Commercial CFD Code Research Articles

CFD Simulation of Solid Suspension for a Liquid–Solid Industrial Stirred Reactor

The present study examines the possibility of using an industrial stirred chemical reactor, originally employed for liquid–liquid mixtures, for operating with two-phase liquid–solid suspensions. It is critical when obtaining a high-quality chemical product that the solid phase remains suspended in the liquid phase long enough that the chemical reaction takes place. The impeller was designed for the preparation of a chemical product with a prescribed composition. The present study aims at finding, using a numerical simulation analysis, if the performance of the original impeller is suitable for obtaining a new chemical product with a different composition. The Eulerian multiphase model was employed along with the renormalization (RNG) k-ε turbulence model to simulate liquid–solid flow with a free surface in a stirred tank. A sliding-mesh approach was used to model the impeller rotation with the commercial CFD code, FLUENT. The results obtained underline that 25% to 40% of the solid phase is sedimented on the lower part of the reactor, depending on the initial conditions. It results that the impeller does not perform as needed; hence, the suspension time of the solid phase is not long enough for the chemical reaction to be properly completed.

Numerical study of the effect of turbulence intensity on VAWT performance

This paper demonstrates the capability of CFD to accurately simulate the effect of the flow turbulence intensity on the performance of vertical-axis wind turbines (VAWT). This effect is quite important as it increases the performance of small VAWTs. For this study, two and three dimensional CFD analysis has been performed on different straight-bladed Darrieus-type rotors. Both a small and a large H-Darrieus VAWT with diameters of 0.5 m and 35 m respectively are investigated using NACA0018 blades. Computational results based on a commercial CFD code (Star CCM+) are compared with experimental measurements. Several simulations based on full URANS calculations are proposed. Firstly, the sensitivity of time step, the number of iterations by time step, and discretization schemes are studied. Secondly, the effect of turbulence intensity on the VAWT performance is simulated and compared with experimental data. Finally, results reveal that the power coefficient of a small turbine is increasing for higher turbulence intensity, up to 20%, but stops increasing afterward. For a small turbine H-Darrieus turbine, the power coefficient is increased by 22% when the turbulence intensity is changed from 0.7% to 20%, however, there is no increase detected in the case of a large H-Darrieus wind turbine. The impact of the turbulence intensity was assessed and a range of behaviors was identified.

Numerical prediction of slurry erosion and its influence on prevailing flow conditions using a dynamic mesh method

With the help of Computational Fluid Dynamics (CFD), the amount and location of slurry erosion can be predicted using renowned models. However, all common models do not change the hydraulic contour of the system and can therefore be interpreted as a CFD-post-processing step. Thus, the influence of slurry erosion on the fluid flow is currently not considered and the effects of changing flow conditions on the system performance or perhaps energy efficiency are not predictable. Building upon this state of the art, a numerical method based on the idea of a dynamic mesh procedure is developed. The method uses the predicted erosion to locally deform the mesh during simulation. The method contains the generation of an array-based mesh structure, the precise movement of affected boundary nodes including the tracking of inner nodes as well as a reconstructing procedure to improve mesh quality after deformation. The whole method is implemented in a commercial CFD-code. The functionality of the method is examined using the example of a standardized water pump. The comparison to corresponding experimental results revealed an accurate prediction of the erosion distribution in the pump’s front casing. Furthermore, the evaluation of the pump’s performance curves indicated an accurate prediction of the changing flow field caused by erosive wear.

