CFD Analysis Research Articles

Exploring the impact of compressibility on reconstructed porous materials: A numerical study

This study underscores fluid density's significance in CFD simulations for porous materials, addressing its impact on accuracy and computational efficiency. The paper proposes a tailored form of Navier-Stokes equations that accounts for fluid density's influence on CFD analyses of porous materials in industrial contexts, including cases where the solid phase is deformable. Numerical analyses demonstrate fluid density's significance (ρ≠constant) and explore the importance of the energy equation in governing equations. The energy equation is essential in setting up the governing equations, as it calculates thermal characteristic length based on cell temperatures. By examining various porous material samples, the study suggests a streamlined approach: employing a single coupled CFD-FEM simulation to directly determine each geometrical parameter. Additionally, the study investigates the capability to accurately simulate turbulent fluid motion at the pore scale and analyze the flow field characterization within porous media. Computational cost analyses underscore the advantages of coupled simulations, establishing their profitability over separate parameter-specific simulations.

CFD Analysis of Gas-Dynamic and Heat Transfer Processes in a Propulsion System Using Polymer Fuel

In the presented work, a computer model of thermodynamic and gas-dynamic processes in a rocket engine of a new type, which uses solid polymers as fuel is considered. The design feature is the presence of a central body - a gasification chamber, where solid polymer fuel is decomposed into volatiles. To conduct the research, a preliminary thermodynamic analysis of the combustion of gasification products was carried out. Based on the results of the thermodynamic analysis using the mathematical model of the turbulent flow of viscous compressible gas, the processes of gas dynamics and heat transfer in the chamber and nozzle of the rocket engine were simulated. Analyses are made for the geometry of a real experimental sample of a polymer-fueled rocket engine developed at Oles Honchar Dnipro National University (Ukraine), which has passed the first successful tests. As a result of CFD simulation, dynamic and thermal fields in the combustion chamber and engine nozzle were obtained, and ways of further improvement of the design were determined.

Анализ воздействия воздушных обтекателей на аэродинамические характеристики токоприемника при увеличенных скоростях движения

Objective: investigation of the aerodynamic interaction of the airflow and the pantograph, taking into account the uneven distribution of pressure on the side edges of the fairings. Methods: the research was conducted based on a theoretical approach that defines the methods of air mass mechanics using mathematical modeling on a computer with the use of software products that include tools for calculating hydrodynamics based on the method of CFD analysis in the Flow Simulation module of the SolidWorks software. Results: a solid-state model of the current collector with integrated air deflectors has been developed, which takes into account the interaction complex in the system “moving structure — deflector — current collector — nodes and elements of the contact suspension” in the context of aerodynamic resistance influence. Practical importance: an innovative system has been developed to optimize the aerodynamic characteristics of the current collector during its motion in the air environment, an air deflector that contributes to reducing the negative impact of aerodynamic resistance, reducing the turbulence of air masses and improving the efficiency of current collection.

Three-dimensional CFD analysis of PHWR exposed core under postulated severe accident condition

A three-dimensional steady-state thermal–hydraulic analyses of a large sized Pressurized Heavy Water Reactors (PHWRs) with varying levels of exposure is carried out for degraded core heat transfer assessment and presented in this paper. Low-frequency postulated severe accident without mitigating actions leads to exposure of fuel channels in PHWRs. Such exposure of fuel channels leads to their heat-up, governed by interdependent heat transfer mechanisms such as radiation, convection and conduction heat transfer and thermo-chemical interactions among the core constituents. In order to understand such complex behavior and plan the severe accident management guidelines, numerical analyses of the exposed core are of necessary. This paper illustrates the influence of the temperature and velocity profiles vis-à-vis different regions of the exposed core on the fuel channel heat-up. The interesting interdependency of convection and radiation heat transfer on fuel channel heat-up is reported. The dominance of convection heat transfer is observed for initial exposures of the fuel channels. However, the advanced stages of fuel channel exposures are observed to be dominated by radiation heat transfer. Intriguingly, it is observed that the convective cooling of exposed fuel channels by steam flow is counter-acted by exothermic heat generation from Zircaloy-made calandria tube surface and steam interaction. This leads to supplemental power addition for fuel channel heat-up. Moreover, it is interesting to note that the heat-up of fuel channels is restricted to central regions of the exposed core due to degraded steam cooling and higher-powered fuel channels. It is worth noting that fuel channel disassembly is observed in the advanced levels of fuel channel exposures. Moreover, fuel channel length equivalent to nearly 7–8 fuel bundle lengths undergo disassembly depending upon the fuel channel elevation and location in the core. The calandria vault water is observed to undergo film boiling at the onset of fuel channel disassembly.

