Unstructured Mesh Approach Research Articles

Experimental and CFD modeling of a progressive cavity pump (PCP) using overset unstructured mesh part 1: Single-phase flow

Progressive Cavity Pumps (PCP) are integral in industries for transporting high-viscosity fluids due to their efficacy. Nevertheless, their computational modeling via Computational Fluid Dynamics (CFD) poses challenges, primarily attributed to meshing algorithms and computational demands. This research underscores that structured meshes are not imperative for assessing PCP efficiency, given that operational parameters reflect a 10% accuracy when juxtaposed with experimental data. An overset mass conservation model was harnessed to rectify mass conservation errors and the computational burden from interpolation. The overset grid methodology emerged as a favorable technique for PCP modeling, with its applicability critically analyzed. Experimental data comparison revealed that variables like volumetric flow rate, power consumption, and efficiency were accurately depicted with a marginal error of less than 10%. Interestingly, while high-viscosity oils resonated with the Hagen-Poiseuille flow equation in clearance zones, water showcased elevated velocities, inducing a non-linear pressure profile. Analysis of slip components indicated that high-viscosity oils offered superior efficiencies due to augmented slip resistance. Thus, CFD modeling of PCPs across different viscosity spectrums is feasible without mandating operations to enhance mesh quality. This study pioneers in offering insights into PCP dynamics, emphasizing the accuracy and optimization potential of the overset unstructured mesh approach.

An Unstructured Mesh Approach to Nonlinear Noise Reduction for Coupled Systems

An Unstructured Mesh Approach to Nonlinear Noise Reduction for Coupled Systems

Scalable self attraction and loading calculations for unstructured ocean tide models

Self attraction and earth-loading effects are important for accurately modeling global tides. A common approach of handling this forcing is to expand mass anomalies into spherical harmonics, which are scaled by load Love numbers to account for elastic earth deformation. We investigate two different approaches to perform these calculations for ocean models that employ unstructured meshes and distributed memory parallelization. The first approach leverages a highly efficient spherical harmonics library, but requires all-to-one and one-to-all communications and interpolation operations between the unstructured and a structured mesh. This approach is compared to a parallel algorithm that computes the spherical harmonic transformations directly on the unstructured mesh with an all-reduce communication. Our results show that although the unstructured mesh calculations are more expensive, the scalability of the unstructured mesh approach allows for more efficient spherical harmonics transforms for high-resolution meshes and large processor counts. This methodology enables the efficient inclusion of tidal dynamics large-scale Earth system model simulations.

On the design of potential turbine positions for physics-informed optimization of wind farm layout

Wind farm layout optimization is a critical step in the design of a wind energy project. In the literature, the potential turbine positions employed in the layout optimization are often obtained by discretizing the field using a Cartesian mesh. In this work, physical understanding is proposed to incorporate in the design of potential turbine positions. Specifically, the known knowledge, that a staggered arrangement is more efficient for extracting energy from wind than an aligned arrangement, is employed and implemented using the staggered mesh approach, the unstructured mesh approach and the sunflower mesh approach. Different mesh approaches are tested using two cases, i.e. case I, unidirectional uniform wind, and case II, uniform wind with variable wind direction. The optimal layout obtained from the staggered mesh approach performs the best for case I. For case II, the farm performance from different layouts is similar. The performance of the layouts under off-design conditions is also tested for case I. For all considered cases, the optimal layout obtained from the sunflower approach shows an overall good performance.

Comparative Study of Neutronics Analysis Techniques for Radioactive Waste Assessment

Computational models created for neutronics assessment through solid geometry conversion are often specific to the analysis being performed. The use of unstructured mesh geometry has the potential to reduce the build time of MCNP models, reduce inaccuracies introduced through flux averaging over different components and material mixing, and make use of computer-aided design models that can also be suitable for other types of analysis. In this paper three neutronics methods were investigated for suitability in performing a radioactive waste assessment of a fusion demonstration reactor. The methods included the conventional cell-based approach, a superimposed structured mesh, and the use of a recently developed capability with unstructured mesh geometry. It was concluded that an unstructured mesh approach has the potential to be an important tool for assessing radioactive waste to inform reactor and component design.