Developing Turbulent Flow in Pipes and Analysis of Entrance Region

Turbulent flows have complex structures due to its nature and its’ analyses are hard either by numerical or experimental means. Hydrodynamic development of turbulent flow is also complex. In this study, velocity distribution in hydrodynamic entrance length of pipes is investigated depending on axial and radial locations. Literature was surveyed for a single empirical expression that provides velocity profile directly according to Reynolds number, radial and axial locations. Requisite for computational fluid dynamics in hydrodynamic entry length of pipes is stressed by assessing turbulence magnitudes in radial and axial directions. Evaluation of the region and its properties are conducted from heat transfer perspective. An axisymmetric pipe entrance region was analyzed by means of a commercial CFD code with nondimensional parameters. Four different Reynolds numbers that are 5x103, 1x104, 5x104, 1x105 were used in calculations. k-ϵ turbulence model and standard wall functions were used for turbulence modeling. Hydrodynamic entry length, velocity profiles and turbulence indicator parameters results are presented by means of axial and radial profiles. According to the obtained results, radial velocity component values exist that would lead to radial thermal convection in hydrodynamic entrance length. It is found that simultaneous development of velocity profiles and turbulence quantities leads to characteristic velocity profiles. Also, it is seen that a good resolution in hydrodynamic entrance length can be easily achieved by computational fluid dynamics.

An alternative Vorticity based Adaptive Mesh Refinement (V-AMR) technique for tip vortex cavitation modelling of propellers using CFD methods

ABSTRACT This study focuses on the investigation of cavitating flow around the benchmark INSEAN E779A model propeller with the main aim of further improving the computational efficiency of the tip vortex cavitation (TVC) modelling by using a commercial CFD solver. Also, the effects of various key computational parameters including, numerical modelling, grid size, timestep, water quality and boundary layer resolution, on the TVC formation and its extension in the propeller slipstream are investigated systematically. The numerical simulations are conducted in uniform and open water conditions using RANS, DES and LES solvers implemented in the commercial CFD code, Start CCM+. In order to achieve the aim of the study, an alternative and new Vorticity-based Adaptive Mesh Refinement (V-AMR) technique is introduced for enhanced modelling of the TVC on the blades and downstream. For the CFD modelling of cavitation, the Schneer Sauer cavitation model based on the reduced Rayleigh Plesset equation is used for the sheet, tip and hub vortex cavitation. The hydrodynamic results and cavity patterns are validated with the experimental data. The results show that the application of the V-AMR technique further improves the representation of the TVC with minimal increase in computational cost. However, the eddy viscosity at the propeller blade tips increases with applying the V-AMR technique using the RANS solver due to its inherent modelling errors for the solution of the flow inside the tip vortex. This consequently results in an insufficient extension of TVC in the propeller slipstream compared to the predictions by the DES and LES based numerical solvers. Also, the evolution of the TVC is found to be sensitive to the boundary layer resolution when the standard RANS solver is used. The study will help to widen further applications of the CFD methods involving TVC, particularly for propeller induced underwater noise prediction and analysis.

Indirect validation of fluid-to-fluid scaling criteria for modeling steam condensation based on empirical correlations and CFD simulations

Several nuclear reactor designs have adopted passive safety systems with condensation inside horizontal tubes, such as the Passive Auxiliary Feedwater System (PAFS) of the APR+, the new generation of the Korean-Standard Pressurized Water Reactors (PWR). Performing steam condensation experiments under high-pressure conditions is needed for the design and the realistic prediction of the condensation phenomena in such systems. To avoid the costs and technical complexities associated with experimentation at high-pressure conditions, a fluid-to-fluid scaling method to model high-pressure steam condensation with a simulant fluid, refrigerant for instance, had been developed. It was determined that the liquid-to-vapor density ratio, the Froude number, and the vapor Reynolds number should be preserved in order to guarantee the flow regime and heat transfer similarity between prototypes and models. The scope of the current work is to validate the developed scaling criteria. Due to the limitation of test data of different fluids with comparable test parameters, indirect validation is proposed based on two approaches. The first approach is based on empirical correlations, in which test data from one fluid are transferred to the equivalent conditions of the other fluid, the transferred data are then compared with condensation correlations to check the validity of the scaling method. The second approach is based on CFD calculations. A CFD model, using the commercial CFD code STAR-CCM+, for the simulation of condensation in hotizontal tubes is developed. The Fluid Film model is used for modeling the condensate film thickness and development. For modeling the phase change process, source and sink terms are introduced to the continuity, momentum, and energy equations at the interface between the vapor and the condensate film. The developed CFD model is then applied in the scaling criteria validation by using it to simulate the condensation phenomena of different models in one fluid and compare its results with the corresponding experimental data in other fluid. The validation results show good agreement between prototypes and their equivalent models, and show good feasibility and reasonable accuracy of the proposed scaling criteria.