Improving the Design of a Multi-Gear Pump Switchgear Using CFD Analysis

Gear pumps are hydraulic machines capable of transferring energy and performing work in pumping fluid. This study presents an analysis of the hydrodynamic model of an external multiple gear pump in order to analyze the fluid flow in combinations of single and different viscosities at the same and different pressures and speeds. Solidworks Flow Simulation 2016 was used to analyze fluid flow. When the radius of the rounding on the collector inner surface is increased from 3 to 15 mm, the pressure drop decreases by 13%. When the radius of the manifold is 3 mm, cavitations are observed. With a liquid distribution system with four input ports and one outlet port in the top cover, the gear pump can handle liquids of viscosity classes 5 to 10. The speed should not exceed 1200 rpm if the liquid has a kinematic viscosity of 10 cSt. The pressure drop and velocity distribution of the liquid in the pressure and suction lines are the same. When the speed changes from 400 to 1200 rpm, the pressure drop increases five times, and the velocity increases three times. At a constant speed of 1000 rpm and an inlet pressure of 10 MPa but with different viscosities, the pressure drop decreases 8 times, and the speed increases 1.5 times. When the inlet pressure is 6 to 24 MPa, with constant speed and the same viscosity, the pressure drop and fluid velocity practically do not change. The dependence of pressure drop on the number of revolutions and radius of the rounding of the inner surface of the collector is statistically significant.

Investigation of CO2 emissions reduction for a 150 m electric catamaran by CFD analysis of various hull configurations

Investigation of CO₂ emissions reduction for a 150 m electric catamaran by CFD analysis of various hull configurations

Simultaneous improvements of thermal efficiencies and smoke emissions in semi-premixed diesel combustion with dual-injectors and a spatially divided combustion chamber

To simultaneously establish the high thermal efficiencies and the low smoke emissions in the semi-premixed diesel combustion with a twin peaked heat release consisting of the first-stage premixed combustion and the second-stage spray diffusive combustion, a combination of dual-injectors and a newly designed divided combustion chamber was proposed and the combustion characteristics were investigated. The divided chamber with a lip at the middle of the side wall can prevent the second fuel spray from entering the burned region of the premixture from the first-stage injection, realizing a suitable spatial distribution of spray flames and suppressing the soot formation. The dual-injectors can independently provide the fuel sprays into the upper and the lower layers of the divided chamber with the optional quantities and timings for the first and second injections, establishing the optimum combustion phasing. The distributions of the equivalence ratios and the soot formation characteristics in the divided chamber as well as in an ordinary re-entrant chamber as a reference were analysed with CFD simulations, showing that the soot formation is smaller in the divided chamber. The second-stage spray diffusive combustion is improved as well as the late afterburning and the combustion duration are reduced with the suppression of interference between the spray flames in the divided chamber. The cooling loss in the divided chamber is smaller due to the weaker gas motion and the lower heat transfer coefficient. The experiments also showed that the thermal efficiencies are better and the smoke emissions are lower in the divided chamber at medium loads. However, at higher loads, the smoke emissions increase due to the offset injector arrangement, and the CFD analysis showed that lower smoke emissions can be expected with optimization of the injector arrangement to locate the injector for the second fuel injection at the centre of cylinder.

RANS study of surface roughness effects on ship resistance

Abstract In marine engineering, optimizing the performance of vessels is a key issue, particularly in increasing fuel efficiency, reducing operating costs, and minimizing environmental impact. One of the most critical determinants of vessel efficiency is hull resistance, which directly affects fuel consumption, power requirements, and cruising speed. We aim to investigate how surface roughness affects hull flow resistance, to quantify the drag variation at different surface roughness levels using special wall functions that reproduce boundary layer dynamics. This approach involves the complex interaction between the intricate complexity of roughness and the nonlinear pressure drag effects on the hull. The KVLCC2 ship model is used as a representative prototype in the CFD analysis based on the RANS equations and the k-omega SST model to independently evaluate the roughness effects on individual ship sections. The comparative analysis with empirical data reveals the complex relationship between surface roughness and ship resistance and provides insights for ship design and operational improvement. The study investigates the interaction between drag coefficient and vessel performance to improve hydrodynamic efficiency.

