Steady-state Computational Fluid Dynamics Model Research Articles

Analysis of the shear-driven flow in a scale model of a phase separator: Validation of a coupled CFD approach using experimental data from a physical model

The effect of shear stress at the interface between a flowing gaseous phase and a liquid-filled cavity, a scenario commonly found in flue gas/slag phase separators, is investigated in this study. This effect is frequently disregarded in computational fluid dynamics (CFD) simulations within metallurgy, primarily due to its limited influence on the motion of liquids (e.g., slag, liquid metal) when compared to other factors such as stirring by natural convection or bubbling. This study was undertaken to investigate shear-driven flow in a 1:4 scale model of a phase separator in which a flue gas stream coming from a furnace is mobilizing the flow of a slag melt. To cover a wide range of operating conditions, silicone oil with varying viscosities (20, 50, and 70 cSt) was considered for mimicking viscous slag. Additionally, different volumetric airflow rates (18, 27, and 36 m3/h) were considered to simulate the flue gas flow. Particle image velocimetry (PIV) measurements were conducted on the model. The experimental results were utilized to validate computationally efficient, coupled steady-state simulations of the system. Notably, the steady-state simulations, requiring approximately one hour of CPU time, demonstrated a computation time decrease of two magnitudes compared to conventional Volume of Fluid (VOF) modeling. A stable, laminar flow pattern of the liquid phase with surface velocities of up to approximately 30 mm/s was observed for the case with the lowest oil viscosity and the highest airflow rate, while a steady, turbulent flow was observed in the gas phase. Conversely, the lowest surface velocities, measuring around 5 mm/s, were recorded and calculated for the scenario with the highest oil viscosity and the lowest airflow rate. It was noted that velocities increased proportionally with the airflow rate but exhibited a disproportionate relationship with oil viscosity. The prediction of velocity magnitudes by the steady-state CFD model was highly accurate, with only minor discrepancies observed between the measured and calculated flow patterns. In summary, valuable insights into the often-overlooked shear stress effects at the phase boundary in gaseous-liquid flow over a cavity are provided by our study.

Prediction of the cohesive zone in a blast furnace by integrating CFD and SVM modelling

ABSTRACT High efficiency and clean emission operation of a blast furnace are mainly determined by its operating stability, which is closely related to the position of the cohesive zone (CZ) in the blast furnace. In order to monitor the CZ position in real time, a prediction model of the CZ was proposed by combining an off-line computational fluid dynamics (CFD) calculation and support vector machine (SVM) modelling. An axisymmetric two-dimensional steady-state CFD model was established to simulate the fluid flow, heat and mass transfer in the blast furnace shaft. The sample dataset of the CZ information was established based on the CFD off-line calculation, and the prediction of the CZ position was realized by SVM modelling. The results show that the established model can predict the CZ position in real time with high accuracy, providing effective guidance to the blast furnace operation and control.

CFD simulation of airflows and ammonia emissions in a pig compartment with underfloor air distribution system: Model validation at different ventilation rates

Pig buildings with underfloor air distribution (UFAD) system provide the animal area with efficient cooling and better air quality compared ceiling air inlets. This is because the air inlets near the floor and the exhaust opening at the ceiling allow the excess heat and the old air to be displaced from the animal area to the upper part of the building. Typical inlet types of UFAD systems in Flanders (Belgium) are the slatted floor units placed in service alley. The main drawback in pig buildings with UFAD systems is that during winter, cold draughts often occur in the animal area, and due to the air displacement ventilation process, there is a risk of NH3 transport from the slurry pit. The effect of NH3 emissions is important as it leads to acidification and eutrophication. Modelling airflows and NH3 emissions using Computational Fluid Dynamics (CFD) can promote the development of techniques for mitigating NH3 emissions, improving indoor air quality and animal thermal comfort. A steady-state CFD model was therefore developed to predict the indoor airflow and NH3 distribution in a pig compartment with a UFAD system. An advanced NH3 emission modelling approach was implemented in the CFD model to simulate NH3 generation in the slurry pit and pen floor. In order to validate the CFD model, two experiments were performed. The first experiment was conducted in a compartment with mock-up pigs at different ventilation rates to validate the modelled air velocity and temperature fields. The second experiment was conducted in a compartment occupied by real pigs to validate the modelled airflow patterns, temperature, CO2 and NH3 concentrations. Overall, there was a good agreement between the simulated and measured results. The field experiment and CFD model results confirmed that NH3 was transported from the slurry pit to the compartment. The air exchange rate of the slurry pit in the CFD model increased from 10.4 to 26.1 h−1 as the ventilation rate was increased from 11 to 92 m3 h−1 pig−1 due to the air displacement in the slurry pit.

