• Title, Summary, Keyword: Froude number

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Characteristics of the plume formed by the buoyant discharges from the river

  • Kim, Ki-Cheol;Kim, Sung-Bo
    • Journal of the Korean Society of Marine Engineering
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    • v.38 no.8
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    • pp.981-994
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    • 2014
  • Density currents formed by buoyancy discharges from rivers are numerically studied using non-dimensional two layer model including Coriolis acceleration, bottom stress, interfacial friction. Some typical numbers such as Froude number, densimetric Froude number and Kelvin number are obtained and some characteristic scales are defined as a result of non-dimensionalization of the governing equations. Besides the Coriolis effect, the configurations of bottom topography, bottom friction coefficient and interfacial friction are found to significantly affect the propagation of the warm water plume. Frontal position can fastly propagate in the case of large density difference between the two layers and small interfacial friction. Left side boundary current is easily formed under the small interfacial friction. With large Kelvin number, both right and left side boundary currents are formed. Wave-like disturbances and eddies are easily formed under the high Froude number.

FRONT PROPAGATION RATE OF DENSITY CURRENTS: DENSIMETRIC FROUDE NUMBER VERSUS DIMENSIONLESS FRONT VELOCITY

  • Choi, Sung-Uk
    • Water Engineering Research
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    • v.3 no.1
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    • pp.9-22
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    • 2002
  • In general, two dimensionless numbers are used in predicting the front propagation rate of density currents: the densimetric Froude number and the dimensionless front velocity. The former expresses the front speed in terms of the characteristic length and reduced gravitational acceleration. Previous papers report that the range of this dimensionless number is wide. The other is the dimensionless front velocity, which is a function of the buoyancy flux per unit width. This paper presents the state of the art review of the dimensionless numbers for the front propagation rate of density currents. Values of the densimetric Froude number are found to be consistent when the proper characteristic length is used for normalization. Then, the densimetric Froude number and the dimensionless front velocity are compared by using the experimental data of density currents over a horizontal surface.

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Evaluation of Hydrodynamic Behavior in Horizontal Settling Basin with Archimedes number (Archimedes number를 이용한 장방형 침전지내 수리흐름 평가에 관한 연구)

  • Park, No-Suk;Lee, Sanguk
    • Journal of Korean Society of Water and Wastewater
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    • v.23 no.6
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    • pp.865-870
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    • 2009
  • In this study, the adequacy of Reynolds numbers and Froude numbers derived from about sixty domestic water treatment plants (WTPs) were analyzed in order to estimate the characteristics of hydraulic behavior within the rectangular shaped sedimentation basins used widely. From the results of analysis, most of domestic WTPs have satisfied the criteria regulated as that Reynolds number should less than 1,000(dimensionless). On the other hand, they have not been able to satisfy the Froude number criteria, which should be higher than $1.0{\times}10^{-6}$. The reasons why most of domestic WTPs could not satisfy the criteria are that its criteria basis has been not only inadequate, but also the concept of external flow occurred around a settling particle has been ignored. Accordingly, this study proved the feasibility of Archimedes number, which indicates the ratio between particle Reynolds number and Froude number, to evaluate the hydraulic efficiency and its function of scale factor.

Measurements of turbulent flows downstream of a spur dike at different Froude numbers (Froude 수 변화에 따른 수제 하류 난류 흐름 측정)

  • Lee, Jiyong;Kim, Yeongkyu;Cha, Jun-Ho;Kang, Seokkoo
    • Journal of Korea Water Resources Association
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    • v.52 no.2
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    • pp.115-123
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    • 2019
  • The effects of the Froude numbers on turbulent flow patterns downstream of a non-submerged spur dike were investigated in a laboratory flume. Three-dimensional velocities and water depths were measured using Acoustic Doppler Velocimetry and distance sensors under three Froude number conditions ($Fr_d=0.31$, 0.38, and 0.46). The results show that there are marginal differences in the velocity fields downstream of a spur dike due to the change of the Froude number. However, an increase of the Froude number was found to reduce cross-sectional area in the flow and to increase the strength of the jet-like flow. The jet-like flow was observed to displace the location of the maximum turbulence kinetic energy within a cross section toward the inner bank in the transverse direction.

The Local Scour around a Slender Pile in Combined Waves and Current (파랑과 흐름이 결합된 공존역에서 파일 주변의 국부세굴)

  • Park, Jong-Hwan;Kim, Kyoung-Ho
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.22 no.6
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    • pp.405-414
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    • 2010
  • In the study, experiments are performed in the mixing region combined wave and current to investigate the characteristics of local scour around a slender pile. Wave generator and current generator are used for the experiments and currents are co-directions with the waves. The local scour depths around the pipeline are obtained according to the various pipe diameters, wave periods, wave heights, and current velocities. The experiments show that the maximum equilibrium local scour depth increases with pipe diameter, wave period, wave height, and current velocity. Using the experimental results, the correlations of scour depth and parameters such as Shields parameter ($\theta$), Froude number (Fr), Keulegan-Carpenter number (KC), Ursell number ($U_R$), modified Ursell number ($U_{RP}$) and ratio of velocities ($U_c/U_c+U_m$) are analyzed. In the mixing region combined with waves and currents, The Froude number of single parameters is the main parameter to cause the local scour around a slender pile due to waves and current and this means that current governs the scour within any limits of the currents.

