Swirling Flow Conditions Research Articles

Swirling flow field reconstruction and cooling performance analysis based on experimental observations using physics-informed neural networks

The design of thermal protection modules (such as film cooling) for combustion chambers requires a high-fidelity swirling flow field. Although numerical methods provide insights into three-dimensional mechanisms of swirling flow, their predictions of key features such as recirculation zones and swirling jets are often unsatisfactory due to inherent anisotropy and the isotropic nature of the Boussinesq hypothesis. Experimental methods, such as hot wire, laser Doppler velocimetry, and planar particle image velocimetry (PIV), offer more accurate reference data but are limited by sparse or planar observations. In this study, considering the outperformed capability of solving inverse problems, physics-informed neural network (PINN) was adopted to reconstruct the mean swirling flow field based on limited experimental observations from two-dimensional and two-component (2D2C) results. It was found that adding partial information characterizing the swirling flow, such as the swirling jet, could significantly improve the reconstruction of flow field. In addition, film cooling effectiveness was the key variable to evaluate the film cooling performance, which was relatively measurable in the scalar field. To further improve the accuracy of the reconstruction, the multi-source strategy was adopted into the neural network, where the film cooling effectiveness (FCE) of the effusion plate was imported as the scalar source. It was found that the prediction of the flow field near the target plate was improved, where the highest error reduction could reach 76.5%. Finally, through the reconstructed three-dimensional vortex distribution, it was found that swirling flow vortex structures near the swirler exit had a significant impact on cooling effectiveness, causing a non-uniform cooling distribution. This study aims to diagnose the three-dimensional swirling flow field with deep learning by leveraging limited experimental data and deepen the understanding of effusion cooling under swirling flow condition so that obtains a more accurate reference in the design of thermal protection modules.

Influence of side dilution jets on swirling and non-swirling pulverised biomass turbulent annular flows

The use of pulverised biomass in non-premixed combustion systems, featuring turbulent annular flows (swirling, non-swirling) with downstream air dilution jets, is of immense practical importance. The overall combustion performance and emissions heavily rely on the underlying flow dynamics, turbulence and dispersion behaviour of the pulverised biomass particles. Despite the practical significance of side dilution jets in aiding complete combustion and controlling pollutants, the fundamental understanding of side dilution jets influence on the biomass particle velocity field, turbulence, and dispersion characteristics is still lacking. However, the presence of a multi-phase (solid-gas) flow field, highly turbulent annular flows, swirl, and cross-wise turbulent dilution jets poses significant challenges to these investigations. This work employs a combination of two-dimensional planar Particle Image Velocimetry (PIV) experiments and three-dimensional multi-phase numerical modelling to resolve the influence of turbulent side dilution jets (Red = 18,000 and 27,000) on the particle flow and dispersion characteristics of turbulent annular jets equipped with a central pulverised biomass-laden jet. The numerical modelling uses Reynolds stress model (RSM) and discrete phase model (DPM) for the solution of gas and dispersed phases, respectively. Walnut flour based raw pulverised biomass is injected at a certain particle loading ratio (Φp=0.33 and 0.49) through a turbulent central jet (Rj = 4500) into non-swirling (S = 0) and swirling (S = 0.3) turbulent confined annular flows (Res = 35,500 and 17,800). Comprehensive Constant Temperature Anemometry (CTA) experiments are conducted to obtain well-defined boundary conditions for experiments as well as numerical simulations. Prior to numerical predictions, the models are duly validated against the experimental data.Results reveal that the characteristic flow feature of side dilution jets, i.e., peripheral recirculation zones (PRZ) significantly entrains pulverised biomass particles from the turbulent particle-laden (central jet) annular flows (both swirling and non-swirling) and alters the particle flow and turbulence characteristics. Under non-swirling conditions (S = 0), side dilution jets reduce mean particle axial velocity by 22.4% and increase turbulent fluctuating velocity by 52.6%. These figures elevate to 32.5% and 100% respectively for swirling conditions (S = 0.3), depicting enhanced turbulent mixing between solid particles and the gas phase. In terms of particle dispersion, side dilution jets significantly enhance lateral dispersion of biomass particles, particularly under swirling flow conditions. In the PRZ region, side dilution jets led to a 108% and 279% increase in normalised particle count for non-swirling and swirling cases, respectively. These findings suggest that swirl doubles the particle dispersion in the PRZ. Furthermore, a 50% increase in Red enables side dilution jets to entrain more biomass particles and disperse them into the PRZ. Conversely, a 50% increase in ṁp leads to a significant increase in particle volume fraction along the central axis of the nozzle.

