scholarly journals The effect of collar width ratio on the flow pattern around oblong pier in bend

2021 ◽  
Author(s):  
Danesh Dehghan ◽  
Mohammad Vaghefi ◽  
Masoud Ghodsian
Keyword(s):  
Flow Pattern ◽  
Cross Section ◽  
Rectangular Cross Section ◽  
Width Ratio ◽  
Curvature Radius ◽  
Reynolds Stresses ◽  
Clear Water ◽  
Flow Conditions ◽  
Channel Bend ◽  
Oblong Pier

Abstract In this paper, the effect of collar width ratio on the flow pattern around an oblong pier in a 180-degree channel bend was experimentally studied. This channel has a rectangular cross section. It is 1 m in width and 0.7 m in height. The upstream and downstream paths are respectively 6.5 and 5 m long. The ratio of the bend's central curvature radius to the channel width is 2; hence, it qualifies as a sharp bend. Experiments were carried out under clear water approach flow conditions. The results showed that the presence of collars around an oblong pier creates vortices in the opposite direction of the longitudinal flow, causes the distortion and disturbance of the streamlines toward the pier downstream, and decreases downflow strength in front of the pier nose. Furthermore, doubling the collar width results in 0.68 and 0.93 times the vorticity and the power of the secondary flow on the pier upstream, respectively. It also reduced the maximum values of the Reynolds stresses perpendicular to the y-plane in x direction and perpendicular to the z-plane in y direction by respectively 45 and 60%, and increased the Reynolds stress perpendicular to the z-plane in x direction by 25%.

Solids Flow Pattern in the Bottom Zone of a Rectangular Cross-Section Circulating Fluidized Bed

2003 ◽  
Author(s):  
Hong-Shun Li ◽  
Yi-Jun Wang ◽  
Shi-Ping Jin
Keyword(s):  
Flow Pattern ◽  
Fluidized Bed ◽  
Cross Section ◽  
Quartz Sand ◽  
Circulating Fluidized Bed ◽  
Rectangular Cross Section ◽  
Temperature Response ◽  
Cold Model ◽  
Hot Particles ◽  
Bottom Zone

Solids flow pattern in the bottom zone of a rectangular cross-section CFB was investigated by using hot particles as the tracer. The experiments were carried out in a cold model circulating fluidized bed. The riser has an inner cross-section of 0.3 m by 0.5 m and a height of 5.8 m. The solids were returned into the riser at a height of 0.75 m above the air distributor within an angle of about 40 degree. Quartz sand was used as the bed material. The hot particles were also quartz sand but with a little smaller size. Specially designed miniature electrically heating devices were installed flush with the inner bed wall or inside the bed. At each run, about 10–15 cm3 hot particles were slowly pulled into the bed. The temperature response around the device was measured with four copper-constantan thermocouples. Based on the experimental results, a 3-D core-annulus model describing the solids flow pattern in the bottom zone of the CFB riser is proposed.

A Numerical Study of Assisting and Opposing Mixed Convective Heat Transfer From a Horizontal Isothermal High Aspect Ratio Rectangular Cylinder

2012 ◽  
Author(s):  
Patrick H. Oosthuizen
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Numerical Study ◽  
Rectangular Cross Section ◽  
Boussinesq Approximation ◽  
Forced Flow ◽  
Width Ratio ◽  
Flow Conditions ◽  
Rectangular Cylinder

Mixed convective heat transfer from an isothermal cylinder with a rectangular cross-section and a relatively large height-to-width ratio has been numerically studied. The axis of the cylinder is horizontal with the longer sides of the rectangular cylinder being vertical. There is a vertical forced flow over the cylinder. The flow conditions considered are such that in general mixed forced and natural convective flow exists. Both the case where the buoyancy forces act in the same direction as the forced flow (assisting flow) and the case where they act in the opposite direction to the forced flow (opposing flow) have been considered. The flow has been assumed to be two-dimensional and the Boussinesq approximation has been adopted. Attention has been restricted to the flow of air and results have therefore been obtained for a Prandtl number of 0.74. The flow conditions considered are such that laminar or turbulent flow can exist. The main attention is this work has been directed at determining the effect of the flow parameters on the mean heat transfer rate from the cylinder and on determining the conditions under which the flow can be assumed to be forced convective and under which it can be assumed to be natural convective.

