• 제목/요약/키워드: Effect of Reynolds number

검색결과 707건 처리시간 0.022초

Reynolds Number Effect on Regenerative Pump Performance in Low Reynolds Number Range

  • Horiguchi, Hironori;Yumiba, Daisuke;Tsujimoto, Yoshinobu;Sakagami, Masaaki;Tanaka, Shigeo
    • 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.

Numerical simulation study of the Reynolds number effect on two bridge decks based on the deterministic vortex method

  • Zhou, Zhiyong;Ma, Rujin
    • Wind and Structures
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    • 제13권4호
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    • pp.347-362
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    • 2010
  • Researches on the Reynolds number effect on bridge decks have made slow progress due to the complicated nature of the subject. Heretofore, few studies on this topic have been made. In this paper, aerostatic coefficients, Strouhal number ($S_t$), pressure distribution and Reynolds number ($R_e$) of Great Belt East Bridge and Sutong Bridge were investigated based on deterministic vortex method (DVM). In this method, Particle Strength Exchange (PSE) was chosen to implement the simulation of the flow around bluff body and to analyze the micro-mechanism of the aerostatic loading and Reynolds number effect. Compared with the results obtained from wind tunnel tests, reliability of numerical simulation can be proved. Numerical results also showed that the Reynolds number effect on aerostatic coefficients and Strouhal number of the two bridges can not be neglected. In the range of the Reynolds number from $10^5$ to $10^6$, it has great effect on the Strouhal number of Sutong Bridge, while the St is difficult to obtain from wind tunnel tests in this range.

Influence of Reynolds Number and Scale on Performance Evaluation of Lift-type Vertical Axis Wind Turbine by Scale-model Wind Tunnel Tests

  • Tanino, Tadakazu;Nakao, Shinichiro;Miyaguni, Takeshi;Takahashi, Kazunobu
    • 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.

저레이놀즈수 k-$\varepsilon$난류모형 개선에 관한 연구 (A Study on the Development of Low Reynolds Number k-$\varepsilon$ Turbulence Model)

  • 김명호;신종근;최영돈
    • 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.

Reynolds 수와 Knudsen 수가 초소형 점성펌프에 미치는 영향 (EFFECTS OF THE REYNOLDS AND KNUDSEN NUMBERS ON THE FLOW OF A MICRO-VISCOUS PUMP)

  • 강동진;이벨리나이바노바이바노바
    • 한국전산유체공학회지
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    • 제13권2호
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    • pp.14-19
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    • 2008
  • Effects of the Reynolds and Knudsen numbers on a micro-viscous pump are studied by using a Navier-Stokes code based on a finite volume method. The micro viscous pump consists of a circular rotor and a two-dimensional channel. The channel walls are treated by using a slip velocity model. The Reynolds number is studied in the range of $0.1{\sim}50$. The Knudsen number varies from 0.01 to 0.1. Numerical solutions show that the pump works efficiently when two counter rotating vortices formed on both sides of the rotor have the same size and intensity. As the Reynolds number increases, the size and intensity of the vortex on the inlet side of the pump decrease. It disappears when the Reynolds number is larger than about Re=20. The characteristics of the performance of the pump is shown to deteriorate, in terms of mean velocity and pressure rise, as the Reynolds number increases. The Knudsen number shows a different effect on the characteristics of the pump. As it increases, the mean velocity and pressure rise decrease but the characteristics of the vortex flow remains unchanged, unlike the effect of Reynolds number.

Effect of Reynolds number on compressible convex-corner flows

  • Chung, Kung-Ming;Chang, Po-Hsiung;Chang, Keh-Chin
    • Advances in aircraft and spacecraft science
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    • 제1권4호
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    • pp.443-454
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    • 2014
  • An experimental study was conducted to investigate the effect of Reynolds number on compressible convex-corner flows, which correspond to an upper surface of a deflected flap of an aircraft wing. The flow is naturally developed along a flat plate with two different lengths, resulting in different incoming boundary layer thicknesses or Reynolds numbers. It is found that boundary layer Reynolds number, ranging from $8.04{\times}10^4$ to $1.63{\times}10^5$, has a minor influence on flow expansion and compression near the corner apex in the transonic flow regime, but not for the subsonic expansion flow. For shock-induced separated flow, higher peak pressure fluctuations are observed at smaller Reynolds number, corresponding to the excursion phenomena and the shorter region of shock-induced boundary layer separation. An explicit correlation of separation length with deflection angle is also presented.

