Swirling Flow Field Research Articles

Simulation and experiment of turbulent particle motions in a hydrocyclone membrane filtration cell optimized for low-fouling water filtration

Particle-laden source waters are ubiquitously present in the natural environment and engineered systems. The demand for facile and energy-efficient treatment of these waters is increasing due to global water shortage aggravated by climate change. Therefore, a hydrocyclone membrane filtration cell (HMFC) enabled by 3D-printing technology was developed in this study and examined for its capability and mechanisms for pretreatment- and backwash-free filtration of inorganic and organic particle suspensions. Computational fluid dynamics simulation results indicate that the particles in the HMFC are subject to a strong swirling and turbulent flow field with turbulent kinetic energy ranging from 0.02-2.42 m2/s2 and shear strain from 104-105 s−1, 106 and 100 times higher than those obtained with conventional membrane filtration systems, respectively. This unique flow condition leads to centrifugal/centripetal, revolving, and rotational particle motions and turbulent-induced diffusion. The experimental results revealed that these particle motions effectively eliminated particle deposition on a porous microfiltration membrane and completely alleviated membrane fouling that were serious in traditional filtration modes. These findings shed light on the development of novel membrane filtration systems with enhanced fluid dynamics, for energy-efficient harvesting of clean water from particle-laden water resources.

A visualized investigation of bubble breakup in a swirl‐venturi bubble generator

AbstractThe dynamics and breakup of bubbles in swirl‐venturi bubble generator (SVBG) are explored in this work. The three‐dimensional movement process and breakup phenomena of bubbles are captured by one high‐speed camera system with two cameras while the distribution of swirling flow field is recorded through Particle Image Velocimetry technology. It is revealed that bubbles have two motion trajectories, which are deeply related to bubble breakup. One trajectory is that mother bubble moves upward in an axial direction of the SVBG to the diverging section, and the other trajectory is that mother bubble rotates obliquely upward to another side‐wall along the radial direction. Meanwhile, binary breakup, shear‐off‐induced breakup, static erosive breakup, and dynamic erosive breakup are observed. For relatively high liquid Reynolds number, vortex flow regions are extended and the bubble size is reduced. Furthermore, it is worth noting that the number of microbubbles increases significantly for intensive swirling flow.

Prediction of swirling flow field in combustor based on deep learning

This paper considers the application of machine learning to the modeling of the swirling flow field in a combustor. A deep learning prediction model based on experimental data from particle image velocimetry is established, with the state parameters and spatial parameters as input and the axial and radial velocities as output. An optimal network framework is determined by comparative analysis of goodness of fit, prediction error, and training cost. The swirling flow field is reconstructed using 1.5, 2.0, 2.5, and 3.0 kPa data sets, and an extrapolation prediction is made using a 4.0 kPa data set. The results indicate that the data-driven deep learning model is able to capture the nonlinear spatial characteristics of the swirling flow field and learn the complex relationship between input and output parameters. The results for the velocity contour distribution, streamline shape, and vortex center position of the swirling flow field are in good agreement with the experimental results. The constructed deep learning prediction model has good prediction accuracy based on previously seen data sets and is able to reconstruct the swirling flow field. In addition, it is able to perform extrapolation prediction based on a previously unseen data set and has some generalization capability. Finally, several potential engineering applications of the deep learning prediction model constructed here are pointed out.

From Pressure Time Series Data to Flame Transfer Functions: A Framework for Perfectly-Premixed Swirling Flames

Abstract We present a two-step optimization (TSO) framework, which uses the pressure data of an unstable combustion process to estimate the Flame Transfer Function (FTF). From the pressure time series, we obtain the instability frequency and the amplitudes of the pressure fluctuations. The first optimization step is based on an acoustic network model of the combustor: the TSO approach uses the pressure data to find a simplified n-tau model, which reproduces the unstable combustion process. This step has already been validated for the Rijke tube, a laminar and a turbulent flame in Ghani et al. (2020). The major contribution of this work adds a second optimization loop to extend the n-tau model to the FTF: the gain and phase obtained by the n-tau model are used to fit a distributed time delay model. Our proposed method is applied to a turbulent, premixed, swirl-stabilized flame operated at two power ratings and two swirler positions. The model results for the FTFs are compared against experimentally measured FTFs for these four configurations and all agree well. To the best of our knowledge, this is the first attempt to estimate the complex-valued FTF solely based on pressure measurements. Compared to classical methods for FTF determination such as experimental tests or numerical simulations, our TSO approach is fast and accurate. The proposed framework is suitable for perfectly-premixed flames stabilized by a swirling flow field, requires two pressure sensors and is easy to implement.

