Computational Fluid Dynamics Scheme Research Articles

Research of PM-ADC scheme for optimized computational CFD analysis in fast reactor cores

Several challenges exist in the analysis of the sodium-cooled fast reactor (SFR) core using computational fluid dynamics (CFD)codes. These include the intricate task of geometric modeling and mesh partitioning and the substantial computational resources required by CFD calculations. These challenges have been shown to create significant impediments to the practical analysis of the SFR core. This paper proposes a CFD scheme called the Parameterized Modeling and Automated Distributed Computing Approach (PM-ADC) to address the challenges. This approach includes a fuel assembly model tailored for the fast reactor core and incorporates parameterized geometric modeling coupled with a system to automate the distribution of parallel computing. The PM-ADC scheme is divided into two critical components: rapid preprocessing design and the generation of geometric models and meshes for core assemblies, enabled by Parameterized Modeling (PM). In contrast, the Automatic Distributed Computing (ADC) component is responsible for the enhancement of computing efficiency and resource utilization. This is achieved by the automatic allocation and distribution of CFD computing resources within a partitioned domain, resulting in the completion of CFD analyses for all fuel assemblies at full height in a significantly reduced timeframe. The performance of the PM-ADC scheme is analyzed on CFD calculations on representative areas of 81 fuel assemblies within the core of the Chinese Experimental Fast Reactor (CEFR). The results show that the PM-ADC scheme can accurately and efficiently simulate the flow and heat transfer characteristics of the CEFR fuel assembly, demonstrating its potential for high-fidelity analysis of large engineering systems. The study's findings also provide new insights and tools for the ongoing development and analysis of SFRs, contributing to the evolution of nuclear reactor design and safety.

Investigation of heat transfer of the frame of entrance door encompassing phase change materials through computational fluid dynamics schemes

Investigation of heat transfer of the frame of entrance door encompassing phase change materials through computational fluid dynamics schemes

Numerical investigation of the effect of tracheostomy on flow and particle transport characteristics in human airways

Tracheostomy is a typical surgical procedure that has been widely practiced to address airway-related difficulties, such as airway obstruction or chronic conditions, that require long-term supportive ventilation. However, it may result in symptoms that detrimental to respiratory system. Computational fluid dynamics (CFD) is a noninvasive and efficient approach for observing the effects of tracheostomy. In this study, we introduced a CFD framework that can reveal the effects of tracheostomy tube insertion based on a comparison with the airflow of a normal airways. An automatic transformation method was developed using a patient's anatomical information to combine subject-specific airways with an artificial tracheostomy tube geometry and an idealized upper airway geometry for later comparison of characteristics of airflow and particle transport. The CFD scheme used for flow simulation in lungs was employed to achieve the behaviors of airflow. The tracheostomy tube generates a jet flow, resulting in twice greater wall shear stress (WSS) and 30 times greater viscous dissipation in the trachea compared to normal airway. The tracheostomized airway induces an intense turbulent jet, which enhances chaotic motion of the particles therein and allows particles to deposit more frequently on the surface. Subsequently, an increase in particle deposition is observed on the central airway's surface. The variation of pressure between inspiration and expiration phase was twice greater and the airflow resistance was also significantly higher compared to normal airway, implying the greater work of breathing. The novel framework could evaluate the efficiency and potential complications in performing tracheostomy beforehand by observing airflow behaviors.

