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1

Internal flow behaviour and microstructural evolution of the bobbin-FSW welds: thermomechanical comparison between 1xxx and 3xxx aluminium grades

Tamadon Abbas, Pons Dirk J., Sued Kamil, Clucas Don

Advances in Materials Science

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2021

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Vol. 21, nr 2(68)

40--64

EN

The influences of processing parameters and tool feature on the microstructure of AA1100 and AA3003 aluminium alloys were investigated using bobbin friction stir welding (BFSW). The research includes flow visualization and microstructural evolution of the weld texture using the metallographic measurement method. Results indicated that the operational parameters of the welding (e.g. feed rate, rotating speed) and the geometry of the tool can directly affect the flow patterns of the weld structure. The microscopic details revealed by the optical and electron microscope imply the dynamic recrystallization including grain refinement and precipitation mechanisms within the stirring zone of the weld region. The microscopic observations for the weld samples show a better performance of the fully-featured tool (tri-flat threaded pin and scrolled shoulders) compared to the simple tool without inscribed surface features. The fully-featured tool resulted in a more uniform thermomechanical plastic deformation within the weld structure along with the precipitation hardening and the homogeneity of the microstructure.

2

The rectangular two-phase closed thermosyphon: A case study of two-phase internal flow patterns behaviour for heat performance

Chompookham Teerapat, Sichamnan Surachet, Bhuwakietkumjohn Nipon, Parametthanuwat Thanya

Archives of Thermodynamics

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2020

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Vol. 41, no 3

223--254

EN

This research explored different types of two-phase flow patterns that influenced heat transfer rate by assessing rectangular two-phase closed thermosyphon (RTPCT) made from glass with the sides of equal length of 25.2 mm, aspect ratio 5 and 20, evaporation temperature of 50, 70, and 90°C, working substance addition rate of 50% by volume of evaporator, and water inlet temperature at condensation of 20°C. Upon testing with aspect ratios 5, three flow patterns emerged which were: bubble flow, slug flow and churn flow respectively. As per the aspect ratio 20, four flow patterns were discovered which were: bubble flow, slug flow, churn flow and annular flow, respectively. Aspect ratio 5 pertains characteristic which resulted in a shorter evaporation rate of the RTPCT than that of the aspect ratio 20, thus, a shorter flow distance from the evaporator section to heat releaser was observed. Therefore, flow patterns at aspect ratio 5 exhibited a faster flow velocity than that of the aspect ratio 20. Furthermore, changes of flow pattern to the one that is important for heat transfer rate can be easily achieved. Churn flow was the most important type of the flow for heat transfer, followed by slug flow. Moreover, with aspect ratio 20, annular flow was the most important flow for the heat transfer, followed by churn flow, respectively. Throughout the test, average heat flux as obtained from the aspect ratio 5 were 1.51 and 0.74 kW/m2 which were higher than those of the aspect ratio 20. The highest heat flux at the operating temperature of the evaporator section was 90°C, which was equivalent to 2.60 and 1.52 kW/m2, respectively.

3

Numerical simulations of gap flow above rotating disk

Wasilczuk F., Flaszyński P., Doerffer P.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2015

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Vol. 19, No 2

89--100

EN

A rotating disk can be considered a basic configuration for the investigations of the impact of various conditions on the flow through the clearance between the shrouded turbine blade and the casing. Numerical calculations using Fine/Turbo Numeca were conducted to examine the influence of the rotational velocity and the pressure difference across the disk on the flow conditions, especially the mass flow through the clearance. The results were validated using the experimental data. Moreover, the flow field was investigated to reveal the vortices induced in the flow. The calculations showed a significant drop of the mass flow with a rise of the rotation velocity. Additionally, the vortex created upstream of the disk at higher rotation velocities was observed. The phenomenon of separation at the edge of the disk was investigated.

4

Modification of the Rigid Finite Element Method in Modeling Dynamics of Lines and Risers

Adamiec-Wójcik I., Brzozowska L., Wojciech S.

Archive of Mechanical Engineering

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2013

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Vol. LX, nr 3

409--429

EN

The paper presents an application of the modified rigid finite element method to analysis of the dynamics of slender structures. The equations of motion are formulated for a system discretized by means of the method, and discussion is limited to planar systems and large deformations. Slender elements can be found in offshore engineering as lines, cables and risers. In these cases the hydrostatic influence of water and sea currents has to be taken into account. While analyzing dynamics of risers it may also be necessary to consider the flow of fluid inside the riser. The influence of hydrodynamic coefficients and the velocity of the internal flow of fluid on displacements and forces is presented.