Efficient Metal Recovery from Industrial Wastewater: Potential Oscillation and Turbulence Mode for Electrochemical System

Efficient metal recovery from industrial wastewater facilitates addressing of the environmental hazards and resource requirements of heavy metals. The conventional electrodeposition recovery method is hampered by the limitations of interfacial ion transport in charge-transfer reactions, creating challenges for simultaneous rapid and high-quality metal recovery. Therefore, we proposed integrating a transient electric field (TE) and swirling flow (SF) to synchronously enhance bulk mass transfer and promote interfacial ion transport. We investigated the effects of the operation mode, transient frequency, and flow rate on metal recovery, enabling determination of the optimal operating conditions for rapid and efficient sequential recovery of Cu in TE&SF mode. These conditions included low and high electric levels of 0 and 4 V, a 50% duty cycle, 1 kHz frequency, and 400 L·h−1 flow rate. The kinetic coefficients of TE&SF electrodeposition were 3.5–4.3 and 1.37–1.97 times that of single TE and SF electrodeposition, respectively. Simulating the deposition process under TE and SF conditions confirmed the efficient concurrence of interfacial ion transport and charge transfer under TE and SF synergy, which achieved rapid and high-quality metal recovery. Therefore, the combined deposition strategy is considered an effective technique for reducing metal pollution and promoting resource recycling.

Transportation of cuttings by drilling mud in horizontal wells. Part 2. Numerical results of drilling at optimal rheological properties of mud

The relevance. Ensuring technological equipment operation efficiency when drilling wells with an arbitrary orientation of their wellbores. In particular, the search for productive hydrocarbon reservoirs requires drilling deeper wells with extended horizontal sections, for which the removal of the cuttings bed is the key problem of modern drilling. The aim. Study the features and establish the patterns of cuttings movement through the annulus eccentric space formed by a drill string and well walls under various modes (in-situ) and drilling conditions within the framework of modern mathematical models of hydrodynamics, numerical algorithms and approaches implemented in ANSYS CFD. Optimize the parameters that determine drilling, such as an inclination angle, mass-average velocity and morphology of the inlet rheologically complex viscous flow to form the maximum allowable drilling velocity for various combinations of mud effective viscosity and mixture flow rate. Give practical recommendations for engineers to reduce time, costs and material resources for maintenance and optimization of well cleaning. The object. A well with an eccentric core and an extended horizontal section operating in modes and conditions close to real drilling. The methods. Complex of physical and mathematical analysis and numerical modeling of hydrodynamics and mass transfer in homogeneous and heterogeneous continuous media. The media were widely tested on the class of internal rheological complex flows, the verification of which was carried out under appropriate conditions, performed by other authors when solving problems of drilling and cleaning wells. The results. The paper presents the results of a numerical study of hydrodynamics of a dispersed flow of a rheological complex viscous mixture of a drilling fluid with the properties of a Herschel–Bulkley type fluid and sand particles in wells with an arbitrary generatrix of its wellbore in an eccentric space. The results are required to clarify the features that accompany direct-flow and swirling flow (the moving wall method), identify the patterns in such modes, accounting for which allows for effective cleaning of the annulus. The calculations were performed within the framework of modern mathematical models of the RANS-method and the Euler–Lagrangian approach to describing the motion of heterogeneous media, implemented in the ANSYS CFD software and efficient numerical algorithms for determining intra- and interfacial processes of mass and momentum transfer in mixtures. The authors have determined that when drilling a vertical section, the most effective parameter in terms of cleaning control is the effective viscosity of the mud; the most problematic configurations for cleaning are wells with sloping sections at angles close to the vertical. When drilling a horizontal section, the eccentricity of the drill string creates “the dead” zone of flow and complicates cleaning. This zone should be removed by creating swirling flow conditions through relatively weak rotation of a drill string (30–60 rpm). When drilling inclined sections, it is necessary to reduce a solution viscosity (preferably to the level of fresh water) and increase the flow rate (in this case, to 2 m/s or higher). When drilling a horizontal section, a mud with a viscosity close to fresh water is recommended at flow rates of about 2 m/s (or 640 gpm) at the well inlet and a maximum drilling velocity of 9 m/h.