Reliability analysis of a large curved-roof structure considering wind and snow coupled effects

Ensuring the safety of large curved-roof structures subjected to blizzards in cold regions remains challenging. This paper assesses the reliability of a large curved-roof structure considering the coupled effects of wind and snow. To this end, a two-way coupled simulation considering the interaction between snow particles and turbulent wind is first carried out using a computational fluid dynamics scheme and a spectral representation method based on the wavenumber-frequency joint power spectrum and stochastic harmonic function; thereby, the uneven snow distribution and stochastic wind field on a large curved roof are revealed. The probability density evolution method is then adopted to conduct a stochastic response and reliability analysis of the structure. The simulation results reveal that a credible uneven distribution of snow on the large curved roof can be obtained using the suggested snowdrift simulation scheme, and the refined spectral representation method can efficiently and accurately simulate the two-dimensional fluctuating wind field of the large curved-roof structure. It is shown that under stochastic wind, snow and self-weight loads for a 100-year return period, the large curved-roof structure has a higher risk of member yielding than of node deflection. Meanwhile, the axial stress acting on the structural member is far less than the maximum allowable stress and the structure is thus deemed to be sufficiently safe.

Design and analysis of RIF scheme to improve the CFD efficiency of rod-type PWR core

This research serves to advance the development of engineering computational fluid dynamics (CFD) computing efficiency for the analysis of pressurized water reactor (PWR) core using rod-type fuel assemblies with mixing vanes (one kind of typical PWR core). In this research, a CFD scheme based on the reconstruction of the initial fine flow field (RIF CFD scheme) is proposed and analyzed. The RIF scheme is based on the quantitative regulation of flow velocities in the rod-type PWR core and the principle that the CFD computing efficiency can be improved greatly by a perfect initialization. In this paper, it is discovered that the RIF scheme can significantly improve the computing efficiency of the CFD computation for the rod-type PWR core. Furthermore, the RIF scheme also can reduce the computing resources needed for effective data storage of the large fluid domain in a rod-type PWR core. Moreover, a flow-ranking RIF CFD scheme is also designed based on the ranking of the flow rate, which enhances the utilization of the flow field with a closed flow rate to reconstruct the fine flow field. The flow-ranking RIF CFD scheme also proved to be very effective in improving the CFD efficiency for the rod-type PWR core.

Analysis of the performances of the CFD schemes used for coupling computation

In this paper, the coupling of fine-mesh computational fluid dynamics (CFD) thermal-hydraulics (TH) code and neutronics code is achieved using the Ansys Fluent User Defined Function (UDF) for code development, including parallel meshing mapping, data computation, and data transfer. Also, some CFD schemes are designed for mesh mapping and data transfer to guarantee physical conservation in the coupling computation. Because there is no rigorous research that gives robust guidance on the various CFD schemes that must be obtained before the fine-mesh coupling computation, this work presents a quantitative analysis of the CFD meshing and mapping schemes to improve the accuracy of the value and location of key physical prediction. Furthermore, the effect of the sub-pin scale coupling computation is also studied. It is observed that even the pin-resolved coupling computation can also create a large deviation in the maximum value and spatial locations, which also proves the significance of the research on mesh mapping and data transfer for CFD code in a coupling computation.

Design and analysis of shell and tube heat exchanger for low temperature applications using CFD

A shell and tube device is deployed for the applications such as oil refinery processes, chemical processes and high pressure technologies. The hot fluid flows to the tubes in the heat exchanger, and the cool fluid moves through the shell section. Hence, heat is transferred from the tube section to the shell section of the heat exchanger. This article is deals with the modelling and analysis of mini shell and tube heat exchanger (MSTHE) for low temperature applications which is less than 250°C. The design of the heat exchanger is made with nine tubes which are of 6 mm diameter and shell of 41 mm diameter. As conventional design does not result in the internal heat transfer, computational fluid dynamics scheme is adopted to design the modified heat exchanger by adopting the conditions such as velocity of tube fluid and pressure drop. The modelling of MSTHE is done by Pro/E whereas CFD analysis is done with ANSYS. The contour obtained from the analysis proves that the MSTHE is applicable for the temperature less than 250°C and have the potential to transfer heat effectively.