PL

W pracy przedstawiono zastosowanie zmodyfikowanej metody elementów skończonych do analizy dynamiki wiotkich struktur. Sformułowano równania ruchu układu dyskretyzowanego prezentowaną metodą, przy ograniczeniu rozważań do płaskich układów i uwzględnieniu dużych ugięć. Elementy wiotkie spotykane są często w technice offshore’owej jako liny, kable i risery. Analizę dynamiki tych elementów trzeba jednak wówczas uzupełnić o hydrostatyczne oddziaływania wody i prądów morskich. W przypadku riserów, należy też uwzględnić możliwość przepływu płynu w ich wnętrzu. Na przykładzie risera pokazano wpływ współczynników hydrodynamicznych i prędkości przepływu płynu we wnętrzu risera na przemieszczenia i siły.

5

Three-dimensional numerical analysis of internal flow phenomena in a diagonal rotor

Bin Y., Keqi W.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2004

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Vol. 8, No 1

27-40

EN

A numerical analysis has been designed to study internal flow phenomena in a diagonal rotor. A calculated diagonal rotor was designed by a quasi-three-dimensional method. Its hub and casing walls were inclined 45o and 25o, respectively. The numerical simulation was based on the Navier-Stokes equations coupled with a k-? turbulence model. We found that the rotor's wake was stronger near the hub and in the casing end wall region. The wake at a lower flow rate was stronger than that at a higher flow rate. Static pressure gradually increased from the hub to the casing along the height of a blade, on the rotor pressure surface and in the front 60% of the chord region of the suction surface. In the back 40% of the chord region of the suction surface, static pressure gradually decreased. A passage vortex formed in the stator flow passage and an 80% axial chord plane. It was located near the hub end-wall. The passage vortex developed into a large vortex centered near the midspan at a 99% axial chord plane of the stator. The casing wall boundary layer downstream of the rotor occupied approximately 10% of the flow passage. Along the height of a blade, the meridian velocity gradually increased upstream of rotor and decreased downstream. The calculated aerodynamic characteristic curve, the meridian velocity distribution upstream and downstream of the rotor, and the streamline distribution on the meridian surface were consistent with experimental results and design data. Our findings proved that the present numerical method is reliable and practicable. It can be used to design and analyze swept diagonal rotors in order to improve their surging and rotation stall state. The present results also provide comparative data for the design of highly-loaded swept diagonal rotors in future studies.

6

Qualitative comparison of 2D and 3D computation of flow field in the cone shaped turbine nozzle

Puzyrewski R., Flaszyński P.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2000

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Vol. 4, No 2

179-192

EN

The paper presents a qualitative comparison of 2D and 3D computation of the flow field in a cone shaped turbine nozzle. The calculation yields a surface, S/sub 2/, for a given conical stream surface S/sub 1/. The S/sub 2/ stream surface represents the curvature of blading passages. This formulation is typical for the inverse problem. Based on a surface it is possible to design the shape of the blade. Results of 3D computation by means of FLUENT have been presented and compared with assumptions in the 2D model.

7

Theoretical analysis of the hydrodynamic characteristics of electrorheological fluid in a parallel duct flow

Shimada K., Nishida H., Yamaguchi T.

Applied Mechanics and Engineering

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2000

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Vol. 5, no 4

803-820

EN

Theoretical analysis was conducted of the hydrodynamic characteristics of the two-dimensional flow of electrorheological fluid between parallel plates by using the mechanical dynamic model proposed herein. The model includes the Voigt model and a slider. It can present four types of relations between shear stress and shear rate. The theoretical results were compared with the experimental data. The theoretical analysis explains the experimental results qualitatively. The qualitative tendency is the same for the four types of relations between shear rate and shear stress. Based on the theoretical results, velocity distribution of flow in four types of relations is not influenced by shear stress and shear rate. This finding differs from that for rotational flow around a rotating disk. The pressure difference depends on apparent viscosity. The local Reynolds number depends on the local velocity at a low given flow velocity and on the local kinematic viscosity at a high given flow velocity.