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To understand the asymmetric flow of a slender body with low-aspect ratio fins, a wind tunnel experiment was carried out, and the asymmetric flow was observed when the pair of fins had a symmetric deflection angle of 30° at a small angle of attack and zero sideslip angle at transonic speeds. The unsteady characteristics of flow around the moving fins, especially for the evolution of the asymmetric flow, was carefully numerically investigated via the RANS method. To verify the numerical method, the experimental steady wind tunnel data of the NACA 0012 airfoil with sinusoidal pitching motion were adopted. A hysteresis loop exists as a function of the deflection angle during the upstroke and downstroke motions. The side force is periodic due to the asymmetric flow peaks at the downstroke and their peak value appeared at around δz = 25°, which was independent of the deflection frequency. As the deflection frequency increased, the asymmetric flow formed at a higher deflection angle during the upstroke motion, but decayed at a lower deflection angle during the downstroke motion, resulting in a more significant unsteady hysteresis effect. [ABSTRACT FROM AUTHOR]

The flow field of a hydrocyclone was investigated using both computational fluid dynamics (CFD) and particle image velocimetry (PIV). A refractive index matching method was employed to improve the precision of the PIV measurements. The CFD results are in good agreement with PIV measurements. Detailed analysis reveals significant axial asymmetry in the velocity components, with the radial velocity component exhibiting notable disparities. This observation is supported by quantitative data comparing different sections of the hydrocyclone. It is further found that the asymmetry might be mainly attributed to the secondary vortexes with the single inlet of the hydrocyclone. And the secondary vortexes, superimposed on the primary flow rather than existing on its own, spiral downwards from near the inlet towards the underflow orifice. It is hypothesized that specific boundary effects and pressure gradients play a pivotal role in the formation of secondary flows. This assumption is grounded on both theoretical considerations and empirical observations, suggesting that these factors significantly influence the flow dynamics within the hydrocyclone. The insights gained from our measurement methodology and enhanced understanding of secondary flows within hydrocyclones are not only poised to serve as valuable references for fellow researchers but also have the potential to inform the design and operational optimization of hydrocyclones for improved efficiency and performance. [ABSTRACT FROM AUTHOR]

To understand the asymmetric flow of a slender body with low-aspect ratio fins, a wind tunnel experiment was carried out, and the asymmetric flow was observed when the pair of fins had a symmetric deflection angle of 30° at a small angle of attack and zero sideslip angle at transonic speeds. The unsteady characteristics of flow around the moving fins, especially for the evolution of the asymmetric flow, was carefully numerically investigated via the RANS method. To verify the numerical method, the experimental steady wind tunnel data of the NACA 0012 airfoil with sinusoidal pitching motion were adopted. A hysteresis loop exists as a function of the deflection angle during the upstroke and downstroke motions. The side force is periodic due to the asymmetric flow peaks at the downstroke and their peak value appeared at around δz = 25°, which was independent of the deflection frequency. As the deflection frequency increased, the asymmetric flow formed at a higher deflection angle during the upstroke motion, but decayed at a lower deflection angle during the downstroke motion, resulting in a more significant unsteady hysteresis effect.

The flow past an axisymmetric body at a sufficiently high angle of attack becomes asymmetric and unsteady. Several authors identified three different flow regions for bodies of large fineness ratio at low subsonic flow and high incidence: a steady region in the forebody and two unsteady regions in the rear body. Unsteady Reynolds Averaged Navier–Stokes (URANS) codes with eddy viscosity turbulence models or Reynolds stress turbulence models fail to capture the unsteady flow region. These methods are overly dissipative and resolve only frequencies far lower than turbulent fluctuations. Scale-Adaptive-Simulation (SAS) provides an alternative method to afford the problem of these massively separated flows at high Reynolds numbers without addressing the problem to Large Eddy Simulation (LES). This paper applies SAS to study the effect of slenderness on the flow. The numerical solutions show that the flow becomes more unstable as the fineness ratio increases, and the three flow regions are clearly recognizable. For low fineness ratios, only one of the two unsteady regions is visible. The good agreement between the sectional forces and pressure coefficients with their corresponding experimental data for an ogive-cylinder configuration allows an analysis of the flow structure with a fair degree of confidence. [ABSTRACT FROM AUTHOR]

