mesh independence
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Abstract Optimal selection of domain discretization for numerical Phase Change Material (PCM) models is useful to establish confidence in model predictions and minimize the time consumption for conducting design analysis. Very detailed and geometrically complex models are usually applied utilizing several million cells. A 2D numerical PCM model of a climate module for thermal comfort ventilation is investigated. The mesh independence was conducted on 22 different mesh sizes ranging from 70 to 10.870 nodes. Convergence criteria was evaluated based on average air supply temperature and total heat transfer between the PCM and the air within the simulation time interval. Less than 0.1 % change in the air supply temperature and the heat transfer between the PCM and the air was achieved with 5250 and 9870 nodes, respectively. Thereby highlighting that a relatively small amount of nodes can be considered to achieve sufficient accuracy to conduct analysis of PCM applications.

Purpose Endwall film cooling protects vane endwall by coolant coverage, especially at the leading edge (LE) region and vane-pressure side (PS) junction region. Strong flow impingement and complex vortexaa structures on the vane endwall cause difficulties for coolant flows to cover properly. This work aims at a full-scale arrangement of film cooling holes on the endwall which improves coolant efficiency in the LE region and vane-PS junction region. Design/methodology/approach The endwall film holes are grouped in four-holes constructal patterns. Three ways of arranging the groups are studied: based on the pressure field, the streamlines or the heat transfer field. The computational analysis is done with the k-ω SST model after validating the turbulence model properly. Findings By clustering the film cooling holes in four-holes patterns, the ejection of the coolant flow is stronger. The four-holes constructal patterns also improve the local coolant coverage in the “tough” regions, such as the junction region of the PS and the endwall. The arrangement based on streamlines distribution can effectively improve the coolant coverage and the arrangement based on the heat transfer distribution (HTD) has benefits by reducing high-temperature regions on the endwall. Originality/value A full-scale endwall film cooling design is presented considering interactions of different film cooling holes. A comprehensive model validation and mesh independence study are provided. The cooling holes pattern on the endwall is designed as four-holes constructal patterns combined with several arrangement choices, i.e. by pressure, by heat transfer and by streamline distributions.

In this work, a 76 mm diameter propeller-type turbine is numerically investigated using a parametric study and computational fluid dynamics. The three-dimensional model of the turbine is modeled using data available in the bibliography. A mesh independence study is carried out utilizing a tetrahedron-based mesh with inflation layers around the turbine blade and the pipe wall. The best efficiency point is determined by the maximum hydraulic efficiency of 64.46 %, at a flow rate of 9.72x10-3 m3/s , a head drop of 1.76 m, and a mechanical power of 107.83 W. Additionally, the dimensionless distance y+, pressure, and velocity contours are shown.

Cardiovascular diseases are the world’s leading cause of death with significant death rates caused by abnormalities in vessels such as aneurysms and stenosis. These conditions can potentially cause blockage and thinning of vessels which may lead to heart attack, stroke, and bleedings. Recently, computational simulation methods are frequently used in blood flow analysis. These methods are frequently used in vascular fluid dynamics analysis which relate to the origin of a disease, efficacy prediction in installation of therapeutic instruments and complements the in vitro studies. This article presents an example of a simple vascular simulation to study the effect of blood flow with respect to vascular wall displacement. Furthermore, this research shows the importance of formal CFD pre-processing such as mesh independence testing which influences the simlation accuracy as well as vascular flow prediction and its effects on vascular wall displacement. In this research, it is concluded that the number of mesh elements affects the accuracy of vascular wall shear stress (WSS) calculations with average WSS difference of 0.8 Pa with no significant difference in wall displacement values. An average WSS of 1.95 Pa and a wall displacement of 5.7 µm are obtained from the blood flow simulation in this study.

