CFD Code ANSYS Fluent Research Articles

Studies on Enhanced Brake Disc Cooling using Wheel Rim with Axial Ventilators

The purpose of this study is to improve the cooling of brake disc by modifying the wheel rim by fitting it with an axial ventilator. The orientation angle of these blades in axial ventilator is varied between 0 and 10. The numerical investigation is carried out using commercial CFD code ANSYS Fluent. The pressure difference induced in 5 model is maximum leading to a better air flow through the wheel rim resulting with enhanced cooling of the brake disc. The 5 model reduced the brake disc temperature from 450C to 207.84C which is nearly 54%. The surface heat transfer coefficient and Nusselt number of 5 model is found to be maximum. The resulting improvement in heat dissipation enhances the performance and hence the lifetime of the brake disc. Therefore, the wheel rim with axial ventilator 5 model is found to the suitable configuration so as to achieve enhanced convective cooling of brake disc.

The Effect of Catalyst Placement on the Stability of a U-Bend Catalytic Heat-Recirculating Micro-Combustor: A Numerical Investigation

This study investigates the combined effect of catalyst placement and solid thermal conductivity on the stability of a U-bend catalytic heat-recirculating micro-combustor. The CFD code ANSYS Fluent 2020 R1 was used for two-dimensional simulations of lean premixed propane/air combustion by varying the inlet gas velocity, i.e., the input power. Three configurations were compared at low (3 W/(m K)) and high (30 W/(m K)) wall thermal conductivity: (A) the configuration in which both inner and outer walls are catalyst coated; (B) only the inner wall is catalyst coated; and (C) only the outer wall is catalyst coated. Numerical results show that, at low thermal conductivity, configuration (B) exhibits the same resistance to extinction as configuration (A), whereas at high thermal conductivity, configurations (B) and (C) exhibit much lower resistance to blowout than configuration (A). Accordingly, for low-power systems, which typically lose stability via extinction and thus require low-conductive materials, an optimal catalyst placement can be the partial coating of configuration (B). Conversely, for high-power systems, which are prone to blowout and thus require high-conductivity materials, a full coating of both the inner and outer walls is needed to guarantee higher stability. To elucidate these findings, a detailed analysis of the combustion behavior of the three configurations is presented.

Fast fluid dynamics simulation of the airflow distributions in urban residential areas

Conventional CFD models can resolve complex physical fields around single or multiple buildings with high spatial resolution, but they are unable to meet the demand for fast simulations with meter-level spatial resolution and minute-level temporal resolution due to the huge computational domain with numerous grids for urban residential areas. In this paper, three fast fluid dynamics (FFD) models with different pressure-correction schemes (i.e., SIPC, NIPC and RIPC) for solving Navier-Stokes (N-S) equations are implemented in OpenFOAM. The computational accuracy and speed of these FFD models is validated and analyzed through three cases. For the prediction of airflow distribution in urban residential areas, the average relative error between the simulation results of the FFD models and the wind tunnel experimental data is less than 15 %. The speeds of these FFD models show SIPC > NIPC > RIPC from fast to slow under the same number of grids, turbulence model and time step size, and these speeds are about 15 times faster than the commercial CFD code Ansys Fluent. The computing time of the three FFD models approximately shows a linear increase with the number of grids, and the difference in computing time between the other two FFD schemes and the SIPC scheme becomes larger and larger as the number of grids increases from 0.3 million to 3.0 million. There is almost no difference in the number of grids required to achieve grid independence for the three FFD models. On the premise of ensuring accuracy, the SIPC scheme has the fastest computational speed, and it could be preferred to quickly evaluate the airflow distribution of different residential areas in urban planning stage.

Combustion of Fuel Surrogates: An Application to Gas Turbine Engines

The previously developed approaches for fuel droplet heating and evaporation processes, mainly using the Discrete Multi Component Model (DMCM), are investigated for the aerodynamic combustion simulation. The models have been recently improved and generalised for a broad range of bio-fossil fuel blends so that the application areas are broadened with an increased accuracy. The main distinctive features of these models are that they consider the impacts of species’ thermal conductivities and diffusivities within the droplets in order to account for the temperature gradient, transient diffusion of species and recirculation. A formulation of fuel surrogates is made using the recently introduced model, referred to as “Complex Fuel Surrogate Model (CFSM)”, and analysing their heating, evaporation and combustion characteristics. The CFSM is aimed to reduce the full composition of fuel to a much smaller number of components based on their mass fractions, and to formulate fuel surrogates. Such an approach has provided a proof of concept with the implementation of the developed model into a commercial CFD code ANSYS Fluent. A case study is made for the CFD modelling of a gas turbine engine using a kerosene fuel surrogate, which is the first of its kind. The surrogate is proposed using the CFSM, with the aim to reduce the computational time and improve the simulation accuracy of the CFD model.

