Dimensional Computational Fluid Dynamics Research Articles

Analysis of aero engine plume potential core infrared signature

Purpose Aero-engine exhaust plume length can be more than the aircraft length, making it easier to detect and track by infrared seeker. Aim of this study is to analyze the effect of free stream Mach number (M∞) on length of potential core of plume. Also, change in infrared (IR) signature of plume and aircraft surface with variation in elevation angle (θ) is examined. Design/methodology/approach Convergent divergent (CD) nozzle is located outside the rear fuselage of the aircraft. A two dimensional axisymmetric computational fluid dynamics (CFD) study was carried out to study effect of M∞ on potential core. The CFD data with aircraft and plume was then used for IR signature analysis. The sensor position is changed with respect to aircraft from directly bottom towards frontal section of aircraft. The IR signature is studied in mid wave IR (MWIR) and long wave IR (LWIR) band. Findings The potential plume core length and width increases as M∞ increases. At higher altitudes, the potential core length increases for a fixed M∞. The plume emits radiation in the MWIR band, whereas the aerodynamically heated aircraft surface emits IR in the LWIR band. The IR signature in the MWIR band continuously decreases as the sensor position changes from directly bottom towards frontal. In the LWIR band the IR signature initially decreases as the sensor moves from the directly bottom to the frontal, as the sensor begins to see the wing leading edges and nose cone, the IR signature in the LWIR band slightly increases. Originality/value The novelty of this study comes from the data reported on the effect of free stream Mach number on the potential plume core and variation of the overall IR signature of aircraft with change in elevation angle from directly below towards frontal section of aircraft.

Ambient wind conditions impact on energy requirements of an offshore direct air capture plant

This study proposes an off-grid direct air (carbon) capture (DAC) plant installed on the deck of an offshore floating wind turbine. The main objective is to understand detailed flow characteristics and CO2 dispersion around air contactors when placed in close proximity to one another. A solid sorbent DAC design is implemented using a commercially deployed air contactor configuration and sorbent. The sorbent is assumed to undergo a temperature vacuum swing adsorption cycle. Computational fluid dynamics (CFD) is used to determine the local conditions entering each unit based on varying wind speed and angle. Two-dimensional (2D) simulations were used to determine the pressure drop through a detailed air contactor design considering the sorbents APDES-NFC, Tri-PE-MCM, MIL-101(Cr)-PEI-800, and Lewatit VP OC 106. Only APDES-NFC was explored for further analysis in the three dimensional (3D) CFD dispersion model. 3D simulations were used to model flow patterns and CO2 dispersion using passive scalars. A worst case scenario is analyzed for all DAC units in adsorption mode with fans running simultaneously. 2D simulations show an under utilization of contactor length, and quantify pressure loss curves for four common sorbents. One commercially deployed sorbent is considered for further analysis; a pressure drop of 390.62 Pa is experienced for a flow velocity of 0.73 m s−1 through a 1.5m×1.5m×1.5m contactor. Using 3D simulations, fan energy demands are computed based on flow velocities and applied pressure gradients. There is found to be a decrease in overall fan power demand as wind speed increases. High wind speeds can passively drive the adsorption process with fans shut off at certain wind directions. This occurs at an average contactor inlet velocity of 17.5 m s−1, correlating to a hub height (150 m) wind speed of 24 m s−1. Thermal energy demands are computed based on inlet CO2 concentrations entering downstream units. Thermodynamic work for desorption based on an assumed second law efficiency is compared to thermal energy for desorption computed using a simplified isotherm method, taking into account the impacts of humidity on CO2 adsorption. Going from 414.72 ppm to 300 ppm CO2 inlet concentration requires an additional 63.9 kWh (t- CO2)−1 using the 2nd law thermodynamic efficiency method and 25.9 kWh (t- CO2)−1 using the isotherm method. Contactor arrangement, wind angles, and wind speeds have a significant impact on flow patterns experienced, and resulting CO2 dispersion. High wind speeds assist in CO2 dispersion, resulting in higher inlet concentrations to downstream DAC units and decreased thermal energy requirement.