Arctic Ocean biogeochemistry in the high resolution FESOM 1.4-REcoM2 model

In the rapidly changing Arctic Ocean, marine primary productivity is tightly linked to the balance between light and nutrient limitation. To capture this balance in ocean general circulation biogeochemical models (OGCBMs), a good representation of the physics is important due to the tight bio-physical coupling in the Arctic. Using a horizontal model resolution of a few kilometers makes it possible to resolve an increasing number of small scale processes, that otherwise need to be parameterized in OGCBMs. Such high resolution is, however, commonly not possible due to computational constrains. Utilizing an unstructured mesh approach, we have run the finite element sea-ice ocean model (FESOM 1.4) coupled to the biogeochemical model REcoM2 in a global configuration with an Arctic-wide resolution of 4.5 km. This resolution is so far unprecedented for a global biogeochemical setup, and here we present an analysis of the mean state of the model. FESOM-REcoM2’s integrated Arctic net primary production (NPP) averages 445 Tg C yr−1 for the years 2011 to 2015, a value that is in the middle of the range compared to estimates from the literature. Most production takes place in the inflow regions of the Nordic and Chukchi Seas, and 32% is associated with the sea ice zone, the latter including the marginal ice zone and below-ice productivity. Light limits production to some degree at all latitudes north of 60°N, with growth becoming nutrient limited following the initial spring bloom in most places. The model reproduces the relatively low surface concentration of dissolved inorganic nitrogen (DIN) that has been observed in the central Arctic Ocean, as well as the low surface DIN concentration towards the end of the growth season further to the south, thereby also capturing widespread subsurface chlorophyll maxima (SCM). The SCMs are found in the whole Arctic except for the areas where sea ice concentration is high the whole year. They have a duration of two weeks to five months. The balance between nutrient and light limitations, both in the vertical and horizontal direction, highlights that decreased light limitation in a future ice free Arctic Ocean will not necessarily induce an increase in NPP due to increasing nutrient limitation, and that further studies of the role of the SCMs are required.

Multiphase flow modelling of volcanic ash particle settling in water using adaptive unstructured meshes

Small-scale experiments of volcanic ash particle settling in water have demonstrated that ash particles can either settle slowly and individually, or rapidly and collectively as a gravitationally unstable ash-laden plume. This has important implications for the emplacement of tephra deposits on the seabed. Numerical modelling has the potential to extend the results of laboratory experiments to larger scales and explore the conditions under which plumes may form and persist, but many existing models are computationally restricted by the fixed mesh approaches that they employ. In contrast, this paper presents a new multiphase flow model that uses an adaptive unstructured mesh approach. As a simulation progresses, the mesh is optimized to focus numerical resolution in areas important to the dynamics and decrease it where it is not needed, thereby potentially reducing computational requirements. Model verification is performed using the method of manufactured solutions, which shows the correct solution convergence rates. Model validation and application considers 2-D simulations of plume formation in a water tank which replicate published laboratory experiments. The numerically predicted settling velocities for both individual particles and plumes, as well as instability behaviour, agree well with experimental data and observations. Plume settling is clearly hindered by the presence of a salinity gradient, and its influence must therefore be taken into account when considering particles in bodies of saline water. Furthermore, individual particles settle in the laminar flow regime while plume settling is shown (by plume Reynolds numbers greater than unity) to be in the turbulent flow regime, which has a significant impact on entrainment and settling rates. Mesh adaptivity maintains solution accuracy while providing a substantial reduction in computational requirements when compared to the same simulation performed using a fixed mesh, highlighting the benefits of an adaptive unstructured mesh approach.