An investigation of a gas–liquid swirling flow with shear-thinning power-law liquids

A gas–liquid swirling flow with shear-thinning liquid rheology exhibits complex behavior. In order to investigate its flow characteristics, experiments and computational fluid dynamics (CFD) simulations are conducted based on dimensional analysis. A Malvern particle size analyzer and electrical resistance tomography are applied to obtain the bubble size distribution and section void fraction. A Coriolis mass flowmeter is applied to obtain the mixture flow rate and mixture density for an entrance gas volume fraction smaller than 7%. The CFD coupled mixture multiphase model and large eddy simulation model are applied, considering the liquid shear-thinning power-law rheology. The results show that the swirling flow can be divided into developing and decaying sections according to the swirl intensity evolution in the axial direction. A gas–liquid swirl flow with shear-thinning liquid prohibits a core-annulus flow structure. A smaller index n contributes to maintaining the development of the swirl flow field and its core-annulus flow structure so that the swirl flow can form over a shorter distance with a stronger intensity. For a more uniform distribution of the apparent viscosity, the gas column in the pipe center is thinner. On the other hand, a larger consistency k enlarges the stress tensor. The amplitude of the velocity and the pressure of the core-annulus flow structure are reduced. A weaker swirl intensity appears with a wider gas column appearing as a consequence. Furthermore, the swirl number decays with an exponential behavior with parameters sensitive to the consistency k and index n of the decaying section of the swirling flow field. These are beneficial to gas–liquid separator design and optimization when encountering the shear-thinning power-law liquid phase in the petroleum industry.

Effects of charge motion on knocking combustion under boosted high load condition of a medium-duty gasoline engine

Due to higher power density and strong swirl flow field, knock tendency is more severe in medium duty (MD) gasoline engines derived from diesel engine platforms. How to design the charge motion reasonably, so as to increase the thermal efficiency and suppress knock simultaneously needs to be further discussed in combination with the actual combustion boundary conditions. The investigations in this study focus on the charge motion roles on knock and thermal efficiency under a high load/low speed operating condition using numerical simulations. The results show that the mechanisms of inducing knocking combustion and the effects of tumble ratio (TR) on knock intensity (KI) are different under swirl, inclined swirl and tumble motion conditions. With strong swirl configurations, weaker turbulence intensity at the bottom of the combustion chamber reduces the convective heat transfer between the fresh charge and hot exhaust gas, resulting in an obvious high temperature region, and inducing the first hot spot. Increasing TR can effectively suppress knock by shortening the residence time of end gas. With inclined swirl and strong tumble configurations, the position of hot spots is determined by the asymmetrical shape of the flame front, which is induced by large-scale tumble motion around the spark plug close to TDC. The end gas reactivity is higher and the temperature distribution in the end gas region is more uniform with the increase of TR, resulting in a sharp increase in auto-ignition velocity and thus KI. Due to the suppression of knock, reduction of heat losses as well as promotion of flame speed, an optimized inclined swirl motion based on the flat cylinder head is more appropriate for MD gasoline engines.

Experimental and Numerical Investigation of Flow Field and Soot Particle Size Distribution of Methane-Containing Gas Mixtures in a Swirling Burner.

The formation of soot in a swirling flow is investigated experimentally and numerically in the context of biogas combustion using a CO2-diluted methane/oxygen flame. Visualization of the swirling flow field and characterization of the burner geometry is obtained through PIV measurements. The soot particle size distributions under different fuel concentrations and swirling conditions are measured, revealing an overall reduction of soot concentration and smaller particle sizes with increasing swirling intensities and leaner flames. An axisymmetric two-dimensional CFD model, including a detailed combustion reaction mechanism and soot formation submodel, was implemented using a commercial computational fluid dynamics (CFD) code (Ansys Fluent). The results are compared with the experiments, with similar trends observed for the soot size distribution under fuel-lean conditions. However, the model is not accurate enough to capture soot formation in fuel-rich combustion cases. In general, soot particle sizes from the model are much smaller than those observed in the experiments, with possible reasons being the inappropriate modeling in Fluent of governing mechanisms for soot agglomeration, growth, and oxidation for CH4-CO2 mixtures.

