Many shell structures used in modern technology consist of regular shell parts joined together along their common boundaries. We review different theoretical, numerical, and experimental approaches ...to modelling, analyses and design of the compound shell structures with junctions. Several alternative forms of boundary, continuity and jump conditions at the singular midsurface curves modelling the shell junction are reviewed. We also analyse the results obtained for special shell structures containing the cylinder–cylinder intersections, cone– , sphere– , and plate–cylinder junctions, tubular joints as well as other special types of junctions appearing in complex multi-shell structures.
•This is the complete review of the whole field “Junctions in shell structures”.•Theoretical, numerical, and experimental analyses of shell junctions are covered.•Different forms of boundary, continuity, and jump conditions are presented.•Specialised types of junctions appearing in multi-shell structures are discussed.•The results of each paper are characterised in the concise descriptive way.
•Review on numerical and experimental studies pertaining to natural convection in enclosures.•Effect of internal bodies such as square, circular and elliptical cylinder on flow ...mechanism.•Summarization of different methodologies used to improve the thermal behavior of buoyancy driven flows within an enclosure.•Effect of wall boundary conditions, position and number of internal bodies.•Categorization of flow regimes and the factors affecting the transition from steady to unsteady state.
Natural convection has been extensively studied due to its presence in many engineering applications. It is one of the most important modes of heat transfer and arises due to buoyancy-induced flows resulting from temperature differences. This review presents a detailed summary of numerical and experimental studies related to laminar natural convection in enclosures with and without internal bodies. Square, circular, and elliptical cylinders are mostly considered as internal bodies. The presence of internal bodies makes significant changes in the flow characteristics within the enclosure. The effects on the flow regime and thermal fields of various parameters have been discussed in detail, including the Rayleigh number, aspect ratio, position of internal bodies, number of internal bodies, and inclination angle. The different flow regimes depending on the input parameters are categorized based on observations made from flow and thermal patterns. This review discusses various methodologies used by a large group of researchers to improve the hydrodynamic and thermal behavior for buoyancy-driven flows within an enclosure.
Pairs of circular cylinders immersed in a steady cross-flow are encountered in many engineering applications. The cylinders may be arranged in tandem, side-by-side, or staggered configurations. Wake ...and proximity interference effects, which are determined primarily by the longitudinal and transverse spacing between the cylinders, and also by the Reynolds number, have a strong influence on the flow patterns, aerodynamic forces, vortex shedding, and other parameters. This paper reviews the current understanding of the flow around two “infinite” circular cylinders of equal diameter immersed in a steady cross-flow, with a focus on the near-wake flow patterns, Reynolds number effects, intermediate wake structure and behaviour, and the general trends in the measurements of the aerodynamic force coefficients and Strouhal numbers. A primary focus is on the key experimental and numerical studies that have appeared since the last major review of this subject more than 20 years ago.
New data and review of the spanwise coherence length is provided for flows over cylinders of different cross-sections: circular of diameter
d
, and rectangular of sectional aspect ratios (breadth (
b
...) to height (
d
) ratio AR =
b
/
d
) of 1, 2 and 3. In the present measurements, the body has both
d
and spanwise length of 70
d
fixed, and the Reynolds number (based on
d
) range 6000–27,000 is covered. Two-point data are obtained from two hot-wire probes, one fixed in the symmetry plane and the other moving on the corresponding spanwise axis. Their position in a cross plane are deduced from preliminary measurement of the mean flow with a single probe, allowing fair comparisons between the different geometries and the introduction of uncertainty bars on coherence length values. At all tested regimes, a very good agreement is noticed between velocity-based and pressure-based coherence experimental data. Coherence length definitions are revisited, and the aeroacoustically consistent, integral length definition is selected, allowing fair synthesis of literature data into a single chart and empirical functions. Definitions for coherence decay models (e.g. Gaussian or Laplacian) are also adapted so that coherence length and coherence integral shall be equivalent. This preliminary work on coherence data and its spanwise integration enables transparent regressions and model selection. Generally, the Gaussian model is relevant for the lift peak, while the coherence exhibits a Laplacian decay at harmonics. On average, at peak Strouhal number, the coherence length for the circular and square cylinders is of 5
d
while it is of the order of 15
d
for the rectangular sections. It is concluded that the flow over those latter geometries is still a two-dimensional dynamics at the tone frequency. These values are almost preserved over the tested Reynolds number range. Coherence length value at harmonics is extensively documented. Spanwise coherence length is also discussed as an ingredient of acoustic efficiency.
In the paper of Manuel et al. 10 the minimum wirelength of embedding hypercube into cylinder was given as a conjecture. We show that Gray code embedding is an optimal strategy for the conjecture. In ...the paper, we prove the lower bound of the wirelength as two parts respectively, one of which is studied by the edge isoperimetric problem (EIP) related to the type sequence. The technique is totally different from the previous work in Refs. 10,11,1,6.
•PCM melting and solidifying in concentric annulus with inner elliptic tube simulated.•Use of elliptical tube instead of circular one decreased only full melting time.•Phase change processes are ...expedited by increasing nanoparticle concentration.•Increasing fin number in melting is less efficient due to suppression of convection.