Investigating the accuracy of continuum models for the simulation of industrial maleic anhydride reactors: A comparative single particle CFD study

The selective oxidation of n-butane to maleic anhydride is a strongly exothermic reaction. Resulting local hot-spots and intraparticle temperatures high above the surrounding fluid temperature are challenging for safe and economic operation of reactors. Detailed modelling on all length scales is therefore required for an accurate description of this process. In this contribution, the one dimensional description of the ring-shaped catalyst, commonly used in continuum reactor modelling, is compared to three dimensional computational fluid dynamics simulations for the case of a single catalyst particle at different inclination angles (0 to 90°). Polytropic chemical reaction is considered under typical n-butane oxidation conditions (Rep=400), representing a catalyst particle close to the inlet, (T=673K) and at the hot-spot (T=730K) of an industrial reactor. Comparative analysis suggests that the one dimensional simplification is justified when external transport phenomena are not the limiting resistance. Otherwise, neglecting two spatial dimensions leads to erroneous predictions.

The methodology of decoupling fuel and thermal nitrogen oxides in multi-dimensional computational fluid dynamics combustion simulation of ammonia-hydrogen spark ignition engines

Under the paradigm of carbon neutrality, ammonia-hydrogen (NH3–H2) blended fuel presents itself as a zero-carbon alternative to petroleum-based fuels, effectively reducing carbon emissions originating from internal combustion engines. In the combustion process of conventional hydrocarbon fuels, the production of nitrogen oxides (NOX) predominantly arises from nitrogen present in the atmosphere, which occurs through the Zeldovich mechanism under high-temperature conditions. These NOX species, commonly referred to as thermal NOX, rely on inert nitrogen. However, the utilization of ammonia fuel activates the reactivity of nitrogen element, leading to the nitrogen-containing species formation, including NOX, termed as fuel NOX. Consequently, the combustion of ammonia-hydrogen fuel entails the coupling of thermally formed nitrogen oxides and fuel-derived nitrogen oxides. The generation of NOX is significantly influenced by the physicochemical environment, while the transient combustion conditions within the engine combustion chamber further complicate the process of NH3–H2 combustion and NOX formation. As a consequence, comprehensively investigating the NOX emission characteristics in NH3–H2 engines presents a considerable challenge. By decoupling fuel NOX and thermal NOX, a more profound understanding of NOX emission control strategies for ammonia-hydrogen engines can be attained. This research paper accomplishes the decoupling of fuel nitrogen elements and atmospheric nitrogen elements in three dimensional computational fluid dynamics engine combustion simulations. The results indicate that this decoupling methodology disregards the differentiation between the fuel NOX pool and the thermal NOX pool, resulting in a slight modification in NOX concentration. Nevertheless, this approach has minimal impact on the combustion process, ensuring that the NOX formation environment remains largely unchanged. Furthermore, it successfully demonstrates the spatial and temporal distribution characteristics of thermal NOX and fuel NOX, thereby furnishing an effective analytical tool for the comprehensive study of NOX emission characteristics in NH3–H2 engines.

Non-isothermal simulation of a corner vortex within entry flow for a viscoelastic fluid

Abstract A modified White-Metzner viscoelastic constitutive equation is incorporated into the state-of-the-art Three Dimensional Computational Fluid Dynamics (3D-CFD) framework for performing isothermal and non-isothermal entry flow simulations of a polymer melt. As a result, the corner vortex becomes smaller with increased isothermal temperature, namely, the so-called temperature-induced vortex reduction. In addition, the vortex grows with raising wall temperatures, whereas the vortex reduction is found under high inlet temperatures. Through the visualized flow patterns, it is significant to investigate the dramatic variations of vortex size in relation to fluid temperature, weighted viscosity and extension rate, as well as Weissenberg number and Trouton ratio.