Comparison of Pressure Pulsation Characteristics of Francis Turbine with Different Draft Tube Arrangement Direction

Hydroelectric power generation is an important clean energy source, and the stability of water turbine operation determines the quality of hydro energy utilization. For hydro turbines, the layout direction of the draft tube is often only considered from a structural perspective, ignoring the hydrodynamic characteristics. This study adopts the computational fluid dynamics method and verifies the effectiveness of numerical simulation with experimental results, analyzing the influence of asymmetric draft tube layout direction on pressure pulsation of mixed flow turbine. The results show that under different working conditions, there is basically no difference in efficiency corresponding to different inclined directions of the draft tube, and the relative difference in performance values is less than 1%. From the perspective of internal flow, the working condition has a greater impact on the flow, and the draft tube tilt has a smaller impact. Under strong swirling flow conditions in the draft tube, the variational mode decomposition of pressure fluctuation is carried out. Research has found 7 characteristic frequency bands including 140 Hz, 80–90 Hz, 40–46 Hz, 5.5–6.5 Hz, 2.5–3 Hz, 1.67 Hz, and <1 Hz. The frequency of the dominant mode corresponding to the left tilt is higher, while the amplitude of the runner frequency is slightly lower. In general, left tilt is not only more suitable for unit layout but also has a better effect on draft tube pressure fluctuation, which is worthy of application in engineering.

Experimental studies on combustion performance of beeswax-paraffin blended solid fuels in a hybrid rocket

The study intends to investigate the physical, chemical and thermal characteristics of paraffin blended fuels to determine their suitability as a solid fuel in a hybrid rocket. Wax fuels are a viable and efficient alternative to conventional rocket fuels, having excellent structural strength and thermal and mechanical properties. By utilizing both axial and swirl injection technique, the combustion performance of paraffin – beeswax blended fuels have been tested with a fabricated cylindrical grain in a laboratory-scale rocket setting along with oxygen. The test outcomes revealed solid fuel compositions of more beeswax content in paraffin wax on an oxygenated gaseous environment with a swirl-flow injection method has the highest average regression rate of 1.649 mm/sec at 181 kg/m2s mass flux. Axially injected oxygen with pure paraffin wax has the lowest value of 0.85 mm/sec at 96 kg/m2s. The regression rate comparisons revealed that oxygen injection by a swirl injector increased the regression rates by 40% for mass fluxes greater than 80 kg/m2s. Compared to other studies, the combustion efficiencies have been obtained in this study are good. Blended fuels can manage and increase combustion efficiencies for axial and swirl flow conditions. Swirl injectors outperform axial injectors for oxygen injection and allow for a higher proportion of Beeswax combined with paraffin. This study exclusively designed and manufactured an axial injector and swirl injector, according to the required dimensions of a lab-scale hybrid rocket's combustion chamber, injector, and exhaust nozzle, and their performances have been evaluated.