Distributed-parallel CFD computation for all fuel assemblies in PWR core

To further understand and monitor the thermal–hydraulic (TH) status of large domain of pressurized water reactor (PWR) core, an applicable engineering approach with high efficiency and high spatial resolution is critical. Traditional engineering computational fluid dynamics (CFD) computation needs too many computing resources to effectively analyze large domain engineering application for PWR core. In this study, a distributed-parallel (DP) CFD scheme is presented. This scheme separates the large domain into some sub-domains in order to optimize computing time and resources. The design completely retains the complex structures and fine-scale CFD mesh. In addition, it also significantly reduces the computing resources and time, and a fine-scale, full-height CFD analysis can be done in hours for all assemblies. Moreover, important design requirements such as energy consumption ratio, relative computing domain, relative assembly number, and the ranking method of important locations are also designed to optimize the applications of DP scheme to satisfy different engineering demands. The performance of the proposed scheme is evaluated using the CFD computation of a representative region from all 121 assemblies in a PWR core. This research serves to advance the development of engineering CFD computation for PWR core.

Three-dimensional VOF simulation of droplet impacting on a superhydrophobic surface

It is very important to analyze and study the motion process of droplets impacting superhydrophobic surface, which is of great significance to understand the mechanism of superhydrophobic surface and guide the design and manufacture of superhydrophobic surface. Taking by three-dimensional volume of fluid (VOF) simulation coupling coupled level set (CLS) algorithm, on the one hand, we simulate the morphological changes in the process of droplet impingement, as well as the internal velocity and the pressure distribution; on the other hand, we focus on the effects of droplet impact velocity, surface wettability, surface tension on the dynamics of the droplets. The CLSVOF model inherits the advantages of the VOF model for accurately constructing the phase interface and inherits the advantage that the level set can accurately calculate the surface tension, which improves the accuracy of the calculation of the droplet impact on the superhydrophobic surface. The computed results distinctly demonstrated there were four stages: falling, spreading, shrinking and rebounding. The time history of each stage agreed well with the pictures captured by high-speed camera, which indicated the computational fluid dynamics scheme was effective. Moreover, the motion mechanism of the droplets impacting on the solid surface is elaborated, which was helpful to control the solid–liquid interface to achieve a variety of solid interface characteristics.

Clinical validation and assessment of aortic hemodynamics using computational fluid dynamics simulations from computed tomography angiography

BackgroundHemodynamic information including peak systolic pressure (PSP) and peak systolic velocity (PSV) carry an important role in evaluation and diagnosis of congenital heart disease (CHD). Since MDCTA cannot evaluate hemodynamic information directly, the aim of this study is to provide a noninvasive method based on a computational fluid dynamics (CFD) model, derived from multi-detector computed tomography angiography (MDCTA) raw data, to analyze the aortic hemodynamics in infants with CHD, and validate these results against echocardiography and cardiac catheter measurements.MethodsThis study included 25 patients (17 males, and 8 females; a median age of 2 years, range: 4 months–4 years) with CHD. All patients underwent both transthoracic echocardiography (TTE) and MDCTA within 2 weeks prior to cardiac catheterization. CFD models were created from MDCTA raw data. Boundary conditions were confirmed by lumped parameter model and transthoracic echocardiography (TTE). Peak systolic velocity derived from CFD models (PSVCFD) was compared to TTE measurements (PSVTTE), while the peak systolic pressure derived from CFD (PSPCFD) was compared to catheterization (PSPCC). Regions with low and high peak systolic wall shear stress (PSWSS) were also evaluated.ResultsPSVCFD and PSPCFD showed good agreements between PSVTTE (r = 0.968, p < 0.001; mean bias = − 7.68 cm/s) and PSPCC (r = 0.918, p < 0.001; mean bias = 1.405 mmHg). Regions with low and high PSWSS) can also be visualized. Skewing of velocity or helical blood flow was also observed at aortic arch in patients.ConclusionsOur result demonstrated that CFD scheme based on MDCTA raw data is an accurate and convenient method in obtaining the velocity and pressure from aorta and displaying the distribution of PSWSS and flow pattern of aorta. The preliminary results from our study demonstrate the capability in combining clinical imaging data and novel CFD tools in infants with CHD and provide a noninvasive approach for diagnose of CHD such as coarctation of aorta in future.

