CFD Approach Research Articles

How can CFD contribute to the understanding of wildfire behaviour?

In addition to the experimental approach, wildfire modelling has been developed over the last decades to better understand the behaviour of wildfires and to propose new management tools to evaluate and reduce this natural hazard. This paper has twofold objective: (1) show how CFD simulation carried out using fully-physical models contributes to the understanding of wildfire behaviour, and (2) present new developments that were brought to FireStar3D – a fully-physical multiphase fire-simulator. The multiphase approach used in this class of models is briefly described, as well as the difficulties arising from the coupling between the various physical mechanisms of this multiscale problem. LES modelling and turbulence-radiation interaction used in FireStar3D is particularly detailed, as well as a new inlet boundary condition allowing to account for fire-induced flow while maintaining a prevailing crosswind far from the flaming zone. The benefits of multiphase CFD approach in addressing wildfire problems is demonstrated by considering three case studies of static and propagating vegetation fires having different length scales, which also highlights the model's potential in various configurations.

A space marching method for sonic boom near field predictions

The conventional sonic boom propagation prediction method widely adopted in supersonic aircraft design involves a two-step procedure. In the first step, a compressible viscous or inviscid Computational Fluid Dynamics analysis is applied to the aircraft geometry at flight conditions to produce a flow field solution near the aircraft. Then in the second step, a one dimensional nonlinear Burgers’ equation model is used to propagate sonic boom signature traces from the near field solution at flight altitude to the ground along a ray path. For an accurate ground signature prediction the near field signature must be accurately modeled at a sufficient distance from the aircraft flight path in order to minimize errors in the one dimensional propagation model. This is a very challenging task for general purpose CFD tools in a design environment because the cost of maintaining highly accurate off-body solutions increases dramatically as the radial distance is enlarged in the computational domain. It is also particularly difficult to apply these tools for wave propagation because the algorithms are normally lower order and numerically dissipative and dispersive. In this work a space marching procedure based on an optimized higher order finite difference method is developed and applied in conjunction with a CFD solution concentrated in the close vicinity of the aircraft. This new approach is much more efficient, compared to previous methods, in providing highly accurate near field signatures for full carpet ground predictions. Results indicate that near field signatures retain more waveform shape information farther from the aircraft geometry while reducing the CFD cost significantly. The predicted ground signature is also shown to converge in shape as the radial distance of the near field signature grows, which is indicative of a more ideal initial condition being supplied to the one dimensional wave propagation to ground. This feature is very difficult to replicate in a tractable manner with common CFD approaches used in design.

Comparison through a CFD approach of static mixers in an emulsification process

Emulsions, characterized by droplet dispersions of immiscible liquids in a continuous phase, are often found in many diverse fields of the chemical industry. The energy needed to break these droplets can be sourced from mechanical agitators in stirred tanks, active mixers like pulse-flow mixers, and ultrasonic mixers. However, static mixers serve as a convenient alternative due to their typically lower maintenance costs and increased resistance to failures. Static mixers are available in diverse shapes and dimensions, with two widely used types being the Kenics Static Mixers and the Sulzer Static Mixers. While these two static mixers have been extensively studied in the literature in terms of pressure drop and mixing efficiency, to the best of the authors’ knowledge there is no study comparing the two in emulsification processes. This work aims to compare the performance of these static mixers in the production of emulsions by employing a Computational Fluid Dynamics approach. Results showed that the Sulzer Static Mixers allow to obtain higher values of turbulent energy dissipation, which in turn leads to smaller droplet diameters.

Multi-fidelity CFD for obtaining the runner blade profile parameters of a Francis turbine for optimum hydrodynamic performance

