CFD Techniques Research Articles

The performance improvement of axial flow fan with large tip clearance by using winglet

An axial flow fan is designed with large tip clearance by using the FANDAS code and then is manufactured by 3-D printer. The fan performance curve is measured by chamber-type test facility, and the measured fan flow capacity and static pressure are much lower than the design values. Through the application of CFD technique to the designed fan, it is shown that the fan performance deterioration results are due to the leakage and the secondary vortex flows through large tip clearance. In order to control the tip clearance flow, the present study employs fan blade equipped with winglet. The CFD analysis results of the fan with winglets show no leakage and secondary vortex flow through tip clearance and performance measurement results also show the performance improvements of flow capacity and static pressure by 300 CMH and 1.3 mmAq compared with the fan without winglets.

Thermal Modeling of a Capacitor Voltage Transformer Using CFD Techniques

Capacitor Voltage Transformers (TPC) are important equipment installed in high voltage substations. They are essential for the measurement, protection and control of the electric power systems. The purpose of this paper is to present a numerical modeling of a TPC aiming to understand the main thermal and fluid dynamics characteristics of it. For this, the computational fluid dynamics tool ANSYS CFX 16.1 was used. The simulations results obtained were experimentally validated.

Superficial transportation model using finite volume method

The work presents a new modeling technique designed for transporting selected property while simultaneously tracking particular value of certain field variable. The model addresses the problem of transportation of superficial properties according to fluid/fluid interface evolution. Such problem arises when some superficial variable needs to be attached to the evolving interface or front defined. Several multiphase models in CFD technique lack such ability. The model proposed is illustrated by the experimental two phase system of toluene/water with surfactant specie (sodium dodecylsulfate SDS). The selected superficial property that is important to be tracked according to interface evolution is Gibbs surface excess. The computation was performed using Ansys/Fluent software with proposed models created and attached using C programming language.

CFD SIMULATION OF A CENTRIFUGAL PUMP IMPELLER WITH VARIATIONS OF NUMBER OF BLADES

The purpose of this paper is to model and simulate the water flow into the impeller of a centrifugal pump. Using CFD techniques two impellers were modeled, differing only by the number of blades of each one (6 and 10). From the results of the simulations, the impeller’s characteristic and the results were compared for each impeller. The model with 10 blades was more efficient for a real application of a centrifugal pump. All the results have shown themselves consistent with the turbomachinery theory, proving the efficiency of CFD simulation tools in the project of this kind of equipment

Cavitation Analysis with CFD Techniques of the Impeller of a Centrifugal Pump

Background/Objectives: The present work evaluates the phenomenon of cavitation in the impeller of a centrifugal pump and observes the behavior of said phenomenon computationally in a simulation as in a physical way in a real pumping system. Methods: The method used is the CFD simulation techniques of ANSYS that allowed designing and analyzing the impeller of the centrifugal pump with convergence criteria of 1000 iterations, an rms value off low lines of 1e-4, a physical scale time of 0.00276 and a conservation value of 1%. In order to analyze the phenomenon of cavitation in the eye of the pumping system impeller, the ball valve V1 was closed an angle of 45°, located in the suction pipe to create an empty pression exceeding the vapor pressure of the pumped fluid. Experimentally recording the pressure reduction at discharge from 42.75 KPa to 19.31 KPa. Findings: The results obtained with the help of the CFD module allowed us to observe the fluid pressure distribution on the pump impeller blades with a value of 2064 Pascals (Saturation Pressure at 18 ° C), indicating the behavior of the fluid, when it passing from a liquid state to a steam state, causing the formation of vapor bubbles whose implosion causes the surface of the impeller to wear out and it is evidenced computationally the areas affected by the presence of the cavitation phenomenon. These surfaces wear out in an area close to the impeller’s eye, and then we observe aware of the material produced by lack of maintenance known as average erosion and finally total impeller damage caused by vapor bubbles. Applications/Improvements: It is suggested for this work to perform an analysis of the other elements that suffer damage due to the erosion of the material of the pump impeller, among them the casing and other elements. Keywords: Cavitation Analysis, Cavitation Phenomenon, Centrifugal Pump, CFD Techniques, Impeller