Diagnostic Performance of a Novel Method for Fractional Flow Reserve Computed from Noninvasive Computed Tomography Angiography (NOVEL-FLOW Study)

Coronary computed tomography angiography (CCTA)-derived fractional flow reserve from computed tomography (CT-FFR) may provide better diagnostic performance over CCTA alone, but the complexity of its method limits the use in clinical environment. The aim of the present study is to validate a newly developed vessel-length based computational fluid dynamics scheme for the computation of FFR based on CCTA data, compare them with invasively measured FFR, and evaluate its diagnostic performance with that of CCTA. One hundred seventeen patients from 4 medical institutions who had clinically indicated invasive coronary angiography for suspected coronary artery disease (CAD) were enrolled. Invasive FFR measurement was performed in 218 vessels and these measurements were regarded as the reference standard. The accuracy, sensitivity, specificity, positive predictive value, and negative predictive value of CT-FFR on a per-vessel basis were 85.8%, 86.2%, 85.5%, 79.8%, and 90.3%, respectively, for CT-FFR ≤0.80, and 66.1%, 75.9%, 59.5%, 55.5%, and 78.8%, respectively, for CCTA ≥50%. A higher area under the receiver operating characteristic curve for CT-FFR was observed compared with CCTA (0.93 vs 0.74, p<0.0001). The CT-FFR and FFR correlated well (r= 0.76, p <0.001) with slight underestimation by CT-FFR (0.014 ± 0.077, p= 0.007). With a novel method of vessel-length based computational fluid dynamics scheme, CT-FFR can be performed at a personal computer enhancing its applicability in clinical situation. The diagnostic accuracy of CT-FFR for the detection of functionally significant CAD was good and was superior to that of CCTA within a population of suspected CAD.

Adaptive CFD schemes for aerospace propulsion

The flow fields which can be observed inside several components of aerospace propulsion systems are characterised by the presence of very localised phenomena (boundary layers, shock waves,...) which can deeply influence the performances of the system. In order to accurately evaluate these effects by means of Computational Fluid Dynamics (CFD) simulations, it is necessary to locally refine the computational mesh. In this way the degrees of freedom related to the discretisation are focused in the most interesting regions and the computational cost of the simulation remains acceptable. In the present work, a discontinuous Galerkin (DG) discretisation is used to numerically solve the equations which describe the flow field. The local nature of the DG reconstruction makes it possible to efficiently exploit several adaptive schemes in which the size of the elements (h-adaptivity) and the order of reconstruction (p-adaptivity) are locally changed. After a review of the main adaptation criteria, some examples related to compressible flows in turbomachinery are presented. An hybrid hp-adaptive algorithm is also proposed and compared with a standard h-adaptive scheme in terms of computational efficiency.

The importance of accurately representing submerged vegetation morphology in the numerical prediction of complex river flow

AbstractThis paper reports a novel method for the incorporation of complex plant morphologies into a computational fluid dynamics (CFD) model, allowing the numerical prediction of flows around individual plants. The morphological complexity, which comprises the vertical and lateral distribution of individual branches and leaves is captured through terrestrial laser scanning (TLS) and is maintained in the numerical prediction of flow fields. This is achieved where the post‐processed, voxelized plant representation is incorporated into a CFD scheme through a mass flux scaling algorithm (MFSA). Flow around Prunus laurocerasus has been modelled under foliated and defoliated states following the removal of leaves. The complex plant morphologies are shown to produce spatially heterogeneous downstream velocity fields, with velocity profiles that deviate significantly from the idealized inflected shape. Rapid transition between the high velocity free stream zone and the zone of reduced velocity in the plant wake indicate shearing of flow, with the point of reattachment extending up to seven plant lengths downstream. The presence of leaves significantly modifies the flow field response, with development of a second, more pronounced wake structure around the dense foliage. This approach provides a full flow numerical description of the pressure field, enabling the vegetative drag force to be quantified. For the example given here, drag force is an order of magnitude greater for the foliated state. The methodology outlined here demonstrates the importance of accurately representing complex plant morphology in hydraulic models, and allows drag forces and coefficients to be calculated for specific plant species. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Two methods for simulating mud discharge after emergency disconnection of a drilling riser

