CFD Tools Research Articles

Performance evaluation of an integrated heatsink and thermoelectric module by two-way coupled numerical analysis

Experimentally validated numerical models contribute to the literature and provide clues to researchers. In recent years, thermoelectric coolers have come to the fore as an alternative to existing cooling systems. The effect of the geometric parameters of a heat sink (wave amplitude, wave width, and wavelength) and the parameters of a thermoelectric module (conductor thickness, solder thickness, and the leg lengths of P and N type) are investigated parametrically. The numerical study has been carried out by coupled CFD and Thermal Electric tools and validated with experimental data. The three-dimensional model has consisted of a heat sink with converging diverging channels integrated with a thermoelectric module. It has been investigated by the numerical model how the specified design parameters of the heat sink and thermoelectric module affect the cooling performance of the fluid flowing through the heat sink. Evaluation of the results has been made according to the temperature of the fluid out of the heat sink, the bottom temperature of the heat sink, the current produced on the thermoelectric module and the heat transfer coefficient. The results showed that the parameters have an effect on the thermal performance, but their effect on the current change is limited.

Determination of the Gas Plenum Temperature of the P2M Instrumented Fuel Rodlets on the Basis of a Thermal-Hydraulic Study of the Belgian Reactor 2 Pressurized Water Capsule

To refine knowledge about pressurized water reactor fuel melting, the Power to Melt and Maneuverability (P2M) project in the Framework for Irradiation Experiments II (FIDES-II) managed by the Nuclear Energy Agency of the Organisation for Economic Co-operation and Development aims to perform two irradiation tests to reach fuel centerline partial melting using instrumented experimental fuel rodlets irradiated in a pressurized water capsule (PWC) of the Belgian Reactor 2 (BR2) [Studiecentrum voor Kernenergie (SCK CEN), Belgium]. Prior to these experiments, two preliminary tests will be performed in the PWC for qualification purpose toward safety. The experimental rodlets will be instrumented with a fuel centerline thermocouple in the lower part of the fuel and a pressure sensor (PS) in the upper part. An objective of the P2M experiments is to determine the amount of fission gas released from the fuel thanks to the PS measurement. The plenum pressure evolution is known from the measurement, and knowledge of the gas plenum temperature is required to determine the amount of fission gas released from the fuel to the plenum. The gas plenum temperature will depend on natural convection of the PWC coolant, and no temperature measurement will be possible within this gap during the test. This paper describes the setting up of a model of the BR2 PWC equipped with the P2M rodlets based on the coupled NEPTUNE_CFD (multiphase fluid calculation code) and SYRTHES (solid thermal module) simulation tools. Simulations performed thanks to this model allow assessment of the thermal-hydraulic (TH) behavior of the pressurized water in the capsule and the thermal behavior of the rodlet, in particular, regarding the temperature of the gas located in the plenum. For consistency of the results, computations presented in this paper were performed using a single and consistent set of TH models. A mesh sensitivity analysis was carried out for all the studied cases. Simulation results related to the water capsule behavior were found to be in good agreement with the available experimental data. The gas plenum temperature results obtained from this study will be used to assess the fission gas release during the test from the plenum pressure measurements. Overall experimental validation of fission gas release during the test will be possible after the transient test in BR2 based on the postirradiation examination program foreseen on the rodlets at the LECA-STAR facility [Commissariat à l’énergie atomique et aux énergies alternatives (CEA) Cadarache, France].

Efficient Gas Leak Simulation Surrogate Modeling and Super Resolution for Gas Detector Placement Optimization

This study introduces an innovative framework that utilizes a limited number of sensors to detect chemical leaks early, enabling a timely and appropriate initial response. Consequently, it mitigates the risk of major industrial disasters. This framework integrates a surrogate model based on differentiable physics with a sensor placement optimization tool. Particularly noteworthy is that the surrogate model provides faster results compared to traditional CFD tools and seamlessly integrates with a CNN-based deep learning model, yielding higher-resolution outputs. This enhances the feasibility of practical application compared to conventional methods. Sensor placement optimization employs MINLP, considering various constraints to achieve more precise optimization. The proposed framework offers an innovative approach to address industrial safety concerns by enabling early chemical leak detection and facilitating timely responses, ultimately reducing risks like fires, explosions, and toxic incidents.