Assessment of an unstructured mesh approach for CFD predictions of the NH90 fuselage rotor

The five year long GOAHEAD project generated a unique and extended experimental database for CFD validation. It is one of the few experimental investigations where a full model helicopter configuration with flexible rotating blades was considered. In this work, an unstructured mesh approach was adopted in order to demonstrate the potential that existing state-of-the-art, general purpose unstructured flow solvers could offer in simulating complex flow phenomena of helicopter aerodynamics. The entire NH90 helicopter model surface and the rotating blades were discretized with triangular elements. A hybrid-type field mesh was generated, where the near wall flow region was represented by triangular base prismatic element layers and the rest of the flow domain was represented by tetrahedral elements. The rotating blades were considered rigid and enclosed in a circular disc which rotated relative to the helicopter fuselage. Time accurate computations were carried out until time periodicity was achieved only then the computed solutions were in reasonable agreement with the measurements.

A two‐dimensional prototype multi‐physics model of the right ventricle of the heart

AbstractThe heart operates as a delicate function of the interactions among its electro‐chemical, structural and fluid components. The objective of this paper is to describe the computational modelling of the interaction between simplified forms of the electro‐chemical, structural and fluid behaviour. It is because the objective here is to evaluate the interactions among the phenomena that the specific models of the electro‐chemical, fluid and structural behaviour are kept as simple as possible. The electro‐chemical model is drawn from that of Clayton and Holden, while the blood is assumed to be a conventional slightly compressible Navier–Stokes fluid and the heart wall is a simple elastic structure modelled via the static equations. The model is implemented within a multi‐physics finite volume solver environment using an unstructured mesh approach, which enables the implementation of models for each of the specific phenomenon and their interactions. The model is two dimensional, but shows how the electric field drives a cross section of the wall so that it pumps the blood in and out of the right ventricle geometry. Copyright © 2008 John Wiley & Sons, Ltd.

A low-order unstructured-mesh approach for computational electromagnetics in the time domain.

Maxwell's curl equations in the time domain are solved using an explicit linear finite-element approach implemented on unstructured tetrahedral meshes. For the simulation of scattering problems, a perfectly matched layer is added at the artificial far-field boundary, created by the truncation of the physical domain prior to the numerical solution. The complete solution procedure is parallelized. The computational challenges that are encountered when attempting simulations at higher frequencies suggest that the implementation of a hybrid algorithm could have certain advantages. The hybrid approach adopted uses a combination of the finite-element procedure and the well-known low operation count/low storage finite-difference time-domain method. Examples are included to demonstrate the numerical performance of the techniques that are described.

A finite volume unstructured mesh approach to dynamic fluid–structure interaction: an assessment of the challenge of predicting the onset of flutter

Computational modelling of dynamic fluid–structure interaction (DFSI) is a considerable challenge. Our approach to this class of problems involves the use of a single software framework for all the phenomena involved, employing finite volume methods on unstructured meshes in three dimensions. This method enables time and space accurate calculations in a consistent manner. One key application of DFSI simulation is the analysis of the onset of flutter in aircraft wings, where the work of Yates et al. [Measured and Calculated Subsonic and Transonic Flutter Characteristics of a 45° degree Sweptback Wing Planform in Air and Freon-12 in the Langley Transonic Dynamic Tunnel. NASA Technical Note D-1616, 1963] on the AGARD 445.6 wing planform still provides the most comprehensive benchmark data available. This paper presents the results of a significant effort to model the onset of flutter for the AGARD 445.6 wing planform geometry. A series of key issues needs to be addressed for this computational approach. • The advantage of using a single mesh, in order to eliminate numerical problems when applying boundary conditions at the fluid-structure interface, is counteracted by the challenge of generating a suitably high quality mesh in both the fluid and structural domains. • The computational effort for this DFSI procedure, in terms of run time and memory requirements, is very significant. Practical simulations require even finer meshes and shorter time steps, requiring parallel implementation for operation on large, high performance parallel systems. • The consistency and completeness of the AGARD data in the public domain is inadequate for use in the validation of DFSI codes when predicting the onset of flutter.