CFD Techniques Research Articles

Behavior of tall masonry chimneys under wind loadings using CFD technique

This study deals with the static behavior of a self-supporting traditional clay brick-gypsum mortar masonry chimneys representative of the large number of chimneys currently used in industrial field in Iraq which plays an important role in dispersion of flue gases and smoke releasing to the atmosphere. The first part of the present study is devoted to review the construction process of chimneys, their shapes and dimensions, and properties of masonry units in which chimneys with heights 45, 50, 60, 70 and 80 m were studied. The second part focused on the wind loading analysis using CFD modelling and compared it with wind loads obtained by ASCE7-10, where three wind velocities were taken 30, 42, and 50 m/s. The third part related to 3D numerical model using finite elements method via ANSYS 2020R1 software to study the structural behavior of chimneys under gravity and wind loads in term of deflections and stresses. It is found that chimneys with slenderness ratio up to 11.6 (height = 60 m) re satisfied the design codes requirements for all wind velocities 30−50 m/s for permissible tensile stress, namely with a the factor safety greater than 2.The lateral deflection at the top of the chimney, of heights 45 m and 50 m, for all wind velocities is within permissible limit i.e. (H/650).Wind loadings estimated by CFD analysis is greater than that calculated by ASCE7−10 by about 37 %.

Analysis of the Effect of Various Impeller Blade Angles on Characteristic of the Axial Pump with Pressure Fluctuations Based on Time- and Frequency-Domain Investigations

In this work, the behaviors of flow field and pressure fluctuations in both time and frequency domains in an axial flow pump through changing various impeller blade angles are studied and investigated by using a CFD technique. The blade angles are changed between 30°, 45o, 60o and 75o. Numerical results are validated with the experimental values, as a good agreement was found between them. The developed flow analysis shows that the blade angle does influence the different flow behaviors and features, such as the static pressure, turbulent kinetic energy (TKE), pressure fluctuations, axial velocity, radial velocity and tangential velocity. The results have revealed that the TKE rises with flow rate decreases and high static pressure increases at the pump outlet region near the tip blade region. Another conclusion of the study is the fact that the blade angle with 60o is the better one in terms of lower-negative-pressure regions, when compared with the other settings. The first dominated frequency was pump rotational frequency, and the second important frequency is the BPF (blade passing frequency). Furthermore, the results showed that impeller blade angles and unsteady flow have a high influence on the pressure fluctuation amplitude. Moreover, the results of the presented numerical simulation would be useful for a future hydraulic design of an axial pump.

Design optimization of hydrodynamic coupling applying response surface method combined with CFD technique

Hydrodynamic coupling is a type of fluid machinery that uses fluid kinetic energy to transmit power. In this paper, meridional profile optimization of fully filled fluid coupling was performed to improve transmitted torque. The response surface method, a global optimization method, combined with CFD was introduced to find optimum meridional profile of blades. The torque coefficient was applied as an objective function. The response surface method was adopted with three design variables: hydraulic diameter ratio of blades, central core position, and meridional profile of the hub. Results showed that the best diameter ratio occurred at d/D =0.67. To specify an optimal position for the central core, a dimensionless parameter (b/d) was introduced. With regression analysis, it was found that the optimal point occurs at about b/d =0.37. It was confirmed with the results of contour and vector plots. Three types of curves (circular, elliptical, and cubic Bezier curve) were employed to optimize the meridional shape of blades. The circular curve was applied in the design of the hub in the reference geometry. Relative to the circular curve hub, the use of elliptic curve had no significant effect on the objective function. Two dimensionless parameters, l1/d and l2/d, were defined to investigate the effect of Bezier curves on the performance of hydrodynamic coupling. The optimum values for design variables of l1/d and l2/d were obtained 0.80 and 0.88, respectively.

Prediction of thickness loss in a standard 90° elbow using erosion-coupled dynamic mesh

Erosion wear is an inevitable problem in particle-laden flows. Generally, the erosive wear is reported as a thickness loss (mm or mm/yr), but in the form of a scar or wear map distribution on the target material surface. Recent advances in CFD techniques now allow the prediction of a time-dependent surface evolution due to the impact of solid particles. With this in mind, an erosion-coupled dynamic mesh approach was employed to predict a realistic surface deformation in a standard 90∘ elbow. Experimental data were used to validate the numerical results. The effects of wall condition, namely, smooth wall, rough wall, and rough wall with particle rotation, on the topology of the deformed surface were investigated. Interestingly, the simulations revealed better performance of the dynamic mesh approach when compared to static mesh cases. Also, it was found that wall roughness and particle rotation significantly influences the shape and magnitude of the surface deformation. The results also showed that particle dynamics in response to the surface deformation might be the key to solve complex erosion-related problems. In such cases, the erosion spots can evolve over time and may be inaccurately assessed when based solely on static mesh erosion calculations.

