aluminum sections. Regionally averaged Nusselt number and channel averaged Nusselt number in turbulent air flows are presented for Reynold numbers from 8,900 to 29,000. We have obtained the following conclusions from the experimental study: 1) The local Nusselt number in the two-sided heated case is higher than that in the four-sided heated condition. 2) In the 4 heating wall channel with twisted tape inserts, Nusselt number based on bottom wall temperature is enhanced by 1.2 - 1.6 times if adding the axial interrupted ribs on the bottom wall only. 3) The twisted tape with interrupted ribs under the two-sided heating condition produces the highest heat transfer coefficient.

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Correlative Experimental Study Between The Results of Circulating Water Channel and Towing Tank Tests

  • Lee, Kwi-Joo;Kim, Kyoung-Hwa;Isaacs, Karl Antony
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • pp.70-75
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    • 2003
  • Model tests using 2.0m model of the series 60 form ($C_{b}$ = 0.6) were carried out in the Circulating Water Channel(CWC) in the Chosun University(CU, Korea) for the purpose of a correlative study with Towing Tank(TT). Resistance, propeller open water, self propulsion, and wake survey tests were carried out and the results were extrapolated to the ship scale. These results were compared with the extrapolated ship values based on the model test of 7.0m model in the TT at the Korea Research Institute of Ships and Ocean Engineering (KRISO, Korea). The CWC test results were correlated with the results of the towing tank tests.

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Simulation of Rothe Micronozzle Using DSMC method SMILE code (DSMC 방법 SMILE 코드를 이용한 Rothe 마이크로 노즐 시뮬레이션)

  • Choi, Young-In;Kim, Young-Hoon;Ok, Ho-Nam;Kim, In-Sun
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • pp.30-33
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    • 2007
  • DSMC method is now widely accepted CFD approach to compute and simulate the nozzle plume in rarefied regimes. In this study, using SMILE(Statistical Modeling in Low-density Environment) code which was developed in ITAM, Russia and coded using DSMC method, the internal flow of the Rothe micronozzle was simulated. Moreover, to show the validity of the SMILE code, the centerline temperatures according to the Reynold's number were compared with the ones obtained by the Rothe's experiment.

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