Forecasting a bubbly-intermittent flow regime transition in helically coiled tubes

Simulations of gas–liquid turbulent flows in helically coiled tubes are conducted by a two-fluid hydrodynamic model coupled with the population balance equation. A model of bubble breakup in a turbulent flow, recently developed by the authors, is incorporated into the ANSYS Fluent CFD code employed as a computational tool. The population balance equation is solved by a discrete method. A realizable k-epsilon turbulence model is used for all computations. Numerous simulations of gas-liquid flows in vertically oriented coiled tubes are conducted. Three different coil diameters are employed for simulations. Computed bubble chord distributions are close to experimental data. Simulated dependencies of the superficial liquid velocity on the superficial gas velocity, corresponding the bubbly-intermittent flow regime transition, are in excelled agreement with measured ones. On the other hand, dependencies, obtained using standard bubble breakup models, significantly deviate from experimental results. Thus, it is demonstrated that employment of the novel bubble breakup model greatly enhances a computational accuracy of gas-liquid flows in helically coiled tubes.

Prediction of Liner Metal Temperature of an Aeroengine Combustor with Multi-Physics Scale-Resolving CFD.

Computational Fluid Dynamics is a fundamental tool to simulate the flow field and the multi-physics nature of the phenomena involved in gas turbine combustors, supporting their design since the very preliminary phases. Standard steady state RANS turbulence models provide a reasonable prediction, despite some well-known limitations in reproducing the turbulent mixing in highly unsteady flows. Their affordable cost is ideal in the preliminary design steps, whereas, in the detailed phase of the design process, turbulence scale-resolving methods (such as LES or similar approaches) can be preferred to significantly improve the accuracy. Despite that, in dealing with multi-physics and multi-scale problems, as for Conjugate Heat Transfer (CHT) in presence of radiation, transient approaches are not always affordable and appropriate numerical treatments are necessary to properly account for the huge range of characteristics scales in space and time that occur when turbulence is resolved and heat conduction is simulated contextually. The present work describes an innovative methodology to perform CHT simulations accounting for multi-physics and multi-scale problems. Such methodology, named U-THERM3D, is applied for the metal temperature prediction of an annular aeroengine lean burn combustor. The theoretical formulations of the tool are described, together with its numerical implementation in the commercial CFD code ANSYS Fluent. The proposed approach is based on a time de-synchronization of the involved time dependent physics permitting to significantly speed up the calculation with respect to fully coupled strategy, preserving at the same time the effect of unsteady heat transfer on the final time averaged predicted metal temperature. The results of some preliminary assessment tests of its consistency and accuracy are reported before showing its exploitation on the real combustor. The results are compared against steady-state calculations and experimental data obtained by full annular tests at real scale conditions. The work confirms the importance of high-fidelity CFD approaches for the aerothermal prediction of liner metal temperature.

CFD analysis of steam condensation with air in the tubes bundle channel under natural convection conditions

The condensation heat transfer characteristics of steam with the non-condensable gases (NCGs) in the tubes bundle channel are quite different from those in the simple geometry structure, such as the single tube and flat plate. In the present work, to evaluate the thermal characteristics of steam condensation with NCGs in the vertical tubes bundle channel, the numerical model of steam condensation was established based on the CFD code ANSYS FLUENT, which combined the gas component transport equations and the diffusion balance model. And several conditions with different thermal parameters were simulated, the simulation results are in good agreement with the experimental data. The condensation heat transfer in a hexagonal 7-tubes bundle channel with various tube pitches (from 1.5d to 5d) is investigated. The results indicate that the distribution of typical thermal parameters, such as velocity, air mass fraction, temperature and density, is quite different from that in the single tube due to the cross and mixture in each condensation tube boundary layer. As the condensation length increases, the air mass fraction rises, the gas flow rate decreases and the sub-cooling decreases, resulting in a lower natural convection intensity. When the tube pitch is less than 4d, the condensation heat transfer capacity in the tubes bundle channel is weakened obviously, and the heat transfer coefficient with the tube pitch 1.5d is only about 32% of that in a single tube. The air mass fraction and pressure have a significant positive effect on the heat transfer coefficient, and the wall sub-cooling has a significant negative effect on that.

