Abstract

Several residential, commercial and industrial applications have their efficiency increased when a thermal energy storage system is incorporated. The PCMs (Phase Change Materials), due to their high latent heat of fusion, are materials that represent a viable alternative to the implementation of thermal energy storage systems. This paper presents a numerical study of RT (Rubitherm Technologies GmbH) PCMs family fusion process in cylindrical cavities. The study was conducted through a CFD ''(''Computational Fluid Dynamics) numerical simulation, with ANSYS Fluent software. The numeric model adopted is two-dimensional and has been validated with numerical and experimental results of literature, achieving a good approximation. For PCMs here studied, increasing the temperature from 10 ''^oC'' to 20 ''^oC'' and 10 ''^oC'' to 30 ''^oC'', above the phase change temperature, for liquid fractions between 0.4 and 0.8, the average reduction of fusion time is approximately 55.8% and 71.8 %, respectively.

Abstract

We present recent developments in the coupling of the finite element method (FEM) and the discrete element method (DEM) for analysis of rock blasting operations in tunnels. The coupled FEM-DEM technique has proven to be an efficient technique for predicting the multi-fracture of rock induced by the loads generated in blasting situations. The coupled FEM-DEM procedure is applied in the tunnel construction, as well as to gas pressure blasting pyrotechnics situations to break rock for excavation of the tunnel front. In the latter case the effect of gas explosion is modelled by solving with the FEM the equations of gas dynamics in the analysis domain. The effect of the gas forces in the underlying rock mass is modelled with an embedded fluid-structure interaction method. This allows us to accurately predicting the progressive multi-fracture of the rock accounting for the penetration of the gas in the fractured domain modelled with the FEM-DEM procedure. The efficiency of the coupled FEM-DEM technique is demonstrated in several examples of fracture tests and rock blasting problems related to tunnel engineering'''.''' The examples presented show that the combination of the DEM with simple 3-noded linear triangular elements correctly captures the onset of fractures and their evolution [1].

Abstract

Abstract

The last decades there is a strong interest in predicting cavitation dynamics as it is a prerequisite in order to predict cavitation erosion. Industrial applications require accurate results in an acceptable time span and as a result there is a focus on large scale dynamics. In this paper the RANS equations are used to investigate the shedding frequency of sheet cavities in two-dimensional simulations. First a verification study is made for the NACA 0015 in 6 degrees angle of incidence. A grid sensitivity study is conducted in wetted flow and in steady (non-shedding) cavitating condition (σ=1.6). Then an investigation is conducted in order to capture the shedding frequency. The results show that only when a correction for turbulent viscosity at the cavity-water interface is used it was possible to capture the shedding frequency as found in other numerical studies. Furthermore, a validation study is conducted on a NACA66-312 α=0.8 for two different angles of attack. The obtained results are compared and validated with the experimental data from Leroux ''et al''. They indicate that the 2D shedding frequency predicted by the numerical simulations is in good agreement with the frequency obtained in the experiment.

Abstract

In this work, the study of smoke fire transportation inside of a subway passenger platform is presented. The study includes a set of numerical simulations to observe the behavior of the air inside the platform. Two smoke transport simulations using the FDS program are also included. Subsequently, the development of a 3D - 1:100 scale model is described and it was used to perform an experimental observation of the phenomenon. The model was built by using a 3D printer which allowed to include more architectural details of the real scenario. The inclusion of these details allowed to observe qualitative similarity between the results of the simulation and the experimental work. Although there are clear differences between what could happen in a real scenario and what was observed in the scale model, it was identified that the model is an important complement to the simulations. In addition to the simulations, the use of this type of 3D models allows the observation of the phenomenon by different specialists such as firefighters, policeman, medical personnel, etc., in the same place and its intention is to provide a more interactive tool to the observation group, increasing the time devoted to the development of contingency actions and reducing the costs associated with the logistics of a real simulacrum. The model allows to better identify the strengths, opportunities, weaknesses and threats of the contingency procedures developed by the safety and hygiene groups and to make their corresponding adjustments if necessary.