Supersonic shock wave boundary layer interactions are common to inlet flows of supersonic and hypersonic vehicles. This paper reports on wall-resolved implicit large-eddy simulations of a canonical Mach 2.5 turbulent shock wave boundary layer interaction experiment at the NASA Glenn Research Center. The boundary layer upstream of the interaction was nominally axisymmetric and two-dimensional. A conical centerbody with a 16 deg half-angle and a maximum radius of 0.147 D of the test section diameter was employed to generate a conical shock wave, where D is the test section diameter. Asymmetric (swept) interactions were obtained by displacing the shock generator away from the test section centerline. The present simulation is for a shock generator displacement of D / 6 . Results from the asymmetric simulation are compared with results from an earlier simulation of a corresponding axisymmetric interaction. The experimental Reynolds number based on test section diameter was R e D = 4 × 10 6 . For the simulations, the Reynolds number was lowered to R e D = 4 × 10 5 to keep the computational expense of the simulations within limits. Compared to the axisymmetric interaction, the streamwise extent of the separation varies considerably in the azimuthal direction for the asymmetric interaction. The separation is strongest at the azimuthal location that is closest to the shock generator. The streamwise extent of the separated flow regions is noticeably reduced and substantial crossflow is observed between the locations that are closest and farthest from the shock generator. A Fourier analysis of the unsteady flow data indicates low-frequency content for the separated region that is closest to the shock generator. Away from this region, with increasing sweep angle and cross-flow, the low-frequency content is diminished. A proper orthogonal decomposition captures spanwise coherent structures for the more two-dimensional parts of the interaction. [ABSTRACT FROM AUTHOR]

The asymmetric flow over a slender body was particularly sensitive to the nose at a high angle of attack (AoA). Two patterns of separation occurred on the noses of the pointed-nosed slender body and blunt-nosed slender body as open- and close-type separation, respectively. The effects of the bluntness were investigated at high AoA (α = 50°) to clarify the evolution of the separated pattern from open-to close-type separation by the nose and by the periodic characteristics of perturbed flow. Wind tunnel experimental tests were conducted to investigate the periodic characteristics of asymmetric flow at a Reynolds number ReD = 1.54 × 105, based on incoming free-stream velocity (U∞) and the diameter (D) of the model. A particle was attached to the tip of the nose to induce the perturbed flow and attain a definite and predictable asymmetric flow in experimental tests. The pressure scanning and surface oil-flow visualization techniques were used to capture the pressure distributions and flow separations. The major findings were that axial flow increases with the increase of bluntness, resulting in open-type separation turning into close-type separation, and the perturbation moved from downstream to upstream of starting points of the separation line. The critical bluntness of separation pattern switching from open-type to close-type located between 1.5 and 3. Thus, the management of perturbation on asymmetric flow pattern switched from directly participating in separation to influencing separation through micro-flow. Therefore, the locations of perturbation and starting points of the separation line were closely related to asymmetric flow management by perturbation, then affecting the periodic characteristics of perturbed flow.

Rolling motion is the motion where a body flies at a constant pitch angle α with respect to the freestream velocity vector, while undergoing a constant angular rotation p about its longitudinal axis. An effect of this motion is the appearance of a Magnus force and moment, which add to the static forces and moments. One problem that arises at high angles of attack is that the flow is not symmetric in these conditions, leading to a non-zero side force at a zero spin rate. Additionally, the roughness induces a roll angle effect on the side and normal forces, and therefore on the moments. Then, at low roll rates, the prediction is difficult to assess due to the complex interactions due to the moving walls, roughness and shedding vortices that appear at the leeside. Computational fluid dynamics (CFD) is an appropriate tool for investigating these non-linear effects, particularly at high angles of attack. It can help provide a more accurate model of the forces and moments and provide insight into the complex flow field. It is necessary to use high-level turbulence models, transient calculations and fine grids in order to capture the flow field and obtain accurate forces, moments and their derivatives. The calculations have shown that the flow is not symmetrical with the roll rate. There are differences depending on the sign of the spin velocity. The Magnus forces are difficult to determine from the total forces, as there are significant non-linear effects. [ABSTRACT FROM AUTHOR]

The flow at low Mach numbers and high angles of attack over axisymmetric configurations is not symmetric. The mechanism that triggers the asymmetry is a combination of a global (temporal) instability and a convective (spatial) instability. This latter instability is caused by roughness and other geometrical imperfections, which lead to roll angle dependent forces. The flow at these conditions has a complex vortex sheet structure, with two or three different flow regions. An accurate simulation by means of Computational Flow Dynamics (CFD) is thus very challenging, and many researchers have therefore employed Large Eddy Simulation (LES) codes. This study demonstrates that Unsteady Reynolds Averaged Navier-Stokes (URANS) methods are a suitable alternative, if Scale Adaptive Simulation (SAS) is used. This method is capable of capturing the main flow features, provided that fine meshes, which achieve geometrical similarity between the meshed geometry and the real object, and small-time steps are used. It is also demonstrated that, by using URANS methods in combination with SAS, strong differences in the global and local forces depending on the surface roughness of the model are obtained, a result which coincides with several wind tunnel tests. [ABSTRACT FROM AUTHOR]