Performance Evaluation of a Tidal Current Turbine with Bidirectional Symmetrical Foils

As one might expect, tidal currents in terms of ebb and flood tides are approximately bidirectional. A Horizontal Axial Tidal Turbine (HATT) with unidirectional foils has to be able to face the current directions in order to maximize current energy harvesting. There are two regular solutions to keep a HATT always facing the direction of the flow, which are transferred from wind turbine applications. One is to yaw the turbine around the supporting structure with a yaw mechanism. The other is to reverse the blade pitch angle through 180° with a pitch-adjusting mechanism. The above solutions are not cost-effective in marine applications due to the harsh marine environment and high cost of installation and maintenance. In order to avoid the above disadvantages, a turbine with bidirectional foils is presented in this paper. A bare turbine with bidirectional foils is characterized in that it has nearly the same energy conversion capability in both tidal current directions without using the yaw or pitch mechanism. Considering the working conditions of the bidirectional turbine in which the turbine is installed on a mono-pile, the effect of the mono-pile on the turbine’s performance is evaluated in this paper, especially when the turbine is downstream of the mono-pile. The paper was focused on the evaluation of the hydrodynamic performance of the bidirectional turbine. The hydrodynamic performance of the bare bidirectional turbine without any supporting structure was evaluated based on a steady-state computational fluid dynamics (CFD) model and model tests. Performance comparison has been made between the turbine with bidirectional foils and the turbine with NACA foils. The effect of the mono-pile on the performance of the bidirectional turbine was studied by using the steady-state and the transient CFD model. The steady-state CFD model was used to evaluate the effect of the mono-pile clearance, which is the distance between the mono-pile and the turbine on the performance of the turbine. The transient CFD model was used to determine the time-dependent characteristics of the turbine, such as time-dependent power and drag coefficients. The results show that the bare bidirectional turbine has nearly the same energy conversion capability in both tidal current directions. The performance of the bidirectional turbine is inferior to the turbine with NACA foils. At the designed tip speed ratio, the power coefficient of the turbine with NACA foils is 0.4498, which increases by 1.6% compared to the 0.4338 of the bidirectional turbine. The turbine’s performance decreases due to the introduction of the mono-pile, and the closer the turbine is to the mono-pile, the greater effect on the turbine’s performance the mono-pile has. At the designed clearance of 1.5 DS, the presence of a mono-pile decreases the peak Cp value by 1.82% and 3.17% to a value of 0.4156 and 0.4004 for the turbine located in the mono-pile upstream and downstream, respectively. The mono-pile can result in the fluctuation of the turbine’s performance. This fluctuation will detrimentally harm the life of the turbine as it will lead to increased wear and fatigue issues.

Computational fluid dynamics study of yield power law drilling fluid flow through smooth-walled fractures

Presence of natural fractures in sub-surface makes an oil well drilling operation very challenging. As one of the major functions of drilling mud is to maintain bottomhole pressure inside a wellbore to avoid any invasion of unwanted high-pressure influx (oil/gas/water), drilling a well through these fractures can cause severe mud loss into the formation and subsequent danger of compromising the wellbore pressure integrity. The aim of this paper is to carry out a Computational Fluid Dynamics (CFD) study of drilling fluid flow through natural fractures to improve comprehensive understanding of the flow in fractured media. The study was carried out by creating a three-dimensional steady-state CFD model using ANSYS (Fluent). For simplicity and validation purpose, the model defines fracture as an empty space between two circular disks. Moreover, it is considered that single-phase fluid is flowing through fractures. By solving the flow equations in the model, correlations to determine the fracture width and invasion radius have been developed for specific mud rheological properties. Prior to onset of drilling and at the end of lost circulation, similar correlations can be developed by knowing rheological properties of drilling fluid which will be very much helpful to take an instantaneous action during lost circulation, i.e., determining lost circulation material particle size and also be useful in the well development stage to determine the damaged area to be treated.

Jetstream 31 national flying laboratory: Lift and drag measurement and modelling

Lift and drag flight test data is presented from the National Flying Laboratory Centre, Jetstream 31 aircraft. The aircraft has been modified as a flying classroom for completing flight test training courses, for engineering degree accreditation. The straight and level flight test data is compared to data from 10% and 17% scale wind tunnel models, a Reynolds Averaged Navier Stokes steady-state computational fluid dynamics model and an empirical model. Estimated standard errors in the flight test data are ±2.4% in lift coefficient, ±2.7% in drag coefficient. The flight test data also shows the aircraft to have a maximum lift to drag ratio of 10.5 at Mach 0.32, a zero lift drag coefficient of 0.0376 and an induced drag correction factor of 0.0607. When comparing the characteristics from the other models, the best overall comparison with the flight test data, in terms of lift coefficient, was with the empirical model. For the drag comparisons, all the models under predicted levels of drag by up to 43% when compared to the flight test data, with the best overall match between the flight test data and the 10% scale wind tunnel model. These discrepancies were attributed to various factors including zero lift drag Reynolds number effects, omission of a propeller system and surface excrescences on the models, as well as surface finish differences.

