Numerical CFD Research Articles

Numerical analysis of a solar air heater with circular perforated absorber plate

Numerical analysis of a solar air heater with perforated circular absorber plate is carried out to study the effect on the thermo-hydraulic performance due to the elimination of laminar viscous layer that otherwise exist in a conventional solar air heater. The study is conducted for configurations of the absorber plate consisting of 5 mm, 8 mm, 10 mm and 12 mm vent diameters and the number of vents is varied as, 24, 36 and 54. The numerical CFD analysis is conducted for Reynolds numbers ranging from 3000 to 21,000. The CFD analysis is evaluated against the experimental results. The average increase in the thermal efficiency of 23.33% is obtained for the configuration with 8 mm diameter vents and 36 number of vents compared to the base model without the absorber plate. The average increase in thermohydraulic efficiency is 21.78% higher for the configuration with 36 vents and a vent diameter of 8 mm compared to the base model. The highest thermohydraulic efficiency of 72.8% is obtained. The thermohydraulic efficiency of the collector is directly proportional to the increase in vent diameter. The study infers that the circular geometry and vented absorber plate causes vortex formation resulting in increase in turbulence induced heat transfer.

Effect of heat pipe failure on performance of residual heatremoval system with heat pipe for small lead-based reactor

Heat pipe have the characteristics of high thermal conductivity, high safety performance, without external power, etc. In this paper, The numerical simulation CFD software FLUENT is used to study the thermal-hydraulic characteristics performance of heat pipe waste heat removal system with heat pipe for lead-based reactor under normal conditions and Station-Black-Out (SBO) with partial heat pipes damage respectively. Results showed that heat pipes promote heat transfer in the reactor and reduced the temperature of the fluid around the reactor during normal operation; Heat in the core could be removed smoothly by the PRHRS during SBO accident without heat pipe damage ; and when the proportion of failed heat pipes is less than 50% during SBO accident , the PRHRS could still ensure safe operation of the reactor and the distribution of failed heat pipes in the reactor results the core temperature variation by less than 5 K.

On a Comparison of Solutions in Verification Problems

The impact of the choice of the proximity measure for the numerical and reference solutions is discussed in terms of the verification of the calculations and software. If no reference solution is available, the deterministic and stochastic options for estimating computational errors are considered using an ensemble of solutions obtained by different numerical algorithms. The relation between the norm of the solution error and the error of valuable functionals is studied via the Cauchy–Bunyakovsky–Schwarz inequality. The results of numerical tests for the two-dimensional Euler equations, which demonstrate how the choice of the proximity measure affects the estimation of the approximation error on the ensemble of solutions and show the efficiency of the considered algorithms, are presented. The comparison of different proximity measures (norms and metrics) both for estimating the computational error and for comparing the flow fields that correspond to both small variations in the flow structure and qualitatively different flow patterns is a new element of the paper. The application of the errors of valuable functionals for the evaluation of the approximation errors in practical terms is also novel. The feasibility for computationally cheap (single-grid, in contrast to the Richardson extrapolation method) quantitative verification of solutions considered and analyzed in the paper seems useful for the implementation of the Russian standards for numerical solution verification and CFD code validation.

Investigation of an axial hydrokinetic turbine with the CFD program Flow Simulation

In the work, the characteristics of a hydrokinetic axial turbine are obtained by numerical CFD modelling. Using the new research tool, Fluid Computational Dynamics, arises the question as to the accuracy of the solution. That’s why for solving the problem, has been used new numerical method “Sliding mesh”, which is included in the “Flow Simulation” soon. Besides, the numerical results for frequency characteristics are compared with the characteristics obtained by modified analytical model. It was found that for both solutions - for the output powersof the turbine, the differ is (5 … 15) % and for the torques of the working shaft the differ is (4…18) %. Because it’s accepted that the analytical solution is more accurate as it is done by a modified classical method, the compliance of the shape and energy performance characteristics is considered to be a numerical model verification obtained by simulation with the Flow Simulation CFD.