레이놀즈 수가 터보펌프 인듀서 캐비테이션 성능에 미치는 영향 측정 (Measurement of Reynolds Number Effects on Cavitation Performance in a Turbopump Inducer)

  • 김준호;송성진
    • 한국추진공학회:학술대회논문집
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    • 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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    • pp.820-823
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    • 2017
  • 터보펌프 인듀서에서 레이놀즈 수가 캐비테이션 성능에 미치는 영향을 실험적으로 연구하였다. 인듀서 입구에서 압력을 측정하여 캐비테이션 수에 따른 양정계수 변화를 구하였다. 물의 온도와 인듀서 회전수를 변화시켜 일정한 무차원 열적 변수에서 레이놀즈 수를 변경시켜 캐비테이션 성능을 측정하였다. 낮은 무차원 열적 변수에서는 캐비테이션 성능 곡선이 레이놀즈 수 변화에 영향을 받지 않는다. 하지만 높은 무차원 열적 변수에서는 레이놀즈 수가 증가함에 따라 임계 캐비테이션 수가 증가하였다.

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Heat Transfer Characteristics of the Spherical Capsule Storage System Using Paraffins

  • Cho, Keum-Nam;Choi, S. H.
    • International Journal of Air-Conditioning and Refrigeration
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    • 제6권
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    • pp.113-123
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    • 1998
  • The present study is to investigate the effect of experimental parameters on the heat transfer characteristics of a spherical capsule storage system using paraffins. N-Tetradecane and mixture of n-Tetradecane 40% and n-Hexadecane 60% were used as paraffins. Water with inorganic material was also tested for the comparison. The experimental parameters were varied for the Reynolds number from 8 to 16 and for the inlet temperature from -7 to 2$^{\circ}C$. Measured local temperatures of spherical capsules in the storage tank were utilized to calculate charging and discharging times, dimensionless thermal storage amount, and the average heat transfer coefficients in the tank. Local charging and discharging times in the storage tank were significantly different. The effect of inlet temperature on charging time was larger than that on discharging time, but the effect of Reynolds number on charging time was smaller than that on discharging time. Charging time of paraffins was faster by 11~72% than that of water with inorganic material, but little difference of discharging time was found among them. The effect of Reynolds number on the dimensionless thermal storage was less during charging process and more during discharging process than the effect of inlet temperature. The effect of the inlet temperature and the Reynolds number on the average heat transfer coefficient of the storage tank was stronger during discharging process than during charging process. The average heat transfer coefficients of the spherical capsule system using paraffins were larger by 40% than those using water.

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Aerodynamic Design of a Novel Low-Reynolds-Number Airfoil for Near Space Propellers

  • Zhang, Shunlei;Yang, Xudong;Song, Bifeng;Song, Wenping
    • 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%.

난류박리 및 재부착 유동의 해석을 위한 비선형 저레이놀즈수 k -$\varepsilon$ 난류모형의 개발 (A Nonlinear Low-Reynolds-Number k -$\varepsilon$ Model for Turbulent Separated and Reattaching Flows)

  • 박태선;성형진
    • 대한기계학회논문집
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    • 제19권8호
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    • pp.2051-2063
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    • 1995
  • An improved version of nonlinear low-Reynolds-number k-.epsilon. model is developed. In this model, the limiting near-wall behavior and nonlinear Reynolds stress representations are incorporated. Emphasis is placed on the adoption of Ry(.iden. $k^{1}$2/y/.nu.) instead of $y^{[-10]}$ (.iden. $u_{{\tau}/y/{\nu}}$) in the low-Reynolds-number model for predicting turbulent separated and reattaching flows. The non-equilibrium effect is examined to describe recirculating flows away from the wall. The present model is validated by doing the benchmark problem of turbulent flow behind a backward-facing step. The predictions of the present model are cross-checked with the existing measurements and DNS data. The model performance is shown to be generally satisfactory.