Impacts of inner/outer reactor heat recirculation on the characteristic of micro-scale combustion system

Flame stability and thermal performance of two different heat recirculation micro-combustors (inner reactor heat recirculation (IHR) and outer reactor heat recirculation (OHR)) are investigated using computational fluid dynamics (CFD) and compared together. A two-dimensional steady state CFD model including temperature dependent properties, laminar flow and transport, one step chemical reaction, surface-to-surface radiation, and heat conduction within solid walls has been carried out to assess flame propagation velocity, flame thickness, excess enthalpy, heat loss, and emitter efficiency. It is observed that both cases significantly extend flammability and blow-off limits due to preheating of the reactive mixture. The maximum flame propagation velocities of IHR and OHR in stoichiometric mixture are predicted 160.2cm/s and 126.1cm/s, respectively. It is found that super-adiabatic flame temperature takes place when dimensionless excess enthalpy is positive and it is maximum in the stoichiometric equivalence ratio. Heat loss can be varied from 245.8 to 248.6W for IHR and from 249.6 to 254W for OHR configuration. Therefore, there is a relative improvement in the Thermal quenching limit of IHR. It is concluded that IHR micro-combustor profoundly affects flame characteristic and stability, but OHR presents a higher range of emitter efficiency.

Numerical investigations on coupled heat transfer and synthetical performance of a pressurized volumetric receiver with MCRT–FVM method

This paper presents an axisymmetric steady-state computational fluid dynamics model and further studies on the complex coupled heat transfer combined radiation–convection–conduction in the pressurized volumetric receiver (PVR), by combining the Finite Volume Method (FVM) and the Monte Carlo Ray-Trace (MCRT) method. Based on this, effects of geometric parameters of the compound parabolic concentrator (CPC) and properties of the porous absorber on synthetical characteristics and performance of the photo-thermal conversion process in the PVR are further analyzed and discussed detailedly. It is found that the solar flux density distributions are always very heterogeneous with large nonuniformities, and the variation trends of the corresponding temperature distributions are very similar to these but with much lower order of magnitude. The CPC shape determined by the CPC exit aperture has much larger effects on synthetical characteristics and performance of the PVR than that of the CPC entry aperture with a constant acceptance angle. And a suitable or optimal thickness of the porous absorber could be determined by examining where the drastic decreasing trends occur at the curves of variations of synthetical characteristics and performance with the porosity.

Numerical prediction of the effect of vent arrangements on the ventilation and energy transfer in a multi-span glasshouse using a bi-band radiation model

The distributed climate inside a greenhouse mainly results from mass, momentum and energy transfers occurring through the openings or through the cover. These transfers can be assessed using computational fluid dynamics (CFD) techniques. However, to date very few studies considered properly the radiative exchanges between the surfaces inside the calculation domain by solving simultaneously the radiative transfer equation (RTE) and the convective ones. The object of this work is to implement this equation in order to get an overview of the resulting climate inside the greenhouse. The analysis focuses on the heterogeneity of the climatic parameters in the canopy vicinity as well as on the ventilation rate. For the purpose of the study, a two-dimensional steady-state CFD model was developed. It is based on the resolution of the Navier–Stokes equations with the Boussinesq assumption and a k–ε closure. Solar and atmospheric radiations were included by solving the RTE and distinguishing short [0–3 μm] and long wavelength [3–100 μm] contributions. The virtual tracer gas technique was implemented to assess the ventilation rate. The model was first successfully validated against experimental data considering a glasshouse divided into two compartments separated by a plastic partition and comparing simulated and recorded temperatures inside the shelter and along the walls (roof and sides). Simulations were then carried out for a 2500 m2 four-span sloped-roof glasshouse covered with a 4-mm-thick horticulture glass and equipped with continuous roof vents and one side-opening. Results show that roof-opening configurations combined with side-vent location strongly affect inside ventilation and microclimate parameters. Thus, for hot summer conditions with relatively low wind, computed ventilation rates varied from 2 to 40 air changes per hour whereas temperature differences varied from 3 to 13 °C. This study also showed that other characteristics such as climate heterogeneity must be investigated in order to define the best ventilation configuration and that strong velocity and temperature heterogeneity can occur at the plant level. Simulations, however, suggest that the symmetric roof-vent configuration seems to be a good compromise between cooling and homogeneity performances.