Optimization of SCR inflow uniformity based on CFD simulation

Abstract The inflow uniformity before selective catalytic reduction (SCR) catalyst carrier is a major issue for DeNO x capability of diesel engine after-treatment. Through the construction of the numerical model and CFD simulation of six perforated plate variations with different structural and positional characteristics, the influence of perforated plates on the uniformity of the airflow velocity at the inlet of the SCR catalyst carrier was analyzed. Comparison of different perforated plate variations shows that the encircling flow is a major hindrance to achieve higher inflow uniformity. Enclosed flow passage can remove the encircling flow and increase inflow uniformity at the cost of increased pressure drop. Rational layout of the perforated plate can achieve uniformity increase, while decrease pressure drop. High-velocity exhaust coupled with larger holes can improve both uniformity and pressure drop. The uniformity index increased from 97.6% of the original design to 98.7% of the optimized design, while pressure drop increased from 11.20 to 12.09 kPa. Weighing the relationship between inflow uniformity and pressure drop is an issue worthy of attention.

DAM BREAK WAVE, TIDAL BORE, IN-RIVER TSUNAMI SURGE: WHAT THE HELL?

Flood waves resulting from dam breaks have been responsible for numerous losses of life through centuries. Both the 26 December 2004 tsunami and 11 March 2011 Tohoku catastrophes were human tragedies of international significance. An important point is the physical analogy between dam break waves travelling downstream, tidal bores progressing deep inland, in-river tsunami propagating upstream, as well rejection surges in hydropower canals. The leading edge is a hydrodynamic shock, with a marked discontinuity in free-surface elevation and velocity and pressure fields, and a tri-phase flow with three distinct flowing phases, i.e. liquid (water), solid (sediment) and gas (air). Seminal features of bores and surges include a net mass flux, the breaking in shallow waters, and the intense turbulence at the front associated with massive sedimentary processes and air entrainment in the breaking roller. In this keynote talk, physical experiments, numerical CFD modelling and field observations are presented and compared. Current knowledge gaps are discussed. Ultimately it is argued that the 'solitary wave' analogy is not directly relevant to model the unsteady turbulent mixing of in-river tsunami surges, tidal bores and dam break waves.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/SQaPoSj2lP4

Numerical investigation and triple-parameters correlations development on the dynamic characteristics of a turbulent offset jet

ABSTRACT The present numerical study aims to numerically investigate the dynamic and turbulent characteristics of a two-dimensional and turbulent offset jet. Three different parameters were investigated: The Reynolds numbers (Re) which was varied from 10000 to 30000, wall inclination angle (α) that was from −20° to +20° and finally the offset ratio (OR) which extends from 3.25–13. Ansys Fluent was numerical CFD solver used in this present investigation. The simultaneous effects of the OR, Re and α were investigated in details. The velocity and pressure contours showed that these three parameters do not contribute equally in the development of such a flow. Also, the turbulent characteristics, such as the turbulence intensities and energies depicted how each parameter influences, separately, the turbulent flow production. Furthermore, different of tripled parameters correlations were developed. These correlations may be of help to more understand certain offset jet flow features more accurately and to predict their exact values.

Industrial wastewater treatment using magnesium electrocoagulation in batch and continuous mode

In the present study, the electrocoagulation (EC) performance of a Mg-Mg system was applied for the industrial wastewater treatment, from an industrial park that covers different activities such as: food, automotive, pharmaceutical, chemistry and cosmetics, after primary clarification. The effects of major operating parameters such as pH, reaction time, and current density were investigated for chemical oxygen demand (COD), color, and turbidity removal efficiency. The batch system was found convenient, achieving 63.52% COD, 96% color, and 99.32% turbidity removal at optimized operating conditions of pH 7.12, reaction time of 75 min, and current density of 201.5 A/m2. On the other hand, for continuous EC, the process removed approximately 46.58%, 95.96%, and 87.19% of the COD, color, and turbidity respectively, at 90 min of retention time, current density 440 A/m2, and a rate of 20 mL/min. Additionally, concerning nutrient removal (N and P), the EC system with Mg electrodes was highly efficient; batch treatment removed 97% of total phosphorus and 67% of ammoniacal nitrogen, whereas the continuous treatment removed 98.5% of total phosphorus and 83% of ammoniacal nitrogen. The sludge characterization before and after EC treatment was made by SEM, EDS, Fluorescence spectroscopy, IR spectroscopy. Minerals such as chlorite, crossite, richterite, pyroaurite, langbeinite as weel as aliphatic and polysubstituted aromatics compounds, sulfates and phosphates inorganic ions, and organic phosphorus were reduced. The energy cost in the batch EC is US$0.05/m3. A numerical CFD model was used to estimate the velocity fields and guarantee the presence of turbulent kinetic energy within a continuous flow reactor.