A two-experiment finite similitude approach to experimental fluid mechanics

Fluid dynamics experimentation at scale provides an important means of investigation that is presently underpinned by dimensional analysis and computational fluid dynamics (CFD). Unfortunately, despite the obvious success of this twin approach, dimensional analysis provides no solution if scale effects are prevalent and CFD offers reduced practical advantage in the absence of a theory that links information across scaled experiments. This issue is addressed in this paper with the introduction of a new approach to scaled experimentation founded on the theory of finite similitude. Finite similitude is founded on the metaphysical concept of space scaling, where experimental apparatuses, facilities, prototypes, systems, wind tunnels etc., are scaled by the means of space contraction or expansion. There exists no practical means to contract or expand space but what is possible is a mathematical description of space scaling and its impact on governing physics, so providing a means for comparison with scaled systems and real-world experimental behaviours. This paper examines an adaptation of the finite-similitude theory, where two scaled experiments are involved but a second-order version of the theory is applied. All previous work has been limited to zeroth and first-order applications, but in the case of fluid dynamics, second order is shown necessary to capture more accurately convective terms. It is demonstrated in the paper by means of two scaled experiments (designed using second-order theory) that the approach is able to represent behaviours at the full scale that hitherto would have been deemed impossible with traditional dimensional analysis. Numerical and analytical case studies on gravity impacted flows are trialled to illustrate the benefits of the approach with percentage errors reduced from double to single digits.

Application of a one-dimensional fuel-oil dilution model coupled with an empirical droplet-to-film formation strategy for predicting in-cylinder oil effects in a direct injection engine

Nowadays climate change due to the unnatural increment of green-house effect is one of the most critical environmental issues. In this context, internal combustion engines are still a short - term valuable solution. This is made possible by the study and the development of synthetic or alternative fuels, such e - gasolines and hydrogen. In this context, direct injection is still the most adopted strategy to improve internal combustion engine efficiency. The installation of the injector on the cylinder head may lead to the impact of the fuel on the wall of the cylinder liner. This phenomenon causes lubricant oil dilution, possibly increasing particulate matter emission at low load and abnormal combustions, known as low - speed pre-ignitions, at high load. The present paper aims to evaluate the influence of a set of established key parameters anticipating the effects of lubricant oil - fuel diffusion through a one - dimensional model implemented in Python. The model accounts for the runtime deposition of the fuel film by means of the results of a three - dimensional Computational Fluid Dynamics spray simulation. The model accounts also for the heat and mass transfer between species and the liquid fuel phase change for a representative setup of nowadays injectors. The dilution of a multigrade lubricant oil caused by synthetic fuels under an engine cold start operative condition is evaluated in this work.

Review of Vent Systems of Space Vehicle, Spacecraft and Aircraft

The main focus of the review article is to present the vent system of space vehicle and spacecraft. Quasi-one dimensional, quasi-steady and isentropic analytical and computational fluid dynamics equations are employed to compute differential pressure inside the compartment. Discharge characteristics of vent system depend on geometry, location of vent and external environment. An inverse analysis is performed to estimate the discharge coefficient using measured and computed compartment differential pressure time history. The reconstructed differential pressures of the compartment are compared with pre- and post-flight data. The differential pressure and the rate of pressure drop in the compartments are analysed via isentropic equations. A numerical scheme based on compressible gas dynamics relation is discussed for pressurization of aircraft cabin. The vent valve with a spring loaded butterfly valve can be evaluated using the isentropic relations.

Multiphysics modeling of thermal behavior, melt pool geometry, and surface topology during laser additive manufacturing

Metal additive manufacturing (AM) processes regularly experience high temperatures, quick velocities and rapid solidification taking place in a small volume melt pool. Accurate capturing of data from the melt pools is very difficult and can require expensive equipment. Physics based numerical models can be used to simulate the AM process. However, there are many thermal and fluid dynamics models that have been developed each with their own sets of physical models and assumptions. In this work, a three dimensional multiphysics computational fluid dynamics model was used to obtain thermal behavior, geometry and surface topology from the melt pool of single laser scan tracks on a bare Inconel 625 substrate. The simulation results were compared with the highly controlled AMB2018-02 series of benchmark tests performed by the National Institute of Standards and Technology (NIST). The complex physics involved in the simulations, including heat and mass transfer, fluid flow, evaporation, and Marangoni convection enabled accurate prediction of the melt pool geometry, thermal behavior and the surface topology. The simulation results for the thermal behavior were mostly within the standard deviation of the experimental results. Simulation results from surface topography were able to capture the peak and valley trends. Overall, the underlying physics involved produced good results in a reasonable amount of time and were accurate enough to form a basis that can be coupled with other models to predict microstructure and other material properties.

