CFD Simulation Results Research Articles

Real-time temperature field recovery of a heterogeneous reactor based on the results of calculations in a homogeneous core

Advanced pressurized water reactors are the main part of a new generation of nuclear power plant projects under development that provide cost-effective power production for various needs (Yemelyanov et al. 1982, Klimov 2002, Boyko et al. 2005, Baklushin 2011, Bays et al. 2019, Nuclear Technology Review 2019). The innovative technologies are aimed at improving the safety and reliability as well as at reducing the cost of NPPs. At the same time, improvements in design, technological and layout solutions are focused primarily on the reactor core. Assessments of the efficiency of these improvements are preceded by numerical simulations of the processes in the core, in particular heat generation and sink, with account for the difference between the study object and the standard version tested in operational practice. The authors of the article propose a method for calculating the temperature field in the core of a heterogeneous reactor (using the example of a pressurized water reactor), which makes it possible to quickly assess the level of temperature safety of various changes in the core and has the necessary speed for analyzing transients in real time. This method is based on the energy equation for an equivalent homogeneous core in the form of a heat equation that takes into account the main features of the simulated heterogeneous structure. The procedure for recovering the temperature field of a heterogeneous reactor uses the analytical relation obtained in this work for the heat sink function, taking into account inter-fuel element heat leakage losses. Calculations of temperature fields in the model of the PWR type reactor (The Westinghouse Pressurized Water Reactor Nuclear Plant 1984) were carried out in stationary and transient operating modes. The calculation results were compared with the results of CFD simulation. The area of competing use of the temperature field recovery method was indicated.

Investigations on tube in tube metal foam heat exchanger

The heat transfer equipments with higher heat transfer ability are needed in several industrial applications. With conventional methods, size of the device increases and it becomes bulky. With the use of metal foam, it is possible to attain large ratios of surface to volume. Therefore, using metal foam in heat exchanging devices is crucial. The main reason behind the use of metal foam over conventional method is its weight-saving and impact-absorbing structures. Insertion of metal foam in heat exchangers for various applications can lead to greater effectiveness and heat transfer enhancement. It has been observed that very few researchers have participated in the area of double tube heat exchangers (DTHE) having annular spaces filled with metal foam. The present work deals with numerical and CFD analysis of double tube heat exchanger (DTHE) with metal foam having different pore densities differing from 10 PPI to 50 PPI & performance evaluation of the same by taking hot water stream and cold water stream as working fluids. The modelling was created in Creo & simulation was done with k-omega (2 equation) viscous model in Ansys fluent flow. In the present work, double tube heat exchanger was considered in counter flow mode with inner sided tube (Stainless Steel) ID 9.5 mm & OD 12.7 mm and outer sided tube (Galvanized Iron) ID 28 mm & OD 33.8 mm. For fully developed turbulent flow, total length was considered as 1.5 m. The water streams through inner tube and annular space were flowing at uniform and constant flow rates of 2 lpm and 10 lpm respectively. Hot water and cold water inlet temperatures were taken at 800c & 300c respectively. For the analysis nickel metal foam with 10 PPI to 50 PPI with 0.9 porosity was inserted in the annular spaces of DTHE. For different pore densities comparative analysis was done. It was found that with rise in pore density of metal foam heat transfer rate (HTC) and pressure drop increased for both numerical & mathematical results. CFD simulation results were in good agreement with results obtained from empirical correlations taken from literature.

Numerical study on the impact of wall structure on the thermal performance of double-channel porous solar wall

With the improvement of people’s living standards, they have higher requirements for indoor thermal comfort in the cold season. Solar wall utilizing solar energy for heating can reduce carbon emissions and achieve carbon neutrality. In the aspect of solar wall research, the influence of wall structure on the thermal performance of double-channel porous solar wall is limitedly investigated. In fact, the optimization design of wall structure is important for the thermal performance of solar wall and its applications. Therefore, a simplified three dimensional room model is built to study the influence of the wall structure on the thermal performance of porous solar wall by numerical simulation. With this model, different channel spacing and thickness of porous walls were used to determine the optimal design for a double-channel porous solar wall in terms of enhancing the heat storage. Moreover, the influence of the surface emissivity on the characteristics of heating and temperature field of double-channel porous solar wall are studied based on the optimal structure. The CFD simulation results indicate that the optimal structure parameters should include spacing of 0.08 m for channel 1, the porous wall thickness should be 0.08 m, and the air channel 2 spacing should be 0.06 m. The temperature of air channel 1 and air channel 2, the indoor temperature, and the heat storage of porous wall decrease with the increase of the surface emissivity of the porous wall. In order to improve the heat storage performance of double-channel porous solar wall, the outer surface of the porous wall should use a lower emissivity material. The outer surface emissivity of porous wall has a significant impact on the heat storage of the porous wall and little effect on the thermal storage wall. The temperature of porous wall is always higher than that of outdoor environment temperature.