Wind tunnel testing of a Formula Student vehicle for checking CFD simulation trends

The aerodynamic performance analysis of Formula Student racecars has been mostly done by teams with CFD tools, for time and cost savings, that often lack proper validation. To address this, the FST Lisboa team performed a detailed wind tunnel (WT) test campaign, using a one-third scale model, under different configurations, including variable ride heights, bullhorn appendix, and rear wing flap settings, also replicated in CFD. The simulations used RANS with the SST k-omega turbulence model, with a 13.7 million polyhedral mesh for the test chamber region domain. Both experimental and numerical errors were estimated from the instrumentation and mesh convergence analysis, respectively. Comparisons were made between WT and CFD both in terms of local flow, using tufts for flow visualization, and global flow, using lift, drag, and pitching moment coefficients. Overall, the numerical streamlines agreed very well with the orientations of the tufts in experiments, but some discrepancies were found in regions of cross-flow and high-frequency unsteadiness, mainly caused by limitations of the visualization technique. The gamma transition model in CFD was abandoned as it could not replicate the WT observations. In terms of aerodynamic coefficients, a strong correlation was found between WT and CFD. The parametric studies revealed that the simulations captured the experimental sensitivity to each car setting parameter studied but the uncertainties did not enable a full quantitative evaluation of the aerodynamic performance. The drag reduction system significantly impacted the aerodynamic balance of the racecar, while the current bullhorn design proved to be ineffective. The ride height increase led to higher downforce, mostly due to the higher pitch angle of the vehicle, with negligible variation of the aerodynamic balance. This work validated the team CFD studies, building confidence in that trends estimated in numerical parametric studies are likely to be translated to the real prototype performance.

Design and optimisation of an Intra-Aortic Shrouded rotor axial pump

Undesirable side effects in patients with a LVAD (Left Ventricular Assist Device) pump fitted include blood damage, thrombosis, blood traumatisation, and End-Organ Disfunctions. These side effects have generally been attributed to the high wall shear stresses and the induced turbulent flow. In this study, we introduce a novel design to address these effects by lowering the rotational speed and providing an optimum flow path design to minimise blood damage. We present an initial scheme for a new Intra-Aortic Shrouded Rotary Axial Pump and develop a sequence of pump geometries, for which the Taguchi Design Optimisation Method has been applied. We apply CFD tools to simulate the pressure rise, pump performance, hydraulic efficiency, wall shear stress, exposure time and mass flow rate. A prototype pump has been tested in a mock cardiovascular circuit using a water-glycerol solution. The optimum design delivered the desired pressure/mass flow rate characteristics at a significantly low rpm (2900 rpm). As a result, the estimated blood damage index is low, matching the design requirements. The theoretical performance was matched by experimental results.

Numerical Simulation of Erosion in Pelton Spear Valve at Different Openings

The spear valve is one of the most eroded hydro-mechanical components of the Pelton turbine operating in sediment-laden conditions. The spear valve is used to regulate or control the flow. In a multi-nozzle system, though having the same design, the spear valves show varying erosion patterns and intensities. The only difference was found to be the openings of the nozzle/spear valve. This demonstrates that there is some sort of connection between the nozzle opening and the erosion of the spear valve. The difference in erosion intensity in different spear valves can be seen on the site but the underlying phenomenon behind the erosion needed to be studied numerically. In this research, erosion patterns were numerically investigated using an open-source CFD tool, OpenFOAM. For this simulation, the sediment particles and their properties were incorporated into the flow using the built-in Lagrangian library of the OpenFOAM. To investigate the erosion in real time, a transient simulation was undertaken for various nozzle openings. This study only focuses on the erosion at the tip of the spear valve neglecting other parts of the nozzle. This study demonstrates that the erosion in the tip of the spear valve increases with the restriction in flow.