Hydrocyclone technology for breaking consolidation and sand removal of the Natural gas hydrate

Natural gas hydrate is a promising substitute energy resource for the future. Currently, the inefficient sand control technology impedes the commercialization of Natural gas hydrate. The main challenge lies in breaking the consolidation of Natural gas hydrate and sands, and then separating micrometer-sized sands from the drilling fluid. In this paper, we present a technology based on hydroscyclone that effectively breaks the consolidations and removes sand. We used polypropylene powders and silica sands as substitutes for the hydrates and sands, and we added cement to replicate the consolidation. Inside the hydrocyclone, the material particles receive a strong shear force from the 3-dimension rotating swirling flow field generated by the device, as well as a centrifugal force produced by their own rotation and revolution. With the high-speed camera, we observed the effect of these forces breaking the consolidation and separating sands. It was further noted that the proportion of residual polypropylene powders in the recovered materials were between 0.46% and 1.05% after the materials were processed by the hydrocyclone. The low residual content of polypropylene powders demonstrated the success of hydrocyclone technology in breaking the consolidation and effectively addressing the problem of sand control in the extraction of Natural gas hydrate and sands.

Micro-nano bubbles production using a swirling-type venturi bubble generator

We designed a swirling-type venturi bubble generator (SVBG) by introducing a swirling flow field into the conventional venturi tube to improve the microbubble generation efficiency. The fan-shaped baffles were added at the entrance and the converging section was replaced by spiral channel to enhance swirling flow intensity so as to facilitate bubble breakup. The influence of geometric parameters on the flow structure of the SVBG was studied through numerical simulation. Then the optimized SVBG was installed at the downstream of the conventional venturi tube to construct a novel micro-nano bubble cavitation reactor. The manufactured cavitation reactor generated bubbles with size down to 780 nm. Moreover, the cavitation reactor exhibited a superior dissolved oxygen value, which was increased by 36.06% when compared with venturi tube, showing great promise for oxygen enrichment. The micro-nano bubble cavitation reactor presented can provide a more effective way to produce micro-nano bubbles.

Effect of acoustic velocity on the primary atomization of a hollow cone spray in a swirling flow field

Effect of acoustic velocity on the primary atomization of a hollow cone spray in a swirling flow field

Experimental investigation of recirculation zone characteristics of a pre-filming airblast injector

The toroidal flow at the recirculation zone has a vital role in combustion process as it helps in mixing hot combustion products with incoming fresh air and fuel which increases combustion efficiency. In the present work, characteristics of recirculation zone are investigated using a pre-filming airblast injector. Particle Image Velocimetry is used to characterize the swirl flow field generated by the airblast injector. Moreover, olive oil is used as a tracer to be captured by a high-speed camera. Different flow rates are investigated in order for finding out the effect of varying flow rates on the characteristics of the recirculation zone. Results for recirculation zone shape, velocity field and shear strength at the primary zone of combustion are represented. Additionally, results show that recirculation zone is almost symmetrical with increasing trend in shear strength with increasing flow rates.

The oxygen-deficient combustion and its effect on the NOx emission in a localized stratified vortex-tube combustor

The oxygen-deficient combustion characteristics of methane in a localized stratified vortex-tube combustor (LSVC) are studied by diluting combustion air with nitrogen. The influences of oxygen mole fraction (0.13–0.21) on flame configuration, combustion stability, combustion efficiency, and NOx emission characteristics are experimental investigated at the inlet temperature of 300 K. Combined with the numerical simulation method, the NOx generation, and emission mechanisms are analyzed in this combustor. Results show that the LSVC can achieve a wide stability limit, in which the global equivalence ratio can be as low as 0.22 at the lowest oxygen mole fraction (β) of 0.13. To ensure high combustion efficiency, the β should be kept above 0.16 since the oxygen-deficient condition reduces the reaction rate and flame temperature. The combustor can achieve ultra-low NOx emission of below 10 ppm (@ 15 vol% O2) due to low oxygen concentration and flame temperature. Furthermore, part of NOx entrained into the fuel-rich reduction zone by the swirl flow field is reduced by the reductive species (i.e., CO and H2) to further lowering NOx emissions. The results of this paper can guide the development of the LSVC in the high-efficiency and low-emission combustion fields.