The high fidelity Navier Stokes equations based CFD codes precisely take care of the turbulent and viscous effects of complex flows passing through the hydraulic turbines. However, for preliminary design synthesis and analysis purposes, this full 3D flow can be assumed as a combination of two 2D flows (meridional axi-symmetric flow and blade-to-blade or cascade flow) which is the basis of low fidelity potential flow theory for hydraulic turbines. This paper presents the utilities of high as well as low fidelity CFD analyses for obtaining a runner blade design which yields an optimum hydrodynamic performance of a prototype Francis Turbine. The complete flow domain of the Francis turbine has been considered for the high-fidelity analysis which is carried out by using ANSYS CFX 16.0 for different operating conditions. Whereas, for the low fidelity investigations, full three-dimensional flow domains of different blade rows (i.e., stay vanes, guide vanes and runner) of the Francis turbine is divided into two 2D flow domains (i.e., an axisymmetric annulus of the turbine space for meridional flow analysis and cascades at different sections from hub to shroud for blade-to-blade analysis). By using the low fidelity analysis, runner blade design parameters have been adequately varied in order to obtain a population of different promising runner blade designs. Performances of these promising designs are evaluated, and the obtained results are thoroughly analysed through the response surface analysis. An optimized hydrodynamic performance design of the runner is obtained for the target values of responses (here, swirl velocity at trailing edge of the runner (Cu2) and stagnation pressure at trailing edge of the runner (P02/ρ)) at different sections from hub to shroud by determining the design parameters of blade profiles at different sections. The adopted multi-fidelity CFD approach is found very effective and has the potential to yield reasonably accurate hydraulic designs of the Francis turbine in considerably lesser time and cost.

Adjoint Solver-Based Analysis of Mouth–Tongue Morphologies on Vapor Deposition in the Upper Airway

Even though inhalation dosimetry is determined by three factors (i.e., breathing, aerosols, and the respiratory tract), the first two categories have been more widely studied than the last. Both breathing and aerosols are quantitative variables that can be easily changed, while respiratory airway morphologies are difficult to reconstruct, modify, and quantify. Although several methods are available for model reconstruction and modification, developing an anatomically accurate airway model and morphing it to various physiological conditions remains labor-intensive and technically challenging. The objective of this study is to explore the feasibility of using an adjoint–CFD model to understand airway shape effects on vapor deposition and control vapor flux into the lung. A mouth–throat model was used, with the shape of the mouth and tongue being automatically varied via adjoint morphing and the vapor transport being simulated using ANSYS Fluent coupled with a wall absorption model. Two chemicals with varying adsorption rates, Acetaldehyde and Benzene, were considered, which exhibited large differences in dosimetry sensitivity to airway shapes. For both chemicals, the maximal possible morphing was first identified and then morphology parametric studies were conducted. Results show that changing the mouth–tongue shape can alter the oral filtration by 3.2% for Acetaldehyde and 0.27% for Benzene under a given inhalation condition. The front tongue exerts a significant impact on all cases considered, while the impact of other regions varies among cases. This study demonstrates that the hybrid adjoint–CFD approach can be a practical and efficient method to investigate morphology-associated variability in the dosimetry of vapors and nanomedicines under steady inhalation.

Simulating Gas-Solid Phase Isomerization of C8 Aromatics Affected by Catalyst Shapes in Fixed Bed Reactors with Particle-Resolved CFD Approach

Paraxylene (PX) is essential for producing polyethylene terephthalate fibers. We conduct particle-resolved CFD simulations, coupled with our reaction kinetics, on a fixed bed reactor randomly filled with catalyst shapes including sphere, cylinder, trilobe and quadrilobe to enlarge PX productivity in the catalytic isomerization of C8 aromatics. Our findings reveal the effects of catalyst shapes on velocity, concentration, temperature fields, and pressure drop. Although all catalyst shapes present particle utilization above 70 %, trilobes and quadrilobes show superior PX yield and ethylbenzene conversion due to their larger surface area and reduced mass transfer distance. Yet, among these catalysts, trilobes have twice the pressure drop of the others for complex geometric surface. Therefore, quadrilobes are more practical as their higher bed voidage, smaller pressure drop, better reactivity for desired reactions, and lower adiabatic temperature rise. This work provides guidance for catalyst design and process optimization to enhance PX productivity in aromatic isomerization.

CFD approach to analyze entropy generation, heat transfer of perforated conical ring turbulators embedded in heat exchanger with biological ternary hybrid nanofluid

Perforated conical rings greatly enhance heat transfer by causing flow disruption and increasing fluid mixing. With minimal impact on friction loss, it improves heat transfer by breaking the thermal boundary layer. In this work, entropy generation, overall performance of cylindrical pipe heat exchanger equipped with perforated conical rings are numerically calculated. Shape of the holes is oval and the number of hole are 4. Ternary hybrid nanofluid is the working fluid (coolant). The combination of graphene, Cu and Al2O3 nanomaterials are considered with water as a base fluid. A particular range of Reynolds number is taken into account (5000 − 9000). 50% increase in Nusselt number is noted for using higher volume fraction (0.5%) of ternary hybrid nanofluid. Thermal performance of heat exchanger is increased more than 50%. Entropy generation is higher by using the perforated conical rings. Thermal- hydraulic performance evaluation criteria (THPEC), i.e. ration between Nusselt number and friction factor decreases with increasing Reynolds number which is a promising result. The differences in THPEC of cylindrical tube with and without perforated conical ring (PCR) are highlighted.