Cavitation Analysis with CFD Techniques of the Impeller of a Centrifugal Pump

Cavitation Analysis with CFD Techniques of the Impeller of a Centrifugal Pump

A new methodology to calculate the cooling law of steel mill lamination coils

In the hot-rolled steel production processes, the cooling control after finishing rolling plays an important role on the final microstructure and mechanical properties of the product. Steel coils produced after lamination must be cooled from a high temperature to the ambient temperature, to be transported and sold. Usually, the coil is stored in a warehouse until it reaches the ambient temperature. Cooling process takes between 4 and 6 days, depending on weather conditions. A new methodology to obtain the coil cooling law has been developed in this paper. Numerical models were used to simulate and study the rate of the coil cooling and to obtain the values of the parameters involved in the cooling law. The geometry of the coil is a hollow cylinder with a height between 1.6 and 1.8 m and an outer diameter of about 0.9 m. Simulations of the coil cooling process were performed by using CFD techniques with ANSYS FLUENT software in transient conditions for 2D (two-dimensional) and 3D (three-dimensional) geometries to obtain the optimal rate of temperature decrease. Vertical and horizontal arrangements of the coils and also a different number of coils and rows were studied. A new equation (cooling law) based on logarithmic and arctangent terms was obtained. This equation describes conduction, convection, and radiations effects that have been proposed and verified, considering the boundary restrictions of the problem.

An OpenFOAM-based model for heat-exchanger design in the Cloud

This paper presents a CFD tool, implemented in OpenFOAM and executed in a Cloud environment, to simulate the performance of shell and tube heat exchangers. In spite of the well-known benefits that CFD techniques can bring, these methods are seldom used by small heat exchangers manufacturers as they are unaffordable to them. The high capital costs (licenses and computing resources) and the high level of expertise required hinder a more widespread usage of these techniques. The characteristics of this tool, such as its user-friendly interface, the high level of automation and its implementation in a Cloud environment, allow to overcome the barriers that prevent the access to CFD techniques by most potential users. The CFD model presented in this paper has been validated successfully with measurements in a existing heat exchanger. Further, it has been used to re-design such heat exchanger, achieving a 30% volume reduction, while maintaining its thermal performance.

Transient boundary condition approach for simulating mechanical mixing in large wine tanks

Since wine is not continuously stirred during or after fermentation, it is common to use movable mixers on a variety of tank sizes or to install small, fast-rotating propeller mixers in large tanks. Many practically relevant optimization problems relate to processes occurring directly after the start of the propeller (flow field initialization period), which require 3D instationary models if CFD simulations are used. Based on traditional instationary models, these simulations are very time-consuming even on fast computers and limit the part of the flow field initialization period that can be computed. In this work, a new method was developed to speed up the transient simulation of mechanical mixing in large wine tanks. The method uses the traditional CFD techniques of moving reference frame (MRF) and several ensuing propeller rotations using sliding mesh (SM), to calculate a steady-state flow field and to compute the flow behavior in the propeller region. Subsequently, the flow’s key figures are extracted for the propeller region at multiple time-points during one rotation and continuously mapped to a new simulation starting from a flow field with zero velocity. This new approach using a transient boundary condition (BC), was validated with tank mixing experiments and literature data. In contrast to the MRF method, it allows e.g. for an estimation of minimum mixing times similar to the SM method, while computation times are reduced by a factor of up to 20 for tank-mixer scenarios evaluated in this work. For a mixing simulation in a wine tank, the new method takes only 3 days compared to more than 60 days using the traditional SM approach.

Francis turbine draft tube parameterization and analysis of performance characteristics using CFD techniques

Abstract The present paper focuses on the parameterization of the draft tube elbow based on the initial geometry of the GAMM Francis turbine model. The goal was to obtain a draft tube geometry that improves the hydrodynamic performance. For this purpose, CFD analyzes were carried out, considering the GAMM Francis turbine pre-distributor, distributor and rotor geometry, and different parameterized draft tube geometries. Related to the draft tube parameterization methodology, it has modified the generatrix geometry of the elbow that defines its contour. Three types of curves were used to define the elbow contour geometry: logarithmic spiral format curve, circle arc format curve and denominated hyperbolic spiral curve. These curves and their combinations were used to define the elbow contour in the longitudinal plane, resulted in four draft tubes geometries. The numerical results were compared with experimental results, showing good conformity. The efficiency of the Francis turbine was higher for the four draft tubes of this work than the original draft tube GAMM Francis turbine. Therefore, it was found that the draft tube in hyperbolic-logarithmic spiral format has the highest efficiency and the draft tube in logarithmic spiral format has the lowest loss coefficient. Consequently the hydrodynamic performance have been discussed in this work.