Computational investigation of hydrodynamics, flow regimes and bubble size distribution in an airlift reactor

Airlift reactors (ALRs) are widely used in the chemical, petrochemical biological industry. A fundamental understanding of the flow field in these airlift reactors are necessary for efficient design and scaling up. In this work, the behavior of the flow field is investigated using the Euler–Eulerian approach. The liquid phase is modeled as continuous and the gas phase is dispersed in the form of bubbles. Three dimensional (3 D) transient computational fluid dynamics (CFD) simulations are performed to characterize flow behavior in ALR. The spatio-temporal variations in the flow field are quantified and an optimum liquid level in the ALR is determined. Various gas source locations are chosen and their effects on bubble plume motion are analyzed to find an optimum gas injection point that supports plume oscillation. Further, CFD simulations are performed to identify the prevailing flow regime in ALR for various gas source locations, and it is compared with experimental observations. The homogeneous and heterogeneous flow regimes are observed at lower and higher flow rates, respectively. The bubble size distribution is predicted using population balance equations through bubble coalescence and breakage models with interphase force formulations. This is computed through the discrete method of moments. The bubble size distribution is found to be narrow at lower gas flow rates and wider at higher gas flow rates. These predictions provide a unified description to characterize flow regimes in ALR.

Numerical estimation of critical local energy dissipation rate for particle detachment from a bubble-particle aggregate captured within a confined vortex

In flotation, interactions of bubble-particle aggregates with turbulent flow structures in the liquid medium result in particle detachment. This study aims to simulate this phenomenon involving a bubble-particle aggregate (bubble diameter ∼ 3 mm and particle diameter ∼ 314 µm) interacting with a turbulent flow structure manifested as a confined vortex in a square cavity connected to a square cross-section channel. An interface resolved three dimensional (3D) computational fluid dynamics (CFD) model was developed to quantify the bubble-vortex interaction dynamics over a range of channel Reynolds numbers. The CFD model produced a good agreement with the experimentally measured vorticity magnitude, local energy dissipation rate, and bubble motion. It was shown that a bubble-particle aggregate could be captured within the vortex by suitably varying the channel Reynolds number, eventually leading to particle detachment. A separate force balance analysis was performed to determine a criterion for particle detachment utilising the CFD model predicted vorticity and local energy dissipation rate. It was shown that a critical local energy dissipation rate ∼ 1.59 m2/s3 was required for particle detachment to occur, which was also verified experimentally.

2-Stroke RCCI Engines for Passenger Cars

Reactivity Controlled Compression Ignition (RCCI) is one of the most promising solutions among the low temperature combustion concepts, in terms of thermal efficiency and pollutant emissions. However, for values of brake mean effective pressure higher than 10 bar, in-cylinder peak pressure rise rates tend to be too high, limiting the specific power of any 4-Stroke (4S) engine. Such a limitation can be canceled by moving to the 2-Stroke (2S) cycle. Among many alternatives, the “Uniflow” scavenging system with exhaust poppet valves on the cylinder head allows the designer to reproduce the same identical combustion patterns of a 4-stroke RCCI engine, while increasing the indicated power output. The goal of the paper is to explore the potential of a 2-stroke RCCI engine, on the basis of a comprehensive experimental campaign carried out on a modified automotive 2.0 L, 4-stroke, four-cylinder, four-valve diesel engine. The developed prototype can run with one cylinder operating in 4-stroke RCCI mode (gasoline–diesel), while the others work in the standard diesel mode. A One Dimensional-Computational Fluid Dynamics (1D-CFD) model has been built to predict the performance of the same prototype, when operating all four cylinders in RCCI mode. In parallel, an equivalent 2-stroke RCCI virtual engine has been developed, by means of 1D-CFD simulations and empirical assumptions. A numerical comparison between the 4S and the 2S engines is finally presented, in terms of performance and emissions at full load. The study demonstrates that a 2S RCCI engine can maintain all of the advantages of the RCCI combustion, strongly reducing the penalization in terms of performance, in comparison to a standard 4S diesel engine.