Aircraft with a blunt-nosed slender body configuration exhibit free-to-roll motion during maneuvering flight. The separation vortex on the forebody and the wing parameters are the two key factors affecting this motion. A blunt-nosed slender body configuration normally includes multiple sets of wings, which enhances the complexity of the roll motion. The strips, narrow wings, and tail rudders are installed at different axial locations on the blunt-nosed body to study the influence of wings on the roll motion. Wind tunnel experiments are conducted to investigate the motion at Reynolds number ReD = 1.54 x 105, which is based on the coming freestream velocity and diameter of the blunt-nosed body. Free-to-roll motion and aerodynamic forces are measured by the free-to-roll sting support and force balance, respectively. The free-toroll motion is first described and divided into six regions based on the motion characteristics at 0° ≤ α ≤ 55°. The strips, narrow wings, and tail rudders are removed to investigate the effect of the wings on the roll motion. The major control performance of strips, narrow wings, and tail rudders on motion in each angle-of-attack (AOA) region are discussed in detail. The experimental results indicate that the coupling between asymmetric flow and tail rudders leads to different characteristics of free-to-roll motion at different AOAs. The asymmetric flow is closely related to the strips, narrow wings and AOA. [ABSTRACT FROM AUTHOR]

This study investigates the asymmetric flow field of a flying wing under high-angle-of-attack crossflow conditions. • The application of dual synthetic jets (DSJ) control effectively improves the flow field structure, enhances leading-edge suction, and significantly improves aerodynamic performance, resulting in an 8.2% increase in lift and strengthened lateral static stability. • After applying DSJ control, the aerodynamic load fluctuations of the flying wing are significantly reduced due to the effective suppression of the separation zone. This improvement is particularly valuable for flow fields under periodic jet disturbances. • The mechanisms of high-frequency and low-frequency DSJ control are thoroughly elucidated from the perspective of flow entrainment. These insights are valuable for designing control strategies for asymmetric flow in crossflow conditions. • The development process of the flow field post-control application is recorded, showing that stabilization is achieved within just 190 milliseconds. This rapid response characteristic of DSJ control meets the high maneuverability requirements of flight. To address the asymmetric flow field of the flying wing under cross-flow conditions at high angles of attack, dual synthetic jet actuators (DSJAs) are positioned at the leading edge of the windward side. DSJ control effectively affects the flow separation structure on the windward side, thereby enhancing leading-edge suction. This leads to both lift enhancement and drag reduction. Furthermore, it strengthens the stabilizing roll moment and improves lateral static stability. Additionally, the effective suppression of the separation zone significantly reduces the aerodynamic load fluctuations of the flying wing after control. In terms of excitation frequency, low-frequency excitation more effectively generates lift, transfers energy downstream, promotes momentum transfer, and results in an 8.2% increase in lift. Moreover, the DSJ excitation exhibits fast response characteristics, with the entire flow establishment process taking only 190 ms. Therefore, through DSJ control, the asymmetric flow under lateral conditions can be effectively corrected, expanding the flight envelope and enhancing the maneuverability and reliability of the aircraft. [ABSTRACT FROM AUTHOR]

The flow past an axisymmetric body at a sufficiently high angle of attack becomes asymmetric and unsteady. Several authors identified three different flow regions for bodies of large fineness ratio at low subsonic flow and high incidence: a steady region in the forebody and two unsteady regions in the rear body. Unsteady Reynolds Averaged Navier–Stokes (URANS) codes with eddy viscosity turbulence models or Reynolds stress turbulence models fail to capture the unsteady flow region. These methods are overly dissipative and resolve only frequencies far lower than turbulent fluctuations. Scale-Adaptive-Simulation (SAS) provides an alternative method to afford the problem of these massively separated flows at high Reynolds numbers without addressing the problem to Large Eddy Simulation (LES). This paper applies SAS to study the effect of slenderness on the flow. The numerical solutions show that the flow becomes more unstable as the fineness ratio increases, and the three flow regions are clearly recognizable. For low fineness ratios, only one of the two unsteady regions is visible. The good agreement between the sectional forces and pressure coefficients with their corresponding experimental data for an ogive-cylinder configuration allows an analysis of the flow structure with a fair degree of confidence.

The flow behaviour of molten steel in the mould has an important influence on the solidification quality of the slab. A three-dimensional transient mould model has been developed to describe the effect of the asymmetric flow behaviour of molten steel on solidified shells in the mould. The causes of the asymmetric behaviour of molten steel in the mould were discussed, and the interaction between deviation flow and solidified shell was analysed. The results show that the asymmetric distribution of the flow field is caused by the difference in flow rate at the outlets on both sides of the nozzle and the irregular interaction between the molten steel and the complex nozzle geometry. The level fluctuation is correlated with the deviation flow of the molten steel on the opposite side. The velocity variation trend of the two models is similar, but the fluctuation amplitude of the velocity on both sides of the nozzle in the non-solidification model is more drastic. The conversion period of the deviation flow in the solidification model is longer than that in the non-solidification model. Moreover, the velocity and angle of incident and return flow on both sides are different due to the deviation flow, which mainly affects the solidification of the shell at and below the impact point of the molten steel. The deviation flow will strengthen the impact of the main stream on the shell, resulting in a significant decrease in the thickness at the impact point, while the thickness of the shell below the impact point fluctuates greatly. [ABSTRACT FROM AUTHOR]

Supersonic shock wave boundary layer interactions are common to inlet flows of supersonic and hypersonic vehicles. This paper reports on wall-resolved implicit large-eddy simulations of a canonical Mach 2.5 turbulent shock wave boundary layer interaction experiment at the NASA Glenn Research Center. The boundary layer upstream of the interaction was nominally axisymmetric and two-dimensional. A conical centerbody with a 16 deg half-angle and a maximum radius of 0.147D of the test section diameter was employed to generate a conical shock wave, where D is the test section diameter. Asymmetric (swept) interactions were obtained by displacing the shock generator away from the test section centerline. The present simulation is for a shock generator displacement of D/6. Results from the asymmetric simulation are compared with results from an earlier simulation of a corresponding axisymmetric interaction. The experimental Reynolds number based on test section diameter was ReD=4×106. For the simulations, the Reynolds number was lowered to ReD=4×105 to keep the computational expense of the simulations within limits. Compared to the axisymmetric interaction, the streamwise extent of the separation varies considerably in the azimuthal direction for the asymmetric interaction. The separation is strongest at the azimuthal location that is closest to the shock generator. The streamwise extent of the separated flow regions is noticeably reduced and substantial crossflow is observed between the locations that are closest and farthest from the shock generator. A Fourier analysis of the unsteady flow data indicates low-frequency content for the separated region that is closest to the shock generator. Away from this region, with increasing sweep angle and cross-flow, the low-frequency content is diminished. A proper orthogonal decomposition captures spanwise coherent structures for the more two-dimensional parts of the interaction.

Sediment abrasion may cause the removal of material and efficiency loss to hydraulic machinery (hydro-turbine, pump, etc.), which may worsen the internal flow and endanger the safe operation of the machines. As abrasion is caused by the impact of sediment on the solid surface, the movement of particles determines the wear intensity. To understand the wear mechanism of hydraulic machinery, the motion characteristics of the asymmetric solid–liquid two-phase flow in a sediment-laden flow around NACA0012 cascades were studied. The laser particle imaging velocimetry (PIV) method was used to measure the flow of quartz particles with median diameters d50 of 82.7 μm, 65.9 μm, and 31.8 μm near the wall of cascades at an impact angle of 10° in a Venturi circuit. The flow characteristics and velocity slip between solid and liquid phases, as well as the effects of particle size and the Reynolds number on velocity slip, were analyzed. The results showed that: (1) the flow is asymmetrically distributed in front of the cascade's leading edge at a 10° impact angle, and there is strong velocity slip between solid and liquid phases; (2) under the influence of particle inertia, the velocity of the solid phase is higher than that of the liquid phase in the deceleration stage, while the velocity of the solid phase is lower than that of liquid phase in the acceleration stage; (3) in the process of approaching the leading edge, the velocity difference between the solid and liquid phase increases by about 10% and the angle difference increases by about 8.8°. [ABSTRACT FROM AUTHOR]

Rolling motion is the motion where a body flies at a constant pitch angle α with respect to the freestream velocity vector, while undergoing a constant angular rotation p about its longitudinal axis. An effect of this motion is the appearance of a Magnus force and moment, which add to the static forces and moments. One problem that arises at high angles of attack is that the flow is not symmetric in these conditions, leading to a non-zero side force at a zero spin rate. Additionally, the roughness induces a roll angle effect on the side and normal forces, and therefore on the moments. Then, at low roll rates, the prediction is difficult to assess due to the complex interactions due to the moving walls, roughness and shedding vortices that appear at the leeside. Computational fluid dynamics (CFD) is an appropriate tool for investigating these non-linear effects, particularly at high angles of attack. It can help provide a more accurate model of the forces and moments and provide insight into the complex flow field. It is necessary to use high-level turbulence models, transient calculations and fine grids in order to capture the flow field and obtain accurate forces, moments and their derivatives. The calculations have shown that the flow is not symmetrical with the roll rate. There are differences depending on the sign of the spin velocity. The Magnus forces are difficult to determine from the total forces, as there are significant non-linear effects.

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Two‐ and three‐dimensional computations have been performed to study incompressible laminar flow of viscous fluids in symmetric channels with gradual expansions. The divergent form advective and viscous terms of Navier–Stokes equations are discretized by means of the UNIFAES scheme, which has been showing unpaired accuracy. Explicit time‐wise integration allows continuity to be imposed via the Poisson equation for the pressure, solved iteratively with several iterations per velocity step in order to ensure mass conservation throughout the transient regime. The proposed finite volume approach uses the semi‐staggered mesh structure, in which pressure is put at the center of the continuity cell and the velocity components at the cell vertexes. Comparative studies have shown this mesh to be highlighted by accuracy, in relation to the traditional, staggered and collocated meshes. Furthermore, it was observed that the semi‐staggered mesh allowed to treat a plane diverging channel in entirely regular fashion without losing accuracy, by appropriate choice of the aspect ratio of the numerical cell, providing geometrical flexibility that does not exist in more common meshes, such as staggered and collocated structures. The present proposal explored the geometric flexibility of the semi‐staggered mesh to solve with simplicity a relevant problem of a channel with gradual expansion. Overall, good agreement was observed against experimental and numerical results in the literature, therefore, it illustrates the capability of the semi‐staggered approach to easily handle flat surfaces nonparallel to the coordinates axes. [ABSTRACT FROM AUTHOR]

The flow at low Mach numbers and high angles of attack over axisymmetric configurations is not symmetric. The mechanism that triggers the asymmetry is a combination of a global (temporal) instability and a convective (spatial) instability. This latter instability is caused by roughness and other geometrical imperfections, which lead to roll angle dependent forces. The flow at these conditions has a complex vortex sheet structure, with two or three different flow regions. An accurate simulation by means of Computational Flow Dynamics (CFD) is thus very challenging, and many researchers have therefore employed Large Eddy Simulation (LES) codes. This study demonstrates that Unsteady Reynolds Averaged Navier-Stokes (URANS) methods are a suitable alternative, if Scale Adaptive Simulation (SAS) is used. This method is capable of capturing the main flow features, provided that fine meshes, which achieve geometrical similarity between the meshed geometry and the real object, and small-time steps are used. It is also demonstrated that, by using URANS methods in combination with SAS, strong differences in the global and local forces depending on the surface roughness of the model are obtained, a result which coincides with several wind tunnel tests.

Sediment abrasion may cause the removal of material and efficiency loss to hydraulic machinery (hydro-turbine, pump, etc.), which may worsen the internal flow and endanger the safe operation of the machines. As abrasion is caused by the impact of sediment on the solid surface, the movement of particles determines the wear intensity. To understand the wear mechanism of hydraulic machinery, the motion characteristics of the asymmetric solid–liquid two-phase flow in a sediment-laden flow around NACA0012 cascades were studied. The laser particle imaging velocimetry (PIV) method was used to measure the flow of quartz particles with median diameters d50 of 82.7 μm, 65.9 μm, and 31.8 μm near the wall of cascades at an impact angle of 10° in a Venturi circuit. The flow characteristics and velocity slip between solid and liquid phases, as well as the effects of particle size and the Reynolds number on velocity slip, were analyzed. The results showed that: (1) the flow is asymmetrically distributed in front of the cascade’s leading edge at a 10° impact angle, and there is strong velocity slip between solid and liquid phases; (2) under the influence of particle inertia, the velocity of the solid phase is higher than that of the liquid phase in the deceleration stage, while the velocity of the solid phase is lower than that of liquid phase in the acceleration stage; (3) in the process of approaching the leading edge, the velocity difference between the solid and liquid phase increases by about 10% and the angle difference increases by about 8.8°.

This paper presents a comparison between optical images and two different modalities of electrical capacitance tomography (ECT), namely an off-the-shelf ECT system and a model one combining an inductance (L) - capacitance (C) - resistance (R) meter with a multiplexer. This comparison was performed to analyse the degree of measurement accuracy and to estimate the spatial resolution of the ECT systems. In this case, the detection of the position of flow boundaries during silo discharging and its translation when discharging changes from concentric to eccentric were investigated. A versatile rectangular silo model was used to generate different types of funnel flow of rice material, which was designated as the most adapted granular material to create both optical and electrical permittivity contrasts between stagnant and flowing zones. When a high temporal resolution is not requested, the model ECT system reduces the measurement error of flow boundary detection between 3% and 9% when compared with optical measurements. Moreover, the system is able to capture boundary translation of about 5% of the silo bin width, which is below the assumed spatial resolution of standard commercial ECT systems. [ABSTRACT FROM AUTHOR]

The self-similarity solutions of the Navier-Stokes equations are constructed for an incompressible laminar flow through a uniformly porous channel with retractable walls under a transverse magnetic field. The flow is driven by the expanding or contracting walls with different permeability. The velocities of the asymmetric flow at the upper and lower walls are different in not only the magnitude but also the direction. The asymptotic solutions are well constructed with the method of boundary layer correction in two cases with large Reynolds numbers, i.e., both walls of the channel are with suction, and one of the walls is with injection while the other one is with suction. For small Reynolds number cases, the double perturbation method is used to construct the asymptotic solution. All the asymptotic results are finally verified by numerical results. [ABSTRACT FROM AUTHOR]

A large eddy simulation (LES) model has been developed to simulate the transient fluid flow, heat transfer and solidification processes in various vertical-bending continuous casting casters with 0 to 5 m of vertical length. The LES with dynamic sub-grid model is used to calculate the transient turbulent flow inside the liquid pool. The enthalpy-porosity approach is used to simulate the heat transfer and solidification of steel in the caster. A criterion is developed using the user-defined functions to model the motion and entrapment of inclusion in the caster based on the Lagrangian approach. The 1/4 and 1/2 inclusion band defects located in a steel plate are found by the UT method, and the distribution of inclusions is intermittent and asymmetric. The transient and asymmetric flow pattern has been obtained in a one-third-scale vertical-bending type water model of mold. The asymmetric flow inside the liquid pool is identified a periodical behavior. The oscillating motion of asymmetric flow inside the mold is induced by the turbulence, rather than the curve shape of the caster. The maximum impact depths of the lower recirculation flow for various casters are almost around 2.8 m below the top surface of the mold. The time for inclusion removal from top surface can be divided into three periods: 3.5–6.5 s, 6.5–30 s, and 30 s after injection. The vertical length has a less effect on the removal ratio of inclusions from the top surface, but determines the entrapment positions of inclusions. [ABSTRACT FROM AUTHOR]

In this paper, the heat transfer of viscoelastic fluid flow has been numerically simulated inside a symmetric planar channel with 1:3 abrupt expansions. For modeling the rheological and nonlinear behavior of inertial flow related to the viscoelastic fluid, exponential form of the Phan Thien-Tanner (EPTT) model has been used. The thermal boundary condition of constant temperature has been considered at the inlet and on the walls of channel. Also, velocity is uniform and constant at the inlet of channel and its value is determined by the Reynolds number of flow. Due to the significant effect of temperature on the viscoelastic fluid properties, viscosity, relaxation time, specific heat capacity and thermal conductivity have been taken as a function of temperature and dissipation term has been employed in the energy equation. For coupling the governing equations, the PISO algorithm is utilized and finite volume method (FVM) is employed for discretizing these equations. In this study, the effect of inertial force is investigated on the velocity distribution, temperature distribution and variation of local and average Nusselt numbers in the expanded part of channel. Despite the symmetry in the planar channel, increasing the Reynolds number forms the symmetric and asymmetric flows inside the expanded part of channel. For asymmetric flows, increase of Reynolds number from 40 to 100 (growth of 2.5 times the Reynolds number) resulted in a 1.7-fold increase for the maximum values of local Nusselt numbers in the vicinity of the upper and lower walls of the channel expanded part. [ABSTRACT FROM AUTHOR]

A numerical study of stress distribution of polymeric viscoelastic fluids passing through planar gradual expansion channels is conducted. To model the viscoelastic behavior in geometries with 1:3 expansion ratios, the exponential form of Phan-Thien Tanner model is employed as the constitutive equation. The PISO algorithm is used to solve the flow field distribution. Three different expansion angles of 30°, 45° and 60° are considered to probe the effects of the gradual expansion and its effect on the stress field distribution. The main purpose of the current study is to analysis the combined effects of the rheological properties and inertia on the normal stress distribution. To achieve this aim, different expansion angles and different ranges of Weissenberg and Reynolds numbers are studied. [ABSTRACT FROM AUTHOR]

When there are several bodies with relative motion in a flow field, such as the flow in the compression system of modern aero-engine, the flow field will have certain special features, one of which is that the time-space structure of such multi-bodies unsteady vorticity flow field would be either of unsteady natural flow (UNF) pattern or of unsteady cooperative flow (UCF) pattern. If we further examine the aerodynamic design system of aero-engine, there is no mechanism for the unsteady cooperative flow to occur, in other words the flow field must be of the unsteady natural flow type. If certain technical measures can be adopted to transform UNF into UCF, the aerodynamic performances will surely be improved. This is the main task the author and their colleague have been devoted to and the results are reviewed in the present paper with emphases laid on basic ideas, technical approaches and experimental verifications.

The asymmetric flow over a slender body was particularly sensitive to the nose at a high angle of attack (AoA). Two patterns of separation occurred on the noses of the pointed-nosed slender body and blunt-nosed slender body as open- and close-type separation, respectively. The effects of the bluntness were investigated at high AoA ( α  = 50°) to clarify the evolution of the separated pattern from open-to close-type separation by the nose and by the periodic characteristics of perturbed flow. Wind tunnel experimental tests were conducted to investigate the periodic characteristics of asymmetric flow at a Reynolds number Re D  = 1.54 × 10 5 , based on incoming free-stream velocity ( U ) of the model. A particle was attached to the tip of the nose to induce the perturbed flow and attain a definite and predictable asymmetric flow in experimental tests. The pressure scanning and surface oil-flow visualization techniques were used to capture the pressure distributions and flow separations. The major findings were that axial flow increases with the increase of bluntness, resulting in open-type separation turning into close-type separation, and the perturbation moved from downstream to upstream of starting points of the separation line. The critical bluntness of separation pattern switching from open-type to close-type located between 1.5 and 3. Thus, the management of perturbation on asymmetric flow pattern switched from directly participating in separation to influencing separation through micro-flow. Therefore, the locations of perturbation and starting points of the separation line were closely related to asymmetric flow management by perturbation, then affecting the periodic characteristics of perturbed flow. ∞ ) and the diameter ( D ) of the model. A particle was attached to the tip of the nose to induce the perturbed flow and attain a definite and predictable asymmetric flow in experimental tests. The pressure scanning and surface oil-flow visualization techniques were used to capture the pressure distributions and flow separations. The major findings were that axial flow increases with the increase of bluntness, resulting in open-type separation turning into close-type separation, and the perturbation moved from downstream to upstream of starting points of the separation line. The critical bluntness of separation pattern switching from open-type to close-type located between 1.5 and 3. Thus, the management of perturbation on asymmetric flow pattern switched from directly participating in separation to influencing separation through micro-flow. Therefore, the locations of perturbation and starting points of the separation line were closely related to asymmetric flow management by perturbation, then affecting the periodic characteristics of perturbed flow., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2023 The Authors. Published by Elsevier Ltd.)

Titanium dioxide (TiO2) has various applications in consumer products and is also used as an additive in food and feeding stuffs. For the characterisation of this product, including the determination of nanoparticles, there is a strong need for the availability of corresponding methods of analysis. This paper presents an optimisation process for the characterisation of polydisperse-coated TiO2nanoparticles. As a first step, probe ultrasonication was optimised using a central composite design in which the amplitude and time were the selected variables to disperse, i.e., to break up agglomerates and/or aggregates of the material. The results showed that high amplitudes (60%) favoured a better dispersion and time was fixed in mid-values (5 min). In a next step, key factors of asymmetric flow field-flow fraction (AF4), namely cross-flow (CF), detector flow (DF), exponential decay of the cross-flow (CFexp) and focus time (Ft), were studied through experimental design. Firstly, a full-factorial design was employed to establish the statistically significant factors (p< 0.05). Then, the information obtained from the full-factorial design was utilised by applying a central composite design to obtain the following optimum conditions of the system: CF, 1.6 ml min–1; DF, 0.4 ml min–1; Ft, 5 min; and CFexp, 0.6. Once the optimum conditions were obtained, the stability of the dispersed sample was measured for 24 h by analysing 10 replicates with AF4 in order to assess the performance of the optimised dispersion protocol. Finally, the recovery of the optimised method, particle shape and particle size distribution were estimated. [ABSTRACT FROM PUBLISHER]

Heterogeneous distribution of red blood cells (RBCs) in downstream vessels of arteriolar bifurcations can be promoted by an asymmetric formation of cell-free layer (CFL) in upstream vessels. Consequently, the CFL widths in subsequent downstream vessels become an important determinant for tissue oxygenation (O2) and vascular tone change by varying nitric oxide (NO) availability. To extend our previous understanding on the formation of CFL in arteriolar bifurcations, this study investigated the formation of CFL widths from 2 to 6 vessel-diameter (2D-6D) downstream of arteriolar bifurcations in the rat cremaster muscle (D = 51.5 ± 1.3 μm). As the CFL widths are highly influenced by RBC aggregation, the degree of aggregation was adjusted to simulate levels seen during physiological and pathological states. Our in vivo experimental results showed that the asymmetry of CFL widths persists along downstream vessels up to 6D from the bifurcating point. Moreover, elevated levels of RBC aggregation appeared to retard the recovery of CFL width symmetry. The required length of complete symmetry recovery was estimated to be greater than 11D under reduced flow conditions, which is relatively longer than interbifurcation distances of arterioles for vessel diameter of ~50 μm. In addition, our numerical prediction showed that the persistent asymmetry of CFL widths could potentially result in a heterogeneous vasoactivity over the entire arteriolar network in such abnormal flow conditions. [ABSTRACT FROM AUTHOR]

Unequal RBC partitioning at arteriolar bifurcations contributes to dissimilar flow developments between daughter vessels in a bifurcation. Due to the importance of the cell-free layer (CFL) and the wall shear stress (WSS) to physiological processes such as vasoregulation and gas diffusion, we investigated the effects of a bifurcation disturbance on the development of the CFL width and WSS in bifurcation daughter branches. The analysis was performed on a two-dimensional (2-D) computational model of a transverse arteriole at three different flow rates corresponding to parent branch (PB) pseudoshear rates of 60, 170 and 470 s − 1 , while maintaining a 2-D hematocrit of about 55% in the PB. Flow symmetry was defined using the statistical similarity of the CFL and WSS distributions between the two walls of the vessel branch. In terms of the flow symmetry recovery, higher flow rates caused larger reductions in the flow symmetry indices in the MB and subsequently required longer vessel lengths for complete recovery. Lower tube hematocrits in the SB led to complete symmetry recovery for all flow rates despite the higher initial asymmetry in the SB than in the MB. Arteriolar bifurcations produce unavoidable local CFL asymmetry and the persistence of the asymmetry downstream may increase effective blood viscosity which is especially significant at higher physiological flow rates. [ABSTRACT FROM AUTHOR]

The effect of wall velocity slip on the stability of a pressure-driven two-dimensional asymmetric channel flow is examined by considering Navier slip condition on the channel walls. The two-parameter families of mean velocity profiles are considered to approximate the underlying asymmetric basic flow. Competing effects of skewness and maximum velocity on the stability of the flow are explored for a range of model parameters. The Orr–Sommerfeld system of the asymmetric flow is solved using a Chebyshev spectral collocation method for both symmetric and non-symmetric type slip boundary conditions. Numerical results indicate that moderate asymmetry in the basic flow has a significant role on the stability of the Poiseuille-kind parallel/nearly parallel flows. Wall slip shows a passive control on the instability of the asymmetric flow by increasing or decreasing the critical Reynolds number and the set of unstable wave numbers. The stabilizing/destabilizing effect of slip velocity on the flow instability is weak or strong depending on the presence of velocity slip at the upper or lower wall. Velocity slip has a profound grip on the flow behaviour by changing the shear rate inside the perturbed flow.

In this paper, viscoelastic fluid flows in planar gradual expansions are studied numerically for the first time. Expansion ratio is considered to be 1:3, and exponential Phan Thien-Tanner (EPTT) model is used as the constitutive equation. The investigation is carried out based on a numerical approach using finite volume method (FVM) and Pressure Implicit with Splitting of Operator (PISO) algorithm. Three angles of 30, 45, and 60° are selected to clarify the effects of gradual expansion angles. Combined effects of dynamics and rheological parameters on bifurcation phenomenon are investigated in detail. An analysis is conducted to elucidate the influences of Reynolds and Weissenberg numbers on the dynamics, shapes, length, and intensity of vortices in stable and unstable situations. The results proved that an increment in expansion angles destabilizes the flow regime. [ABSTRACT FROM AUTHOR]

• An improved VOF-based subgrid-scale model for mass transfer simulation. • Complicated time-periodic flow behavior of asymmetric twin-liquid films. • Several interesting concentration patterns produced by vortices. • Global mass transfer enhancement by large waves and vortices. Twin-liquid films are a combination of wall-bounded films and confined free films. The asymmetric flow is investigated with the VOF method. A new integration algorithm is developed for interfacial mass transfer (Pe =8400) with the subgrid-scale model [1]. Due to the dynamic balance of the surface tension and the spanwise inertia force, periodic interface oscillation at the lower edge of the window is observed. Then the capillary waves in the window become asymmetric, which induces different flux distributions on two sides of the lower wall, accompanied by large waves and vortices. The vortices extrude a scalar plume (local high concentration liquid) from the interface into the liquid bulk and roll it up once or twice in a reverse direction, significantly promoting the mixing and diffusion of scalar in the liquid bulk. As a result, the local mass transfer rate can be enhanced by 100%∼400% on the lower wall. [ABSTRACT FROM AUTHOR]

An asymmetric incompressible gas flow past a body of revolution was studied in a subsonic wind tunnel. Characteristics of the velocity field at the stern of the experimental model, where a laminar boundary-layer separation and concomitant destabilization of the flow occur under axisymmetric conditions, were determined. Declination of the axis of symmetry of the body within several angular degrees results in a radical change of the time-average velocity field, the amplitude distribution of growing hydrodynamic disturbances, and their spectral distribution. [ABSTRACT FROM AUTHOR]