Investigations on Multiple Injection Strategies in a Common Rail Diesel Engine Using Machine Learning and Image-Processing Techniques

<div>The present study examines the effect of the multiple injection strategies in a common rail diesel engine using machine learning, image processing, and object detection techniques. The study demonstrates a novel approach of utilizing image-processing tools to gain information from heat release rates and in-cylinder visualizations from experimental or computational studies. The 3D CFD combustion and emission predictions of a commercial code ANSYS FORTE© are validated with small-bore common rail diesel engine data with known injection strategies. The validated CFD tool is used as a virtual plant model to optimize the injection schedule for reducing oxides of nitrogen (NO<sub>x</sub>) and soot emissions using an apparent heat release rate image-based machine learning tool. A methodology of the machine learning tool is quite helpful in predicting the NO–soot trade-off. This methodology shows a significant reduction in soot and NO emissions using a pilot–main–post-injection schedule of 25% pilot, 25% post-, and 50% main injection, compared to a baseline pilot–main injection schedule. In addition, this work attempts a robust and high-fidelity optimization of the fuel injection schedule using the random forest algorithm for predicting the NO and soot emissions using 73 simulations done with different pilot–main and pilot–main–post-injection strategies on a small-bore diesel engine. Further, the object detection algorithm is trained on simulation data from the small-bore engine for detecting the interaction between the developed combustion from the pilot or main with sprays of subsequent injections using in-cylinder 3D CFD simulation and experimental data. A small-bore engine dataset shows that the trained object detection algorithm successfully corroborates the simulation and experimental data interaction. This investigation, therefore, presents a novel application of object detection methodology by automating the process and providing a general-purpose object detection algorithm. This approach can be used on any new simulation or experimental data for automated detection of the spray–thermal zone interaction without human intervention.</div>

Effect of the heat flow distribution and thermophysical properties of the pipe wall and fluid on the wall temperature response to a rising Taylor bubble

A novel non-intrusive thermal diffusion measurement (TDM) method has been proposed for measuring the phase flowrates of gas–liquid slug flows in our previous research. Since the structure of TDM was arbitrarily designed and needed to be optimized for accurate measurement, the effect of the heat flow distribution and the thermophysical properties of the pipe wall and fluid on the wall temperature response to a rising Taylor bubble (TB) is further investigated by using the CFD tool in this paper. The wall temperature and temperature rise are used to describe the wall temperature response, and their variation rules with heat flow distribution and the thermophysical properties of the pipe wall and fluid are presented and analyzed based on heat transfer. The simulation results indicate that the optimal heating length for a large wall temperature rise and small power consumption is 0.6D, and the optimal pipe material should be with small density and specific heat and a suitable thermal conductivity of about 15 W/(m·K). Moreover, the wall temperature response is obvious, especially for TBs moving in the liquid with large fluid thermal conductivity, density, and specific heat, and small viscosity. The paper can clarify the wall temperature response mechanism of the heated pipe wall and provide a theoretical basis for the development of the TDM method.

Structural parameters of Wrench – C shape building using CFD

Wind flow pattern and generation of strong and large eddies is mainly responsible to the wind pressure and suction intensity in and around the tall building. If the shape of the structure is not vary common then the wind generated effects need to evaluate for the high rise structure this is because of the reason that the data for the regular plan cross sectional shape is available in the various international standards. This study investigating the wind effects on irregular cross sectional shape tall building using CFD tool ANSYS CFX. The current study evaluates the wind impacts for a boundary layer atmospheric wind flow from 0° to 180° at a 15° interval. The power law described in IS: 875 (Part 3): 2015 for terrain category II follows the wind profile. For a rectangular model, the values of the pressure coefficients are compared using the numerical simulation and the information supplied in IS 875. Results are given at numerous locations, including pressure coefficients around the building model’s periphery and force and moment coefficients for wind incidence angles ranging from 0° to 180° at 15° intervals.

Numerical investigation of store separation from cavity problems at high speeds

In this work, the ability of open-source CFD tools to conduct store separation simulations from cavities is evaluated and validated using a generic test case from the literature. Firstly, the ability and accuracy of these tools for solving cavity flows at high speeds are evaluated. Secondly, their competence in predicting the trajectory of a generic store from a generic deep cavity is checked. Finally, and in order to reduce the associated computational costs, a release-time dependability factor from the recent literature is studied and evaluated. The obtained results using the selected open-source CFD tools matched quite well with the wind tunnel results. Furthermore, the results show that predicting the release-time dependability using a quantified index/factor can be a potential remedy for reducing the computational cost for this type of CFD simulations.