The Effect of Wind Energy on Microclimate: Lessons Learnt from a CFD Modelling Approach in the Case Study of Chios Island

During the last three decades, rapid growth of wind energy has led to questions regarding the possible impacts of wind farms on local weather and microclimates. Physically, the increased turbulence due to the wind turbine operation affects the mixing processes, may slightly disturb the pressure and temperature distributions downstream of wind farms and may have an impact on natural ecosystems such as the famous mastic tree population located on the island of Chios in the North Aegean Sea. This study explores the wind farms and their wake effects downstream with a particular focus on the effect on the southern part of the island where the mastic trees cultivation is located. The analysis is carried out with the use of the commercial CFD code ANSYS Fluent. Steady state computations of full 3D Navier–Stokes equations, using the k-ε turbulence closure scheme are carried out. The development of the multiple wake effects of the wind farms and their propagation downstream is examined under low and high turbulence intensities. Results clearly indicate that for both test cases there is no impact to the local microclimate and to the mastic Tree population.

Effect of the Preheated Oxidizer Temperature on Soot Formation and Flame Structure in Turbulent Methane-Air Diffusion Flames at 1 and 3 atm: A CFD Investigation

This article presents the results of computations on pilot-based turbulent methane/air co-flow diffusion flames under the influence of the preheated oxidizer temperature ranging from 293 to 723 K at two operating pressures of 1 and 3 atm. The focus is on investigating the soot formation and flame structure under the influence of both the preheated air and combustor pressure. The computations were conducted in a 2D axisymmetric computational domain by solving the Favre averaged governing equation using the finite volume-based CFD code Ansys Fluent 19.2. A steady laminar flamelet model in combination with GRI Mech 3.0 was considered for combustion modeling. A semi-empirical acetylene-based soot model proposed by Brookes and Moss was adopted to predict soot. A careful validation was initially carried out with the measurements by Brookes and Moss at 1 and 3 atm with the temperature of both fuel and air at 290 K before carrying out further simulation using preheated air. The results by the present computation demonstrated that the flame peak temperature increased with air temperature for both 1 and 3 atm, while it reduced with pressure elevation. The OH mole fraction, signifying reaction rate, increased with a rise in the oxidizer temperature at the two operating pressures of 1 and 3 atm. However, a reduced value of OH mole fraction was observed at 3 atm when compared with 1 atm. The soot volume fraction increased with air temperature as well as pressure. The reaction rate by soot surface growth, soot mass-nucleation, and soot-oxidation rate increased with an increase in both air temperature and pressure. Finally, the fuel consumption rate showed a decreasing trend with air temperature and an increasing trend with pressure elevation.

CFD Simulations for the Selection of an Appropriate Blade Profile for Improving Energy Efficiency in Axial Flow Mine Ventilation Fans

Purpose This study focuses on one of the key design aspects of mine ventilation fans, i.e. the selection of an appropriate aerofoil blade profile for the fan blades in order to enhance the energy efficiency of axial flow mine ventilation fans, using CFD simulations. Methods Computational simulations were performed on six selected typical aerofoil sections using CFD code ANSYS Fluent 6.3.26 at angles of attack varying from 0° to 21° at an interval of 3° and at Reynolds number Re = 3 × 106 , and various aerodynamic parameters, viz. coefficients of lift (Cl) and drag (Cd) as a function of angle of attack (α) were determined to assess the efficiency of the aerofoils. Results The study revealed that the angle of attack has a significant effect on the lift and drag coefficients and stall condition occurred at α values of 12° and 15° in most of the aerofoils. Based on the criterion of higher lift to drag ratio (Cl/Cd), a blade profile was chosen as the most efficient one for mine ventilation fans. Practical implications This study forms a basis for selecting appropriate blade profiles for the axial flow fans used for ventilation in mining industry. Originality/value The application of an appropriate aerofoil blade profile will impart energy efficiency to the mine ventilation fans and thereby result in energy saving in mine ventilation.

Auto-Ignition and Numerical Analysis on High-Pressure Combustion of Premixed Methane-Air mixtures in Highly Preheated and Diluted Environment