A New Investigation on Tunnel Pool Fire Phenomenon Using CFD Technique

In this study, the amount of generated pool fire, as a result of the release of chemicals in the case of an accident in tunnels, was simulated and the results were compared to the experimental data. At first, various amounts of spatial resolution (R*) were considered to compare the existing experimental data at different heights at the upstream, downstream and above the pool fire. The comparison studies showed that both numerical predictions and experimental measurements were, in general, comparable. Furthermore, FDS code was used to simulate the tunnel fire scenario for both cases of natural and forced ventilation. The grid using in the simulations is assessed by cells with the optimal spatial resolution and the influence of the ventilating systems on pool fire dynamic and its development was investigated. As a consequence, the temperature profile, O2, CO2, and visibility were compared in the two cases. These results showed that the ventilation system plays an important role in both fire development and heat removal by providing a safely evacuate rout in the tunnel.

Study of Effect of Metal Delivery Tube on Flow characteristics of Fluids and Melt in Convergent- Divergent nozzle used for Gas Atomization Process using CFD techniques

Study of Effect of Metal Delivery Tube on Flow characteristics of Fluids and Melt in Convergent- Divergent nozzle used for Gas Atomization Process using CFD techniques

Comparison of wind pressure measurements on Silsoe experimental building from full-scale observation, wind-tunnel experiments and various CFD techniques

The paper is the result of extensive research concentrated on analyzing the accuracy and numerical stability to assess the various turbulence models available widely and the state of the art techniques for the numerical simulation of turbulent fluid flow with a view of finding the most appropriate models for computational wind engineering. These investigations suggest that a turbulence model, suitable for wind engineering applications, should be able to model the anisotropy of turbulent flow while maintaining the ease of use and computational stability. Keeping this in mind five turbulence models such as Standard k −ε , RNG k −ε , Realizable k −ε , Reynolds Stress Method and Large Eddy Simulation have been tested in an attempt to account for anisotropic turbulence and curvature related strain effects and the same have been compared with the full-scale and wind-tunnel data for the present study. Better turbulence models that will be more accurately predict bluff body flow fields and that are numerically stable for complex geometries are of paramount importance if the uses of CFD techniques are to gain wide acceptance by the wind engineeringcommunity.Keywords: Silsoe Experimental Building, CFD, Low-rise building, Wind-tunnel

Numerical study of the thermal behaviour of a water heater tank with a corrugated coil

This work proposes a method based on CFD techniques for the study of thermal water heater tanks. The method is based on using the Navier-Stokes equations to calculate the internal movements of the fluid and the transport of energy through the flow. The Boussinesq approximation is applied to solve the fluid movements that occur by natural convection, which represents a great computational savings compared to other methods based on variable densities with very short time steps. Because the tank has a corrugated coil whose mesh poses major computational challenges, a fitting method is used to calculate the heat transfer of the corrugated surface in a smooth coil. The model is applied to a tank with 150 L of water, which is heated by a heat exchanger in the form of an outer jacket. The heat accumulated in the tank is exchanged with the drinking water by means of a corrugated coil located inside the tank. The model is tested by simulating several steady-state continuous consumption experiments and by conducting a transient test of heating and subsequent cooling. For the comparison of results, the data used include the flow rates through the water jacket and the inner coil, the inlet and outlet temperatures of these flows and various temperatures recorded by thermocouples located inside the tank at different heights. The results obtained from the simulations are reasonably close to the experimental observations. The experimental data show an aggressive temperature increase in all thermocouples, except the highest, at the beginning of heating and a softer increase at the end. A similar behavior occurs during cooling, aggressive at the beginning and softer as time progresses. This behavior is also obtained in the model predictions, especially in the lower thermocouples. The greatest discrepancy is found for the highest thermocouple during cooling. The experimental tests show a noticeably slower cooling than the model predictions.

