• International Journal of Fluid Machinery and Systems
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• 제1권1호
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• pp.101-108
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• 2008

The effect of Reynolds number on the performance of a regenerative pump was examined in a low Reynolds number range in experiment. The head of the regenerative pump increased at low flow rates and decreased at high flow rates as the Reynolds number decreased. The computation of the internal flow was made to clarify the cause of the Reynolds number effect. At low flow rates, the head is decreased with increasing the Reynolds number due to the decrease of the shear force exerted by the impeller caused by the increase of leakage and hence local flow rate. At higher flow rates, the head is increased with increasing the Reynolds number with decreased loss at the inlet and outlet as well as the decreased shear stress on the casing wall.

• 한국분무공학회지
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• 제4권1호
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• pp.55-61
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• 1999

The first maximum point in the stability curve of liquid jet, i.e., the critical point is associated with the critical Reynolds number. This critical Reynolds number should be predicted by simple means. In this work, the critical Reynolds number in the stability curve of liquid jet are predicted using the empirical correlations and the experimental data reported in the literatures. The critical Reynolds number was found to be a function of the Ohnesorge number, nozzle lengh-to-diameter ratio, ambient Weber number and nozzle inlet type. An empirical correlation for the critical Reynolds number as a function of the Ohnesorge number and nozzle length-to-diameter ratio is newly proposed here. Although an empirical correlation proposed in this work may not be universal because of excluding the effects of ambient pressure and nozzle inlet type, it has reasonably agrees with the measured critical Reynolds number.

• Journal of Mechanical Science and Technology
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• 제19권8호
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• pp.1632-1648
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• 2005

The effects of Reynolds number on the non-nulling calibration of a typical cone-type five-hole probe have been investigated for the representative Reynolds numbers in turbomachinery. The pitch and yaw angles are changed from - 35 degrees to 35 degrees with an angle interval of 5 degrees at six probe Reynolds numbers in range between $6.60{\times}10^3\;and\;3.17{\times}10^4$. The result shows that not only each calibration coefficient itself but also its Reynolds number dependency is affected significantly by the pitch and yaw angles. The Reynolds-number effects on the pitch- and yaw-angle coefficients are noticeable when the absolute values of the pitch and yaw angles are smaller than 20 degrees. The static-pressure coefficient is sensitive to the Reynolds number nearly all over the pitch- and yaw-angle range. The Reynolds-number effect on the total-pressure coefficient is found remarkable when the absolute values of the pitch and yaw angles are larger than 20 degrees. Through a typical non-nulling reduction procedure, actual reduced values of the pitch and yaw angles, static and total pressures, and velocity magnitude at each Reynolds number are obtained by employing the calibration coefficients at the highest Reynolds number ($Re=3.17{\times}10^4$) as input reference calibration data. As a result, it is found that each reduced value has its own unique trend depending on the pitch and yaw angles. Its general tendency is related closely to the variation of the corresponding calibration coefficient with the Reynolds number. Among the reduced values, the reduced total pressure suffers the most considerable deviation from the measured one and its dependency upon the pitch and yaw angles is most noticeable. In this study, the root-mean-square data as well as the upper and lower bounds of the reduced values are reported as a function of the Reynolds number. These data would be very useful in the estimation of the Reynolds-number effects on the non-nulling calibration.

• 대한기계학회논문집
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• 제17권6호
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• pp.1596-1608
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• 1993

본 연구에서는 좀더 정량적인 이론에 바탕하여 제레이놀즈수 2차모멘트 난류모형을 유도하려 한다.

• 대한기계학회논문집
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• 제16권10호
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• pp.1940-1954
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• 1992

본 연구에서는 가공기 자체의 파라메터와 성능에 관한 연구로서 출력 에너지 가 서로 다른 가공기를 사용하여 SUS 304 스테인리스 시험편을 관통, 절단하면서 출력 에너지와 최대 출력을 비교하여 보고, 시험편 관통시 주파수와 출력 에너지와의 관계, 시험편 관통시 응융 금속 제거량에 의한 절단 속도의 예측, 서로 다른 출력의 가공에 있어서 슬릿 절단 폭, 커프 폭, 드로스 길이, 절단면의 표면 거칠기 등을 비교하여 출 력차에 따른 가공 특성을 고찰하였다.