In marine floating drilling, emergency disconnection of a drilling riser is required in harsh environments or loss of dynamic positioning control. After disconnection, drilling mud in the riser discharges directly from the riser bottom, and seawater refills the vacancy emptied out after mud falling through refill valves. This paper presents two new simulation procedures for this unsteady flow. The first one is a whole fluid column (WFC) model and it is solved by a cubic equation. The second one is a computational fluid dynamics (CFD) procedure, in which two high-resolution CFD schemes are applied for the first time to discrete a special governing equation, and Level Set method is adopted to track the interface between mud column and refilled seawater at each time step. Two methods can respectively provide variations of flow velocity, fluid pressure, whole column weight and flow friction force in a whole mud release duration. In particular, WFC method can easily predict overall trends of several parameters during a whole discharge period, which are prerequisite parameters for dynamic analysis of a riser in hanging state; CFD method is very sensitive to every detailed fluctuation of velocity and pressure in the initial moment of mud discharge, and can be integrated into a structural model for riser recoil response analysis. For a drilling riser with 2150 m, it takes 195.83 s to replace all mud column by seawater, and the maximal discharge velocity is 14.61 m/s. During mud falling, the top of mud column keeps static for 2.29 s before the first pressure wave reaches, and fluid pressure of part column section drops to zero and lasts 1–3 s. In addition, the maximal values of fluid weight-loss and friction force are both close to half of the whole column weight. These results are beneficial for riser system design and risk control of riser recoil.

Modelling of hydraulic fracturing process by coupled discrete element and fluid dynamic methods

A three-dimensional model is presented and used to reproduce the laboratory hydraulic fracturing test performed on a thick-walled hollow cylinder limestone sample. This work aims to investigate the implications of the fluid flow on the behaviour of the micro-structure of the rock sample, including the material strength, its elastic constants and the initialisation and propagation of fractures. The replication of the laboratory test conditions has been performed based on the coupled Discrete Element Method (DEM) and Computational Fluid Dynamics scheme. The numerical results are in good agreement with the experimental data, both qualitatively and quantitatively. The developed model closely validates the overall behaviour of the laboratory sample, providing a realistic overview of the cracking propagation towards total collapse as well as complying with Lame’s theory for thick-walled cylinders. This research aims to provide some insight into designing an accurate DEM model of a fracturing rock that can be used to predict its geo-mechanical behaviour during Enhanced Oil Recovery applications.

A hybrid DEM/CFD approach for solid-liquid flows

A hybrid scheme coupling the discrete element method (DEM) with the computational fluid dynamics (CFD) is developed to model solid-liquid flows. Instead of solving the pressure Poisson equation, we use the compressible volume-averaged continuity and momentum equations with an isothermal stiff equation of state for the liquid phase in our CFD scheme. The motion of the solid phase is obtained by using the DEM, in which the particle-particle and particle-wall interactions are modelled by using the theoretical contact mechanics. The two phases are coupled through the Newton's third law of motion. To verify the proposed method, the sedimentation of a single spherical particle is simulated in water, and the results are compared with experimental results reported in the literature. In addition, the drafting, kissing, and tumbling (DKT) phenomenon between two particles in a liquid is modelled and reasonable results are obtained. Finally, the numerical simulation of the density-driven segregation of a binary particulate suspension involving 10 000 particles in a closed container is conducted to show that the presented method is potentially powerful to simulate real particulate flows with large number of moving particles.