Inhibition of the erosion-corrosion of elbow by synergistic action of swirling flow and inhibitor

The experiments of using inhibitors to inhibit the erosion-corrosion of elbows under the conditions of liquid-solid non-swirling flow and swirling flow were designed to evaluate the inhibition of erosion-corrosion of elbows under the combined action of swirling flow and inhibitors. The experiments were carried out by a circulating loop system in combination with a variety of test methods and computational fluid dynamics (CFD) simulation. It is demonstrated that the addition of inhibitors under non-swirling flow and swirling flow conditions can inhibit effectively the erosion-corrosion rate and its four components (pure corrosion, pure erosion, corrosion-enhanced erosion, and erosion-enhanced corrosion). The comprehensive inhibition efficiencies of the synergistic action of swirling flow and inhibitor on the four components of erosion-corrosion are higher than the inhibition efficiencies of inhibitor acting on the four components alone. The hydrodynamic characteristics of swirling flow produce the sand suspension effect and mass transfer enhancement effect which facilitate the adsorption of inhibitor on the working electrode surface and acting in conjunction with the oxide film to form a lamellar protective corrosion product layer with stronger integrity and compactness.

Fuel-lean ammonia/biogas combustion characteristics under the reacting swirl flow conditions

Ammonia has been identified as a viable energy vector for power generation. Using dual-fuel operation that mixes the ammonia with higher reactivity gaseous fuel can be vital in enhancing ammonia combustion. This study examined the fundamental swirl combustion characteristics of fuel-lean premixed ammonia/biogas via a numerical approach. The flame was established at an input thermal power of 7 kW and a global equivalence ratio of 0.8. The numerical model was validated with biogas emissions data acquired through experimental work. At 20 mm downstream the burner, increased carbon dioxide mass fraction in the biogas lowered the peak flame temperature by around 300 K. Moreover, the deformation of flame temperature radial profiles was also found aggravated as carbon dioxide concentration in the biogas elevated from 0 % to 40 %. The reduction in premixed reactant mixture reactivity not only initiated flame temperature profile deformation but also reduced the peak Damköhler number significantly. The peak Damköhler number was lowered by a factor of ∼ 1.5 when carbon dioxide dilution in the biogas elevated by 40 %. The premixed combustion was directed into the thin reaction flamelets zone with elevated carbon dioxide mass fraction, owing to the intensified flow fluctuation. This, in turn, elevates the normalised flame turbulent propagating speed, gas flow average velocities and turbulent kinetic energy, notwithstanding that heat release rate and averaged laminar flame speed declined. In all, the presence of carbon dioxide has been shown to lower the ammonia/methane mixture reactivity whilst escalating the reacting flow fluctuation.

An experimental investigation of droplet morphology in swirl flow

The interaction of a droplet with a swirling airstream is investigated experimentally using shadowgraphy and particle image velocimetry techniques. In swirl flow, the droplet experiences oppose-flow, cross-flow and co-flow conditions depending on its ejection location, the velocity of the airstream and the swirl strength, which results in distinct droplet morphologies as compared with the straight airflow situation. We observe a new breakup phenomenon, termed as ‘retracting bag breakup’, as the droplet encounters a differential flow field created by the wake of the swirler's vanes and the central recirculation zone in swirl airflow. A regime map demarcating the various modes, such as no breakup, vibrational breakup, retracting bag breakup and bag breakup modes, is presented for different sets of dimensionless parameters influencing the droplet morphology and its trajectory. In contrast to the straight flow, the swirl flow promotes the development of the Rayleigh–Taylor instability, enhancing the stretching factor in the droplet deformation process, resulting in a larger number of fingers on the droplet's surface. In order to gain physical insight, a modified theoretical analysis based on the Rayleigh–Taylor instability is proposed for the swirl flow. The experimental behaviour of droplet deformation phenomena in swirl flow conditions can be determined by modifying the stretching factor in the theoretical model.

Experimental study on erosion-corrosion behavior of liquid–solid swirling flow in pipeline

A multifactorial experimental research on erosion-corrosion behavior of liquid–solid swirling flow in pipeline was carried out by a circulating loop system in combination with a variety of test methods. The analysis of statistical significance reveals that the variation of erosion-corrosion rate is explained by three main effects (velocity, sand size, and sand concentration) and two interactions (velocity/sand size and sand size/sand concentration). An empirical linear regression equation with a R2 value of 0.9043 was established to describe the correlation of erosion-corrosion rate with the test parameters and their interactions. It is concluded by microstructural examination of the working electrode surface that under the condition of liquid–solid swirling flow, cutting and corrosion pits are the primary forms of surface damage. The comparative analysis of erosion-corrosion between swirling flow and non-swirling flow shows that the net effect of swirling flow on erosion-corrosion varies with sand size. The corrosion product analysis by EDS and XPS show the presence of Fe2O3 and CaCO3 under swirling flow and non-swirling flow conditions. Furthermore, the element content analysis of EDS and XPS showed that compared with the non-swirling flow, the oxygen content on the electrode surface under the swirling flow condition increased by 42.42% and 35.06%, respectively.