ABSTRACT This work investigates both autoignition and combustion characteristics in highly preheated and diluted combustion of a laminar premixed stoichiometric CH4/O2/N2 mixture in a cylindrical combustor operating at elevated pressures. The analysis was carried out for a range of operating parameters, including reactant preheat temperatures of 1100–1500 K, combustor pressures of 1-10 atm, and in a highly diluted mixture, achieved by decreasing the oxygen content in the oxidizer from 21% to 3% on volume basis. Simulations were conducted using the laminar premixed adiabatic PFR (plug flow reactor) model of Ansys Chemkin Pro. Two-dimensional pictorial representation was performed using the finite volume-based CFD code Ansys Fluent 19.2. Finite-rate chemistry with the detailed chemical mechanism GRI Mech 3.0 was used for combustion analysis. Results showed that OH and HCO mole fractions decreased with increasing combustor pressure and N2 dilution (or decreased O2 content), while the mole fractions increased with reactant temperature. It was also found that, by reducing the oxygen content in the mixture, the flame stabilized far away from the combustor inlet. In contrast, an increase in combustor pressure and reactant temperature stabilized the flame toward the combustor inlet. These flame stabilization characteristics at different locations of the combustor are explained in terms of ignition delay time, which were calculated using the closed homogenous reactor (CHR) model available in the Ansys Chemkin Pro package. The flame peak temperature decreased with increased N2 dilution and increased by increasing the reactant temperature. Moreover, the peak temperature varied marginally when the combustor pressure was increased. Finally, a regime diagram was prepared to show the various combustion modes, such as HiTAC, MILD combustion, and the no ignition region as a function of O2 content and reactant temperature for different operating pressures. The CO and NO emission were reduced with an increase in pressure in the MILD combustion region.

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.

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.

Study of a New Type of Flettner Rotor in Merchant Ships

Abstract Wind energy is a clean and renewable source of energy. This study seeks to explore the potential for utilising wind power for merchant ships. A new type of Flettner rotor (rotating cylinder) mounted on the superstructure of a ship is proposed and numerically simulated. The construction and installation of the rotating cylinder is designed and a numerical simulation of the ship-mounted cylinder is carried out, using the commercially available CFD code Ansys Fluent to obtain parameters such as lift and drag coefficient of the cylinder in different conditions. Specifically, it is found that the cylinder type superstructure can play a certain role in reducing the effect of friction by comparing traditional and cylindrical superstructures; the rotating cylinder can generate auxiliary thrust for the ship. After analysis, the wind speed around the cylinder and spin ratio will have a direct influence on its thrust effect; there is an inflection point in the lift coefficient with the increase of α; the thrust coefficient (8.63) reaches the maximum environmental wind speed at 10 m/s and spin ratio is 2.5. For the rotating cylinder, the greater the environmental wind, the greater the thrust contribution generated under the same spin ratio conditions. The maximum thrust can reach 750,000 N; the cylinder’s auxiliary propulsion contribution shows a better advantage in α = 2.0. The effective power generated by the cylinder reaches a maximum of 2,240 kW for environmental wind speed = 20 m/s and α = 1.0.

Kinetic model study on biomass pyrolysis and CFD application by using pseudo-Bio-CPD model

Pyrolysis is the key step in biomass thermochemical conversion process. The network model can accurately predict the pyrolysis process but generally cannot incorporate the combustion and gasification sub-models due to its complexity. This paper used the Bio-CPD model to predict the pyrolysis products of softwood and hardwood respectively; based on the predicted results, two empirical-simple forms of pyrolysis models were further optimized. The ultimate kinetic parameters obtained are suitable for biomass pyrolysis at high heating rate. For softwood, after being optimized, the apparent frequency factor and E/R of single rate are 4.3106e + 07 s−1, 10042 K respectively. While for two-competing rates model, the parameters are, α1 = 0.75, α2 = 0.89, A1 = 7992 s−1, E1/R = 7000 K, A2 = 8.3e + 09 s−1, E2/R = 14520 K, respectively. The numerical simulation of biomass pyrolysis and combustion process were performed by using CFD code Ansys Fluent. The results reveal that the release of volatile predicted by the default parameters have a delay compared with the actual process and is not appropriate for biomass simulation, while the optimized parameters in two simple models are accurate enough to simulate the biomass pyrolysis at high heating rate (103–105 K/s).

Effect of rib arrangements on the flow pattern and heat transfer in internally ribbed rectangular divergent channels

In this article, a numerical investigation is conducted to analyze three-dimensional incompressible Navier-strokes flows through the rectangular divergent square ribbed channels with different Reynolds number value 20,000, 40,000 and 60,000 having five different configurations of square ribs (p/e = 2.5, 3.33, 5, 10, and 20) has been used as roughness element. The commercial finite-volume based CFD code ANSYS FLUENT is used to simulate turbulent airflow through the channels. The RNG k-ε turbulence model is used to solve the transport equations for turbulent flow energy and dissipation rate. Detailed results about average heat transfer and fluid friction in a rectangular divergent square channel are presented and discussed.