Combustion monitoring in an industrial cracking furnace based on combined CFD and optical techniques

Ethylene is one of the most important building blocks of current chemical industry with a global production of 150 million tons in 2016. Most ethylene nowadays is produced via thermal cracking with steam of fossil feedstocks in cracking furnaces. This process accounts for approximately 8% of the petrochemical sector primary energy consumption making it the single most energy-consuming process in the chemical industry. Combustion of hydrocarbon fuels supplies the required energy to cracking units resulting in substantial CO2 emissions. Also, new emission regulations have a strong influence on older units with partially premixed burners, which produce larger amounts of NOx than modern designs. Therefore, an improvement of energy efficiency and a reduction of pollutants in cracking furnaces are environmentally and economically driven. In this work, both issues have been addressed based on numerical (CFD) techniques and experimental measurements at the plant. Firstly, to monitor burner efficiency a new methodology based on CFD calculation of OH- and CH- radicals via reduced chemical kinetics, combined with industrial-scale experimental validation through flame spectroscopic measurements and UV CCD cameras, has been carried out. Based on these measurements, a quick diagnosis of combustion performance by flame emission chemiluminescence can be made, which has successfully tested for the first time at full-scale industrial cracking furnaces. Secondly NOx emissions have been simulated by the usual approach of reduced chemistry and post-processing over the CFD fields, demonstrating with plant data at the stack that reasonable predictions can be achieved in this context. The method has been used to study modifications of burner geometry to abate NOx formation.

Investigation on performance of an asphalt solar collector: CFD analysis, experimental validation and neural network modeling

This paper presents a numerical model, development, and experimental validation of an Asphalt Solar Collector (ASC) which subsequently is modeled by Artificial Neural Network (ANN). In this research, 2 m long galvanized pipes are connected in parallel and embedded into an asphalt slab with 1 m2 area. The slab is buried in the ground to have thermal heat transfer with adjacent soil and to resemble real conditions. Several experiments are carried out in both warm and cold months of the year with different water flow rates from 9:00 to 17:00. The ASC is modeled with CFD techniques and the desired parameters effect are independently studied based on a reference condition. An ANN model is proposed to expand the parametric study and reduce the high computational cost of numerical modeling. The inputs of the ANN include the design and the operating parameters and the outlet water temperature is considered as the output. These models are capable of evaluating the performance of the ASC at every hour during the day and under different boundary conditions. The parametric study shows that improvement of surface absorptivity and thermal conductivity of asphalt leads to a higher increase of the daily efficiency in August, however, the inlet water temperature has the same effect in November. The maximum water temperature difference and the thermal efficiency of the ASC can reach up to 24 °C and 45% in August and 14 °C and 35% in November respectively.

Analysis of the effect of hydrodynamics over the activity and selectivity of the oxidative dehydrogenation of propane process in a packed bed reactor through CFD techniques

A study of the effect of hydrodynamics on the activity and selectivity of the oxidative dehydrogenation of propane (ODHP) of a non-isothermal Packed Bed Reactor (PBR) was implemented. 2D and 3D CFD models were employed, considering the mass, energy and momentum transport, and a 5-step oxidation Eley-Rideal kinetic model. The effect of the inclusion of porosity function was also carried out in order to capture non-homogeneities in the radial void fraction distribution on the predictive quality. The CFD model was validated against experimental and theoretical data reported in the literature. The validated model was used to perform a parametric sweep in order to determine the process inlet temperature which maximizes the conversion, selectivity and yield. The CFD model that considers the multiphysics in the ODHP led to an increase from 30% to 33% and from 20% to 24% in the conversion and the selectivity, respectively, which represents an increase of 22% and 20% with respect to the plug flow model. The 3D model exhibited a higher activity and reactivity respect to the plug flow model, similar to that reported for the membrane reactor. This reveals that incorporating hydrodynamics in all coordinates, results similar to dose one reactant, which emphasize the low predictive quality by using the plug flow model.

Integration of TRIZ and CFD to New Product Development Process

This paper facilitates the integration of TRIZ and CFD techniques to resolve design challenges and drive innovation in flow handling equipment new product development processes. A new methodology is proposed based on an integrated product lifecycle suited for flow handling equipment product development processes. The methodology accomplishes novel design solutions by designing geometrical flow paths using recommendations from TRIZ and testing same using CFD until the desired design outcome is achieved. The efficacy of this new methodology is tested through a pilot study. Flow problem areas in a valve were visualised and tested using CFD, while TRIZ was used in detecting useful recommended solutions to the identified problems. The result of the pilot process was a novel hybrid control valve design. The new method presented in this paper can be used to manage the entire NPD process, thereby proffering innovative solutions to flow handling equipment new product development.