The paper presents the results of numerically investigating viscous gas flow in a simulated low-discharge stage of a super high-pressure type compressor, using the ANSYS CFX software package. We studied the low-discharge centrifugal compressor stage prototype designed and tested at the Compressor, Vacuum and Refrigerating Technology Department of Peter the Great St. Petersburg Polytechnic University. In order to conduct the numerical experiment, we performed a mesh independence study. We compared the properties obtained in the numerical investigation to the experimental data. In our mathematical simulation the magnitude of the axial clearance between the covering disc of the runner and the compressor body varies in the range of 1--5.5 mm; we estimate the effect that varying this number has on the loss complex characteristic 1 + βfriction + βleakage

In the present work, a university-industry linkage project was carried out in which the hydrodynamic performance of three existing impellers in agitated tanks in a Paint manufacturing plant of the company Axalta Coating Systems is compared. These are 45 ° inclined four vane impeller (PBT4), 35 ° inclined six vane impeller (PBT6), and Chemineer type curved tip three inclined vane high efficient impeller (HE3). For this, Computational Fluid Dynamics and experimental measurements of power consumption were used. The study was carried out in a 4-liter cylindrical tank operating in a turbulent regime (Reynolds numbers greater than 14,000) using two types of fluids; water and white coating like Newtonian fluid and slimming fluid. In all the simulations and experimental validations, geometric similarity was maintained with the existing conditions in the plant. An analysis of mesh independence was carried out, comparing meshes with an increase of twice the number of elements, in which the one with the least variability of the hydrodynamic properties with respect to the previous one was chosen. Once the independent mesh was obtained, the speed fields, the dependence of the power numbers (NP) and pumping numbers (NQ) of each of the impellers under study were obtained at different operating conditions similar to those existing in the plant. It was found that in turbulent regime for both Newtonian and non-Newtonian fluid, the power number is higher for the PBT4 impeller and the lower for the PBT6. For both fluids, the pumping number was higher for the PBT4 impeller and the lowest was obtained for the PBT6. The mixing effectiveness ratio (NQ/NP) that was found is that Chemineer's HE3 impeller has the highest value for Newtonian fluid, while for non-Newtonian fluid, the values are very similar for PBT4 and HE3 impellers. For the specific case study of this work, it was concluded that for the homogenization of a white coating manufactured in the company Axalta Coating Systems using the PBT4 and HE3 impellers they would have a very similar performance, while the PBT6 impeller would have the worst performance. Considering that the PBT4 impeller is a general purpose agitator and can be used in a large number of applications, and furthermore, it is easier to manufacture and its cost is lower, the PBT4 agitator would have a better performance than the HE3 impeller.

Abstract The development of an accurate digital performance twin of a tug requires a complete understanding of its propulsive capacity and hull-thruster interactions. In this study, the propulsion characteristics of an Azimuth Stern Drive (ASD) tug is investigated using model-scale Reynolds-averaged Navier-Stokes (RANS) simulations. The propulsion plant consists of two counter-rotating thruster units, with each having a Ka4-70 series propeller and 19A duct profile. Comparisons in propulsive performances using the steady-state moving reference frame (MRF) approach and the transient rigid body motion (RBM) models are shown, and validated against data from openwater experiments. The MRF method gives sufficiently accurate predictions of thrust and torque in forward flow and moderate angles-of-attack, while the RBM method performs better at larger inflow angles. The effects of thruster-hull and thruster-thruster interactions on wake characteristics and propulsion performance are also investigated over a range of advance and inflow/azimuth angles. Convergence and mesh independence studies are conducted to determine the optimal spatial and temporal simulation parameters. Results from this study identify flow regimes where hull and thruster interactions are significant.

Introduction: Conventional topology optimization approaches are implemented in an implicit manner with a very large number of design variables, requiring large storage and computation costs. In this study, an explicit topology optimization approach is proposed by movonal morphable voids whose geometry parameters are considered as design variables. Methods: Each polygonal void plays as an empty-material zone that can move, change its shapes, and overlap with its neighbors in a design space. The geometry eters of MPMVs consisting of the coordinates of polygonal vertices are utilized to render the structure in the design domain in an element density field. The density function of the elements located inside polygonal voids is described by a smooth exponential function that allows utilizing gradient-based optimization solvers. Results & Conclusion: Compared with conventional topology optimization approaches, the MPMV approach uses fewer design variables, ensure mesh-independence solution without filtering techniques or perimeter constraints. Several numerical examples are solved to validate the efficiency of the MPMV approach.