Flow deviation and critical choking in transonic turbine cascades operating with non-ideal compressible flows

In this work we examine the flow deviation and its relationship to critical choking, i.e., choking of the meridional component of velocity, in transonic turbine cascades operating with non-ideal compressible flows. To this purpose, a generalized expression of the corrected flow per unit area as a function of both the thermodynamic state and the molecular complexity of the working fluid, the Mach number, and the amount of swirl is derived. The trends of the corrected flow with respect to these quantities are used to infer physical insights on the flow deviation and on the operability of transonic turbine cascades in off-design conditions. Moreover, reduced-order models for the estimation of the flow deviation and the preliminary assessment of the losses have been developed and validated against the results of CFD simulations performed on a representative transonic turbine stator. Results suggest that flows of dense organic vapors exhibit larger deviations than those pertaining to compounds made of simple molecules, e.g., air. Furthermore, transonic turbines expanding dense vapors reach critical choking conditions at lower Mach numbers than the ones operating with simple molecules, and are affected by larger dissipation due to viscous mixing.

Solar Still for Water Distillation

Abstract: To produce pure water, it is known that the desalination of saltwater using solar systems and since a long time is a practical solution, especially in remote areas of rural, which suffer from the scarcity of drinking water due to poor infrastructure, many of which are not connected to the national water grid. The model was produced in ANSYS-CFD. The simulation was performed transient state to validate Practical experiments on solardistillation performance under the different climatic conditions of the city of Karbala, Iraq (latitude 32.6 °N and longitude 44.02 °E). The results of the ANSYS CFD simulation compared with the results obtained from conducting experiments, it showed a good agreement to solar still performance.

Aerodynamic performance of hovering micro revolving wings in ground and ceiling effects at low Reynolds number

Numerous investigations have been conducted to understand the wall effects on rotors. The purpose of this study is to further investigate the aerodynamic performance of revolving wings, especially when it is very close to the ground and ceiling (i.e., less than half the wingspan) at low Reynolds numbers. Hence, the ground and ceiling effect for hovering micro revolving wings at low Reynolds numbers are investigated by improving the theoretical models. The theoretical model for the ground effect is established based on the wall-jet assumption, and that for the ceiling effect is improved by considering the uneven spanwise distribution of induced velocity. These two models are validated by comparing the results of experiments and CFD simulations with the Lattice-Boltzmann Method (LBM). Both ground and ceiling effects are found helpful to enhance the thrust, especially with small wing-wall distances, by making a difference to the induced velocity and the pressure distribution. By comparing the thrust generation and aerodynamic efficiency between the ground and ceiling effects, the former is found more helpful to the thrust augmentation, and the latter is more beneficial for the aerodynamic efficiency promotion.

Erosion prediction of bypass crossover sub in eccentric operating positions in horizontal wells

Erosion wear is a serious problem in the fracturing process. The erosion of the bypass crossover sub, particularly in eccentric position, during fracturing in high flow rate and high proppant concentration can make a big difference in erosion results. CFD technology with Euler–Lagrangian approach is employed to solve the continuous phase and the discrete phase. In the fluid phase, realizable k−ϵ model was used to calculate the turbulent flows, and the Lagrangian method was applied to track the particle motion in the solid phase. In order to validate the accuracy of numerical simulation, scale model testing is used to obtain velocity of flow field in bypass crossover sub. The velocity profile is measured by a laser Doppler Anemonmetry (LDA). CFD simulation results are in a good agreement with experiment data. In this study, the particle trajectories and volume fraction in central and eccentric positions were obtained by simulation. This work aimed to conduct a detailed study on the flow phenomena of bypass crossover sub and analyze the difference in the bypass crossover sub between central and eccentric positions in terms of the magnitude of erosion rates and severe erosion locations and find out which erosion model is the most applicable to predict erosion. The numerical results show that the erosion contours predicted by the three erosion models have huge differences. Oka et al. erosion model is in a good agreement with practical observations by analyzing erosion patterns of the three erosion equations at specified locations and comparing them with actual image. The simulation of different flow rates and sand volume fraction were carried out. This research can help predict the erosion of bypass crossover sub more accurately and provide references for erosion prediction, as well as experiences for designing and improving the bypass crossover sub of horizontal wells in engineering.