Method and experimental study of cell manipulation based on swirl

The development of a multifunctional noncontact manipulation method is desired in cell manipulation. In this paper, we theoretically study and experimentally demonstrate the method of cell manipulation based on swirl. We analyze the swirl flow field features and the cell manipulation mechanism. The swirl is constructed by jetting fluid through three microtubules, and the cells are manipulated using the low pressure of stagnation point and the constant vorticity in the flow field. The experimental results indicate that the cell can be trapped robustly using the stagnation point of swirl. Moreover, the cell rotates with the same angular velocity at any position of the swirl flow field, and the cell is transported along with the movement of the stagnation point. Finally, we extend the application of swirl to manipulate multiple cells. Overall, this method can achieve trapping, rotating, transporting, pairing and enriching for cells, which realizes multifunctional cell manipulation.

Gas-liquid-solid swirling flow polishing and bubble collapse impact characteristics

The mechanism of three-phase abrasive flow polishing method is first analyzed and then volume of fluid (VOF) method is introduced into three-phase abrasive flow modeling, combined with piecewise linear interface construction (PLIC) method to realize the tracking and calculation of bubble interface in the constrained flow channel. It shows the jet effect produced by bubble collapse can effectively enhance the velocity and turbulent kinetic energy of local fluid; bubbles collapse under the action of turbulent vortex, which in turn induce fluid to generate turbulence, which is an action-reaction process; the directional randomness of the turbulent vortex can avoid the directional strips induced by particles polishing in the same direction. The particle image velocimetry (PIV) measurement was used to observe the bubble collapse near the wall and the three-phase swirling flow field for validating the model and polishing experiments show that the target surface roughness can be down to 2.59 nm.

Burning rate augmentation in solid fuel ramjets by swirling inlet air stream

The influence of the inlet swirling flow on the regression rate of the fuel in the combustion chamber of the solid fuel ramjet is investigated in this study using numerical simulations. The finite-volume solver of the compressible turbulent reacting flow is developed to study the flow field where the burning rate is computed using the conjugate heat transfer method for the solid fuel. The correlation is found for the maximum regression rate versus an imposed inlet swirl when the linear distribution of the circumferential velocity is applied at the inlet stream. Although the regression rate augmentation is considerable due to the swirling flow field in the combustor, it is shown that the swirl is effective if is applied near the shear layer of the backstep flow in the combustor. The modified swirler with short blades is suggested to be used in solid fuel ramjets to increase the regression rate of the fuel and improve the performance, but with lower pressure loss.

Experimental study of droplet behavior in a swirl flow field induced by two kinds of guiding vanes and inlet structure optimization

Droplet breakage is a common phenomenon in converting a pipe flow to a swirl flow in a vane-type pipe separator (VTPS)’ inlet. The evaluation of the dispersed droplet sizes after breakage is crucial to the optimum design of the inlet structure and the estimation of the oil-water separation performance. This paper studies the droplet behavior in a swirl flow produced by guiding vanes. Experiments are performed with two different guiding vanes at the inlet of the VTPS. The sizes of the produced oil droplets at the downstream of the guiding vanes are measured in situ using a Malvern Insitec SX. The results indicate that the streamlined deflector is superior to the semi-elliptical plate for the VTPS’ optimization based on the comparison of the droplet sizes in their respective induced swirl flow fields, which can be explained by a modified T-model. Our study suggests that the use of the modified T-model is a reliable method to optimize the design of the guiding vane in the swirling generating stage.

Numerical Investigation of Tip Vortex Cavitation Inception and Noise of Underwater Propellers of Submarine Using Sequential Eulerian–Lagrangian Approaches

In this study, the high-fidelity numerical methods are developed to investigate the tip vortex cavitation (TVC) inception and noise of underwater propellers, namely, Model-A and Model-B, which are designed to investigate the effects of sweep angle on cavitation inception and noise. In addition, the entire body of the DARPA Suboff submarine is included to consider the effects of the inflow distortion originating from the boundary layer flow of the submarine body on the cavitating flow of the propellers. The Eulerian approach consisting of Reynolds-averaged Navier–Stokes (RANS) solver and the vortex model is coupled with the Lagrangian approach using the bubble dynamics equations and the acoustic analogy for nuclei initially distributed in inlet flow. First, three-dimensional incompressible unsteady RANS simulations are performed to predict the hydrodynamic flow field driven by underwater propellers installed on a DARPA Suboff submarine body. The Scully vortex model and dissipation vortex model (DVM) are used to regenerate the tip vortex dissipated by artificial numerical damping and low grid resolution around the vortex core center, which is identified by using minimum λ2-criterion in the swirling flow field originating from the propeller blade tip. Then, tip vortex cavitation inception is simulated by applying the bubble dynamics equations to nuclei initially distributed in the inflow region. The volume and location of each nucleus are obtained by solving the bubble dynamics equations on the flow field obtained using the Eulerian method. Finally, the cavitation noise is predicted by modeling each bubble with a point monopole source whose strength is proportional to its volume acceleration. The validity of the present numerical methods is confirmed by comparing the predicted acoustic pressure spectrum with the measured ones.