Natural Convection between A Pair of Elliptical Cylinders in Blunt and Slender Situations (Dept.M)

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Confined-crest impact: Forces dimensional analysis and extension of the Goda's formulae to recurved parapets

In this paper, an extended numerical analysis of the “confined-crest impact” (hereinafter referred as “C–CI”), induced by non-breaking waves on recurved parapet walls, is presented to better understand the physics and characteristics of this impulsive wave phenomenon, which significantly depends on the geometry of the parapet (here made by a sector of circumference) as well as on non-breaking wave steepness. A dimensional analysis of the forces has been carried out and used to analyse the results obtained by numerical CFD computations. The numerical simulations, performed for different radii of curvature, opening angles and incoming wave characteristics (changing both the wave height H and wave period T), have shown that the maximum impulsive pressure: (i) takes place on the top of the recurved parapet and decreases moving towards the SWL, where it tends to vanish; (ii) tends to decrease as the radii of curvature and the incoming wave characteristics (wave height H and period T) increase. However, this reduction in the maximum pressure, is always accompanied by an increase of the forces acting on the recurved parapet and a decrease of the wave overtopping volumes. Moreover, the maximum wave induced pressures have been examined by means of regular and irregular wave conditions in order to analyse the possibility of schematising the effects (i.e. forces) of an irregular sea state with those of a regular one, providing an equivalent force and therefore saving computational time. Based on the new results, a schematization of the pressure diagram induced by the C–CI impact has been proposed, used to extend the Goda-Takahashi pressure diagrams, valid for vertical walls in non-breaking wave conditions, including recurved walls.

Investigation of Numerical Hydrodynamic Performance of Deformable Hydrofoil (Applied on Blade Propeller)

The hydrofoil is a hydro-lifting surface that significantly contributes to marine transportation such as a boat, ship, and submarine for its movement and maneuverability. The existing hydrofoils are in fixed-shaped National Advisory Committee for Aeronautics (NACA) profiles, depending merely on the variation of Angle of Attack (AOA) such as rudder, hydroplane, and propeller blade. This research is concerned with the deformable hydrofoil that aims at modifying its NACA profile rather than its AOA. However, there is still a lack of knowledge about designing an appropriate deformable hydrofoil. Therefore, a numerical investigation of hydrodynamic characteristics for selected hydrofoils was conducted. After undergoing the 2D numerical analysis (potential flow method) at specific conditions, several NACA profiles were chosen based on the performance of NACA profiles. NACA 0017 was selected as the initial shape for this research before it deformed to the optimized NACA profiles, NACA 6417, 8417, and 9517. The 3D CFD simulations using the finite volume method to obtain hydrodynamic characteristics at 0 deg AOA with a constant flow rate. The mesh sensitivity and convergence study are carried out to get consistent, validated, and reliable results. The final CFD modeled for propeller VP 1304 for open water test numerically. The results found that the performance of symmetry hydrofoil NACA 0017 at maximum AOA is not the highest compared to the other deformed NACA profiles at 0 deg AOA. The numerical open water test showed that the error obtained on K.T., K.Q., and efficiency is less than 8% compared to the experimental results. It shows that the results were in good agreement, and the numerical CFD setting can be used for different deformed profiles in the future.

АНАЛІТИЧНИЙ ТА CFD-РОЗРАХУНОК ТЕПЛОВОГО СТАНУ ФОЛЬГОВИХ ОБМОТОК МАСЛЯНИХ РОЗПОДІЛЬНИХ ТРАНСФОРМАТОРІВ

An analytical method of calculating the thermal condition of foil windings of lower voltage oil distribution transformers has been developed. At known oil temperatures in the tank, this technique provides the identification of heat-recoil ratios on winding surfaces, taking into account their design features and heat loads, as well as calculating the excess esexcesses of the average temperature of the winding and its most heated point above the oil and over the cooling environment. In order to calculate the excess temperature of the winding over the oil by the method of separating variables using the final cosinus-conversion Fourier obtained the solution of the edge problem for the Poisson equation with heterogeneous boundary conditions on the surfaces of the rectangular section winding with anisotropic properties and with its uneven distribution of losses. In addition, an alternative approach has been developed to determine the thermal state of an axisymmetric transformer model by numerical CFD modeling of the system of equations of motion and continuity of the Navier-Stokes coolant. This allows you to obtain the distribution of the oil velocity field and absolute temperatures, both of the oil in the tank, and of the foil and ball windings of the transformer using the minimum empirical data on the physical properties of the oil and the heat transfer of the tanks. The methods are verified by known experimental data for transformers TM-1000/35 and TM-630/10. References 11, figures 4, tables 2.