Effect of swirling flow and particle-release pattern on drug delivery to human tracheobronchial airways

The present study aims to investigate the effect of swirling flow on particle deposition in a realistic human airway. A computational fluid dynamic (CFD) model was utilized for the simulation of oral inhalation and particle transport patterns, considering the k-ω turbulence model. Lagrangian particle tracking was used to track the particles' trajectories. A normal breathing condition (30 L/min) was applied, and two-micron particles were injected into the mouth, considering swirling flow to the oral inhalation airflow. Different cases were considered for releasing the particles, which evaluated the impacts of various parameters on the deposition efficiency (DE), including the swirl intensity, injection location and pattern of the particle. The work's novelty is applying several injection locations and diameters simultaneously. The results show that the swirling flow enhances the particle deposition efficiency (20-40%) versus no-swirl flow, especially in the mouth. However, releasing particles inside the mouth, or injecting them randomly with a smaller injection diameter (dinj) reduced DE in swirling flow condition, about 50 to 80%. Injecting particles inside the mouth can decrease DE by about 20%, and releasing particles with smaller dinj leads to 50% less DE in swirling flow. In conclusion, it is indicated that the airflow condition is an important parameter for a reliable drug delivery, and it is more beneficial to keep the inflow uniform and avoid swirling flow.

Analysis of Tube in Tube Heat Exchanger Fitted with Twisted Tape with Square Cut

Numerical investigations of heat transfer and friction factor characteristics in swirling flow conditions using CFD simulation. A commercial CFD package, Ansys R1 2021, was used in this study. 3D models for circular tube fitted with Square-cut twisted tape (QCT) inserts with two pitch 100mm, 50 mm and different cut depths (d = 4 mm, 5mm and 7 mm) were generated for the simulation. Insertion of twisted tapes into the tubes of the heat exchangers is important for enhancement of heat transfer to increase the performance of heat exchangers. In the present Research work, computational analysis has been carried out to analyse the enhancement of rate of heat transfer using Square cut cross sectional twisted tape inserts in a pipe heat exchanger. Geometrical model of heat exchanger has been generated and computational mesh is created using ICEM CFD, an advanced meshing software. The analysis has been carried out for plain tube and with Square cut cross sectional twisted tape inserts with different twist ratio analyse the temperature distribution, velocity distribution and pressure distribution along the tubes and shell using ICEM CFD.

Research on the flame structure characteristics and NOx pathways of low swirl combustion

Low swirl combustion (LSC) technology has the advantage of ultralow NOx emissions, which is of great significance to the development of low-emission gas turbine engines in the future. To investigate the flow field and flame structure characteristics of LSC, a test rig of low swirl burner was designed and developed. Particle image velocimetry measurement results show that the location and size of the recirculation zone are different, and the flow field shows typical “W”- and “U”-shaped distributions under various swirling flow conditions. The self-luminous results of LSC show that there are three flame modes including attached flame, “W”-shaped flame, and “U”-shaped flame. To deeply understand NOx generation pathways, a chemical reactor network model was developed based on experiments and computational fluid dynamics simulations, and the effects of premixed gas components on NOx pathways were calculated by using Chemkin software. It was verified that the NOx production of the CH4 mixture mixed with H2, N2, and CO2 was mainly formed by the thermal NO pathway in the recirculation zone. The increase of H2 promotes the generation of NNH-type NOx in the main flame zone and inhibits prompt NOx. The addition of N2 and CO2 greatly promotes the generation of prompt NOx and at the same time inhibits NNH-type NOx. In addition, there is little prompt NOx formation in the post-flame zone.