The main disadvantage of phase change materials (PCM) is related to their low thermal conductivities. In this study, the melting and solidification of a PCM within three various horizontal annulus configurations including two circular cylinders, one elliptical cylinder in a circular cylinder and one finned cylinder in a circular cylinder are investigated numerically in terms of the aspect ratio and the orientation of the ellipse and the number of fins. Different volume fractions of the copper nanoparticles are added to the base PCM to examine the effect of nano-particles on the heat transfer rate. Results indicate natural convection plays important roles in the melting process where the melting rate at the bottom section of the annulus is lower than that at the top section. By using the vertical-oriented tube instead of the circular one the melting rate increases. Adding nanoparticles to the base PCM enhances the melting and solidification rate as well. However, it does not eliminate the stable heat transfer at the bottom section of the annulus. Inserting fins leads to the significant enhancement of the melting and solidification rate. It is more efficient during the solidification process due to the suppression of the natural convection effect during the melting process.
The current work concentrates on the transient entropy generation and mixed convection due to a rotating hot inner cylinder within a square cavity having a flexible side wall by using the finite ...element method and arbitrary Lagrangian-Eulerian formulation. Effects of various relevant parameters like Rayleigh number (104 ≤ Ra ≤ 107), angular rotational velocity (-1 ≤ Ω ≤ 1), dimensionless elasticity modulus (1012 ≤ E ≤ 1015) on the convective heat transfer characteristics and entropy generation rates are analyzed for dimensionless time 10-8 ≤ τ ≤ 3.5. It is observed that various complex shaped wall deformations are established depending on the non-dimensional elastic modulus of the flexible right wall and cylinder rotation direction. The local and average Nusselt numbers rise with Ra and secondary peaks in the local Nusselt number are established for lower values of Ra. The local heat transfer along the hot cylinder does not change for the case of clockwise rotation of the heated cylinder even if there is a wall deformation in the positive x-direction. The highest average heat transfer and global entropy generation rates are achieved for the case of counter-clockwise rotation of the circular cylinder and for lower values of the flexible wall deformation.
This paper presents an experimental study on the added masses associated with the cylinders of different cross-sectional geometries (circular, square and rectangular of side ratio of 4) and angles of ...attack (θ = 0°- 90°) with respect to incident flow. Two fluid media are considered, i.e. water and paraffin oil. The added mass is investigated from three different perspectives. Firstly, the added mass is estimated from a shift in the oscillation frequency of the cylinder in water or paraffin oil from that in still air, referred to as the average added mass. Thus defined added mass is dependent on both cylinder cross-sectional geometry and orientation but is independent of the fluid medium. The average added mass decreases from 1.52 at θ = 0°to a minimum of 1.20 at θ = 45°for the square cylinder but grows monotonically from 0.55 at θ = 0°to 4.90 at θ = 90°for the rectangular cylinder. Secondly, the added mass is calculated from the equation of structural dynamics. This added mass decreases linearly with the decreasing oscillation amplitude, thus called the amplitude-dependent added mass. Thirdly, the amplitude-dependent added mass is reduced to the unique added mass in the absence of vibration. The unique added mass is in general smaller (< 11.3% depending on geometry and θ) than the average added mass but displays a similar dependence on the cylinder cross-sectional geometry and θ.
In order to reduce the climate impacts, methanol produced from carbon-neutral methods plays an important role. Due to its oxygen content and high latent heat, methanol combustion can achieve low soot ...and NOx emissions. In the present study, direct injection (DI) of methanol is investigated in a non-premixed dual-fuel (DF) setup with diesel pilot. The present DF engine study is carried out via a specially-designed new cylinder head operating with a centrally located methanol injector and with an off-centered diesel pilot injector. The target is to inject methanol close to top dead center (TDC) in a similar fashion as in standard diesel combustion enabling robust operation with high efficiency. The ignition of the DI methanol is achieved with an almost simultaneously injected diesel pilot. The experiments were conducted in a single-cylinder heavy-duty research engine at a constant engine speed of 1500 rpm with a compression ratio of 16.5. The indicated mean effective pressure (IMEP) varied between 4.2 and 13.8 bar while the methanol substitution ratio was swept between 45 and 95%. In addition, the diesel pilot and methanol injection timings were varied for optimum efficiency and emissions. The introduced non-premixed DF concept using methanol as the main fuel showed robust ignition characteristics, stable combustion, and low CO and HC emissions. The results indicate that increasing both the load and the methanol substitution ratio can increase the thermal efficiency and the stability of combustion (lower COV) together with decreased CO and HC emissions.
Experiments on the flow around stationary circular cylinders with very low aspect ratio piercing the water free surface were carried out in a recirculating water channel. Eight different aspect ...ratios were tested, namely L/D=0.1, 0.2, 0.3, 0.5, 0.75, 1.0, 1.5 and 2.0; no end-plates were employed. Forces were measured using a six degree-of-freedom load cell and the Strouhal number was inferred through the transverse force fluctuation frequency. The range of Reynolds number covered 10000<Re<50000. PIV measurements were performed in some aspect ratio cases, namely L/D=0.3, 0.5, 1.0 and 2.0 for Reynolds number equal to 43000. The results showed a decrease in drag force coefficients with decreasing aspect ratio, as well as a decrease in Strouhal number with decreasing aspect ratio. The PIV measurements and the PSD of forces showed different behavior for cylinders with L/D≤0.5, in which cases the free-end effects were predominant. Even without von Kármán street main characteristics around the majority length of the cylinder, in the range of 0.2<L/D≤0.5, the vortex shedding around it is capable of producing alternating forces in the transverse direction. Therefore, alternating forces were not observed in the transverse direction for cylinders with L/D≤0.2.
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