시뮬레이션 시간 단계에 따른 FOWT 서지방향 항력계수 결정에 관한 CFD해석 연구

시뮬레이션 시간 단계에 따른 FOWT 서지방향 항력계수 결정에 관한 CFD해석 연구

Multi-field coupling vibration patterns of the multiphase sink vortex and distortion recognition method

Fluid-induced vibration sensing technology plays an essential role in the safety and stable operation of fluid control equipment. The sensing works oriented to the multiphase sink vortex-induced vibration (MSVIV) face significant challenges in state recognition, such as the aero-engine oil pipe, metallurgical casting ladle, and microfluidic equipment. This paper presents a multi-field coupling vibration modelling and solving strategy to investigate the MSVIV transition patterns. Based on the volume of fluid and level set method, an efficient volume-correction strategy is presented to consider the mass variation and keep velocity fields without divergence. Then, a fluid–structure-acoustic dynamic model is conducted to explore multiphase vortex transport regularities. Considering the solution singularity of the fluid–solid-acoustic coupling system, a residue theorem-based solution strategy is presented to obtain the MSVIV evolution behaviors. Finally, a multichannel sensing MSVIV water-model experiment (MSVIV-WME) platform is conducted to verify the above results, and a wavelet transform-based processing approach can be utilized to obtain mutation energy features. Research results illustrate that the proposed strategy has revealed the MSVIV transition behaviors. The MSVIV process in critical states dominates nonlinear vibration patterns. The self-development sensing platform can monitor the MSVIV evolution process in real-time, and the wavelet transform-based sensing attribute with the dw3 frequency band can identify distortion characteristics. Relevant results can offer useful references for MSVIV state recognition and offer technical solving strategies for microfluidics monitoring equipment.

Numerical and experimental studies of airflows at exhaust hoods with inlet extensions

Local exhaust ventilation is used to capture contaminants and maintain a comfortable atmosphere in premises. Exhaust hoods with extension units (canopy hoods) are commonly used in open-type local exhaust devices. The goal of this study was to use computational and experimental methods to determine the effect of adding an extension to a local exhaust hood on the separated-flow streamlines, vortex zones, exhaust velocity distribution, and local drag coefficient. We used the discrete vortex method together with computational fluid dynamics to investigate air flows near round and slotted extended exhaust hoods. We then compared the computed airflow velocity field, vortex zone outlines at the inlet of a local exhaust hood, and local drag coefficient factor with data from a field experiment. Outlines of vortex zones resulting from flow separation at the inlet of the hood were considered for a hood length of 5 times gauge (the radius of a round hood or half-width of a slotted exhaust hood), hood tilt angles of 90°, 75°, 60°, 45°, and 30°, and extension lengths of 0; 0.5; 1; and 2 times gauge. We found that longer extensions caused the first vortex zone to enlarge, and the contaminant capture velocity of the local exhaust hood to decrease. We identified the behavior of the local drag coefficient at various hood tilt angles, extension lengths (as listed above), and hood lengths (including 2, 3, and 5 times gauge), and translated them into equations for computing the local drag coefficient.

Numerical Investigation of Model Support, Closed Engine Nacelle and Scale Effect on a Wind Tunnel Test Model

In the frame of the H2020 MORE&LESS project co-funded by European Commission, a test campaign for a hypersonic vehicle demonstrator took place at the INCAS Trisonic Facility. CFD analysis was used to quantify the effects of the wind tunnel model support, the closed engine nacelle, and to perform the Reynolds number extrapolation. Three sets of simulations were used in order to generate the corrections. The wind tunnel configuration with sting, sting cavity, and closed nacelle was used as the baseline, with the aim of matching the experimental results as precisely as possible. A configuration with a flow-through nacelle and the shock cone in the appropriate position for each Mach number and no sting or cavity was used to determine the effect of the sting and the closed nacelle. For the Reynolds extrapolation, a 1:1 model was used, with the boundary conditions deriving from the theoretical trajectory of the vehicle. The CFD results for the wind tunnel configuration closely align with the experimental data. Significant differences between the three configurations can be observed just for the pitching moment, and those are caused by the presence of the sting and the open nacelle. The difference in Reynolds number does not seem to have a significant effect on the aerodynamic coefficients.

