Effects Of Horizontal Spacing Research Articles

Bounce behaviors of double droplets simultaneously impact cold superhydrophobic surface

The real physical process of ice formation involves multiple droplets rather than a single isolated one. Clarifying the mechanism of multi-droplet impact-freezing is important for designing functional surfaces for anti-icing. The rebound behavior of double droplets simultaneously impinging on a cold superhydrophobic surface (SHS) was investigated experimentally and numerically, which is a classical simplified case in multi-droplet impingement. We found five impacting-freezing modes, including no-coalescence rebound (NCR), partial-coalescence rebound (PCR), complete-coalescence rebound (CCR), no-coalescence adhesion (NCA) and coalescence adhesion (CA). Moreover, the effects of horizontal spacing, impact velocity and surface temperature on the spreading factor and uprising sheet height during the impacting-freezing process were also analyzed. The contact time of PCR mode is even shorter than that of a single droplet impact at room temperature, which is verified and explained in our results. However, as the surface temperature decrease, the behavior of the coalescing droplet transitions from PCR to CCR and CA mode. The increase in Weber number could cause the adhesion of double droplets. Moreover, the horizontal spacing strongly affects the coalescing process. Multiple droplet impact-freezing will lead to severe icing on the substrate due to multiple droplets interaction involved. This study is beneficial for anti-icing and de-icing technologies.

Effect of Horizontal Spacing on Natural Convection Heat Transfer from Two Aligned Horizontal Cylinders in a Vented Enclosure

Effect of Horizontal Spacing on Natural Convection Heat Transfer from Two Aligned Horizontal Cylinders in a Vented Enclosure

Ground movements induced by installation of twin large diameter deeply-buried caissons: 3D numerical modeling

The assessment and control of ground movements during the installation of large diameter deeply-buried (LDDB) caissons are critically important to maintain the stability of surrounding infrastructures. However, for twin LDDB caissons which have been installed worldwide, no well-documented guidelines for assessing the induced ground movements are available due to the complexities of caisson–soil interaction. To this end, considering the mechanical boundaries of caissons and mechanized installation process, this paper presents a simple kinematic mechanical model balancing both computational cost and accuracy, which can be easily incorporated in commercial finite-element (FE) programs. Based on a project of twin LDDB caissons alternately installed employing a newly developed installation technology in wet ground with stiff clays in Zhenjiang, China, a three-dimensional (3D) numerical model is developed to capture the ground movements in terms of surface settlements and radial displacements induced by the installation of twin LDDB caissons. Moreover, hardening soil model with small-strain stiffness (HSSmall model) conceptually capable of capturing the nonlinear soil stiffness from very small to large strain levels is used to simulate undrained ground. The validations against field observations, empirical predictions and centrifuge test data are carried out to demonstrate the accuracy and validity of the developed FE model. Subsequently, the comparisons of ground movements numerically obtained in three frequently used installation schemes (i.e., synchronous, asynchronous and alternating installation) are conducted for installation sequence optimization of twin caissons. It is found that synchronous installation is the optimal scheme for limiting ground movements. Parametric studies considering the effects of horizontal spacing between twin caissons, staged penetration depth, inner diameter, controllable soil-plugging height, frictional coefficient between caisson–soil interface, as well as cutting edge gradient are thus performed in synchronous installation scheme. Based on an artificial data set generated through FE calculation, the multivariate adaptive regression splines (MARS) model capable of accurately capturing the nonlinear relationships between a set of input variables and output variables in multi-dimensions is used to analyze the sensitivity of caisson design parameters. Finally, the MARS mathematical equations for predicting the maximum surface settlement and radial displacement used in preliminary caisson design are proposed.

Effect of horizontal spacing and tilt angle on thermo-buoyant natural convection from two horizontally aligned square cylinders

Laminar natural convection heat transfer from two horizontally aligned square cylinders has been investigated numerically using a finite-volume method (FVM). Computations were performed to delineate the momentum and heat transfer characteristics under the following ranges of parameters: horizontal spacing between the cylinders (0 ≤ S/W ≤ 10), tilt angle of the square cylinder (00≤δ ≤ 600), and Grashof number (10 ≤ Gr ≤ 105) for some specific Newtonian fluids having Prandtl number (0.71 ≤ Pr ≤ 7). Computed results are presented in terms of temperature contours and streamlines, velocity and temperature profiles, the mass flow rate in the passage between the cylinders, local and average Nu, and the drag coefficient. The average Nu increases with decrease in the horizontal spacing up to a certain limit, whereas it significantly degrades with a further decrease in the spacing. The square cylinder having δ = 450 shows a higher heat transfer, whereas it is least for δ = 00. At higher Gr and Pr, the average Nu is found to be in excess of 22% at δ = 450 compared to at δ = 00. Overall, the average Nu has a strong dependence on both Gr and Pr, whereas it is a weak function of S/W and δ. Furthermore, the total drag coefficient (Cd) shows an adverse dependence on both Gr and Pr. The flow resistance is higher at the optimum horizontal spacing and decreases significantly with decrease in the spacing. The Cd is found to be lower for δ = 450 and in excess of 30% at δ = 00. Finally, a correlation for the average Nu has been developed, which can be useful for some engineering calculations.

Effect of horizontal spacing between inner circular cylinders on three-dimensional natural convection in rectangular channel

Three-dimensional numerical simulations were conducted for natural convection phenomena around a horizontal array of hot inner circular cylinders positioned in a cold rectangular channel in the range of 104 ≤ Ra ≤ 106 at the Prandtl number of Pr = 0.7. The immersed boundary method (IBM) was used to capture the virtual wall boundary of the inner cylinders based on the finite volume method (FVM). This study investigated the thermal and flow regimes with various patterns at different Rayleigh numbers and horizontal spacing between the inner cylinders. Detailed effects of the spacing (1 L ≤ S ≤ 4 L) were analyzed by visualization of three-dimensional isothermals and vortical structures. The three-dimensionality and heat transfer characteristics resulting from flow and thermal structure changes were also investigated.

Force and Stability Measurements on Models of Submerged Pipelines

The effect of currents on pipes anchored just above the ocean floor is the subject of this study. Lift, drag, and stability of two parallel pipes, parallel to a flat plane (the sea floor) were measured for simulated ocean currents up to two knots at several subcritical, free stream Reynolds numbers. First, a wind tunnel was utilized to find the lift and drag coefficients on two parallel, rigid, cylindrical models. The effects of horizontal spacing, vertical spacing from the ground plane, and orientation angle of the horizontal free stream velocity were observed. These results were compared to date available for the single and double cylinder cases where the ground plane was absent. Second, a water tow tank was utilized to observe conditions for vortex-shedding induced vibrations for fixed end, flexible, parallel cylinders. The natural frequencies and buoyancies of these models simulated pipelines of reasonable span clamped to evenly spaced anchor blocks. A numerical example illustrates the use of these data in the design of a dynamically stable piping system close to the ocean floor.