Flow Simulations of Modified Diffuser Augmented Wind Turbine

In order for wind technology to compete with conventional sources of energy, in terms of energy production costs, researchers are working on different ways to increase the energy density in wind. Development of wind power augmentation system is one of the most promising concepts in this field. The main objective of this research is to propose a new diffuser design for Diffuser Augmented Wind Turbine (DAWT) by introducing air vents and vortex generators. This study also investigates the effect of wind velocity and air pressure on the proposed modified diffuser to develop a suitable diffuser for DAWT. The purpose of this modified diffuser is to create a low-pressure region in the centre of the diffuser to increase the inlet mass flow rate. Three modified designs were developed and were simulated using CFD techniques. Results showed an outstanding increment in wind speed, which is 8.56 m/s (2.14 times increment), over the 4 m/s initial wind speed in a modified diffuser (Model 3 Air vents with splitter). This modified diffuser is based on the parameters: rotor diameter (D) = 500 mm, diffuser length (L) = 1000 mm, diffuser open-angle (θ) = 12º, flange size = 221.73 mm and inner splitter with 14º open-angle (α).

Estimating Fluid Parameters of Submarine Outfall Using Neural Networks

Disposal of the urban and industrial liquid waste has become important by paying attention to environmental and human health recently. Submarine outfall diffusers are the major parts of the marine disposal systems. Pipe of the diffuser, risers and ports, internal and external flows which form the discharge system are modelled and fluid-structure interaction (FSI) method is utilized by ABAQUS finite elements program. Coupled CFD & Explicit technique is performed in FSI analysis. Method of bidirectional fluid-structure interaction (FSI) is used in finite elements method (FEM). Internal and external flows constitute fluid domain and diffuser constitutes the structure domain. While internal velocity and pressure values are obtained from the program, predictions of these results are performed by Artificial Neural Network (ANN) analysis. The average discharge velocities provide to avoid water intrusion into the ports. According to results obtained by FEM it can be said that the discharge system works efficiently. Numerical and estimated values are compared and the relationship between these values is investigated. The correlation coefficients are calculated by using numerical and estimated values and it is observed that a strong relationship is obtained between them.

Simulation on the dynamic stability derivatives of battle-structure-damaged aircrafts

Accurately evaluating the aerodynamic performance of a battle-structure-damaged aircraft is essential to enable the pilot to optimize the flight control strategy. Based on CFD and rigid dynamic mesh techniques, a numerical method is developed to calculate the longitudinal and longitudinal-lateral coupling forces and moments with small amplitude sinusoidal pitch oscillation, and the corresponding dynamic derivatives of two fragment-structure-damaged and two continuous-rod-damaged models modified from the SACCON UAV. The results indicate that, at the reference point set in this paper, additional positive damping is generated in fragment-damaged configurations; thus, the absolute values of the negative pitch dynamic derivative increase. The missing wingtip induces negative pitch damping on the aircraft and decreases the value of the pitch dynamic derivative. The missing middle wing causes a noticeable increase in the absolute value of the pitch dynamic derivative; the missing parts on the right wing cause the aircraft to roll to the right side in the dynamic process, and the pitch-roll coupling cross dynamic derivatives are positive. Moreover, the values of these derivatives increase as the damaged area on the right wing increases, and an optimal case with the smallest cross dynamic derivative can be found to help improve the survivability of damaged aircraft.

Development of Multi-GPU–Based Smoothed Particle Hydrodynamics Code for Nuclear Thermal Hydraulics and Safety: Potential and Challenges