Numerical solution and experimental investigation for hydro-acoustic analysis and noise reduction assessment of ship ducted propeller

Ship noise emission has many environmental impacts. Recognizing noise-generating source and investigating noise reduction techniques is the first step in elimination or reduction of these harmful effects. Studies show that ship propeller is one of the main sources of ship noise emission. Ducted propeller is one of the well-known solutions for noise reduction. In this paper, results of numerical solution for governing mathematical equations of noise emission in far field is presented and sound pressure level is calculated using Ffowcs Williams and Hawkings (FWH) equations. Numerical solution is validated by valid research resources. Propeller noise emission is also calculated by experimental measurements and filtering ambient noise frequencies. Finally, a comparison has been made between numerical solution and experimental results and the effect of duct on noise reduction is calculated. The measured SPL emitted from the propeller in CFD approach (solving the FWH) shows 28% reduction for ducted propeller in comparison with the propeller without the duct. In experimental approach (after removing the ambient noise) shows 37% reduction for ducted propeller in comparison with the propeller without the duct.

A numerical investigation on a diesel engine characteristic fuelled using 3D CFD approach

The exhaust and performance characteristics of engine combustion are one of most highly researched area due to climate concerns. These phenomena are direct consequence of combination of air–fuel and quality of combustion. The air–fuel. The ratio of fuel to air in the combustion process plays an important role in the quality of the burn. In this study, the effects of varying the fuel spray angle (FSA), using a variety of fuels, and operating at full load are analysed. According to the findings, a variation of 120 degrees in the FSA can have a substantial advantage in terms temperature reduction for full operating range, without influencing other parameters or fuel consumption. Present numerical investigation influence and importance of FSA on engine emission, even minuscule change FSA either during production of service could have significant impact on engine emission. These variations could take place for a variety of reasons, including but not limited to: production, service, or both.

Numerical analysis of generation of Colburn j and friction f factor for the pin fins of a compact heat exchanger using CFD approach

Numerical analysis of generation of Colburn j and friction f factor for the pin fins of a compact heat exchanger using CFD approach

Towards a uniform description of recombiners performance by a consistent CFD approach with the use of a detailed mechanism of hydrogen oxidation

For a consistent CFD substantiation of the recombiner performance, a detailed mechanism of hydrogen and oxygen recombination is used. The detailed mechanism of chemical kinetics (multi-step recombination reaction) makes it possible to claim universality, both in the numerical justification of the recombiner performance and in the justification of the flameless recombination threshold and makes it possible to justify the method for optimizing the recombiner to improve its characteristics. The models developed based on this approach were applied to both flat and cylindrical catalytic elements, which are used in FR and RVK recombiners, respectively. As part of the numerical studies, the detailed recombination mechanism was verified, namely the temperature distribution along the catalytic elements was compared and the performance of catalytic elements was compared as well. Good agreement was obtained between the calculated and experimental data. The approach considers not only the mechanism of surface recombination of hydrogen and oxygen on platinum, but also the mechanism of recombination in the gas phase. This makes it possible to calculate the onset of intense combustion outside the catalytic plates, which is a sign of volumetric ignition of the hydrogen-air environment. The concentrations at which such ignition is possible were obtained at different contents of water vapor in the medium. Thus, the proposed approach and the created models make it possible to fully describe the performance of recombiners of distinct designs without the use of additional experimental data, which is extremely necessary when justifying the hydrogen explosion safety of nuclear power plants.

Analysis of brush-molten metal interaction in brush atomizers: a CFD approach

Analysis of brush-molten metal interaction in brush atomizers: a CFD approach

From past to future: The role of computational fluid dynamics in advancing nuclear safety in Spain and Portugal

This document explores the role of CFD in nuclear safety studies, with a particular focus on advancements in Spain and Portugal. The field of nuclear safety has increasingly included CFD models to address complex safety–critical phenomena, given their ability to capture three-dimensional behavior with high resolution. While traditional one-dimensional codes remain very valuable, they often rely on conservative approximations, making 3D CFD approaches indispensable for accurate predictions across various nuclear scenarios. In the context of Spain and Portugal, this document shows the contribution to CFD applications for nuclear safety research. The topics covered include code development and validation, combustion studies, simulations of nuclear spent casks, fuel assembly analyses, and investigations into containment safety issues. These advances have mainly contributed to improving the predicting capabilities of CFD models for applications in various safety–critical domains. In addition to detailing the achievements and contributions in the field of CFD in Spain and Portugal, readers will find a comprehensive overview of the current challenges and future perspectives of CFD within the domain of nuclear fission technology.