Heavy Fuel Oil Combustion Characteristics Evaluation in Various Swirling Flow Conditions

Abstract Heavy fuel oil (HFO) is an economical fuel alternative for power generation as its low production cost and high energy density. However, its incomplete combustion induced by the presence of long-chain petroleum molecules in the fuel results in high levels of emissions. Here, we investigate the influence of the swirl flow on the combustion and emissions of a spray HFO swirling flame. To this end, HFO is sprayed into a hot swirling air, using an air-blast nozzle. The flame blowout limits are tested under different swirl flows. An investigation of the in-flame temperature fields, gaseous emissions including CO, CO2, O2, NOx, SOx, UHC (Unburned Hydrocarbon) and solid particles in the form of cenospheres are used to quantify the performance of the HFO combustion. The influence of the HFO swirling flame is tested under different conditions of global equivalence ratio, swirling number, and tangential and axial airflow rates. A comparison of two different flame regimes that fuel-jet dominate flame and air-driven vortex flows are investigated and compared in various swirling flow conditions. The results show that the tangent air is the primary factor for preheating and evaporating the fuel, thus defining the flame operating regimes.

Study on supersonic swirling condensation characteristics of CO2 in Laval nozzle

Supersonic swirl separation technology has been widely used in natural gas processing and has achieved good results. However, there are few studies on the application of supersonic separation technology to the removal of CO2 from natural gas, and the condensation rule of CO2 under supersonic swirling flow condition is still unclear. In order to study the supersonic swirling condensation characteristics of CO2 in Laval nozzle, the Euler mathematical model of the condensation flow of CO2–CH4 two-component mixed gas was established, and the feasibility of CO2 removal by supersonic separation technology was verified by numerical simulation. The results show that, in the process of axial flow and swirling flow, the variation trend of CO2 condensation parameters is basically the same along the axial direction of the nozzle, but the distribution of parameters is significantly different along the radial direction. The increase of swirl intensity will increase the nozzle's liquefaction efficiency and reduce the working flow of the nozzle. The inlet temperature and inlet pressure had a significant influence on the liquefaction efficiency of the nozzle, while the inlet CO2 content had little influence on the liquefaction efficiency.

Experimental and Numerical Investigation of Swirling Flow on Triple Elbow Pipe Layout

The secondary flow downstream of a triple elbow layout was studied experimentally and numerically to visualize the flow behavior under swirling inlet flow conditions. The inlet swirling condition was generated by a swirl generator, consisting of a rotary pipe and honeycomb assembly. The experiments were carried out in turbulent water flow condition at Reynolds number Re = 1 × 104 and inlet swirl intensity S = 1. Ultrasonic measurements were taken at four locations downstream of the third elbow. The two-dimensional velocity field of the flow field was measured using the phased array ultrasonic velocity profiler technique to evaluate the flow field with separation. Furthermore, a numerical simulation was performed and its results were compared with the experimental data. The numerical result was obtained by solving three-dimensional, Reynolds-averaged Navier-Stokes equations with the renormalization group k-ε turbulence model. The experimental results confirmed that the swirling flow condition modified the size of the separation region downstream of the third elbow. A qualitative comparison between the experimental and CFD simulation results of the averaged velocity field downstream of the third elbow showed similar tendency on reverse flow.

Effects of swirling flow on ultralight particle dispersion characteristics in coaxial jet combustor

AbstractThe dispersion characteristics of ultralight particle (expanded graphite) in swirling mixture particle‐laden coaxial jet combustor was modeled and numerically predicted using developed second‐order moment gas‐particle multifluid turbulent model. An improved gas‐particle and particle‐particle Reynolds stress transport to describe its anisotropic behaviors was proposed. Experimental validation for single‐phase particle flow has been conducted with satisfied agreement. The multifluid hydrodynamic parameters, that is, number density, particle velocity, fluctuation velocity, Reynolds stress correlation of gas‐particle and particle‐particles, and effects of swirling number are investigated. The results found that the ultralight particles exhibited the distinctive anisotropic behaviors, and their unique flow structures were quite different from those of heavier particles. Under the strong swirling flow condition, the anisotropic dispersions were enhanced and concentration at recirculation regions increased. The axial velocities and fluctuations, and the axial‐axial and tangential‐tangential stress correlations of gas‐particles were weakened. The effect of swirling strength on ultralight particle dispersions is more sensitive in comparison with heavier particle.