Abstract

This paper has the objective to analyze passive flow control technologies that can reduce the shock wave intensity and thus the interference drag in the strut-wing junction, in transonic flight. Two possible flow control devices were investigated by means of CFD, Kuchemann Carrot (KC) and shock control bumps (SCB). Also a combination of these two configurations was studied. Drag and lift coefficients were monitored for each component and the angle of attack was modified to match the lift of the baseline configuration while comparing the drag. The mesh is based on hexahedral cells using a cut-cell approach and y+ approx. 1 near the walls. This mesh strategy was adopted to ensure constant mesh distribution from one configuration to the other. All the simulations were performed using the k-ω SST with Intermittency Transition model.
Anti-shock bodies have been used for civil and military aircrafts in order to improve drag performance in transonic conditions. A particular case of anti-shock bodies used at the junction of the vertical and horizontal tail to improve cross section area variation is the KC. The KC shape used in this study was limited to the pressure side of the wing and extended only beyond the leading edge. It contained a “fuselage waisting” at the location of the maximum thickness of the airfoil in the vertical strut. The KC showed a decrease of the angle of attack to match the baseline lift and reduced total drag. The drag reduction compared to baseline although less than 1% was due to the pressure drag mitigation and displayed an adverse effect for the
viscous drag; justified by the increase in wetted area. The pressure drag effect is
explained through the reduction of the shockwave in the vicinity of the wing-strut
junction.
The second option for passive flow control devices used in transonic flows is the
SCB. Classically they are presented in the literature for controlling flow on the
suction side of a wing at transonic Mach numbers that generate an acceleration
above Mach number 1.3. In the case of the wing-strut junction, the flow is
accelerated on the pressure side of the wing to Mach numbers of that magnitude;
this fact alone suggest the possibility to use SCB as drag reduction devices. The SCB
has a 3D wedge type geometry with rounded sides. The bumps are aligned with the
flow and placed at 0.25 m distance from each other on both the suction side of the
strut and the pressure side of the wing. The SCB have an extended tail, flat top, a
width to height ratio of approx. 9 and a length to width ratio of 4. The height of the
bump differs from wing to strut, and are determined from 2D analysis at three span
wise locations of 15, 15.5 and 16m. The height of the bump on the wing is roughly
70% of the boundary layer thickness while on the strut is around 95%. The height is
kept almost constant in the span wise direction on the strut and also on the wing.
The SCB showed an increase of the angle of attack to match the baseline lift and
reduced total drag. The drag reduction compared to baseline, although almost
identical to the KC, was due to the pressure drag mitigation and displayed a positive
effect for the viscous drag also.
When compared to the baseline, both KC and SCB were able to reduce the total
drag but with complementary effects. Firstly, in order to match the lift, the KC
generates a decrease in incidence that is roughly half of the increase in incidence
needed for the SCB to match the lift. Secondly, the KC affects the reduction of
maximum Mach number at the junction stronger, while the SCB has a more span
wise distributed effect. The pressure drag reduction for the KC is almost double, for
lift matching; while at the same angle of attack, 1 deg., the opposite is observed. In
order to investigate further the benefits of both passive flow control devices by
combining them, several configurations have been analyzed, and abbreviated by
KC_SCB.
The first configuration of the KC_SCB was the combination of the separate versions
of them. This version showed the worst performance in terms of drag reduction
due to large flow separation at the junction. By removing the first three SCB, located
near the junction, the performance improved from the previous version, but remained worst that the baseline, again due to separated flow induced by the SCB. The third version kept the number of SCB and their span wise locations, but moved them in the stream wise direction with respect to the new shock position. The drag performance improved again, but the separated flow region persisted and induced a drag higher than the baseline. Although this mix of KC and SCB didn’t produce an improvement, the drag reduction trend was positive and it is expected that when using an optimization process will generate a superior solution. Considering that for both KC and SCB no 3D optimization, only design based on literature review was used, can be argued that the performance can be further improved.

Abstract

Wedge shaped blocks spillways are an innovative solution that allows spilling over the downstream shoulder of earth and rock-fill dams in a safe way. However, they have been barely used as main spillway due to the lack of practical design criteria. An innovative procedure for computer-aided design of wedge shaped blocks spillways is presented in this paper. It includes the design of the drainage and supporting layer considering its seepage capacity and stability. The leakage flow through the joints between blocks is estimated by means of a numerical model calibrated and validated from experimental results. Stability against sliding of the downstream shoulder or the drainage layer is ensured, considering the properties of the granular material selected by the designer and non-linear resistance laws. The procedure will also suggest the shape of a toe protection.

Abstract

An unstructured finite element solver to evaluate the ship‐wave problem is presented. The scheme uses a non‐structured finite element algorithm for the Euler or Navier–Stokes flow as for the free‐surface boundary problem. The incompressible flow equations are solved via a fractional step method whereas the non‐linear free‐surface equation is solved via a reference surface which allows fixed and moving meshes. A new non‐structured stabilized approximation is used to eliminate spurious numerical oscillations of the free surface.

Abstract

A weighted least squares finite point method for compressible flow is formulated. Starting from a global cloud of points, local clouds are constructed using a Delaunay technique with a series of tests for the quality of the resulting approximations. The approximation factors for the gradient and the Laplacian of the resulting local clouds are used to derive an edge‐based solver that works with approximate Riemann solvers. The results obtained show accuracy comparable to equivalent mesh‐based finite volume or finite element techniques, making the present finite point method competitive.

Abstract

Current work presents a monolithic method for the solution of fluid–structure interaction problems involving flexible structures and free-surface flows. The technique presented is based upon the utilization of a Lagrangian description for both the fluid and the structure. A linear displacement–pressure interpolation pair is used for the fluid whereas the structure utilizes a standard displacement-based formulation. A slight fluid compressibility is assumed that allows to relate the mechanical pressure to the local volume variation. The method described features a global pressure condensation which in turn enables the definition of a purely displacement-based linear system of equations. A matrix-free technique is used for the solution of such linear system, leading to an efficient implementation. The result is a robust method which allows dealing with FSI problems involving arbitrary variations in the shape of the fluid domain. The method is completely free of spurious added-mass effects.