Film Cooling Modeling in a Turbine Working under the Unsteady Exhaust Flow of Pulsed Detonation Combustion

Pressure gain combustors (PGCs) have demonstrated significant advantages over conventional combustors in gas turbine engines by increasing the thermal efficiency and reducing the pollution emission level. PGCs use shock waves to transfer energy which contributes to the increase in outlet total pressure. One of the major obstacles in the actual implementation of PGCs in the gas turbine cycle is the exploitation of the highly unsteady flow of the combustor outlet with the downstream turbine. Because of the higher outlet temperature from the PGCs, the turbine blade cooling becomes essential. Due to the highly fluctuating unsteady flow of PGCs, 3D CFD simulation of turbines becomes very expensive. In this work, an alternative approach of using a 1D unsteady Euler model for the turbine is proposed. One of the novel aspects of this paper is to implement the turbine blade cooling in the unsteady 1D Euler model. The main parameters required for the turbine blade cooling are the cooling air mass flow rate, temperature, and pressure. Due to the introduction of coolant flow, the blades are no longer adiabatic and the mass flow rate across the turbine is not constant. Comparing the 1D Euler results against zero-dimensional calculation and 3D CFD approach showed a very good match for both steady and unsteady simulations confirming the applicability of the 1D method.

Lipwall Effects on a Shore-Front Oscillating Water Column Based on DBEM and Computational Fluid Dynamic Approaches

Abstract The oscillating water column (OWC) is an economical and feasible type of wave energy converter with minimal maintenance costs which have been widely investigated. In this study, the effect of lipwalls for a shore-front OWC is investigated using dual boundary equation method (DBEM) and computational fluid dynamics (CFD) approaches. The boundary value problem is solved using the DBEM method within the framework of linear water wave theory. Whilst in the CFD approach, the volume-of-fluid (VOF) approach is used for simulating the numerical wave tank, with appropriate boundary conditions and regular wave inlet. The DBEM approach is beneficial to understand the complex phenomena inside the chamber, viz., radiation conductance and susceptance. It is inferred that case-B (vertical + shoreward-slant lipwall) is found to exhibit better performance for a wider range of non-dimensional wave frequencies due to its wave trapping configuration where the position of the lower lipwall is orthogonal. The CFD studies provide interesting insights into the optimal damping ratio concerning wave amplification factor at higher relative water depths, power output, and correlation of phase difference. Besides, the study reveals that the pressure and wave elevation inside the chamber are associated with the inhalation and exhalation process of air is attributed to the lower half of the lipwall.

Evaluation of free convection cooling and entropy efficiency in a porous W-shaped cavity using RSM and CFD approaches

The cooling and entropy efficiencies of natural convection inside cavities within fully saturated metal foam play a vital role in thermal engineering applications systems. The current study employed response surface methodology (RSM) coupled with ANSYS FLUENT-CFD for a two-dimensional W-shaped cavity, which has not been examined previously. Several effective physical factors were considered, including the aspect ratio (W = h/H = 0, 0.2, 0.4, 0.6 and 0.8) and the applied temperature variation (ΔT = Th − Tc = 10, 20, 30 and 40 K). Additionally, the thermal performance (NumW/NumO and QW/QO ) and entropy generation (EGW/EGO ) improved under the optimum design of pore per inch (10 ≤ PPI ≤ 30), the number of wave amplitude (1 ≤ n ≤ 3) and aspect ratio (0.2 ≤ W ≤ 0.8) utilizing both RSM and CFD. The results showed that the optimal design of natural convection within a fully saturated metal foam W-shaped cavity at PPI = 10, n = 3 and W = 0.8 resulted in enhancements of approximately 2.875 times for both NumW/NumO and QW/QO while maintaining reasonable EGW/EGO at 1.193 times. Moreover, the novelty aspect of this research lies in the successful achievement of multi-objectives improving NumW/NumO , QW/QO and EGW/EGO by applying the RSM approach in combination with ANSYS FLUENT-CFD. Thus, the optimal working procedure of RSM and CFD is aligned with the desired goals, as the cooling and entropy efficiencies of the porous W-shaped cavity are considered acceptable and satisfactory.