Local instantaneous heat transfer characteristics around a rising single Taylor bubble and the temperature response of relatively thick pipe wall under local constant heat flux

A novel non-intrusive thermal diffusion measurement (TDM) method is proposed to measure the flow rate of gas–liquid two-phase flows under the slug flow state in our previous research. To improve the measurement accuracy of TDM by clarifying the real-time correspondence between wall temperature change and Taylor bubble (TB) location, the local instantaneous heat transfer characteristics around a rising single TB and the corresponding temperature response of the pipe wall are further investigated in detail by using the CFD tool in this paper. During the passage of TB, the local heat transfer between the pipe wall and fluid was analyzed based on the dynamic velocity field and temperature boundary layer, and the temperature on the fluid–solid interface presents the opposite trend with the heat transfer coefficient. For the zone upstream of the heat flux center, the lag time and increase of the wall temperature become large and weak along the radial direction, respectively, whereas the lag time is independent of the axial location, TB velocity, and TB length. Meanwhile, the increase in wall temperature shows an upward trend with the TB length for short TBs but is the same for long TBs.

Comparative analysis of 2D simulations and isentropic equations for compressible flow in experimental nozzles

Experimental studies for supersonic airflow in different supersonic nozzle geometries are recurrent, and the turbulence of the flow can be reproduced with the CFD tool by applying the RANS model and suitable turbulence models. The objective of this investigation is to carry out a comparative analysis of 2D numerical simulation curves for viscous flow with averaged data against equation curves for quasi-one-dimensional isentropic flow, for three experimental supersonic nozzle geometries that are used in the laboratory, for the flow condition without the presence of shock waves in the divergent. For the numerical simulations, three computational domains were discretized with structured grids, the Spalart-Allmaras turbulence model was used, and the Sutherland's law equation was used for the viscosity as a function of temperature. The results of the curve trajectories for Mach number, pressure and temperature obtained with averaged data from the 2D simulations are close to the curves of the analytical and empirical equations for isentropic flow. It is concluded that the numerical error of the total temperature for the planar nozzle with 𝛼𝛼 = 11.01° and NPR = 8.945 reports 0.008%; for the conical nozzle with 𝛼𝛼 = 15° and NPR = 14.925 it reports 1%; and, finally, for the conical nozzle with 𝛼𝛼 = 4.783° and NPR = 7, it reports 0.04%.

Motion Modelling of the Floating Bushing in an External Gear Pump Using Dimensional Analysis

A new approach to model the motion of floating bushings in external gear pumps is presented in this article, where lubrication conditions have been introduced using dimensional analysis. This model is based on Bond Graph diagrams and has been experimentally validated in lab tests measuring the movement of the floating bushing inside the gear pump by means of laser micrometers. The novelty of this research is the creation of a simple and experimentally validated tool for the behaviour study of these types of pumps, which allows the simulation of a dynamic rigid solid in a fluid boundary with clearances of the order of microns, without using powerful CFD tools, with very short execution times, and using conventional computational tools. The qualitative behaviour of the model with respect to the experimental results is very similar, adjusting the numerical values with very acceptable accuracies by taking into account the precision of the experimental measurements, and allows us to use the model to interpret the volumetric and mechanical efficiency variations according the operating conditions.

Analysis of a Marine Propeller using Panel Method

In the recent past National Science and Technological Laboratory (NSTL) has taken up work in Naval CFD for high-speed submerged vehicle and weapon applications. In this paper a problem handled at NSTL using CFD tools in conjunction with the model tests on some cases of submerged body propulsor design will be described and the advantages of such a method will be highlighted. A code developed by National Aerospace Laboratories (NAL) using constant source and doublet distributions, has been used for the analysis and the results have been compared with model tests carried out in the High Speed Towing Tank (HSTT) at NSTL.