Specification Design and Performances Using Computational Fluid Dynamics for Mini-Remotely Operated Underwater Vehicle

Remotely Operated Underwater Vehicle (ROV) is a submersible robotic system, used to examine various underwater characteristics and controlled by operators from shore. The applications of ROV are widely diverse, especially for exploration and marine industry. This research is to investigate pressure and drag on underwater vehicles using the CFD approach. A low-cost mini ROV with a 300 mm length was used for the research and to determine the hardware and material type required for prototype production by observing pressure and drag from the CFD simulation result. Simulation is solved using CFD software with RANSE method and Shear Stress Transport based k- ɷ was used as turbulence setting. The result indicated that to pull the mini ROV from the surface to a depth of 50 m requires a thrust of 3,9 kg and the mini ROV receiving the pressure of 7,7 bar.

Effect of heat transfer through the release pipe on simulations of cryogenic hydrogen jet fires and hazard distances

Jet flames originated by cryo-compressed ignited hydrogen releases can cause life-threatening conditions in their surroundings. Validated models are needed to accurately predict thermal hazards from a jet fire. Numerical simulations of cryogenic hydrogen flow in the release pipe are performed to assess the effect of heat transfer through the pipe walls on jet parameters. Notional nozzle exit diameter is calculated based on the simulated real nozzle parameters and used in CFD simulations as a boundary condition to model jet fires. The CFD model was previously validated against experiments with vertical cryogenic hydrogen jet fires with release pressures up to 0.5 MPa (abs), release diameter 1.25 mm and temperatures as low as 50 K. This study validates the CFD model in a wider domain of experimental release conditions - horizontal cryogenic jets at exhaust pipe temperature 80 K, pressure up to 2 MPa ab and release diameters up to 4 mm. Simulation results are compared against such experimentally measured parameters as hydrogen mass flow rate, flame length and radiative heat flux at different locations from the jet fire. The CFD model reproduces experiments with reasonable for engineering applications accuracy. Jet fire hazard distances established using three different criteria - temperature, thermal radiation and thermal dose - are compared and discussed based on CFD simulation results.

Numerical Investigation of Flow Force and Cavitation Phenomenon in the Pilot Stage of Electrical-Hydraulic Servo Valve under Temperature Shock

The flow field structure in the pilot stage of the electro-hydraulic servo valve is small and complex, and the extreme temperature environment will aggravate the self-excited oscillation, resulting in a decrease in the control accuracy of the servo valve. With the increase in temperature, the size of the orifice, the temperature characteristics of the fluid and the pressure loss in the flow pipe will influence the characteristics of the pilot stage. Considering the influence of temperature and pressure loss, a theoretical mathematical model is established to describe the flow force in the pilot stage. To verify the accuracy of the theoretical model, CFD simulations of the flow force at different inlet pressures and deflection positions and temperatures are analyzed in this paper. As the temperature rises, the oil viscosity rapidly decreases, which results in the flow force acting on the flapper increasing with the temperature. When the temperature exceeds 50 °C, the effect of oil viscosity is small, and the flow force tends to decrease slightly with the combined effect. As the supply oil pressure increases and the flapper moves toward the nozzle, the flow force acting on the flapper increases, and the trend is consistent with the CFD simulation results. An experimental device is designed, including establishing the experimental conditions and measuring the flow force to validate the theoretical model and to observe the cavitation phenomenon of the pilot stage.