Experimental Study on the Behaviour of Interfacial Layer in Saltwater Wedge (정상염수쐐기 경계층 거동에 대한 실험적 연구)

  • Lyu, Siwan;Kim, Young Do;Choi, Jae Hoon;Seo, Il Won;Kwon, Jae Hyun
    • Journal of Korean Society of Water and Wastewater
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    • v.23 no.6
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    • pp.833-842
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    • 2009
  • A series of laboratory experiments has been performed to investigate the behaviour of interfacial layer of saltwater wedge in estuary. Experimental conditions have been established according to densimetric Froude number, which is a dimensionless number comparing inertia force with buoyancy due to the density difference. To observe the behaviour of saltwater wedge, conductivity meter has been used to detect salinity. Time averaged and temporal variation of observed properties have been analyzed to determine and investigate the interfacial layer. The location and profile of interfacial layers have shown the dependency on densimetric Froude number. The thickness of interfacial layer has been also dependent on the variation of densimetric Froude number.

The Local Scour around Submarine Pipelines in the Interaction Region Combined with Waves and Currents (파랑과 정상흐름의 공존역에서 해저관로 주변의 국부세굴)

  • Kim, Kyoung-Ho;Lee, Ho-Jin;Kim, Wan-Shik
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.20 no.5
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    • pp.510-521
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    • 2008
  • In the study, experiments are performed in the interaction region combined with wave and current to investigate the characteristics of local scour around submarine pipelines. Wave generator and current generator are used for the experiments and two current directions were used; co-direction and counter direction to the wave. The local scour depths around the pipeline are obtained according to the various pipe diameters(D), wave periods(T), wave heights(H), and current velocities(V). The experiments show that the maximum equilibrium local scour depth increases with pipe diameter, wave period, wave height, and current velocity. Using the experimental results, the correlations of scour depth and parameters such as Shields parameter($\theta$), Froude number(Fr), period parameter, Keulegan-Carpenter number(KC), Ursell number($U_R$), modified Ursell number($U_{RP}$) and ratio of velocities($U_{c}/(U_{c}+U_{m})$) are analyzed. In the interaction region combined with waves and currents, Froude number and Shields parameter are found the main parameters to cause the local scour around the submarine pipelines and this means that current governs the scour within any limits of the currents.

Effect on Stratification due to Diffuser Shape in a Thermal Storage Tank (온도 성층축열조 가시화 및 실증분석에 관한 고찰)

  • Lee Young-Soo;Lee Sang-Nam;Kim Jong-Ryul
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.17 no.11
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    • pp.990-997
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    • 2005
  • The stratified effect was investigated with three different types of diffuser shape in a thermal storage tank with variation of diffuser diameter, velocity, Froude number etc. Its effect was estimated by the degree of stratification. No matter of diffuser diameter and shape, the degree of stratification was the best as the Froude number gets closer to 1. In the case of a curved diffuser, when its diameter is a quarter of tank diameter and ejection velocity in a diffuser is approximately 0.2 m/s, the Froude number was almost 1. In the case of a flatted diffuser, when ejection velocity was 0.05 m/s, the Froude number was 1.5. Both cases which Froude number were nearer 1, showed the good degree of stratification.

The Mixing of Forced Plume In the Coastal Waters (연안해역 중력 분류의 혼합 과정)

  • Jang, Seon-Deok;Seo, Jeong-Mun;Lee, Jong-Seop
    • Journal of the Korean Society of Fisheries and Ocean Technology
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    • v.26 no.1
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    • pp.26-33
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    • 1990
  • The behavior and mixing process of the forced plume are studied in the hydraulic laboratory. The dilution rate of discharged waste water from the port in various hydraulic condition was analized. The effect of densimetric Froude number and the discharge type on the dilution rate are discussed: In the vertical discharge, the forced plume of small densimetric Froude number mixes more actively than that of the large one. In the horizontal discharge, forced plume of large densimetric Froude number dilutes more rapidly than that of the small one. The mixing takes place more vigorously in the horizontal discharge than in the vertical one. The multi-port diffuser is more effective for the waste water discharge system than the single port diffuser in the tidal swinging coastal sea.

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Theoretical Study on the Behavior of Momentum-controlled Buoyant Jet and Flame of Hydrogen (운동량에 의해 제어되는 수소 부양 제트 및 화염의 거동에 관한 이론적 해석)

  • Yang, Won;Won, Sang-Hee;Kim, Min-Kook;Chung, Suk-Ho;Kim, Jong-Soo
    • Journal of the Korean Society of Combustion
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    • v.10 no.3
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    • pp.34-41
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    • 2005
  • Hydrogen safety is one of the key technical issue with growing attention on utilization of hydrogen energy. This study is aimed to predict behavior of momentum-controlling buoyant jet and flame caused by hydrogen leakage from a high pressured tank. Approximate solutions were derived for the case of turbulent buoyant jet and diffusion flame in still air. In case of hydrogen jet with low Froude number (100-4000), computed jet trajectories were compared with experimental data and showed good agreement with them. Jet and flame trajectories and flame length of hydrogen are predicted and compared with the buoyant flame of propane. The results well show that buoyancy is dominant in the range of low Froude number, while initial momentum is dominant in the range of high Froude number. That effect is more distinct for hydrogen flame than the case of propane.

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