CFD analysis in effects of spacer-vane on thermal–hydraulic performance of two-phase flow in annular channel

Spacer performs a key function in the construction of nuclear rod assembly. It is utilized to ensure the appropriate spacing and firmness of the rods in assembly. In rod bundle structures, spacers are typically incorporated with vanes to promote turbulence and improve heat transfer. The aim of this work is to analyze the impacts of spacer-vane on the thermal–hydraulic performance of two-phase flow in an annular channel. CFD model of an upward flow annular channel with spacer-vane has been developed. In addition, an annular channel model with a spacer but without vane has been generated and modeled in order to examine the impact of the spacer-vane in a two-phase flow. Transient simulations were performed with flow considerations of mass flux 714.4 kg/m2s, liquid temperature 330 K, volume fraction 0.35, heat flux 197.2 kW/m2, and atmospheric pressure conditions. CFD results have been validated with experimental data. Results show that the core zone of the annulus gap exhibits the highest level of turbulent intensity, and the outer pipe wall temperature is lower for spacer-vane relative to spacer alone. It is observed that the majority of water vapor is concentrated at the center of the channel in the farthest downstream location.

Effect of Injector Type and Intake Boosting on Combustion, Performance, and Emission Characteristics of a Spray-Guided Gasoline Direct Injection Engine—A Computational Fluid Dynamics Study

<div>In general, GDI engines operate with stratified mixtures at part-load conditions enabling increased fuel economy with high power output, however, with a compensation of increased soot emissions at part-load conditions. This is mainly due to improper in-cylinder mixing of air and fuel leading to a sharp decrease in gradient of reactant destruction term and heat release rate (HRR), resulting in flame quenching. The type of fuel injector and engine operating conditions play a significant role in the in-cylinder mixture formation. Therefore, in this study, a CFD analysis is utilized to compare the effect of stratified mixture combustion with multi-hole solid-cone and hollow-cone injectors on the performance and emission characteristics of a spray-guided GDI engine.</div> <div>The equivalence ratio (<i>ϕ</i>) from 0.6 to 0.8 with the constant engine speed of 2000 rev/min is considered. For both injectors, the fuel injection pressure of 200 bar is used with 60° spray-cone angles. For lean boosting conditions, intake pressures of 1 bar, 1.2 bar, and 1.4 bar are maintained for 0.8 equivalence ratio cases for both injectors. Results from the CFD analysis are compared with those of the available experimental results with good agreement. Analyzing the results, naturally aspirated and intake boosting conditions for <i>ϕ</i> of 0.8, mixture distribution and flame propagation for the multi-hole solid injector are better than hollow-cone injector. Also, for the <i>ϕ</i> of 0.8, naturally aspirated mode, the soot emissions by the hollow-cone injector are higher by about 90%, and the NO<sub>x</sub> emissions are higher by about 19% compared to that of the multi-hole solid-cone injector. Under boosted intake pressure conditions, for the hollow-cone injector, the soot emissions are higher by about 97%–99%, and NO<sub>x</sub> emissions are higher by about 7%–6% compared to the multi-hole solid-cone injector. Also, HC and CO emissions are considerably lower for the hollow-cone injector than that of the multi-hole solid-cone injector.</div>

Experimental investigation of BIPV/T application in winter season under Şanlıurfa's meteorological conditions

AbstractConsidering that nearly 39% of the total CO2 emission released into the atmosphere today are thought to be due to the energy consumed by buildings, the importance of taking measures through buildings to combat global warming is evident. Therefore, the concept of nearly zero‐energy buildings (NZEB) is come to the forefront. Building integrated photovoltaic thermal (BIPV/T) systems are used to enable buildings to generate their own energy. However, buildings have limited facade and roof areas required for BIPV/T systems. Therefore, in this study, various configurations of bifacial (double‐sided) and monofacial (single‐sided) panels were compared to investigate ways to enhance the efficiency of BIPV/T systems. Different air flow velocities and varying air gap distances were tested for both panel types. By placing a reflective surface on the wall behind the bifacial panel, the electrical efficiency of the bifacial panel was increased and proven through PVsyst analysis. Both panels provided maximum heat efficiency at the shortest air gap distance under high air flow conditions. In addition, it was shown in both the experimental setup and Comsol CFD analysis that it provides significant benefit in the thermal energy load of the building when heating the interior environment in winter. In terms of electrical power production surplus, the bifacial panel outperformed the monofacial panel in all configurations, with a minimum advantage of 8.33% and a maximum of 12.73%. Additionally, the maximum electrical efficiency was obtained from the bifacial panel in configurations with the longest air gap distance. Using the bifacial panel in the BIPV/T system with the shortest air gap distance during the heating season and the longest air gap distance during other seasons can provide the highest efficiency for the building throughout the year.