An adaptive approach to duct optimization of an industrial boiler air supply system using airfoils

The purpose of this paper is to examine the pressure drop caused by placing an airfoil at different angles of attack in the straight part of the rectangular air duct, as the first step of investigating the possibility of using a staggered cascade of airfoils for gradual deflection of the air-flow in radial elbows of an air supply system used in industrial boilers. The initial problem was approached by using the commercial CFD code based on the finite volume method to numerically simulate a 2-D incompressible turbulent flow and by conducting direct experimental measurements in the wind tunnel. The results of CFD simulations have been compared to experimentally measured data for two considered cases of inlet velocities and five different angles of attack. Numerical solutions show an adequate level of agreement with experimental measurements. The obtained results indicate the possibility of using a staggered cascade of airfoils for gradual deflection of the air-flow.

Hydrothermal analysis of heat transfer and thermal performance characteristics in a parabolic trough solar collector with Turbulence-Inducing elements

In present survey, a numerical study of fluid flow and heat transfer in a solar parabolic trough collector containing turbulence-inducing elements on wall of collector has been performed. Elements have helical profile throughout the pipe. The three-dimensional numerical simulations have been done by finite volume method using a commercial CFD code. The spatial discretization of mass, momentum, turbulence kinetic energy, turbulence dissipation rate and energy equations has been achieved by a second-order upwind scheme. SIMPLE algorithm has been used for velocity–pressure coupling. To calculate gradients, Green-Gauss cell-based method has been utilized. Generally, obtained numerical results are presented in two sections. In first part, examinations have been done to indicate impact of number of elements on collector efficiency. Five models including two, four, six, and eight numbers of turbulence-inducing elements have been analyzed. The results indicated that at VInlet = 0.32 m/sec, thermal efficiencies of models with two to six number of elements are greater than plain PTC by 6.6, 13.2, 20.6, and 27.6%, respectively. In second section, various types of element cross-section including rectangular, triangular, trapezoidal, and quasi-triangular has been investigated. Results depicted that maximum thermal efficiency belongs to case with rectangular cross-section at VInlet = 0.2 m/sec by 29% improvement.

Design Optimization of High Specific Speed Prototype Francis Turbine by Design of Experiments

In general, Francis turbines are known to last for 40 to 50 years of use. However, exchanging an old turbine for a new is expensive because of modernization costs. Therefore, many modernization projects will take place through new runner changes. The Francis turbine in this paper has a high specific speed of about 330m-kW and a runner diameter of about 4.3m. The new runner can be expected to have a more stable flow and improved performance by flow analysis. In this paper, the performance analysis of the runner was performed using the CFD by Design Of Experiments (DOE). The sensitivity of variables was examined using L18 method. Numerical analysis was performed via BladeGen, Turbogrid, ICEM CFD, and CFX, which are commercial CFD codes. The design goal is to enable not only the best efficiency point but also a more stable operation than before even at partial load conditions. Find out how to find the shape of a runner blade by searching for design points that maximize annual power generation according to newly selected operating conditions.

Three-Dimensional CFD Modeling of Serpentine Flow Field Configurations for PEM Fuel Cell Performance

A complete three-dimensional Proton Exchange Membrane Fuel Cell (PEMFC) model is proposed to study the influence of right-angle turn single serpentine (RAT1S), right-angle turn double serpentine (RAT2S), right-angle turn triple serpentine (RAT3S), and right-angle turn 3–2–1 serpentine (RAT321S) flow fields configuration on PEMFC performance with a commercial CFD code (ANSYS FLUENT). Simulations have been performed to envisage the pressure drop in the channel, the mass fraction of H2 and O2 along the anode and cathode channels, current flux density dispersion on the catalyst layer (CL), the membrane water content and proton conductivity as well as cell performance for proposed 4 flow field designs. A comparison of the simulation results of the four models was carried out. It has been found that the output of RAT321S flow field has improved compared to the RAT1S, RAT2S, and RAT3S flow field designs for the flow of the fixed-flow reactants, and RAT321S flow field model has been validated with experimental literature evidence. The results also show that the pressure drop losses are reduced as the number of passes increases.