The use of cubic interpolation method for transient hydrodynamics of solid particles

Research on numerical schemes on fluid–solid interaction has been quite intensive in the past decade. The difficulties associated with accurate predictions of the interaction at specific spatial and temporal levels. Traditional computational fluid dynamics schemes are struggling to predict at high level of accuracy for this type of problem. Hence, in the present study, an alternative numerical scheme was proposed to predict the fluid flow and coupled with a Lagrangian scheme on the prediction of solid phase. The dynamics of solid particle in a lid-driven cavity was investigated at a wide range of Reynolds numbers. The results show that the particle trajectories are critically dependence on the magnitude of Reynolds numbers and the vortex behavior in the cavity. Good comparisons with the experimental and previous studies demonstrate the multidisciplinary applications of the present scheme.

Top Fuel Injection Design in an Entrained-Flow Coal Gasifier Guided by Numerical Simulations

A computational fluid dynamics scheme is employed to simulate the effects of potential fuel injection techniques on gasification performance. The objective is to help design the top-loaded fuel injection arrangement for an entrained-flow gasifier using coal water slurry as the input feedstock. Two specific arrangements are investigated: (a) coaxial dual jet impingement with slurry coal in the center and oxygen in the outer jet and (b) four jet impingement with two single slurry coal jets and two single oxygen jets. When the heterogeneous finite-rate solid-gas reaction scheme is implemented, it is discovered that the particle collision model cannot be implemented with the heterogeneous gasification scheme in the present computational model. The instantaneous gasification model is later employed to examine the particle collision phenomenon by implementing the particle collision model, in which the coal (consisting of carbon and volatiles) is injected as gas, and the water is injected as droplets. The result of droplet tracks shows that the droplets are not bounced around, as speculated, at the intersection where the jets meet, and majority of the droplets pass through the jet impingement section and hit the wall as in the finite-rate case. This implies that the results of the finite rate are acceptable even though the particle collision model is not implemented. The finite-rate result actually presents a worst-case scenario for predicting wall erosion. The particle tracks for both the two concentric and four separate injection configurations show that the coal particles hit the wall and can accelerate the deterioration of the refractory bricks. The case employing two concentric injections provides better fuel-oxidant mixing and higher heating values than the case using four separate injections.

Numerical simulation and mock-up experimental measurement of the air conditioning system for the 3 GeV Taiwan Photon Source electron storage ring

National Synchrotron Radiation Research Center, Taiwan, is currently constructing the civil buildings and utility system of the Taiwan Photon Source. The air conditioning (AC) system of the storage ring tunnel was designed based on those of existing Taiwan Light Source and some international advanced accelerators. To predict the air temperature variation and flow pattern in tunnel more precisely, we applied 3D computational fluid dynamics scheme and built up a one-cell mock-up equipped with AC system. In the 3D numerical model, effects of magnets of the booster and the storage ring, girders, cable trays, front ends and the supplied air wind duct are all taken into account. The temperature variations and flow pattern were shown through the numerical simulation. Measured air temperature data in the one-cell mock-up were also collected.

Reduced-Order Model for Viscous Aerodynamic Flow Past an Airfoil

A method is presented to obtain reduced-order models of multiparametric, steady, transonic aerodynamic flows around two-dimensional airfoils. The method is based on proper orthogonal decomposition and appropriate projection on the proper orthogonal decomposition manifold of the governing equations and boundary conditions, and it includes various ingredients that are new in this field. Proper orthogonal decomposition modes are obtained from a set of snapshots calculated by computational fluid dynamics based on the compressible Navier―Stokes equations and a turbulence model, but projection on the proper orthogonal decomposition manifold is made using the inviscid Euler equations, which makes the method independent of the computational fluid dynamics scheme; projection is made using only a limited number of mesh points, obtaining quite good results. Shock waves are treated specifically in the proper orthogonal decomposition description, to avoid the need of using a too-large number of snapshots. The method is checked and discussed on a specific aerodynamic problem.