A 3D model to solve U-tube steam generator secondary side thermal-hydraulics with coupled primary-to-secondary side heat transfer

The U-tubes of steam generators (SG) are concerned by vibration issues. The vibration behavior is driven by the local secondary flow (velocity, void fraction, two-phase pattern). Fluid-elastic instability (FEI) can be considered as the most severe vibration phenomenon, since it features high vibration amplitudes and tube-to-tube contacts, which can rapidly cause tube rupture. In order to predict if the fluid forces exerted along the tube bundle can trigger a FEI, numerical tools able to calculate the secondary side of a SG are needed. In the frame of its mission of assessing methods adopted by utilities for demonstrating the safe operation of nuclear facilities, the French Institut de Radioprotection et de Sûreté Nucléaire (IRSN) has developed such a numerical model. The model is based on a 3D homogeneous drift-flux formulation of the SG steam-water mixture, together with a porous media approach to account for the tube bundle. The model is implemented in the ANSYS Fluent CFD code. The SG primary side is solved using a dedicated meshing. The secondary side and the primary side meshes communicate through heat transfer, which is fundamental to obtain consistent numerical results. The details of the numerical approach are described in the first part of this paper. Then, numerical versus experimental results comparisons in terms of heat transfer are provided for a SG test facility: numerical and experimental results are in good agreement. The model was then applied to a real SG: numerical results are in good agreement with nominal operating parameters.

Computational Fluid Dynamics Study of Roughened Solar Air Heater

A 2-dimensional numerical investigation has been conducted to examine the effect of three distinct turbulators (namely M shaped, Wedge shaped and Reverse wedge shaped) on the performance of solar air heater (SAH) for relevant Reynolds number ranges from 4000 to 18000. CFD code ANSYS FLUENT is used for simulation of turbulent airflow. For all three geometries constant ratio of e/Dh = 0.021 (where e = 0.7 and Dh = 33.33) and ratio P/e = 14.285 (where p = 10) is used. Turbulence Kinetic energy and velocity contours for all turbulators have also been studied in this analysis. M-Shaped turbulators outperformed the other two turbulators with maximum value of THPP.

STH/CFD coupled calculations of postulated transients from mixed to natural circulation conditions in the NACIE-UP facility

In the present paper, coupled STH/CFD calculations are performed addressing two operating conditions in the frame of the NACIE-UP experimental campaign. In order to simulate mixed and natural circulation phenomena related to liquid metals thermal hydraulics, the RELAP5/Mod3.3 STH code and the CFD code ANSYS Fluent are adopted in an integrated manner. The combined use of STH and CFD codes aims to help the user overcoming the limits of the individual techniques and thus achieving a better predicting capability with respect to each stand-alone application.Measured values and calculated results are compared. In particular, the coupled application provides the best results in terms of predicted mass flow rate and comprehensiveness of information giving the possibility to analyse the local and cross-sectional distributions. Furthermore, as an additional beneficial aspect, CFD results can be used as a tuning tool for some of the STH code parameters. The aim of the present work is highlighting the advantages and drawbacks of the adopted techniques, also reporting the margins of error that may presently be expected from these applications. Though perfectly matching results were not obtained, coupled STH/CFD application report promising modelling capabilities and may be consequently considered as a sound candidate for addressing liquid metal thermal hydraulics in complex geometries and large systems.

Some Recent Fluid-Structure Interaction Approaches for the Wave Current Behaviour With Offshore Structures

The effects of the surface waves generated by the wind have a significant effect on the currents. A wave current coupled model plays an important role in the design offshore structures. The interaction between fluids such as incompressible ocean waves and current and offshore structures is significant with many real-time applications in offshore engineering. These coupled models can be applied to Offshore Floating Production Operating and offloading (FPSO), Wind or current turbines and offshore pipelines. The complex issues related to the design are analyzed by using Computational Fluid Dynamics, which requires an investigation of the multiphase flow between wave and current and the structure which is considered restrictive due to the computational cost. If viscous effects are neglected then the single-phase flow models have been recommended, where wave-current interaction have been modelled successfully. Models have been developed where velocities and pressure are computed and the results can be verified with the experimental results available in the literature. In this study the existing numerical methods, mesh types are discussed along with their coupling methods. Here single-phase and multiphase models with small and medium movement are reviewed and their applications are highlighted. Commercial CFD code ANSYS Fluent has been found most reliable and easy to use tool for the analysis of fluid flow interacting with offshore structures near the free surface. It can successfully be used for determination of fluid dynamics of offshore environments installed complex multi-component structures. Dynamic mesh facility is more useful for multiphase modelling of floating structures.