Characterization and Scaling of Forced Convective Swirl in Sinusoidal Wavy-Plate-Fin Cores of Compact Heat Exchangers

Abstract The characterization and scaling of the thermal-hydraulic performance in wavy plate-fin compact heat exchanger cores, based on the understanding of the physical phenomena and heat transfer enhancement mechanism is delineated. Experimental data are presented for forced convection in air (Pr = 0.71) with flow rates in the range 50 ≤ Re ≤ 4000. A variety of wavy-fin cores that span viable applications, with geometrical attributes described by the cross section aspect ratio α (ratio of fin spacing to height), fin corrugation aspect ratio γ (ratio of 2× corrugation amplitude to wave pitch), and fin spacing ratio ζ (ratio of fin spacing to wave pitch), are considered. To characterize and correlate the vortex-flow mixing in interfin spaces, a Swirl number Sw is introduced from the balance of viscous, inertial and centrifugal forces. It is shown that the laminar, transitional and turbulent flow regimes can be explicitly identified by this Swirl number. Based on the experimental results and extended analysis, new correlations for Fanning friction factor f and Colburn factor j are developed with Sw, α, γ, and ζ as scaling parameters. Requisite expressions are devised by a superposition of both enhancement components due to the corrugated surface area enlargement and induced swirl flow field, and they are combined to cover the laminar, transitional and turbulent regimes by the method of asymptotic matching. The resulting generalized correlations are further shown to predict all available experimental data for f and j factors to within ±20% and ±15%, respectively.

Experimental study on the design of light phase outlets for a novel axial oil-water separator

Oil-water separation plays a serious role in oil exploitation to reduce the production cost. Centrifugal separation is one of the feasible methods due to its large capacity, high separation efficiency and low maintenance cost. Besides, the centrifugal separation equipment can be divided into tangential inlet separators and axial inlet separators. The ones with tangential inlet have received a large number of investigation on structure optimization but some shortcomings limit the further improvement of separation performance. In this paper, an axial separator with multiple-stage separation was introduced and investigated experimentally with water flow rate range from 3 to 7 m3/h and inlet oil fraction below 10%. Additionally, the schedule for Light Phase Outlets (LPOs) was studied experimentally and theoretically to ensure high separation efficiency and low split ratio. The results show that the multiple stage separator can keep high separation performance that the oil concentration in HPO is below 200 ppm while the split ratio ranged from 0.2 to 0.45 within experimental conditions. Besides, the reasonable schedule can lead an obvious drop in split ratio with high separation performance. Additionally, based on the analysis of flow field characteristic, the LPOs positioned in the two sides of the oil core can ensure the discharge of oil droplets in high swirl flow field and the LPO located downstream has better potential to separate small size droplets.

Effect of electrode configuration on plasma spatial distribution and gas temperature in multi‐arc plasma generator with three pairs of electrodes

AbstractIn this paper, a novel nonthermal multi‐arc plasma generator with three pairs of electrodes is presented to obtain large‐volume plasma. The discharge behaviour of multi‐arc is investigated through high‐speed photography. Statistical process of the photographic images of arc discharge is used for analysis of the effect of electrode configuration on arc spatial distribution and fluctuation of plasma flow. Besides, the gas temperature is diagnosed by diatomic molecular OH fitting method. Results show that the electrode configuration has vital effect on the spatial distribution of plasma in discharge area. A relatively stable region with high luminance is obtained in the centre of the discharge area by adjusting the electrode arrangements, in which the plasma gas temperature in swirl flow field is higher than that in straight flow field in multi‐arc generator. Furthermore, the fluctuation of plasma flow weakens in multi‐arc generator with electrode configurations capable of producing swirl flow field.