Atmospheric Boundary Layer Simulation Using Wall Function Approach in OpenFoam CFD Software

The significant development in computer resources in the past years has increased the awareness of computational fluid dynamics as an alternative tool to the costly wind tunnel testing. The paper presented the application of CFD technique for a case study in simulating an existing site together with a proposed building and the local landscape. Finally, the limitations of the code analytical methods to the CFD method for wind around building analysis were discussed. From the result obtained, it was observed that the British standard (BS6399-2:1997) procedures are based on general assumptions and are not always conservative and do not provide accurate wind load results due to complex geometrical shapes, aerodynamic interaction, torsion, and load combinations as discussed in section VII.

Atmospheric Boundary Layer Simulation Using Wall Function Approach in OpenFoam CFD Software

The significant development in computer resources in the past years has increased the awareness of computational fluid dynamics as an alternative tool to the costly wind tunnel testing. The paper presented the application of CFD technique for a case study in simulating an existing site together with a proposed building and the local landscape. Finally, the limitations of the code analytical methods to the CFD method for wind around building analysis were discussed. From the result obtained, it was observed that the British standard (BS6399-2:1997) procedures are based on general assumptions and are not always conservative and do not provide accurate wind load results due to complex geometrical shapes, aerodynamic interaction, torsion, and load combinations as discussed in section VII.

Temporal Variation of the Pressure from a Steady Impinging Jet Model of Dry Microburst-Like Wind Using URANS

The objective of this study is to investigate the temporal behavior of the pressure field of a stationary dry microburst-like wind phenomenon utilizing Unsteady Reynolds-averaged Navier-Stokes (URANS) numerical simulations. Using an axisymmetric steady impinging jet model, the dry microburst-like wind is simulated from the initial release of a steady downdraft flow, till the time after the primary vortices have fully convected out of the stagnation region. The validated URANS results presented herein shed light on the temporal variation of the pressure field which is in agreement with the qualitative description obtained from field measurements. The results have an impact on understanding the wind load on structures from the initial touch-down phase of the downdraft from a microburst. The investigation is based on CFD techniques, together with a simple impinging jet model that does not include any microphysical processes. Unlike previous investigations, this study focuses on the transient pressure field from a downdraft without obstacles.

Computational fluid dynamics analysis for improving temperature distribution in a chili dryer

Computational fluid dynamics is a numerical tool that is highly accurate to simulate a very large number of applications and processes. The CFD analysis has emerged as a viable technique to provide effective and efficient design solutions. In this paper, a CFD analysis for improving temperature distribution in a chili dryer is presented. The CFD technique is used to simulate the temperature distribution inside the chamber. For this purpose, the continuity, momentum and energy equations are considered. The results obtained by CFD analysis based on a specific geometry are presented in order to improve the temperature distribution. In addition, these results were verified experimentally. The distribution of temperatures showed small differences around 4 K during the warming up period. The simulation and experimental results can be useful for further designs of chili dryers with different specific geometries.

Computational and Experimental Study of the Effect of Operating Parameters on Classification Performance of Compound Hydrocyclone

Compound hydrocyclone is a kind of dynamic hydrocyclone also with the advantages of static hydrocyclone. In this investigation, the effect of operating parameters on separation performance of compound hydrocyclone is studied using both CFD technique and experimental method. The flow field of compound hydrocyclone was simulated by the RSM turbulence model; the particles with different size were simplified to 6 phases and simulated by the mixture multiphase model. The central composite design method was used to conduct the separation experiment of compound hydrocyclone. The results indicated that compound hydrocyclone can be used for finer particles separation and the flow field of compound hydrocyclone can still achieve a higher centrifugal force in lower inlet velocity. When the minimum partition size is required, the optimized operating condition of the compound hydrocyclone is v = 2.5 m/s, n = 1865 rpm, and c = 7.5%, while when the maximum partition size is required, the optimized operating condition is v = 2.5 m/s, n = 905 rpm, and c = 24.5%.

Numerical Investigation of Flow Control by Passive Blowing

Identifying the performance of a free and moving hydrofoil requires extensive numerical and experimental investigations. This research topic is devoted to the study of hydrofoils used in the maritime domain. The stall of the boundary layer poses a problem of instability of the marine vehicle influencing the hydrodynamic performance, for these circumstances a method to force the attachment of these boundary layers by natural means has been proposed. In this context, a hydrofoil model was studied numerically based on a three-dimensional approach using CFD techniques for three configurations of which the first is smooth, the second with three holes and the third with seven holes from the intrados to the extrados inclined 23 ° relative to the X axis. The numerical result shows an advantageous gain in the lift force and a decrease in the drag force.