Analysis of heat transfer characteristics with triangular cut twisted tape (TCTT) and circular cut twisted tape (CCTT) inserts

Abstract The paper represents the numerical investigation of heat transfer characteristics in a pipe provided with twisted tape inserts is analyzed. The heat transfer was analyzed in a swirling flow conditions using CFD simulation. A commercial CFD package was used for analyze twisted tape for circular tube fitted with triangular cut twisted tape and circular hole cut twisted tape inserts. The twisted tape system allows a significant increase of convective heat transfer coefficient by introducing the swirl flow motion. The swirl flow motion provides greater heat transfer rate extracted from the solid surface of the tube. The depth of cuts for triangular cut 5 mm and depth of hole cut 5 mm twisted tapes were used for simulation generation. In this paper CFD analysis was used for enhancement of heat transfer rate of fluid of laminar flow. The experimental investigation were conducted in double pipe heat exchanger and these value of plain twisted tape, triangular twisted tape and circular hole cit twisted tape were taken for used simulation analysis. The performance of heat transfer rate was enhanced 1.1–1.3 times compared that the plain twisted tape and circular cut twisted tape. The data obtained from the simulation correlations for triangular cut twisted tape and circular hole cut twisted tape; and these data were correlated with plain twisted tape.

Numerical investigations on feasibility of Quasi “MR-Process” for 2-valve diesel engines

MR-Process consists two stage combustion mechanism in twin swirl flow conditions which is created by special design of 2 intake manifolds and combustion chamber (CC) geometry of a 4-valve engine. It is a question if it is possible to apply a Quasi MR-Process by modifying CC of a 2-valve engine which has only one intake manifold. Previously engine tests were successfully conducted on a 2-valve and modified CC (MR-2 CC) single cylinder test engine with one intake manifold using LPG and diesel fuels. Nevertheless because of there is no optical access inside the engine, it is not clear whether required twin swirl flow (to create Quasi MR-Process) occurs inside CCs of proposed 2-valve engines. In this study, our aim is to improve the clarification of the swirl motion and air-fuel mixture formation for said Quasi MR-Process CC application in 2-valve diesel engines. Two different CC geometries were investigated in terms of Quasi MR-Process generation potential by using KIVA3V-R2 code. CFD predictions of air flow motion, air-fuel mixture formation and diesel spray combustion were analyzed and compared with each other in a methodical manner. The results showed that 2 valve engine CC is not capable of creating optimal twin swirl. However, it is presented that generation of twin swirl can be improved by application of modified (MR-2 CC) piston head design.

Numerical study of non-reacting flowfields of a swirling trapped vortex ramjet combustor

In this work, 3D numerical investigations of a trapped vortex combustor operated in different swirling flow conditions are performed by solving Reynolds-averaged Navier–Stokes equations with Reynolds-stress model. Emphasis is placed on the non-reacting flowfield characteristics and the stability of the locked vortex. Validation is performed first by comparing the present results with experimental data available. It shows that the Reynolds-stress model can provide good predictions for flows with a swirl number up to 0.98. It is also found that the cavity vortex can be trapped well in flows with different swirl numbers. To further study the “locked” vortices, flow disturbances are introduced to the trapped vortex combustor via suddenly increasing swirl number from 0.6 to 0.98. The transient simulation results reveal that the cavity vortex is highly resistant to the flow disturbances and is still well trapped in the cavity, while vortex shedding of the conventional breakdown vortex is observed in the presence of the flow disturbances. Turbulence intensity and kinetic energy are found to be significantly increased by approximately 300%, which indicates that the fuel–air mixing can be dramatically improved. This study shows that the swirling trapped vortex combustor is an alternative promising robust and efficient combustor concept.