Quasi-two-dimensional ejector model for anode gas recirculation fuel cell systems

An anode gas recirculation ejector plays an important role in the performance and service life of fuel cells. This study establishes a new quasi-two-dimensional ejector model by considering the flow phenomena of the boundary layer, shock train, and mixing layer. The two-dimensional flow field of the mixing process of the primary and secondary flows is calculated using the compressible turbulent shear layer development theory. The effects of both compressible flow friction and nozzle flow separation caused by the boundary layer are considered. Furthermore, the dynamic pressure loss and mixing acceleration caused by the shock train are calculated in the model. The mixing-length theory proposed by Prandtl is used to calculate the momentum transfer between fluids, and a method for calculating the viscous dissipation of the mixing layer is presented. In addition, the effects of the flow phenomena are introduced into the governing equations through source terms. Finally, an experimental system is built to test the ejector performance under room-temperature, high-temperature, and wet-secondary-flow conditions. The performance and flow parameters obtained using the proposed model are verified through experiments and CFD simulations. The results show that the quasi-two-dimensional ejector model can accurately predict the overall performance and axial flow parameters of the ejector. The root-mean-square errors of the mass flow rates of the primary and secondary flows are 2.29% and 8.78%, respectively. The two-dimensional flow field obtained using the quasi-two-dimensional ejector model is in good agreement with the CFD simulation results. The development of the mixing layer affects the axial parameters and performance of the ejector because it influences the momentum transfer, friction loss, and viscous dissipation of the flow field. This study is of significance for accurately predicting the ejector performance as well as for optimizing the design of the ejector for anode gas recirculation fuel cell systems. This contributes to the efficient operation of fuel cells and simplification of supporting auxiliary systems, which has energy and economic benefits. The proposed ejector model can also be extended to ejectors in other fields.

Experimental, Analytical and ANSYS Computation of Novel Cascade Solar Desalination Still

This study presents a simple device using solar radiation as a source of energy to convert brackish water to freshwater. To enhance the productivity of the cascade of solar stills, a new structure of the absorber plate with sloped surfaces and baffles was proposed to present a slight water layer thickness and improve the amount of solar radiation incident. A physical model is developed taking into account various parameters which affect the distillate yield of solar sills. In the present work, the modeling of the cascade solar still uses ANSYS Fluent V18 to investigate the yield. A three-dimensional model was considered to simulate the temperature of the water, absorber plate, and freshwater productivity. A comparison was conducted based on the CFD simulation results, experimental and approximate analytical model data. It showed a reasonable agreement of the results obtained using the analytical model with the experimental and the simulation using ANSYS Fluent of different working parameters especially the productivity. The best performance was obtained on 15/07/2018, with a productivity rate of more than 1.67 kg/m2.hr.

Study of natural gas emission from a hole on underground pipelines using optimal design-based CFD simulations: Developing comprehensive soil classified leakage models

Gas leaks from natural gas pipelines can lead to catastrophic incidents, especially in the case of sour natural gas owing to the combination of its toxicity and flammability. As a safety consideration, these pipelines are underground to protect humans and installations. However, no comprehensive model has yet been proposed that can predict the leakage rate from the damaged buried pipelines in a wide range of influential factors. In this work, to compensate for this shortcoming, a set of soil classified models are presented considering the emission of sour natural gas in silty, sandy, and gravelly soils using the results of optimal design-based CFD simulations. In this way, a wide range is selected for effective factors of pipe pressure (2–100 bara), leakage hole diameter (2–40 mm), pipe diameter (4–56 in), soil porosity (0.3–0.45), and soil particle diameter (0.002–40 mm). These ranges cover the specifications of both urban distribution pipeline systems and transmission ones. A two-step solution strategy is implemented to consider the effect of pressure drop on the leakage rate. The CFD simulations are in good agreement with experimental data reported in literature. The leakage models are capable to predict the results of random simulations with a mean absolute percentage error of 13%, 9%, and 7.7% for silty, sandy, and gravelly soils, respectively, over a wide range of pressure and leakage hole diameter. Furthermore, the effects of soil mass properties and pipe wall thickness on the leakage process are investigated. To clarify the effect of soil mass on leakage rate, the CFD analysis of an aboveground leaking pipe is also performed comparatively.