Air demand prediction and air duct design optimization method for spillway tunnel

ABSTRACT Accurate calculation of air demand is fundamental in the design of air ducts in a spillway tunnel. However, it was often underestimated by empirical formulas in previous studies. In this paper, an air–water stratified flow model, in which the air and water are coupled by a new interfacial shear stress formulation, is proposed. The model is verified by using prototype data and numerical CFD results and proved to give better prediction of air demand for the spillway tunnel of the Jinping-I hydraulic project in China. In order to reduce the unfavourable high velocity of air in the air ducts, the model is also applied to optimize the design of air ducts of the Jinping-I project. We conclude that the model proposed in this paper can give more accurate results than the previous empirical formulas for air demand and is more convenient than 3D numerical models for engineering designers.

Verification of structural integrity and cooling performance of DRCS cabinet in power plant

The digital rod control system (DRCS) is an important component in nuclear power plants. Thus, the structural integrity of the isolation cabinet of the DRCS should be verified, considering the seismic loading and cooling performance of the heating source of electric equipment. In general, the structural safety and functionality of the DRCS are verified through ground excitation and flow experiments. Numerical structural analysis and CFD analysis provide preliminary assessments of dynamic behavior and temperature distribution of the cabinet in order to establish guidelines for designing experiments. This also reduces time, cost, and design cycles involved in the experimentation. Response spectrum analysis was adopted in ANSYS for seismic analysis, which gives the peak response of the structure. The analysis was performed based on required response spectra (RRS), which envelop the floor response spectra (FRS). The maximum stresses are less than the allowable stresses, and the deflections meet the requirements. Electric equipment should operate within a limited temperature range for acceptable reliability. In the direct heat removal approach, six fans are installed as heat sink and air is forced through the heat sink by the fan. The cabinet and internal modules should be designed such that adequate ventilation with the fans is provided to maintain the temperature difference between the inside and outside within 5°C. Flow and thermal analyses were carried out by a CFD program, Icepak. As a result of this analysis, the number and the capacity were determined to meet the design requirement.

Fluid dynamic and acoustic optimization methodology of a formula-student race car engine exhaust system using multilevel numerical CFD models

Fluid dynamic and acoustic optimization methodology of a formula-student race car engine exhaust system using multilevel numerical CFD models

Roughness Effect on Velocity Distribution in Selected Reach of Shatt al-Arab River

Shatt al-Arab is the only navigational artery in Iraq, extending from the city of Qurna to its mouth in the Arabian Gulf at the city of Al-Fao within the governorate of Basrah for a length of approximately 204 km. Its width ranges from 400 m to 2000 m, and its depth ranges from 8 m to 20 m. The southern part of it, 93 km long from Umm al-Rassas Island to Ras al-Bisha, represents the international border between Iraq and Iran, where the Thalweg line represents the border between the two countries, which is the deepest point in the riverbed (according to the 1975 Algiers Agreement). The western bank (the Iraqi side) within the common border of Shatt al-Arab is subject to continuous erosion, which leads to the shifting of the Thalweg line towards Iraqi territory and thus leads to loss of Iraqi land to Iran. Reducing flow velocity along the Iraqi side can lead to reducing or preventing erosion in the river. Increasing the riverbed roughness will reduce the velocity of flow and then reducing the erosion. This principle was adopted in this study to investigate the effect of increasing roughness in a strip along a reach of the riverbed on the distribution of longitudinal velocity in cross-sections at the rest of the selected reach. A reach of Shatt al-Arab with a length of 2500 m, located 34 km north of Fao City, was selected to represent the study area. This reach was simulated by using numerical modeling CFD solver (fluent) with three different roughnesses for an upstream part of the river bed and the velocities compared with the natural (original) roughness of Shatt al-Arab. The results showed an appreciable effect of the increased bed roughness on the velocity distribution and the maximum velocity location by shifting it to the other side.