FEM Analysis of Active Reduction of Torsional Vibrations of Clamped-Free Beam by Piezoelectric Elements for Separated Modes

2015 ◽  
Vol 39 (4) ◽  
pp. 639-644 ◽  
Author(s):  
Elżbieta Augustyn ◽  
Marek S. Kozień ◽  
Michał Pracik
Keyword(s):  
Cross Section ◽  
Rectangular Cross Section ◽  
Fem Analysis ◽  
Width Ratio ◽  
Torsional Vibrations ◽  
Fem Simulations ◽  
Natural Modes ◽  
Piezoelectric Elements ◽  
Large Length ◽  
Free Beam

Abstract Beams with rectangular cross-section, with large length-to-width ratio, can be excited to torsional vibrations. If the piezoelectric elements are mounted to the beam in pairs at the same cross-section with two separated elements positioned on the same side of the beam, and the voltages applied to them are in the opposite phase, they produce twisting moments which can be applied to reduce the torsional vibrations. Results of FEM simulations are presented and analysed in the paper. All analyses are performed for a steel free-clamped beam. The piezoelectric elements made of PZT material are mounted in pairs on one side of the beam. The analyses are done for separated natural modes.

scholarly journals Numerical Simulation of Turbulent Jets With Rectangular Cross-Section

1998 ◽  
Vol 120 (2) ◽  
pp. 285-290 ◽  
Author(s):  
R. V. Wilson ◽  
A. O. Demuren
Keyword(s):  
Reynolds Number ◽  
Cross Section ◽  
Stokes Equations ◽  
Rectangular Cross Section ◽  
Turbulent Jets ◽  
Reynolds Numbers ◽  
Scale Model ◽  
Reynolds Stresses ◽  
Spatial Discretization ◽  
Low Reynolds

Three-dimensional turbulent jets with rectangular cross-section are simulated with a finite-difference numerical method. The full Navier-Stokes equations are solved at a low Reynolds number, whereas at a higher Reynolds number filtered forms of the equations are solved along with a sub-grid scale model to approximate effects of the unresolved scales. A 2-N storage, third-order Runge-Kutta scheme is used for temporal discretization and a fourth-order compact scheme is used for spatial discretization. Divergence-free velocity field is obtained by solving a Poisson equation for pressure with the same spatial discretization scheme for consistent accuracy. Computations are performed for different inlet conditions which represent different types of jet forcing within the shear layer. The phenomenon of axis-switching is observed in some cases. At low Reynolds numbers, it is based on self-induction of the vorticity field, whereas at higher Reynolds numbers, the turbulent structure becomes the dominant mechanism in natural jets. Budgets of the mean streamwise velocity show that convection is balanced by gradients of the Reynolds stresses and the pressure.

scholarly journals Experimental study of the structure of a gas flow in curvilinear channels of variable cross-section

2020 ◽  
pp. 44-48
Author(s):  
С.В. Чехранов ◽  
Р.Р. Симашов
Keyword(s):  
Kinetic Energy ◽  
Flow Structure ◽  
Cross Section ◽  
Rectangular Cross Section ◽  
Energy Losses ◽  
Radius Of Curvature ◽  
Curvature Radius ◽  
Variable Cross ◽  
Flow Angle ◽  
Study Results

Целью работы является изучение влияния степени конфузорности и радиусов кривизны на структуру потока и уровень потерь кинетической энергии в единичных криволинейных каналах. Такое исследование проводится в связи с тем, что межлопаточные каналы малорасходных турбин с большим углом поворота потока в рабочем колесе оказывают определяющее влияние на к.п.д. турбин такой конструкции. Поэтому для исследования выбраны каналы прямоугольного сечения с углом поворота потока 167 град. при степени конфузорности 0,5 и 0,7. При использовании в качестве рабочего тела воздуха результаты исследования показали, что уровень потерь кинетической энергии тем ниже, чем меньше значение степени конфузорности и меньше радиус кривизны. А исследование структуры потока показало, что увеличение радиуса кривизны приводит к смыканию вторичных вихрей и увеличению протяженности поверхности трения, что и является причиной возрастания потерь энергии в каналах с повышенным радиусом кривизны. The aim of this work is to study the influence of the degree of confusion and radii of curvature on the flow structure and the level of kinetic energy losses in single curvilinear channels. Such a study is carried out due to the fact that the interscapular channels of low-consumption turbines with a large flow angle in the impeller have a decisive effect on the efficiency of turbines of this design. Therefore, for the study, channels of rectangular cross-section with a flow rotation angle of 167 at a degree of confusion of 0.5 and 0.7 were selected. When using air as a working medium, the study results showed that the level of kinetic energy losses is lower, the lower the value of the confusion degree and the smaller the curvature radius. And the study of the flow structure showed that an increase in the radius of curvature leads to the closure of secondary vortices and an increase in the length of the friction surface, which is the reason for the increase in energy losses in channels with an increased radius of curvature.