Gas-solid flow characteristics in turbulent fluidized bed with variable gas velocity

In turbulent fluidized bed (TFB), the superficial gas velocity usually varies since chemical reactions can change the number of gas moles. However, information from the study without considering the variation of gas velocity is usually used to guide the design and operation of industrial TFB reactors. In order to reveal the difference of constant and variable gas velocity and to address the possible effect of without considering variation of gas velocity, experiment and three-dimensional Computational Fluid Dynamics (3D CFD) simulation were performed on the gas-solid flow characteristics in TFB. Results show that the nonuniformity of axial flow field can be overestimated while the nonuniformity of radial flow field can be underestimated without considering the variation of gas velocity for the system in which the number of gas mole increases due to chemical reactions. Such different flow hydrodynamics with and without considering the variation of gas velocity can be more clearly observed at higher solids handle capacity. CFD simulation results indicate that the presence of particle clusters can provide reliable explanations on the different flow behavior at constant and variable gas velocity. The particle tracer information and the residence time distribution (RTD) of gas phase indicate that the back-mixing of gas and solids can be overestimated without considering the variation of gas velocity. Results indicated that the guiding information from the constant gas velocity study can largely misguide the estimation of the conversion process if this guiding information is applied in the actual industrial process with the number change of gas moles in chemical reactions.

Integrated BIM and VR for Interactive Aerodynamic Design and Wind Comfort Analysis of Modular Buildings

Modular building is becoming a common sight due to government policies promoting greater automation and productivity. When moving towards modularity, indoor comfort within volumetric modules, such as levels of humidity and temperature, natural ventilation, and air pollutant transport, have a major effect on human health and well-being. Computational fluid dynamics simulations (CFD) are used to evaluate the efficiency of natural ventilation. However, designers usually find it difficult to visualize the CFD simulation results, which can deepen users’ understanding of the wind environment and help optimize the design of modular buildings. To overcome this challenge, this paper presents an integrated approach based on building information modeling (BIM) and virtual reality (VR), with the aim of analyzing the aerodynamic design and wind comfort for modular buildings. The framework consists of four salient components. First, a new method, combining OpenStreetMap and Dynamo, is proposed to achieve rapid urban modeling of modular buildings. The second step involves the use of CFD to simulate the outdoor wind environment surrounding modular buildings. The third step emphasizes the integration of CFD-computed data with VR applications to create an immersive virtual environment for designers to analyze the wind environment of design alternates. Finally, the visual experience of non-professional users is used to improve the ventilation of the building and support more informed decision marking at the early stage of building design. The proposed framework is illustrated via a case study that focuses on a group of modular housings in the urban area of Singapore. The results indicate that visualization of CFD simulations in VR provides designers with more details regarding the actual space, and it is expected to help optimize the architectural design.

Artificial Neural Network- Genetic ‎Algorithm based Optimization of Baffle ‎Assisted Jet Array Impingement Cooling ‎with Cross-Flow

The objective of this research is to numerically investigate heat transfer and pressure drop characteristic ‎of a baffle assisted multi-jet impingement of air on a heated plate subjected to constant heat flux and ‎cross flow. Two baffle configurations were considered for the present study. An array of jets with 3 x 3 ‎configurations discharging from round orifices of diameter D=5 mm and with jet-to-heated plate distance ‎ranging from 2D to 3.5D were studied. SST k-ω turbulence model was used for numerical simulation to ‎examine the effect of blow ratio and baffle clearance on heat transfer and pressure drop characteristics. ‎Blow ratios of 0.25, 0.5, 0.75 and 1.0 and baffle clearances of 1 mm, 2 mm, and 3mm were considered ‎for CFD simulations. The split baffle configuration with baffle clearance of 3 mm is found to be more ‎advantageous when both heat transfer and pressure drop are considered. However, the segmented baffle ‎configuration with a baffle clearance of 1 mm gave better results for heat transfer alone. The present ‎study also deals with determination of optimal operating parameters with the help of Genetic Algorithm ‎and Artificial Neural Network. A pareto front was obtained for selecting the desired value of heat transfer ‎or pressure drop. It was found that Artificial Neural Network based predictions strongly agree with CFD ‎simulation results, and hence seems to be very useful in arriving at the optimum values of operating ‎parameters‎.