Advanced modeling and analysis techniques are always essential for development of safe and reliable nuclear systems. The numerical methods in nuclear thermal-hydraulics and safety analysis are generally based on mesh-based (or grid-based) methods. These mesh-based methods have a long history and thus are very mature both mathematically and numerically. Based on their robustness and efficiency, they have been successfully applied to many applications for decades. However, the mesh-based methods suffer from difficulties in handling complex phenomena accompanied by highly non-linear deformations, which are frequently encountered in the recent nuclear safety issues related to natural disaster and severe accidents. Recent advances in Lagrangian-based CFD techniques have opened up possibilities for addressing this issue effectively. In this study, a Lagrangian-based CFD code (named as SOPHIA) has been developed based on Smoothed Particle Hydrodynamics (SPH), one of the best-known Lagrangian methods which can extensively handle various physics because of its simplicity in expressing and solving mathematical equations. The SOPHIA code incorporates basic conservation equations (mass, momentum, and energy) and various physical models including heat transfer, turbulence, multi-phase, surface tension, diffusion, etc. In addition, to handle multi-phase, multi-component, and multi-resolution flows, the code newly formulates density and continuity equations in terms of a normalized-density. One of the biggest technical challenges in the Largrangian-based CFD is its high computational cost. Therefore, the code is parallelized using multi-GPUs through multi-parallel computing techniques. Through the optimized algorithm based on these techniques, the computational performance has been improved drastically and the code obtains the capability of high resolution and large scale simulation. In order to demonstrate its applicability to nuclear safety-related issues, this study performs the simulations on three benchmark experiments related to nuclear safety: (1) water jet breakup of FCI, (2) LMR core sloshing, and (3) bubble lift force. The simulation results are compared with the experimental data both qualitatively and quantitatively, and they shows a good agreement with highly reliable visualizations.

Hydrodynamic Studies on Split Cylinder Reactor: Experimental and CFD Technique

Hydrodynamic Studies on Split Cylinder Reactor: Experimental and CFD Technique - written by T. Bhalamphiga Arasi , K. Saravanan , N. Deepa Priya published on 2020/05/13 download full article with reference data and citations

Investigation on slug flow phenomenon in Alborz morning glory spillway and preventing its destructive effects

Slug flow is a flow pattern which occurs in conveyance systems containing a two phase-fluid flow. Large air bubbles entrapped along these systems interrupt the flow and conduct to undesirable pressures and their fluctuations. Most of the previous concerning studies on slug flow phenomenon were performed in micro-channels with small scales in which the expansion of the air bubbles was negligible. In contrast, we investigated the systems with large pressure drops which conduct to abrupt increases on the volume of air phase. In this research, the verification tests applying CFD techniques were performed in OpenFOAM software by interFoam solver. The performance of morning glory spillways is investigated under steady states. While during the occurrence of flood, by increasing the depth over the spillway crest, the discharge is augmented which conducts to entrap the air pockets with pressure and velocity fluctuations. These fluctuations influence on the life of structures and their performances. This study aimed on unsteady flow in a glory morning spillway and its consequences and proposing the measures for reducing the destructive effects of slug flow. The pressure and velocity fluctuation were considered as the indices for the performance of a hydraulic structure. Spatial and temporal variations of pressure and velocity along the spillway are evaluated. Also, the influences of spillway geometry on slug flow and the measures to attenuate its destructive effects are analyzed. The results showed that the better performances of morning glory spillway are coincided by the diameter of tunnel superior than the height of water above the crest.

CFD simulation model and experimental study to implement a new flowrate formula for a rounded broad crested weir considering the end depth as control section

Weirs can be considered as the major types of flow measurement structures which are implemented along open channels to represent a controlling section to estimate the quantity of flowrate. This study depended on considered the control section at the end edge of weir and relate the depth of water at this edge (Ye) as a function of the critical depth flow (Dc). Consequently, a laboratory study was conducted for ten experiments tests of open canal flow with ten different longitudinal slopes ranged from (0 to 0.0495) in order to estimate such a relationship. The statistical regression analysis results illustrated that the relationship for (Dc with Ye) for all experiments is about 1.45831 as an average. As consequence, a new formula for predicting flowrate over weir was derived. Different statistical indexes were used to investigate the precision of the suggested formula where it appeared a very good agreement with all experimental data. A commotional fluid dynamic simulated model CFD with volume of fluid (VOF) method and (k-ɛ) turbulent models was also applied to verify the formula using FLUENT ANSYS ver. 16. The results indicated that the CFD techniques are able to simulate the flow over the weir and satisfactory the results of the suggested formula with less than 10% percentage error for all experimental tests.

Numerical Study on a Novel Type of High Gravity Rotary Gas-Liquid Separator

In textile printing and dyeing industry, a novel type of separator called high gravity rotary gas-liquid separator (HGRGS) is designed, which includes a rotary drum with multi-layer fins and an impeller. First, the structure and separation principle of HGRGS are introduced in this paper. Then, the flow field and separation efficiency are studied by CFD techniques. To ensure the accuracy of the numerical simulation, the results are verified by the available experimental data. Compared with the typical cyclone, the maximum pressure drop reduction rate in HGRGS is 64.7% when the gas enters at 10 m/s. Besides, for droplets less than 5 μm, the separation performance in HGRGS is more efficient and it will be greatly improved by 30% for 1 μm droplets. The numerical results also show that the tangential velocity inside the rotary drum is linear with the radius and the higher the rotating speed, the greater the tangential velocity. Moreover, the maximum tangential velocity between the forced and quasi-free vortex has moved to the vicinity of the outer wall, which is beneficial for droplets to move outward. Additionally, the droplets in HGRGS can be captured with enough residence time owing to the lower axial velocity than that in a typical cyclone.