Fatigue Crack Growth Rate under Different Bending to Torsion Ratios in 10HNAP Steel

2011 ◽  
Vol 465 ◽  
pp. 187-190
Author(s):  
Zbigniew Marciniak ◽  
Dariusz Rozumek
Keyword(s):  
Growth Rate ◽  
Cross Section ◽  
Stress Ratio ◽  
High Cycle Fatigue ◽  
Rectangular Cross Section ◽  
Width Ratio ◽  
Loading Frequency ◽  
Test Results ◽  
Cycle Fatigue ◽  
Specimen Height

The paper contains the fatigue test results of rectangular cross-section specimens made of 10HNAP steel. The specimen height to width ratio was 1.5. Bending with torsion tests were carried out for the following ratios of bending to torsional moments MaB / MaT = 0.47, 0.94, 1.87 and the loading frequency 26.5 Hz. The tests were performed in a high cycle fatigue regime for the stress ratio R = - 1 and phase shift between bending and torsion loading equal to  = 0.

Nonlinear mechanics of fluidization of beds of spherical particles

1987 ◽  
Vol 177 ◽  
pp. 467-483 ◽  
Author(s):  
A. F. Fortes ◽  
D. D. Joseph ◽  
T. S. Lundgren
Keyword(s):  
Cross Section ◽  
Rectangular Cross Section ◽  
Two Dimensions ◽  
The Other ◽  
Three Dimensions ◽  
Spherical Particles ◽  
Inertial Effects ◽  
Nonlinear Mechanics ◽  
Clear Water ◽  
Cooperative Motion

Experiments on fluidization with water of spherical particles falling against gravity in columns of rectangular cross-section are described. All of them are dominated by inertial effects associated with wakes. Two local mechanisms are involved: drafting and kissing and tumbling into stable cross-stream arrays. Drafting, kissing and tumbling are rearrangement mechanisms in which one sphere is captured in the wake of the other. The kissing spheres are aligned with the stream. The streamwise alignment is massively unstable and the kissing spheres tumble into more stable cross-stream pairs of doublets which can aggregate into larger relatively stable horizontal arrays. Cross-stream arrays in beds of spheres constrained to move in two dimensions are remarkable. These arrays may even coalesce into aggregations of close-packed spheres separated by regions of clear water. A somewhat weaker form of cooperative motion of cross-stream arrays of rising spheres is found in beds of square cross-section where the spheres may move freely in three dimensions. Horizontal arrays rise where drafting spheres fall because of greater drag. Aggregation of spheres seems to be associated with relatively stable cooperative motions of horizontal arrays of spheres rising in their own wakes.

Analysis on Axial Stresses of Crossbars on Aqueduct

2012 ◽  
Vol 238 ◽  
pp. 329-332
Author(s):  
Xin Li Bai ◽  
Jiang Yan Li ◽  
Bing Ma
Keyword(s):  
Cross Section ◽  
Axial Force ◽  
Water Depth ◽  
Rectangular Cross Section ◽  
Tensile Force ◽  
Side Wall ◽  
Width Ratio ◽  
Simply Supported ◽  
Axial Forces ◽  
Axial Tensile

By use of finite element method, the axial stresses of crossbars on the top of a simply supported rectangular-sectioned aqueduct were calculated in this paper. Three factors were considered, namely height-width ratio, water depth and crossbars spacing. The results show that, most crossbars are in compression when the height-width ratio of aqueduct cross-section is small, and with the height-width ratio increasing, the axial forces of crossbars change from compression to tension; Under a certain height-width ratio, when water depth is relatively small, most crossbars are in compression, and with the increase of water depth, axial forces of crossbars change from compression to tension; big axial tensile force is harmful to the rectangular cross-section floor (mid-span), but favorable to the side wall bottom. The obtained change rules of axial force and the influence of axial force on aqueduct body stress can be referenced to aqueduct design.

Sign in / Sign up

Export Citation Format

Share Document