Cfd Tools as Applied to Indian Combat Aircraft Configuration-an Experience

Computational Fluid Dynamics (CFD) tools are extensively used by aircraft industries all over the world in design and development of airplanes, with emphasis on reducing both the cost and design cycle time. This paper deals with the use of CFD tools at Aeronautical Development Agency (ADA) in design and development of Indian combat aircraft. The applications include: (1) evaluation of incremental changes in aerodynamic configuration, (2) wave drag evaluation, (3) aerodynamic loads, (4) flow field around air data sensor locations, (5) Euler calculation for coupled internal and external flow field, and (6) viscous computation of high angles of attack flows. In the initial design phase, codes based on the potential theory were used for wing design and fuselage shape optimization. Later indigenously developed Euler and Navier-Stokes codes were employed for the various applications. This paper brings out the strength and weakness of CFD as experienced at ADA and its comparison with the Wind Tunnel and Flight Data.

Application of Flexible Tools in Magnesia Sector: The Case of Grecian Magnesite

In this paper, two flexible model tools (CO2 emissions/cost tool and CFD tool) that simulate the production process of Grecian Magnesite (GM) and extract economic and technical conclusions regarding the substitution of fossil fuels with various types of biomass are presented and analyzed. According to the analysis, the higher the substitution, the higher the profit in both CO2 emissions and cost reduction. The reduction in CO2 emissions that can be achieved through biomass fuel substitution ranges from 15% for a 30% substitution to 35% for a 70% substitution. Accordingly, production costs are also reduced with the use of biomass. The initial results of this decision-making cost tool showed that the most profitable solution is a 70% substitution, for which production costs can be reduced by up to 38.7%, while the most beneficial type of biomass proved to be the olive kernel. A proposed and feasible solution is the substitution of 50% sunflower husk pellets, which will result in a reduction of 25% in CO2 emissions and almost 10% in production cost. From CFD simulation, a reduced order model (ROM) has been developed that allows the running of scenarios in real time, instead of the usual long times required by complex simulations. Comparative studies of fuel blend and biomass type can be carried out easily and rapidly, allowing one to choose the most suitable substitution.

Endoscopic balloon dilation of a stenosed artery stenting via cfd tool open-foam: Physiology of angioplasty and stent placement

The blood flow analysis inside an arterial segment of the left main coronary artery having stenosis is mathematically modeled. Numerical simulations are provided for the very first time for two considered cases that cover the thorough process of angioplasty and stent placement inside a coronary artery having symmetric stenosis. Firstly, the numerical simulations are disclosed for the section of a stenosed artery having a catheter placed inside it with a balloon plus stent over it. The second case covers the numerical simulations of blood flow inside the artery after a stent is placed that keeps the artery wide open and minimizes the effect of stenosis. Thus, the prime novelty of this work entertains the thorough mathematical modeling and FVM based numerical simulations for angioplasty of a coronary artery having a symmetric shape of stenosis. The current research work is modeled for the non-Newtonian Casson fluid to consider a more realistic approach of blood flow. This computational fluid dynamics (CFD) analysis is interpreted through the free source CFD C++ toolbox Open-FOAM. Numerical solutions are provided by using Open-FOAM that works on the principle of finite volume method. The detailed graphical results are disclosed for the process of angioplasty in addition to the simulation work obtained after completion of angioplasty and stent placement. The work provided is beneficial for surgical interpretations, detecting location of stenosis, place the balloon and stent at exact location via catheter, minimizing the effect of stenosis by placing a stent inside the artery, reducing the experimental cost by using simulations data. The catheter and balloon is removed after angioplasty, and the stent keeps the artery wide open to normalize the blood flow. Eventually, the coronary artery disease (CAD) is cured through this angioplasty and the risk of a heart attack is eliminated. A more developed and easily passing blood flow is revealed after the placement of stent.

Combined Effect of Fluid Cavitation and Inertia on the Pressure Buildup of Parallel Textured Surfaces

A mathematical model is developed to investigate the combined effect of fluid cavitation and inertia on the fluid pressure buildup of parallel textured surfaces. The fluid cavitation is analyzed using the Rayleigh–Plesset model, and the fluid inertia is analyzed with an averaged method. The finite element method and Newton-downhill method are employed to solve the governing equations. The numerical model is validated by comparing the experimental and numerical results, and the combined effect of fluid cavitation and inertia on the fluid pressure buildup is analyzed and discussed. The research indicates that the cavitation weakens the fluid inertia effect on the pressure distribution at the inlet area of textures. The fluid inertia greatly enhances the hydrodynamic effect and effectively limits the excessive extension of the low-pressure zone caused by cavitation. The fluid cavitation and inertia, especially their interaction, significantly affect the fluid pressure buildup and generate a net load-carrying capacity (LCC). The numerical model with the fluid inertia and cavitation is more time saving than the commercial CFD tools in solutions, which gives a novel and optional HD foundation for developing a more efficient and accurate THD or TEHD model by numerical programming.

