摘要:

Laboratory experiments and analytical studies investigating the interaction of two-dimensional, uniform stratified flow with a submerged horizontal circular cylinder are presented. Measurements were made of the interfacial waves formed behind the cylinder towed horizontally at constant speeds, and of the drag and lift forces exerted on the cylinder. An analytical linear model that describes the wave field and the associated wave induced drag force is formulated. In this model, the water is modeled as a uniform flow of three layers of inviscid and immiscible fluids. A solution is found for the case of the cylinder located in the upper layer. The experiments showed that large amplitude first mode internal waves are generated when the cylinder is towed at about one half of the long wave celerity of first mode waves, and that drag and lift forces change significantly with stratification. The analytical model demonstrates the role of a finite stratified layer. For the shorter waves it predicts wave lengths well, but it underestimates wave heights and drag. Better performance was obtained by introducing an effective cylinder radius factor. For the longer waves an inviscid model seems improper and the model is not applicable. The results are applied to the proposed submerged tube bridge across Høgsfjorden in Norway.

ISSN:0022-1686    

DOI:10.1080/00221689709498404

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Experiments with merging buoyant jets revealed the existence of an intermittent flapping motion in the flow trajectory. The flapping commences beyond the point where the initially axi-symmetric buoyant jets merge to form a plane plume. The size and relative positions of large-scale vortices on either boundary of the plane plume determine whether the flapping flow state occurs. The effect of the flapping on the short term timeaveraged flow properties was measured and the flapping was found to increase the spreading rate and also change the shape of the concentration fluctuation distribution in the plane plumes. The intermittent presence of flapping in plane plumes is shown to be the cause of widely accepted differences between plane and axisymmetric plumes. The new findings on the flapping behaviour were used to improve an integral model which describes merging buoyant jets.

ISSN:0022-1686    

DOI:10.1080/00221689709498405

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A Lagrangian approach is used to quantify the dispersion of particles in turbulent flows. Particles are tracked in a turbulent field taking into account crossing trajectory effects by solving their equation of motion. Further the CFD Phoenics* [1] code allows to model the turbulence of the carrier phase in which the particles disperse: a (K-ε) model supplemented with algebraic stress relations deduced from a second order closure scheme is used here. The coupled Eulerian-Lagrangian model is then optimized by taking into account a space-time random distribution for the turbulent scales. Droplets dispersion predictions are presented for the turbulent pipe flow experienced by Calabrese & Middleman [2], and the computational results agree well with their experimental results.

ISSN:0022-1686    

DOI:10.1080/00221689709498406

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The dead zone equations were solved with the use of the Laplace transform technics. The solution was a base to derive the three moments of the pollution concentration distribution in a river. They differ from the moments published so far, because they were calculated from the solution of the pure boundary problem. This approach is easier to apply in calculations of the pollution concentration distributions and it covers a wider range of cases when we deal with natural field data.

ISSN:0022-1686    

DOI:10.1080/00221689709498407

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A new approach has been developed for designing the shape and dimensions of the cross section of a straight threshold channel based on the concepts of entropy and probability. A formula for the lateral distribution of transverse slopes, and hence the cross-sectional bank profile, was derived by the entropy-maximisation principle and the calculus of variations. The bank profile is a new type of simple parabolic curve. The results of numerical experiments based on the approach of boundary shear stress distribution support the conclusion that the entropy-based channel bank profile is at threshold. Bank profile equations are coupled with an appropriate frictional relationship to obtain a new design method. Channel dimensions and bank profiles predicted by this method are compared with those given by other design methods. The predicted channel dimensions are in reasonable agreement with laboratory experimental data.

ISSN:0022-1686    

DOI:10.1080/00221689709498408

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The characteristic flow parameters of an open channel flow with an erodible hydraulically smooth sand bed were investigated for sand grains at rest, and for the flow regime in which an intermittent transport occurs. The experimental results show the following: (1) The grains are only transported by sweeps. (2) The sediment transport is responsible for up to 30% of the wall shear velocity. (3) No noticeable drag reducing effect occurs. (4) At high intermittent sediment transport the sweep frequency was found to be constant over the water depth. (5) With increasing wall shear stress the intensity distribution of the sweeps becomes more homogeneous and the maxima smaller.

ISSN:0022-1686    

DOI:10.1080/00221689709498409

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The characteristics of an ultrasonic instrument, the bistatic acoustic Doppler velocity profiler (ADVP) are described. The bislatic system can measure profiles of two components of the instantaneous velocity vector with no restrictions on the flow conditions. Results of the bistatic ADVP measurements of water velocity and turbulence in uniform flow in laboratory open channels, were found to coincide well with the laws for mean velocity, variance and Reynold's stress. This indicates that the turbulence scales are sufficiently resolved in the ADVP measurements. Two-dimensional flow patterns derived from the ADVP measurements demonstrate the presence of coherent structures. The instrument was found to be a useful research tool for non-intrusive and accurate instantaneous profile measurements under turbulent flow conditions unaffected by water quality.

ISSN:0022-1686    

DOI:10.1080/00221689709498410

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:0022-1686    

DOI:10.1080/00221689709498411

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:0022-1686    

DOI:10.1080/00221689709498412

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor