Non-swirling Flow Research Articles

Hydrodynamic modeling of non-swirling and swirling gas-particle two-phase turbulent flow using large eddy simulation

Flow structures of non-swirling and swirling particle-laden turbulence are modeled using the large eddy simulation. Four-way coupling to reveal the interaction mechanism of gas to particle, particle to gas and particle-particle collisions is adopted by a new proposed subgrid scale (SGS) particle kinetic energy-granular temperature model. Evolution of particle vortices, particle coherent structures and particle dynamics are predicted numerically, and comparisons are also conducted. Predictions are in good agreement with experimental measurements. For non-swirling flows, the typical coherent structures, and larger vortices at downward region of gas flow are dominantly. However, particle transport characteristics are significantly different, distinctly coherent structures and more vortices have not been generated in additions to fewer ones at far distance from entrance. Meanwhile, fewer coherent structures and vortices that dispersed at corner recirculation are observed for swirling flow. Compared to gas flow, the number of particle vortices is less and Reynolds stress and kinetic energy transport behaviors of particle flow are relatively independent due to inertia. Gas fluctuations of shear stresses are approximately twice greater than those of particle in non-swirling flows. A novelty finding is that turbulent fluctuations and instantaneous gas vortices of non-swirling flow are stronger than swirling case.

New Lagrangian view of vorticity evolution in two-dimensional flows of liquid and gas

Purpose of the study is to obtain formulas for such a speed of imaginary particles that the circulation of the speed of a (real) fluid along any circuit consisting of these imaginary particles changes (in the process of motion of imaginary particles) according to a given time law. (Until now, only those speeds of imaginary particles were known, at which the mentioned circulation during the motion remained unchanged). Method. Without implementation of asymptotic, numerical and other approximate methods, a rigorous analysis of the dynamic equation of motion (flow) of any continuous fluid medium, from an ideal liquid to a viscous gas, is carried out. Plane-parallel and nonswirling axisymmetric flows are considered. The concept of motion of imaginary particles is used, based on the K. Zoravsky criterion (which is also called A. A. Fridman’s theorem). Results. Formulas for the speed of imaginary particles are proposed. These formulas include the parameters of the (real) flow, their spatial derivatives and the function of time, which determines the law of the change in time of the (real fluid) velocity circulation along the contours moving together with the imaginary particles. In addition, it turned out that for a given function of time (and, as a consequence, for a given law of change in circulation with respect to time), the speed of imaginary particles is determined ambiguously. As a result, a method is proposed to change the speed and direction of motion of imaginary particles in a certain range (while maintaining the selected law of changes in circulation in time). For a viscous incompressible fluid, formulas are proposed that do not include pressure and its derivatives. Conclusion. A new Lagrangian point of view on the vorticity evolution in two-dimensional flows of fluids of all types is proposed. Formulas are obtained for the velocity of such movement of contours, at which the real fluid velocity circulation along any contour changes according to a given time law. This theoretical result can be used in computational fluid dynamics to limit the number of domains when using a gridless method for calculating flows of a viscous incompressible fluid (the method of viscous vortex domains).

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.

The Impact of Swirls on Slurry Flows in Horizontal Pipelines

In deep ocean transportation pipeline, the swirling internal flow has a significant impact on the marine minerals transportation efficiency and safety. Therefore, the present work investigates various swirl flow motions for the slurry transport characteristics of the multi-sized particulate flow in a horizontal pipeline. Since the internal flow is a liquid-solid-solid mixture, a steady-state three-dimensional Eulerian-Eulerian multiphase approach in conjunction with the k-ω SST turbulence model is implemented for numerical simulation in the commercial CFD software ANSYS FLUENT 17.0. Numerical predictions of the mixture solid concentration distributions are generally in good conformance with experimental measurements. It is clearly revealed the transition of flow regime from heterogeneous to pseudo-homogeneous with the increasing level of swirl intensity at inlet. Compared to non-swirling flow, the swirling flow is of benefit to the multi-sized solid suspension capacity and the transportation efficiency. Moreover, the intense swirling vortex results in a strong influence on the characteristics of the lubrication layer formed by fine solid particles near the bottom of the pipe. These results provide valuable insights regarding the influence of swirl flow on the transport process for deep ocean mining.

Effect of swirl flow on the performance of parallel hub axial annular diffuser

In the present work, the parallel hub axial flow annular diffuser's performance characteristics with divergent casing varying between equivalent cone angle (10°, 15°, and 20°) with area ratio 3 have been evaluated computationally as well as experimentally. The performance of three diffusers were tested at different inlet swirl angles (from 0° to 25°) for swirling and non-swirling flow. Simulations have been carried out on a fully developed flow at Reynolds number 2.5×105. The results were analyzed based on the velocity profiles, static pressure recovery coefficient, and the total pressure loss coefficient. The result analysis shows that the inlet swirl flow improves the recovery of pressure and also delays the flow separation on the casing. Moreover,the findings also show that the best performance was achieved in equivalent cone angle 10° at the inlet swirl angle of 7.5° compared to other diffusers.

Recovery of radial-axial velocity in axisymmetric swirling flows of a viscous incompressible fluid in the Lagrangian consideration of vorticity evolution

Swirling laminar axisymmetric flows of viscous incompressible fluids in a potential field of body forces are considered. The study of flows is carried out in a cylindrical coordinate system. In the flows, the regions in which the axial derivative of the circumferential velocity cannot take on zero value in some open neighborhood (essentially swirling flows) and the regions in which this derivative is equal to zero (the region with layered swirl) are considered separately. It is shown that a well-known method (the method of viscous vortex domains) developed for non-swirling flows can be used for regions with layered swirling. For substantially swirling flows, a formula is obtained for calculating the radial-axial velocity of an imaginary fluid through the circumferential vorticity component, the circumferential circulation of a real fluid, and the partial derivatives of these functions. The particles of this imaginary fluid “transfer” vortex tubes of the radial-axial vorticity component while maintaining the intensity of these tubes, and also “transfer” the circumferential circulation and the product of the circular vorticity component by some function of the distance to the axis of symmetry. A non-integral method for reconstructing the velocity field from the vorticity field is proposed. It is reduced to solving a system of linear algebraic equations in two variables. The obtained result is proposed to be used to extend the method of viscous vortex domains to swirling axisymmetric flows.

Experimental study of liquid-carrying by swirling flow in a U-shaped tube

In natural gas pipelines, temperature and pressure vary along the line, leading to liquid condensation in undulating sections of the pipelines. This phenomenon has a significant impact on the gas transportation efficiency and safety. In this study, an experimental investigation on liquid-carrying by a swirling flow in an undulating pipeline was carried out. As the condensate liquid would usually accumulate in the pipeline, a U-shaped tube with a diameter of 0.025 m was used to simulate a low-lying part. The effect of swirl on flow patterns in the U-shaped tube was observed using a high-speed camera and processed with image processing technology. Five flow patterns, namely stratified, stratified wave, slug, plug and annular flow, were observed in the U-shaped tube under gas superficial velocities ranging from 0.17 to 14.15 m/s, and with the height of liquid accumulation ranging from 15 to 125 mm. Compared to a non-swirling flow, the swirling flow was observed to increase the liquid-carrying capacity; which however, was a function of the flow pattern. The liquid-carrying capacity of the swirling flow for different flow patterns in the order of highest to lowest was: annular, slug, plug, stratified wave and stratified flow. The initial liquid volume and inlet gas velocity also influenced the liquid-carrying efficiency of the swirling flow. With an increasing gas flow rate, the fluctuation of gas–liquid interface increased, and the liquid-carrying efficiency also increased. Furthermore, Swirling flow reduced the critical gas velocity needed to carry the liquid phase by 14.14% compared to a non-swirling flow.

Performance characteristics of flow in annular diffuser using CFD

Abstract An annular diffuser is a critical component of the turbomachinery, and its prime function is to reduce the flow velocity. The current work is carried to study the effect of four different geometrical designs of an annular diffuser using the ANSYS Fluent. The numerical simulations were carried out to examine the effect of fully developed turbulent swirling and non-swirling flow. The flow behavior of the annular diffuser is analyzed at Reynolds number 2.5 × 105. The simulated results reveal pressure recovery improvement at the casing wall with adequate swirl intensity at the diffuser inlet. Swirl intensity suppresses the flow separation on the casing and moves the flow from the hub wall to the casing wall of the annulus region. The results also show that the Equal Hub and Diverging Casing (EHDC) annular diffuser in comparison to other diffusers has a higher static pressure recovery (C p = 0.76) and a lower total pressure loss coefficient of (C L = 0.12) at a 17° swirl angle.

Performance characteristics of flow in annular diffuser using CFD

Abstract An annular diffuser is a critical component of the turbomachinery, and its prime function is to reduce the flow velocity. The current work is carried to study the effect of four different geometrical designs of an annular diffuser using the ANSYS Fluent. The numerical simulations were carried out to examine the effect of fully developed turbulent swirling and non-swirling flow. The flow behavior of the annular diffuser is analyzed at Reynolds number 2.5 × 105. The simulated results reveal pressure recovery improvement at the casing wall with adequate swirl intensity at the diffuser inlet. Swirl intensity suppresses the flow separation on the casing and moves the flow from the hub wall to the casing wall of the annulus region. The results also show that the Equal Hub and Diverging Casing (EHDC) annular diffuser in comparison to other diffusers has a higher static pressure recovery (C p = 0.76) and a lower total pressure loss coefficient of (C L = 0.12) at a 17° swirl angle.

Decay law and swirl length of swirling gas-liquid flow in a vertical pipe

Decaying swirling flow is widely utilized in multiphase flow devices for separation, stabilization and heat transfer enhancement. In this paper, based on the image processing technique, the decay law and swirl length of swirling gas-liquid flow induced by a vane-type swirler in a vertical pipe is experimentally and theoretically studied. According to the visual observation, four swirling flow patterns including chain, swirling gas-column, swirling intermittent and swirling annular flow are recognized at the swirler outlet. Due to swirl decay, the chain, swirling intermittent and swirling annular flow revert to inlet non-swirling flows downstream of the swirler, whereas the swirling gas-column flow transforms to slug flow rather than inlet bubble flow. The swirl length of swirling gas-column and swirling intermittent flow increases with liquid superficial velocity increasing or gas superficial velocity decreasing. By contrast, the swirling annular flow exhibits a reverse trend. Based on the theory of angular momentum and the parameter of two-phase swirl number, comprehensive decay models are proposed to predict the swirl length of various swirling flow patterns. The prediction is correlated reasonably well with the experimental data within ±25% deviation in varied flow conditions.

Swirling turbulent pipe flows: Inertial region and velocity–vorticity correlations

Swirling pipe flows are studied here with an aim towards understanding the onset of the inertial region — where the turbulent-inertia term in the mean momentum equation is balanced by pressure gradient and viscous term is sub-dominant — as well as the clarifying the velocity–vorticity correlations that make up the turbulent inertia. To this end, we first manipulate the mean momentum equation in both axial and azimuthal directions and find some exact results in the inertial region, and carry out direct numerical simulations of swirling pipe flows at axial friction Reynolds numbers of 170 and 500. The swirl number considered in our simulations is S≈0.3, and we compare our results to non-swirling pipe flows at similar Reynolds numbers. We find that swirling produces a drag increase and an influence on the turbulence statistics similar to increasing the Reynolds number except for the streamwise turbulence intensity. An analysis on the axial and azimuthal mean momentum equations shows that swirling shifts the beginning of the inertial region wall-normal location closer to the wall. The turbulent inertia decomposition reveals that the near-wall region the velocity–vorticity correlations of the axial direction are similar to a 2D channel flow and interpreted as vorticity stretching/reorientation and dispersion, whereas in the new correlations in the azimuthal direction can also be given a similar physical meaning in the near-wall region. In the outer-region, however, the pipe axial correlations are different to the 2D-channel, and so are the azimuthal correlations. We find that the pipe has new a ‘geometric’ contribution in both axial and azimuthal directions that play an important role in contributing towards vorticity dispersion in the outer core region of a swirling pipe flow.

Experimental investigation and modeling of boundary layer flashback for non-swirling premixed hydrogen/ammonia/air flames

Carbon free fuels such as hydrogen/ammonia blends show a promising potential to become sustainable and renewable fuels for gas turbines and other combustion systems. One interesting aspect about these blends is the possibility to adjust different combustion properties like the laminar burning velocity or ignition delay time by changing the ratio between H2 and NH3. Such fuel blends can be produced via partial catalytic decomposition of NH3. However, such mixtures can lead to flame instabilities such as flashback, especially if the hydrogen content is high. In the present study, the boundary layer flashback of premixed hydrogen/ammonia/air mixtures is investigated experimentally for non-swirling flows at normal temperature (293 K) and normal pressure (101 kPa). A new experimental setup for boundary layer flashback investigation with a fully automated measurement procedure is introduced. With preliminary studies, the influence of various measurement procedures on the flashback limits is firstly investigated. For a broad flashback study, the data of 351 flashback experiments are collected. The ammonia content in H2/NH3 fuel mixtures is varied from 0 vol% to 50 vol% in 10 vol% steps. The fuel–air equivalence ratio is ranging from 0.38 to 1.17. As the ammonia content is increasing, the mean flow velocities at flashback are exponentially decreasing. Additionally, theoretical modeling is performed. A model is derived based on the concept of the critical velocity gradient which is able to predict the measured data with high accuracy. For two exemplary cases with H2/air and 80% H2/20% NH3/air mixtures, the process of boundary layer flashback is investigated in detail with low and high speed direct imaging and image post-processing. During the flashback onset of H2/NH3/air flames a separate reaction of H2 followed by the reaction of NH3 can be observed. Also, a flame-oscillation between fused silica tube and burner head with approximately 10 Hz was observed. Furthermore, indications for an adverse pressure gradient based on the flame propagation speed is seen. Details about the flame structure during the flashback process of H2/NH3/air flames are shown. During the upstream flame propagation of H2/NH3/air flames, high frequency oscillations with about 830 Hz of the leading flame tip are observed, which are assumed to be related to thermoacoustic instabilities.

Effect of swirl on fluctuation of pressure drop in a gas–liquid slug flow

Slug flow as one of the typical two-phase flow patterns occurs widely in industry. The fluctuating phenomenon in slug flow is harmful to the pipeline system and should be suppressed. Flow-pattern modulation by swirl has been widely used to satisfy practical application. In this work, influences of swirl on pressure gradient and interface morphology in a gas–liquid slug flow were studied by visualization experiments. The results showed that slug flow will transform to swirling intermittent flow when the gas and liquid velocity is relatively high. In this case, pressure drop in the slug flow is higher and its fluctuation within a relatively narrow range compared with those in a non-swirl slug flow; the probability density function distribution is more concentrated in the swirling intermittent flow; the slug flow transforms to the flow pattern altering between gas column and gas slug. The slug flow was kept downstream of the swirler when the gas and liquid velocity is relatively low. In this case, effects of swirl on both pressure drop and interface morphology are not obvious. Along the streamwise direction, the morphology interface, fluctuation of pressure drop and pressure signals showed that the swirling intermittent flow gradually transforms to non-swirl slug flow. Finally, the transition boundaries between these flow patterns were proposed and compared with other published transition boundaries in swirling and non-swirling flows.

Effects of casing angle on the performance of parallel hub axial annular diffuser

AbstractIn this paper, the effects of non-swirling and swirling flow on the performance of parallel hub axial annular diffuser has been investigated. The study was conducted on a fully developed swirling flow and non-swirling flow to predict the separation of the flow from the wall. Three different annular diffusers were used with casing wall angles of 3°, 6°, and 9°. Furthermore, various swirl angles (0–25°) at the inlet of diffusers have been investigated to analyze the performance across the length. It was found that parallel hub axial annular diffuser performance increases up to a certain length as the inlet swirl angle increases. However, the performance also improves as the diffuser area ratio (AR) increases. The performance is evaluated based on the static pressure recovery coefficient (Cp) and the total pressure loss coefficient (CTL). The highest possible pressure recovery is achieved by the 12° swirl angle with a casing angle of 6°.

Effects of casing angle on the performance of parallel hub axial annular diffuser

Abstract In this paper, the effects of non-swirling and swirling flow on the performance of parallel hub axial annular diffuser has been investigated. The study was conducted on a fully developed swirling flow and non-swirling flow to predict the separation of the flow from the wall. Three different annular diffusers were used with casing wall angles of 3°, 6°, and 9°. Furthermore, various swirl angles (0–25°) at the inlet of diffusers have been investigated to analyze the performance across the length. It was found that parallel hub axial annular diffuser performance increases up to a certain length as the inlet swirl angle increases. However, the performance also improves as the diffuser area ratio (AR) increases. The performance is evaluated based on the static pressure recovery coefficient (Cp) and the total pressure loss coefficient (CTL). The highest possible pressure recovery is achieved by the 12° swirl angle with a casing angle of 6°.

Transition from non-swirling to swirling axisymmetric turbulence

Strictly axisymmetric turbulence, i.e., turbulence governed by the Navier-Stokes equations modified such that the flow is invariant in the azimuthal direction, is a system intermediate between two-and three-dimensional turbulence. We investigate statistically steady states of this system by direct numerical simulation using a forcing protocol, which allows the injected energy in the toroidal and in the poloidal directions to be tuned independently. A sharp transition between a two-dimensional two-component (2D2C, non-swirling) flow and a two-dimensional three-component (2D3C, swirling) flow is observed. We derive a statistical model which reproduces this transition.

Возникновение вращения жидкости при охлаждении свободной границы

For the Navier-Stokes system and the heat equation with vanishing viscosity, the stationary thermocapillary flow of an incompressible fluid in a horizontal layer of infinite thickness is calculated. The layer is bounded above by a free non-deformable boundary on which an uneven temperature distribution is specified. In the approximation of the boundary layer, asymptotic expansions of the solution of the problem are constructed. The main terms of the asymptotics satisfy the Prandtl equations of the boundary layer. Two types of regimes in the boundary layer are calculated - non-swirling and rotational fluid flows. Rotational regimes of fluid flows arise as a result of bifurcation of non-swirling regimes in the boundary layer. Bifurcation points are found by solving a boundary value problem for eigenvalues. It is shown that rotational regimes arise only when the free boundary is locally cooled. When the boundary is heated, fluid rotation does not occur. Two types of rotational modes are numerically calculated. All modes exist only if the velocity of the external fluid flow does not exceed the bifurcation value. The modes of the first type have axial symmetry. There are only two such modes. Other modes do not have axial symmetry. For modes of the second type, an exact solution in cylindrical coordinates is obtained. These modes depend on two independent parameters that fill the circle of unit radius. So, at the bifurcation point, many rotational regimes arise, which are a two-parameter family.

Effect of Swirl on Thermal and Hydraulic Properties of Ice Slurry Flow

Accumulation of ice particles inside the pipes of an ice slurry refrigeration system is a problem that should be avoided to ensure the efficient performance of the system. In the present research, the swirling flow of ice slurry is numerically investigated using the Eulerian-Eulerian model coupled with the kinetic theory of granular flow. The swirling flow is generated by twisted tapes inserted into a smooth pipe. The results show that by swirling the flow, the ice particle diameter may be increased up to about three times larger than the typical particle diameter used in the ice slurry, without particle accumulation. Moreover, for the swirling flow of ice slurry with the ice particle diameter of 0.3 mm, the rate of mass transfer increases 25% while the ice volume fraction at the pipe outlet decreases 30%, compared to the non-swirling flow. Based on the obtained results of swirling flow, correlations for friction factor, mean Nusselt number, and performance parameter are proposed.

Two-step numerical simulation of the heat transfer from a flat plate to a swirling jet flow from a rotating pipe

PurposeImpinging jets have been widely studied, and the addition of swirl has been found to be beneficial to heat transfer. As there is no literature on Reynolds-averaged Navier Stokes equations (RANS) nor experimental data of swirling jet flows generated by a rotating pipe, the purpose of this study is to fill such gap by providing results on the performance of this type of design.Design/methodology/approachAs the flow has a different behaviour at different parts of the design, the same turbulent model cannot be used for the full domain. To overcome this complexity, the simulation is split into two coupled stages. This is an alternative to use the costly Reynold stress model (RSM) for the rotating pipe simulation and the SST k-ω model for the impingement.FindingsThe addition of swirl by means of a rotating pipe with a swirl intensity ranging from 0 up to 0.5 affects the velocity profiles, but has no remarkable effect on the spreading angle. The heat transfer is increased with respect to a non-swirling flow only at short nozzle-to-plate distances H/D < 6, where H is the distance and D is the diameter of the pipe. For the impinging zone, the highest average heat transfer is achieved at H/D = 5 with swirl intensity S = 0.5. This is the highest swirl studied in this work.Research limitations/implicationsHigh-fidelity simulations or experimental analysis may provide reliable data for higher swirl intensities, which are not covered in this work.Practical implicationsThis two-step approach and the data provided is of interest to other related investigations (e.g. using arrays of jets or other surfaces than flat plates).Originality/valueThis paper is the first of its kind RANS simulation of the heat transfer from a flat plate to a swirling impinging jet flow issuing from a rotating pipe. An extensive study of these computational fluid dynamics (CFD) simulations has been carried out with the emphasis of splitting the large domain into two parts to facilitate the use of different turbulent models and periodic boundary conditions for the flow confined in the pipe.

The effect of droplets thermophysical properties on turbulent heat transfer in a swirling separated mist flow

The numerical investigation of the effect of the swirl number and the thermophysical properties of water, ethanol, and acetone droplets on the particle scattering, turbulence modification and heat transfer in a droplet-laden flow is carried out. The set of 3D steady-state Reynolds-averaged Navier–Stokes (RANS) equations for the two-phase flow is utilized. The dispersed phase is modeled by the Eulerian approach. The flow swirling significantly shortens the length of the recirculation zone (up to two times in comparison with non-swirling flow at swirl number S = 0.5) for all types of the studied liquids. The highest value of heat transfer rate is obtained for the ethanol droplets (up to 10%), and the lowest one is obtained for the acetone droplets (up to 50%), both in comparison with water droplets. The swirling of the turbulent mist flow causes heat transfer enhancement (more than 1.5 times in comparison with the non-swirling droplet-laden flow). In the swirling flow, the value of the volume fraction of the dispersed phase has a maximum in the axial region of the pipe, and further in the direction of the wall its value is very small. The effect of heat transfer enhancement weakens with increasing Reynolds number of the flow. A region without droplets appears in the wall zone of the swirling two-phase flow, and the region is largest for acetone droplets.