CFD analysis of blade coating from a reservoir onto a horizontal substrate using a homogeneous two‐phase model

AbstractA two‐phase numerical analysis is performed of two‐dimensional, laminar, liquid flow from a reservoir onto a horizontal, rigid, moving substrate. The homogeneous two‐phase model in commercial CFD code CFX is used to model the liquid plus a region containing both liquid and air near the phase interface and downstream of the blade region. Slow convergence due to surface tension modelling required initialization from intermediate results omitting surface tension. Comparisons made with two previous numerical analyses demonstrate the performance of this approach. For a particular upstream reservoir geometry, the effects of changing the substrate speed and the liquid properties from a Newtonian fluid to a Carreau‐Yasuda non‐Newtonian fluid on the pressure field and the downstream film height are studied. The details of the liquid recirculation in the reservoir and the overall pressure distribution are discussed. New results are presented for the meniscus position and contact angle, which are fully predicted by the two‐phase approach. The meniscus position was strongly influenced by substrate speed and liquid properties, whereas the contact angle did not change significantly with changes in substrate speed and dynamic viscosity for the Newtonian fluid nor with changes in the functional parameters for the non‐Newtonian fluid.

Design of Pelton Turbine and Bucket Surface using Non-Uniform Rational Basis Spline and its Analysis with Computational Fluid Dynamics

Hydraulic turbines are used to convert the energy in flowing water to rotational mechanical energy. The design of high head Pelton turbine is difficult due to complex flow pattern on different parts. The basic dimensions can be obtained from interpolation techniques and design trends but the main challenge is to model the hydrodynamic surface. The surface must be designed such that it would harvest energy in an efficient manner and the manufacturing of the surface is also economic and simple. For the design of Pelton turbine, the data from Kulekhani-I hydropower is taken. Pelton turbine is designed for the given head (550 m), flow rate (6.05 m3/sec) and speed (600 rpm). For basic dimensions, interpolation techniques and design trends are used. Number of buckets is calculated for maximum efficiency condition and found to be twenty. Nozzle and spear are selected based on hydraulic efficiency. Spear angle and nozzle angle of 70° and 100° respectively are selected. The bucket surface is designed with the help of second order B-Spline. Circular and Second order B-spline surfaces with different depths are analyzed using commercial CFD code. The second order B-Spline with depth 186.22 mm is found to be more effective in terms of force exerted by the jet among the given surfaces. Finally, Bucket surface is generated using non-uniform rational B‑spline (NURBS) modeling after all the basic dimensions are determined. For verification, the design is compared with the design of commercial design software and the turbine in Kulekhani-I hydropower plant.

Design and Three-Dimensional Simulation of a Solar Dish-Stirling Engine

Design and three-dimensional simulation of a solar Dish-Stirling (SDS) engine is currently performed. The design starts with the GPU-3 Stirling engine, which is originally built to generate power from the fossil fuel exclusively. The design is conducted through three subsequent phases. Firstly, several parabolic dishes with different rim angles and number of facets are investigated to optimally design the dish concentrator. Secondly, different relative positions of the receiver aperture to the dish focal plane are tested to reach the optimal position. The optical simulation of the solar concentration process is carried out using SolTRACE software. Finally, an optimal design for a cavity receiver that involves a new structure of the heater tubes is performed. The simulation of the engine with the designed receiver is implemented using the commercial CFD code ANSYS FLUENT. Having finished the design, a comprehensive energy analysis of the designed SDS engine is carried out. The results show that a nearly uniform temperature distribution of the heater tubes throughout the cycle is achieved. The overall thermal efficiency of the designed SDS engine is about 31.8 % at a DNI of 1000 W/m2.