• 대한기계학회논문집
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• 제18권5호
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• pp.1203-1217
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• 1994

In the present study, in order to analyze a turbulent flow in a square sectiond 180.deg. bend, Kim's low Reynolds number second moment turbulence closure is adopted. In this model, turbulence model constants in the wall region are modified as functions of turbulent Reynolds number by use of near wall turbulent universal properties based on Laufer's experimental results of Reynolds stress distriburions. Algebraic stress model and Reynolds stress equation model are used to verify the low Reynolds number second moment closure. The application of the present low Reynolds number algebraic stress model to the prediction of a square sectioned 180.deg. bend flow gives improved velocities and Reynolds stresses profiles compared with those obtained by using the van Driest mixing length model and present low Reynolds number Reynolds stress equation model.

• 한국기계가공학회지
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• 제14권4호
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• pp.92-99
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• 2015

The deformation of injection molding is seriously affected by injection molding conditions, such as melt and mold temperature and injection and holding pressure. In these conditions, the mold temperature is controlled by flowing coolant, which can be classified by the Reynolds number in the mold-cooling channel. In this study, the deformation of the automotive side molding according to the variation of the Reynolds number in the coolant was simulated by Moldflow. In the results, as the Reynolds number was increased, the mold cooling was also increased. However, when the Reynolds number exceeded a certain range, the mold cooling was not increased further. In addition to the Moldflow verification, the mold cooling by the coolant was simulated by CFX. The CFX results confirmed that the Reynolds number significantly influenced the mold cooling. The coolant, which has a high Reynolds number value, quickly cooled the mold. However, the coolant, which has a low Reynolds number value, such as 0 points, hardly cooled the mold. In an injection molding experiment, as the Reynolds number was high, the deformation of the moldings was reduced. The declining tendency of the deformation was similar to the Moldflow results.

• International Journal of Aerospace System Engineering
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• 제2권1호
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• pp.53-57
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• 2015

For improving the efficiency of near space propellers working over 20km, performances of their streamwise sections, i.e. low-Reynolds-number airfoils which work at $10^4-10^5$ Reynolds numbers, are significant. Based on the low-Reynolds-number CFD technology, this paper designs a novel low-Reynolds-number airfoil. Unsteady characteristics of the laminar separation bubble on novel airfoil and a typical conventional airfoil are studied numerically, and the Reynolds number effect is investigated. Results show that at $10^4-10^5$ Reynolds numbers, unsteady aerodynamic characteristics of the novel airfoil are severely weakened and its lift-to-drag ratio can increase about 100%.

• International Journal of Fluid Machinery and Systems
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• 제4권2호
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• pp.229-234
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• 2011

For Lift-type Vertical Axis Wind Turbine (VAWT), it is difficult to evaluate the performance through the scale-model wind tunnel tests, because of the scale effect relating to Reynolds number. However, it is beneficial to figure out the critical value of Reynolds number or minimum size of the Lift-type VAWT, when designing this type of micro wind turbine. Therefore, in this study, the performance of several scale-models of Lift-type VAWT (Reynolds number : $1.5{\times}10^4$ to $4.6{\times}10^4$) was investigated. As a result, the Reynolds number effect depends on the blade chord rather than the inlet velocity. In addition, there was a transition point of the Reynolds number to change the dominant driving force from Drag to Lift.

• 설비공학논문집
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• 제20권12호
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• pp.795-801
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• 2008

An experimental study has been performed on the single phase flow and convective heat transfer in trapezoidal microchannels. The microchannel was about $270{\mu}m$ wide, $800{\mu}m$ deep. and 7 mm long, which might ensure hydrodynamically fully-developed laminar flow at a low Reynolds number. The experiments were conducted with R1l3 and water, with the Reynolds number ranging from approximately 30 to 5000 for friction factor and 30 to 700 for the Nusselt number. Friction factors in laminar are found to be in good agreement with the predictions of existing correlation suggesting that a conventional analysis approach can be employed in predicting flow friction behavior in microchannels. However turbulent friction factors are hardly predictable by the existing correlations. The experimental results show that the Nusselt number is not a constant but increases almost linearly with the Reynolds number even the flow is fully developed (Re < 100). The dependence of the Nusslet number on the Reynolds number is contradictory to the conventional theory. At a Reynolds number greater than 100, the Nusselt number increases slowly with the Reynolds number, where thennally developing flow is responsible for the increase of the Nusselt number with the Reynolds number.