Unsteady numerical investigation of the full geometry of a horizontal axis wind turbine: Flow through the rotor and wake

Aerodynamics of the Mexico wind turbine was investigated using CFD techniques. The complete wind turbine was modelled. In order to accomplish this goal, the computational domain was discretized with a multi-block structured hexahedron grid, which was generated manually to ensure a good quality mesh and optimize the number of cells. Furthermore, a sliding mesh technique was applied to the moving mesh zone to calculate in detail the flow around the blades. All the relevant operating conditions were considered: turbulent wake state, nominal condition and stall state. The simulations were performed using the unsteady Reynolds-Averaged Navier-Stokes equations for incompressible flow and the SST k-ω turbulence model to close the governing equations. The CFD predictions were compared with the experimental data available from the MEXICO experiment: global forces and torques, pressure distributions around the blades and velocity distributions along the radial and axial traverses were all in a good agreement. The flow through the rotor, the interaction between the blades and the tower, and the development of the wake were then investigated. The CFD simulations have provided more accurate results, contributing to a deeper understanding of the wind turbine aerodynamics.

A dynamic approach for evaluating the consequences of toxic gas dispersion in the chemical plants using CFD and evacuation modelling

Accidental releases of toxic gas in the chemical plants have caused significant harm to the exposed occupants. To evaluate the consequences of these accidents, a dynamic approach considering the gas dispersion and behavior evacuation modelling has been proposed in this paper. This approach is applied to a hypothetical scenario including an accidental chlorine release in a chemical plant. CFD technique is utilized to calculate the time-varying concentration filed and evacuation modelling is used to obtain the evacuation routes. The exposure concentrations in the evacuation routes are calculated by using the code of data query. The integrated concentration toxic load model and probit model are used to calculate the probability of mortality of each occupant by using the exposure concentrations. Based on this dynamic approach, a new concept of average probability of mortality (APM) has been proposed to quantify the consequences of different accidental scenarios. The results show that APM decreases when the required detection time decreases or emergency evacuation mode is implemented. The impact of the detection time on APM becomes small as the wind speed increases. The effect of emergency evacuation mode is more obvious when the release occurs in an outdoor space.

Application of double glazed façades with horizontal and vertical louvers to increase natural air flow in office buildings

The results of previous researches clearly indicate that the main concern in applying double skin façades (DSF) is overheating of the cavity and increasing the cooling energy consumption in warm seasons. The present study intends to consider the excessive heat trapped between two skins of double glazed façades in hot arid climates as a driving force to reinforce the natural airflow across the floors of an office building. To meet this purpose, numerical simulation of airflow and heat transfer inside the cavity of the double glazed façades and the adjacent floors, as well as the effect of different types of solar shading systems in horizontal and vertical modes on the airflow has been investigated using the CFD technique. The results show that the stack effect formed inside the cavity has enough power for air suction from the floors of the building and reinforcement of the natural airflow. The type of shading device has a significant effect on the airflow behavior and the heat transfer rate in the facade. In double skin facades with horizontal louvers, the buoyancy forces inside the cavity are stronger and the ventilation rate in the building floors is higher than the model with vertical louvers. On the other hand, due to the stronger convective flow in the cavity with horizontal louvers, the heat flux on the interior glass is higher than the cavity with vertical louvers and part of the heat inside the cavity is transmitted through the interior skin to the occupied spaces.

Design and Modelling of a 90-Degree Ball Valve with a Linear Pressure Drop

Globe valves also known as ball or gate valves are used to control fluid flow in a vast number of applications. Most of the existing applications use them because of their simplicity and very low cost. However, these valves are known for their poor precision for controlling the flow and the lack of electromechanical means for their actuation. Moreover, because of their low linearity their use in closed loop control applications make them nearly unusable. The goal of this research project was to investigate means for redesigning the metering area of a ball valve in such a manner that the pressure vs. flow characteristic would be close to a linear trend. Two different profiles where designed and tested experimentally and modelled using CFD techniques for the estimation of their valve flow coefficients. The model was able to accurately predict the behaviour of the valve with less than a 10% error when fully open. The model can be used for scaling the size of the ball for larger applications and for tuning controlling strategies for flow dispensation in real life applications.