Performance analysis of hubless rim-driven thruster based on the number of blades: a CFD approach

Performance analysis of hubless rim-driven thruster based on the number of blades: a CFD approach

Coupling vibration analysis of heat exchanger tube bundles under different stiffness conditions

A two-dimensional tube bundles fluid–structure coupling model was developed using the CFD approach, with a rigid body motion equation and the Newmark integral method. The numerical simulations were performed to determine the vibration coupling properties between various tube bundles of stiffness. Take the corner square tube bundles with a pitch ratio of 1.28 as the research object. The influence of adjacent tubes with different stiffness on the vibration of the central target tube was analyzed. The research results show that the vibration characteristic of tube bundles is affected by the flow field dominant frequency and the inherent frequency of tube bundles. The vibration of adjacent tube bundles significantly impacts the amplitude and frequency of the central target tube. The equal stiffness and large stiffness tubes upstream or downstream inhibit the vibration displacement of the target tube to some extent. The low-stiffness tubes upstream or downstream significantly enhanced the amplitude of the target tube. The findings can be used to provide a basis for reasonable design and vibration suppression of shell-and-tube heat exchangers.

Comparative Analysis of Simulation Methodologies for Spindle Pumps

This research conducts a comprehensive comparative analysis of simulation methodologies for spindle pumps, with a specific focus on steady-state CFD, transient-CFD, and lumped-parameter approaches. Spindle pumps, renowned for their reliability, efficiency, and low noise emission, play a pivotal role in Thermal Management for Battery Electric Vehicles, aligning with the automotive industry’s commitment to reducing pollutants and CO2 emissions. The study is motivated by the critical need to curtail energy consumption during on-the-road operations, particularly as the automotive industry strives for enhanced efficiency. While centrifugal pumps are commonly employed for such applications, their efficiency is highly contingent on rotational speed, leading to energy wastage in real-world scenarios despite high efficiency at the design point. Consequently, the adoption of precisely designed spindle pumps for thermal management systems emerges as a viable solution to meet evolving industry needs. Recognizing the profound impact of simulation tools on the design and optimization phases for pump manufacturers, this research emphasizes the significance of fast and accurate simulation tools. Transient-CFD emerges as a powerful Tool, enabling real-time monitoring of various performance indicators, while steady-CFD, with minimal simplifications, adeptly captures pressure distribution and machine leakages. Lumped-parameter approaches, though requiring effort in simulation setup and simplifying input geometry, offer rapid computational times and comprehensive predictions, including leakages, Torque, cavitation, and pressure ripple. Breaking new ground, this paper presents, for the first time in the literature, accurate simulation models for the same reference machine using the aforementioned methodologies. The results were rigorously validated against experiments spanning a wide range of pump speeds and pressure drops. The discussion encompasses predicted flow, Torque, cavitation, and pressure ripple, offering valuable insights into the strengths and limitations of each methodology.

Numerical Analysis of Gurney Flap Impact on NACA 4415 Airfoil Aerodynamics Performance

Improving airfoil aerodynamic performance is an essential aspect of aerodynamic technology. The use of passive flow control is one way to enhance the aerodynamic performance of the airfoil. The influence of using gurney flaps as passive flow control was explored through the CFD approach employing the RANS control equations with the k-epsilon turbulence model. The airfoil model utilized in this investigation was the NACA 4415 operating at a Reynolds number of 1×106. This study explored three different variations of flap height, namely 0.5%, 1%, and 2% of chord length. The outcomes showed that adding gurney flaps showed quite positive results in increasing the lift and drag performance of NACA 4415. An airfoil with a 0.5%c height flap has an average percentage increase in Cl of 12%, followed by a height flap of 1%c, which is 23%, and a percentage Cl of 37% for a height flap of 2%c. Meanwhile, each variation in height flap affected the increase in Cd. A height flap of 0.5%c increased Cd with an average percentage of 2%, while a height flap of 1%c increased the percentage of Cd by 4% and 6% for a height flap of 2%c. Moreover, visualization of fluid flow with pressure and velocity contours given at AoA 12º to determine the effect on the increase in Cland Cd in NACA 4415.