A numerical study on particle tracking and heat transfer enhancement in a solar cavity receiver

The thermochemical dissociation of natural gas into hydrogen and carbon involves the presence of solid phase carbon particles. In addition to the produced carbon, carbon particles can be seeded to the process as a catalyst which act both as a heat transfer enhancing medium and nucleation site for the dissociation reaction. However, presence of discrete phase particles imposes various challenges such as deposition on solar reactor walls and windows, and clogging of the exhaust. Meticulous reactor-receiver design optimization is therefore required and is presented in this study. The Discrete Phase Model (DPM) was implemented in a numerical CFD model to track injected carbon particles in a Lagrangian framework. Validation of the model was done with respect to available experimental data and showed similar deposition phenomena on the reactor window. A parametric design study was performed taking into account flow rates, particle size, particle loading and receiver geometry. Use of a finer particle size distribution demonstrated the ability of the flow to entrain more particles to the exhaust and reduce deposition on the bottom wall of the cavity. Three design iterations on an existing 1 kW solar cavity receiver were proposed, depicting an increase of at least 6.5% on the outlet gas temperature and 4% on the overall average gas temperature within the receiver. Results of this study highlighted the importance of flow configuration, flow parameters and particle size on the deposition and heat transfer inside solar cavity receivers. Outcome of this study can serve as a reference for solar reactor design involving presence of particulate media.

Unsteady Natural Convection in a Cylindrical Containment Vessel (CIGMA) With External Wall Cooling: Numerical CFD Simulation

In the case of a severe accident, natural convection plays an important role in the atmosphere mixing of nuclear reactor containments. In this case, the natural convection might not in the steady-state condition. Hence, instead of steady-state simulation, the transient simulation should be performed to understand natural convection in the accident scenario within a nuclear reactor containment. The present study, therefore, was aimed at the transient 3-D numerical simulations of natural convection of air around a cylindrical containment with unsteady thermal boundary conditions (BCs) at the vessel wall. For this purpose, the experiment series was done in the CIGMA facility at Japan Atomic Energy Agency (JAEA). The upper vessel or both the upper vessel and the middle jacket was cooled by subcooled water, while the lower vessel was thermally insulated. A 3-D model was simulated with OpenFOAM®, applying the unsteady Reynolds-averaged Navier–Stokes equations (URANS) model. Different turbulence models were studied, such as the standard k-ε, standard k-ω, k-ω shear stress transport (SST), and low-Reynolds-k-ε Launder–Sharma. The results of the four turbulence models were compared versus the results of experimental data. The k-ω SST showed a better prediction compared to other turbulence models. Additionally, the accuracy of the predicted temperature and pressure were improved when the heat conduction on the internal structure, i.e., flat bar, was considered in the simulation. Otherwise, the predictions on both temperature and pressure were underestimated compared with the experimental results. Hence, the conjugate heat transfer in the internal structure inside the containment vessel must be modeled accurately.

Performance of wavecatcher intakes at angles of attack and sideslip

A wavecatcher type scramjet intake, that reduces the Mach number number from 4 to 1.552, is used as the basis for a study of flow starting/unstarting as affected by freestream angles of attack and sideslip. The intake design is based on a morphed streamtube consisting of two conical flow streamlines using streamline tracing and osculating axisymmetric design theory. Intake flow and performance is modeled using the numerical CFD code and the k-ε turbulence model. The intake unstarts at a sideslip angle of 2°, a positive angle of attack of 1°. Both positive angle of attack and sideslip angle have an adverse effect on the startability of the MBus intake. At negative angles, the intake initially unstarts at −5° angle of attack, due to the thickened shear layer induced by the streamwise vortex. Then it re-starts at −8° angle of attack, mainly due to the expansion fan formed at the leading edge, causing the shock wave structures inside the intake to be re-established.

An immersed boundary method for geometrical shock dynamics

A new algorithm is presented for the resolution of the Geometrical Shock Dynamics model in presence of obstacles in an Eulerian framework. The numerical method relies on a Fast-Marching like algorithm on a Cartesian grid, which allows dealing with complex geometrical configurations and shock waves interactions at a reduced computational cost. The application of an homogeneous Neumann condition at the border of rigid obstacles, not aligned with the mesh, is based on the Immersed Boundary Method. For a given obstacle, a set of ghost points is defined in the solid area and the corresponding unknown flow parameters are updated using a compatibility condition. A good agreement is observed between numerical results, experimental data and CFD simulations, both in 2D and 3D, which demonstrates the validity and the capabilities of this method.