Aerodynamic reduced-order Volterra model of an ornithopter under high-amplitude flapping

The unsteady aerodynamics of flapping low-aspect-ratio ellipsoidal-wings in ornithopters is analyzed and modeled by the use of three dimensional Computational Fluid Dynamics (CFD) simulations. The range of interest is high amplitude, moderate frequency flapping, and low to moderate angles of attack at Reynolds around 105, where autonomous ornithopters like GRIFFIN are able to perform complex maneuvers such as perching. The results obtained show that the Leading Edge Vortex is produced above a certain Strouhal and angle of attack at downstroke. The frequency response of the aerodynamic loads are compared with the classical analytical models, observing that analytical models based on absence of viscosity and small perturbations are not appropriate for the range of interest. Through the 3D CFD aerodynamic loads database, a finite memory Volterra model is identified in order to predict the characteristics of forces and moments produced by the flapping wing. A good agreement with the 3D CFD simulations has been found by considering a reduced-order model depending on the effective angle of attack of the surrogate airfoil located at 70% of the semi-span at three-quarters chord on the airfoil, in agreement with the literature. Finally, a methodology for validation with a high-accuracy Motion Capture System and without the need of wind tunnel is proposed. As a result the proposed model provides better estimates than classical analytical ones.

Three-dimensional computational fluid dynamic analysis of a large-scale vertical axis wind turbine

The vertical axis wind turbine (VAWT) configuration has many advantages for an offshore wind turbine Installation. In this paper, the three dimensional (3D) computational fluid dynamics analysis of a large-scale 5 MW VAWT is conducted. At the optimum tip-speed ratio (TSR), the VAWT maximum inline force was 75% larger than the maximum lateral force. It was found the dynamic stall effects cause the VAWT flow field to become increasingly asymmetrical at the mid-span plane, when the TSR is reduced. The attachment of end plates to the blade tips, resulted in a performance improvement during the upwind phase with the average blade torque coefficient in this range being increased by 4.71%. Conversely, during the blade downwind phase a reduction in performance was found due to the increase in drag from the end plates and the average blade torque coefficient in this phase was reduced by 23.1%.

Numerical study of the impact of glottis properties on the airflow field in the human trachea using V-LES

The influences of the profiles and cross-sectional areas of glottal aperture on the upper respiratory airway are investigated using an idealized cast-based mouth-throat model and three dimensional computational fluid dynamics (CFD). The open source CFD code OpenFOAM is employed. The transient flows are modeled using the very-large eddy simulation with the Smagorinsky sub-grid scale (SGS) model. Five different shapes of glottis are considered, including circular glottis with 100 %, 75 % and 50 % cross-sectional area and elliptic glottis with 75 % and 50 % cross-sectional area. Both instantaneous and averaged flow fields are analyzed. It is found that the variations of glottis have great impacts on the properties of downstream flow fields such as the secondary flow, laryngeal jet, recirculation zone, turbulent kinetic energy, and vortex. Evident impacts are observed in the region within 6 tracheal diameters downstream of the glottis. The profile of the glottis has more impacts on the laryngeal shape, while the cross-sectional area has more impacts on velocity of the laryngeal jet and turbulent intensity. It is concluded that both the glottal areas and profiles are critical for an idealized geometrical mouth-throat model.

Spread of virus laden aerosols inside a moving sports utility vehicle with open windows: A numerical study.

A three dimensional Computational Fluid Dynamics (CFD) model to study the dispersion of virus laden aerosols in a car moving with its windows open is reported. The aerosols are generated when a possibly infected passenger speaks. A sports utility vehicle having three rows of seats has been considered. As the vehicle moves forward, its interior will exchange air from the surroundings. The CFD model captures the flow patterns generated both outside and inside the vehicle. This internal aerodynamics will in turn dictate how aerosols will spread across the interior and whether or not they will be transported outside the vehicle. A Lagrangian approach is used to determine the transport of the aerosol particles and the effect of particle size on the simulation result has been studied. Four sets of scenarios of practical interest have been considered. The first set shows the effect of vehicle speed on aerosol transport, and the second set describes what happens when some of the windows are closed, while the third set describes how aerosol transport is affected by the location of the passenger speaking. The fourth set describes how a gush of cross wind affects aerosol transport. Simulation results reveal that when all windows are open, aerosols can go out of one window and then return back to the vehicle interior through another window. Results also reveal that when a passenger sitting in the second row speaks, the aerosols generated span across the entire volume of the car interior before going out through the open windows.