Thermal analysis of nanofluids flow in a double pipe heat exchanger with twisted tapes insert in both sides

In this paper, heat transfer enhancement in a double pipe heat exchanger with a twisted tape as a swirl generator in both sides is investigated numerically. The three-dimensional numerical simulations have been done by finite volume method using a commercial CFD code. The spatial discretization of mass, momentum, turbulence dissipation rate, and turbulence kinetic energy equations has been achieved by a second-order upwind scheme. A SIMPLE algorithm has been used for velocity–pressure coupling. To calculate gradients, Green–Gauss cell-based method has been utilized. The swirl generator is considered in both channels of the heat exchanger (hot and cold streams). Three types of nanofluids containing Al2O3, CuO, and SiO2 are considered as heat transfer fluid in the inner channel (hot fluid flow). Results showed that the maximum thermal performance belongs to CuO/water nanofluid at Re = 5492 by 7% enhancement in thermal performance in comparison with net water. Also, the SiO2/water nanofluid at Re = 3343 has the minimum enhancement in thermal performance by 2.5% in comparison with the net water. In a lower Reynolds number (Re = 3343), the greatest thermal performance is obtained for a case with ϕ = 4% by 1% improvement in thermal performance compared to pure water. However, the case with ϕ = 5% presents a lower thermal performance by 3.7% compared to pure water. However, in higher Reynolds number (Re = 5492), the highest thermal performance is achieved for the case with ϕ = 4% by 6.4% improvement in thermal performance compared to pure water and the lowest improvement belongs to the case with ϕ = 3% by 1.3% enhancement in thermal performance compared to pure water.

Acoustic analysis of an actively controlled pipe subject to vortex induced vibration

Pipe-like structures are utilised in a wide variety of engineering applications, which must often consider the impact of noise and vibration. This paper presents a numerical study into the Vortex Induced Vibration (VIV) of a flexible pipe in laminar flow and the resulting acoustic radiation, and explores the potential of an active vibration control strategy. The VIV is solved using a commercial CFD code, coupled with a finite element model (FEM) to obtain the pipe displacement. The hydrodynamic noise is solved using the FW-H equation based on the acoustic analogy and the vibrational noise is calculated by an acoustic FEM in the time-domain. Without control, when the vortex shedding frequency is approximately equal to the first structural natural frequency of the pipe, large amplitude vibration is induced. The fluid-pipe interaction causes hydrodynamic noise and the vibration of the pipe generates significant vibroacoustic noise. The simulations show that when the first mode of the pipe is well excited, the vibroacoustic noise dominates the sound radiation. A velocity feedback controller is then utilised to control the VIV of the pipe, which reduces both the vibrational and hydrodynamic noise, with the latter reduced to about the same level as a rigid stationary pipe.

CFD simulation of anti-fogging coatings performance in refrigerated display cabinets

A numerical procedure for the simulation of both fogging and the defogging process on the glass door of a vertical refrigeration display cabinet for chilled food is presented. The large scale problem within the cabinet (convective air flow and heat transfer, moisture mass transport, unsteady conduction through a multi-glazed door) is modelled via a commercial CFD code, whereas the water layer is modelled, via in-house user defined routines, as a collection of tiny droplets in order to take into account the surface wetting properties, the latent heat contributions and the area effective wet fraction. Local water layer equivalent thickness and time needed for the complete defogging are evaluated for different indoor conditions. The influence of anti-fog coatings is investigated comparing different droplets contact angle, from 30° to 90°.

Lean blow-off characteristics of a tangential entry type dual swirling free and impinging flame

An experimental study has been carried out to investigate the lean blow-off (LBO) characteristics of a tangential entry type dual swirling flame under different operating and geometrical parameters. The amount of swirl is controlled by changing the ratio of tangential to axial in-flows (T:A). The qualitative flame structure is accessed by taking the direct flame images and the radial distribution of static impingement pressure. The flame structure has also been illustrated using commercial CFD code ANSYS Fluent®. The results showed that the flame behavior and the mixing between the reactants are strongly influenced by the outer flame Reynolds number (Re(o)) and the intensity of swirl (S). Significant transitions in flame shapes were observed owing to these flow alterations. These transitions in flame shapes strongly govern the stability near blow-off conditions. It has been seen that LBO limits are considerably improved with the presence of an inner supporting flame and also in presence of the impingement surface. The inner conical flame significantly supports the outer swirling flames for stability at high flow rates and under fuel-lean operating conditions. The outer flame could be sustained stably up to ϕ(o) of 0.1 with inner stoichiometric flame and both inner and outer flames could be stabilized for simultaneous variation of equivalence ratio up to ϕ of 0.6 (S = 0.86). Geometrical design parameters of the burner showed a major impact on improving the LBO limits. Thus, the dual flame presents significant improvements to lean blow-off limits as compared to the single outer swirling flame.