Melt Conveying in Co-rotating Twin Screw Extruders

Abstract Computational fluid dynamics (CFD) based on a finite-volume method was used to simulate three-dimensional pressure and velocity fields for non-Newtonian fluids in fully filled screw elements in a co-rotating twin screw extruder. The employed method also allows the calculation of temperature fields for non-isothermal flow which requires a non-steady state calculation. The CFD code was first evaluated on simple flow cases such as flow of a Newtonian or non-Newtonian fluid through a cylindrical die or flow in single screw extruders equipped with different screws. The results agreed very well with analytical calculations (die flow) and experimental results (single screw extruder). In a next step, we wanted to establish the reliability of the numerical results for twin screw extruders by performing experiments on a 40 mm and a 58 mm screw diameter machine. Temperature and pressure distribution along the screw in the fully filled section in front of the die were measured. Melt conveying in several screw elements (different pitches) was studied for different materials (amorphous polystyrene and partially crystalline polypropylene) at various flow rates and screw speeds. It was attempted to measure axial pressure build-up for flow rates from nearly zero to beyond the drag capacity of the specific element. The measured bulk values of pressure were then compared to the corresponding values extracted from the CFD simulation results. So far, only isothermal calculations (at different temperatures) have been performed. The temperature profile along the screw was determined by calculating the energy dissipation in isothermal slices and converting the dissipated energy into internal energy (temperature increase, neglecting heat losses at the wall). General agreement between experimental and numerical results is good.

Modelling, analysis and experimental study of the prop-rotor of vertical/short-take-off and landing aircraft

The main objective of this work is to characterise the prop-rotor of V/STOL (Vertical/short-take-off and landing) aircraft in various operating conditions, especially in transition flight. To this end, a BET (Blade element theory) based analytic model/tool with a low computational cost has been built to predict the aerodynamic performance of the prop-rotor. This BET-based model can predict prop-rotor thrust, torque, normal force, and yaw moment as well as their corresponding 1P load (once-per-revolution load on the single blade) regarding oblique flow. This model is verified and shows good consistency with the wind tunnel experimental data and CFD simulation results. Furthermore, by using this BET model/tool, the effects of axial advance ratio, tilt angle and collective pitch angle on these component loads on the prop-rotor are explored. Moreover, the effects of these variables on the vibratory amplitudes of the 1P load on the single blade and 3P harmonic loads on the prop-rotor due to inclined flow are presented as well.

Numerical investigation on evaluating nonlinear waves due to an air cushion vehicle in steady motion by a higher order desingularized boundary integral equation method

The problem of nonlinear ship waves generated by an air cushion vehicle is studied and modelled in the framework of potential flow theory. A higher order desingularized boundary integral equation method (HODBIEM) using Rankine source is developed. A stationary iterative method is adopted to solve the nonlinear free surface which is discretized into the inner area disturbed by cushion pressure and the outer undisturbed area. Techniques for numerical implementation are described in detail. To save computing time, grid density and domain size are refined.Both straight-ahead and yawed cases are considered for validations. Wave-making resistance versus various speeds in deep and shallow water are calculated for straight-ahead vehicles. The resistance curves obtained by HODBIEM agree well with results of nonlinear CFD simulations. The linear theory predicts higher peak value of resistance than nonlinear methods. The experimental data fit at low Froude number but deviate from numerical predictions when exceeding primary hump speed. Effects of speed and water depth are analyzed by wave patterns and wave profiles. Resistance, side force and yaw moment are calculated at Fn = 0.533 for drift angle from 0° to 90°. Satisfactory results are given by present method. Details about wave patterns and wave angles are discussed.

Aerothermal databases and load predictions for Retro Propulsion-Assisted Launch Vehicles (RETALT)

The assessment of thermal loads occurring on reusable launch vehicles during the entire trajectory is essential for the correct dimensioning of the thermal protection system. Due to the costs and limitations of ground-based testing for large-scale vehicles, these predictions rely intensively on numerical simulations (CFD). The need of aero-thermal databases, as a fast-response surrogate model for the aero-thermodynamic heating, arises from the practical impossibility of performing unsteady CFD analysis over the entire trajectory due to the large disparity of fluid mechanical and structural time scales. The construction of these databases is based on a representative set of CFD simulations which cover, at a minimum, the flight regimes with significant thermal loads. The aim of this paper is to analyse the results of these representative CFD simulations during both the ascent flight and atmospheric entry for the RETALT1 vehicle to show typical flow field phenomena occurring during these phases and the resulting heating patterns.