Effect of Cavity Geometry and Location on Base Pressure in a Suddenly Expanded Flow at Mach 2.0 for Area Ratio 3.24

The primary goal of this study is to use CFD analysis to investigate the impact that a cavity has on the pressure at the base of a structure. In this analysis, we took into account the NPR, the cavity aspect ratio, and the cavity position. In this case, the area ratio is 3.24 and the Mach number is 2.0. Simulations were run with L/D ratios between 1 and 6, and NPRs of 3, 5, 7.8, 9, and 12. The 2-dimensional model was developed using ANSYS Fluent's Design Modeler. The nozzle is operating at Mach 2.0. Base pressure and wall pressure in the duct were the primary research foci. The C-D nozzle was created for this research. ANSYS Fluent was used to verify the CFD findings. When the nozzles are under-expanded and the cavity is at 0.5D, passive control as a cavity is shown to be effective. It appears that 1D is the bare minimum for duct length. Because the shear layer gets reattached to the duct wall at 1D and the boundary layer grows after reattachment, passive control is not observed in the flow process regardless of whether the cavity is located at 1D, 1.5D, 2D, or 3D. An oscillating base pressure is seen at shorter duct lengths. This phenomenon does not occur at longer duct lengths. Whether or not there are cavities in the duct, the flow field is the same.

Towards vortex-based wind turbine design using GPUs and wake accommodation

Vortex methods are often cited as a promising alternative to the classical Blade Element Momentum (BEM) theory for wind turbine design, overcoming some of its limitations such as imposing steady-state, uniform, and aligned inflows. BEM assumptions are being questioned, especially for large rotors with very flexible blades or even floating wind turbines. However, vortex methods are not yet widespread due to their computational costs. The following work demonstrates how free vortex wake methods using filament discretizations can become an affordable and viable alternative to BEM. This is achieved by combining filament number reduction as well as graphical processing units (GPUs) computations. The efficiency and accuracy of the proposed approaches are demonstrated against simple test cases, including an elliptical wing and a rigid horizontal axis wind turbine (HAWT). Finally, the approaches are applied to the aero-hydro-servo-elastic simulation of floating horizontal axis wind turbines.

CFD analysis of flow over ogee spillway with varying upstream face slope

CFD analysis of flow over ogee spillway with varying upstream face slope

CFD analysis of local influences in offshore wind measurements employing a floating LiDAR system

In the present work, the CFD modeling of neutral and stable atmospheric boundary layers regarding the horizontal homogeneity condition is discussed to assess the impact of local influences in wind measurements made by a Light Detection and Ranging (LiDAR) remote sensor installed at an offshore site. The LiDAR will be mounted on a real floating, production, storage, and offloading (FPSO) vessel, 200 km far from the coast, and the simulations serve as preliminary study for the impact of the geometry presence, in the air flow and in the measurements taken by the LiDAR. The reproduction of the homogeneity condition is discussed and the impacts of the presence of the ship structure are quantified considering the scanning scheme of the LiDAR. Turbulence is modeled with the k-ε and k-ω models for the neutral case, and k-ε with a modification following the Monin-Obukhov Similarity Theory for the stable boundary laye. By carrying out simulations with empty and blocked (i.e., with the FPSO installed) domains, we show that the effect of the platform is local and only significant at small heights. The neutral and stable cases show similar deviations (≤ 2 %) between the velocity fields in the blocked and empty domains. The neutral case shows locally a little more impact than the stable case, and the reason for that is discussed. We also found that the LiDAR scanning scheme could attenuate the impacts of the flow distortion in comparison with direct punctual measurements.

A CFD Analysis of Oscillating Airfoil with Leading Edge Roughness: Comparing Correlations for Equivalent Sand Grain Roughness

Numerical simulations express surface roughness as equivalent sand grain roughness values, so the correlation is required to convert realistic roughness into equivalent sand grain roughness values. The correlations were designed to match the wall velocity distributions for static cases with roughness, and they accurately predicted roughness effects when applied to URANS simulations. Several studies have examined the roughness effect on dynamic pitching airfoils. Still, they have only considered the presence of roughness, neglecting the process of converting the actual roughness to equivalent sand-grain roughness. Thus, in the present study, we apply a static case-based equivalent sand-grain roughness correlation to dynamic pitching analysis to validate the suitability of each correlation and verify the significance of correlation parameters. It was observed from a comparison study between numerical aerodynamic coefficients and experimental data from Ohio State University that physical parameters such as skewness and roughness height were important parameters to predict the dynamic stall behaviour more accurately. It was also observed that dynamic stall prediction accuracy is affected by the frequency and type of airfoil, and through this, it was confirmed that there are additional factors to consider when using an equivalent sand grain roughness correlation on pitching airfoils.