Cooling of high-performance electronic equipment using graphite foam heat sinks

In the present research, highly-conductive graphite foams have been employed to effectively dissipate the heat generated in electronic components. The heat sinks suggested have been configured from staggered foamed-baffles arranged either in parallel or perpendicular to the air paths through the slots in between to reduce the pressure drop resulted while improving the heat dissipation. The performance of the currently proposed heat sinks has been examined numerically based on the volume averaging concept of porous media, with employing the local thermal non-equilibrium model to account for the interstitial heat exchange between the foam solid matrix and the fluid particles flowing across. The Simcenter STAR-CCM+ CFD commercial code has been utilised to implement the iterative solution based on the SIMPLE algorithm. A wide range of design parameters have been tested including the heat sink configuration along with geometrical characteristics of the graphite foam used. The impact of operating conditions, including the inlet airflow strength and the heat flux applied, has been inspected as well. The currently proposed heat sinks have been found efficient to meet the extremely thermal demands of high-performance electronic equipment and sweep away the heat generated there with a reasonable cost of pressure drop, where hot spots can be eliminated entirely with proper manipulation of design conditions.

Effect of added struts and intake velocity on flame stabilization in supersonic combustors

In the present computational study, the impact of strut positions and the effect of inlet Mach numbers on the combustion efficiency are investigated in a strut-based supersonic combustor. An experimentally investigated model combustor developed at the German Aerospace Center (DLR) is simulated and validated. Then, a model combustor with three struts placed at different positions is investigated. Two-dimensional, compressible, reacting-flow governing equations are solved along with single-step chemistry reaction and k-ω SST turbulence model using a commercial CFD code FLUENT. The oblique shock from the struts has a profound influence on the mixing and combustion process. The H2O mole fraction, H2 mole fraction contours, and combustion efficiency of various configurations are compared for finding better mixing and flame stabilization. The combustion efficiency reduces when the two struts are located in farther downstream or placed at the same downstream location. At higher Mach numbers, the combustion is delayed, and the mixing of fuel with the supersonic mainstream is incomplete.

Eulerian–Lagrangian CFD-microphysics modeling of a near-field contrail from a realistic turbofan

Aircraft contrails contribute to climate change through global radiative forcing. As part of the general effort aimed at developing reliable decision-making tools, this paper demonstrates the feasibility of implementing a Lagrangian ice microphysical module in a commercial CFD code to characterize the early development of near-field contrails. While engine jets are highly parameterized in most existing models in a way that neglects the nozzle exit-related aspects, our model accounts for the geometric complexity of modern turbofan exhausts. The modeling strategy is based on three-dimensional URANS simulations of an aircraft nozzle exit involving a bypass and a core jet (Eulerian gas phase). Solid soot and ice particles (dispersed phase) are individually tracked using a Lagrangian approach. The implemented microphysical module accounts for the main process of water-vapor condensation on pre-activated soot particles known as heterogeneous condensation. The predictive capabilities of the proposed model are demonstrated through a comprehensive validation set based on the jet-flow dynamics and turbulence statistics in the case of compressible, turbulent coaxial jets. Simulations of contrail formation from a realistic nozzle-exit geometry of the CFM56-3 engine (short-cowl nozzle delivering a dual stream jet with a bypass rate of 5.3) were also carried out in typical cruise flight conditions ensuring contrail formation. The model provides reliable predictions in terms of the plume dilution and ice-particle properties as compared to available in-flight and numerical data. Such a model can then be used to characterize the impact of nozzle-exit parameters on the optical and microphysical properties of near-field contrails.