CFD analysis of combustion and emission characteristics of biodiesel under conventional and late-injection based premixed combustion conditions

The simultaneous reduction in NOx and smoke emissions can be achieved with biodiesel under a late-injection based low temperature combustion (LTC) strategy. However, this occurs at the expense of a substantial increase in unburned hydrocarbon (HC) and carbon monoxide (CO) emissions. It is worthwhile to understand the reasons behind the formation of these emissions, emphasizing comparison with conventional combustion, which is known to result in significantly low HC and CO emission levels, particularly with oxygenated biodiesel fuel. The present investigation attempts to examine the same with 3D CFD simulation. Experimental data were obtained from a light-duty diesel engine using biodiesel from non-edible Karanja oil. The unmodified engine with OEM low-pressure mechanical fuel injection system was utilized for conventional combustion operation. It is replaced with a modified common rail injection system for a late-injection-based LTC mode of operation. By combining retarded high-pressure injection with EGR, sufficient premixing was sustained to enable late injection-based premixed combustion (LI LTC). The combustion simulation was performed using CONVERGE CFD tool, utilizing a two-component surrogate of methyl butanoate (MB) and n-dodecane to represent biodiesel. A reduced chemical kinetic mechanism, developed and validated in an earlier investigation on biodiesel combustion, was utilized in the current study. The mechanism was solved using the SAGE Detailed CHEMKIN solver in CONVERGE. Validation was conducted at two engine operating conditions defining low and high loads for both combustion modes. The cylinder pressure and heat release rates were predicted with a maximum error of 1.5 and 13%, respectively. The validated CFD tool was employed to compare and analyze the equivalence ratio, in-cylinder gas temperatures, and HC and CO contours between conventional and LI LTC modes. Under LTC mode, the cylinder pressure and heat release rates were predicted with a maximum error of 10 and 15%, respectively. The comparison revealed fuel-rich regions concentrated near the bowl in conventional combustion, while the fuel was spread throughout the combustion chamber in LI LTC mode with over-rich and over-lean regions near the cylinder wall. The cylinder temperature is significantly higher for conventional combustion than LI LTC mode. The O and OH radical concentrations are higher for conventional combustion, corroborating with lower CO emissions, as they aid in CO oxidation. Fuel-rich regions contribute to increased CO emissions, whereas over-lean regions at a low-temperature result in high HC emissions, exhibited by the emission contours. Possible countermeasures to reduce high HC and CO emissions in LI LTC mode include maintaining higher coolant temperatures to enable HC and CO oxidation in the near-wall regions and fuel injection system modification to alter the air–fuel mixing.

Compressible and Viscous Effects in Transonic Planar Flow around a Circular Cylinder—A Numerical Analysis Based on a Commercially Available CFD Tool

Transonic planar flows around a circular cylinder are investigated numerically for laminar and turbulent flow conditions with Reynolds numbers of 50≤ReD≤300 and 8890≤ReD≤ 80,000 and free stream Mach numbers in the range of 0.2≤Ma∞≤2. A commercially available CFD tool is used and validated for this purpose. The results show that the flow phenomena occurring can be grouped into eight regimes. Compared to the incompressible flow regimes, several new phenomena can be found. In contrast, at higher Ma∞ of 0.6≤Ma∞≤0.8 vortices in the wake of the cylinder are suppressed for ReD=50. In some cases, Ma∞=0.8 and ReD≥300, λ-shocks are formed in the near cylinder wake. For supersonic Ma∞, two different phenomena are observed. Beside the well-known oblique and detached shocks, for 50≤ReD≤300 a wake with instabilities is formed downstream of the cylinder. Furthermore, the temporal mean drag coefficient C¯D, the Strouhal number Str, as well as the critical Mach number Macrit are calculated from the simulation results and are interpreted.