Numerical Studies on Temperature and Material Flow During Friction Stir Welding using Different Tool Pin Profiles

A three dimensional computational fluid dynamics (CFD) model has been developed to study the effect of tool pin profile on the material flow and temperature development in friction stir welding (FSW) of high specific strength AA 7068 alloy. Numerical simulations were carried out using a RNG k-e turbulence model. Three tool pin profiles, viz. cylindrical, conical and straight cylindrical threaded were considered for the simulation. The temperature distribution and material flow pattern obtained from the simulation were compared for different pin profiles. Simulation results predicted Temperature distribution and material maxing was better in straight cylindrical tapered thread pin welds. Weld joints were fabricated using the straight cylindrical threaded pin with the same parametric combinations as in the simulation. Peak temperature measured in the experiment was less than that obtained by simulation. Hardness measurements taken at different weld regions has showed that about 71% of that of the base metal hardness is obtained with the threaded tool pin. The microstructure study revealed a defect free weld joint. Precipitates distributed in the microstructure indicate sufficient heat input to join the material without dissolving precipitates. The developed numerical model is helpful in optimising FSW process parameters.

Modelling of the pulverized coal plasma preparation for combustion

The main goal of this research is to show the action of pulverized coal in the plasma chamber throughcomputer simulation and numerical experiments carried out with the aid of developed well knownthermodynamic, kinetic and multi dimensional computational fluid dynamics based on mathematicalmodels. The data needed for the validation of the numerical procedure were obtained from a cylindricaldirect flow burner equipped with a plasmatron (plasma generator) with 100kW of electric power andmounted on a full-scale boiler (Gusinoozersk TPP, Eastern Siberia). The experiments were carried outusing ‘Tugnuisk’ bituminous coal. Two mathematical models were employed: the one (‘1D Plasma-Coal’) being one-dimensional, but with an emphasis on complex chemistry, the other (3D FAFNIR) beingfully three-dimensional with emphasis on the geometry and overall combustion processes. 1D Plasma-Coal numerical experiments gave the predicted temperatures and velocities of gas and solids along thechamber length; while the concentrations of the gas components (CO, CO2, H2, CH4, C6H6, N2, H2O)were reported for the chamber exit. The degree of coal gasification showed that 54% of coal carbon wasgasified within the plasma chamber. 3D numerical results for plasma jet spreading length were in goodagreement with the measured data, while the temperature profiles within the plasma chamber were overpredicted. The predictions of main species concentrations reveal that oxygen was completely consumedwith the exit product stream consisting of combustible gases, un-burnt volatiles and char particles.

Three-Dimensional Computational Fluid Dynamic Analysis of a Large-Scale Vertical Axis Wind Turbine

The vertical axis wind turbine (VAWT) configuration has many advantages for an offshore wind turbine installation. The VAWT is omnidirectional and its rotating mechanical components can be placed close to sea level. In this paper, the three dimensional (3D) computational fluid dynamics analysis of a large-scale 5 MW VAWT is conducted. At the optimum tip-speed ratio (TSR), the VAWT maximum inline force was 75% larger than the maximum lateral force.

Experimental and simulation study of rectangular and circular primary clarifier for wastewater treatment

Clarification is an essential process in wastewater treatment which removes suspended solids using flocculants The efficiency of the primary clarifier is important as it affects the performance of the subsequent processes. The modeling of clarifiers are carried out using one-dimensional flux theory or two dimensional computational fluid dynamics. In this paper one-dimensional modeling of sedimentation process based on flux theory applied to lab-scale circular and rectangular primary clarifiers is reported. The experiments were carried out for three operating conditions i.e. low, medium and high solid concentrations using lab-scale setup. The one-dimensional sedimentation process model was implemented on MATLAB platform and simulation was carried out. The model simulation is able to predict effluent total suspended solids as well as TSS present along the height of the lab-scale primary clarifiers. The average R 2 value 0.97 was observed between measured and simulated total suspended solids present along the height of circular clarifier for the three operating conditions whereas average R 2 value 0.96 was found in the case of rectangular clarifier for identical conditions. Based on the simulation and experimental results the removal of suspended solids is found better in circular clarifier as compared to rectangular clarifier for the influent flow rate of 134 mL/min with influent total suspended solids from 300 to 600 mg/L. • One-dimensional sedimentation process model applied to the two primary clarifiers. • Experiments were performed using lab scale setup of the two primary clarifiers. • Simulation was carried out to generate profiles of the Total Suspended Solids (TSS). • TSS removal is found better in circular as compared to the rectangular design.