An investigation of bimodal jet trajectory in flow through scaled models of the human vocal tract

Pulsatile two-dimensional flow through static divergent models of the human vocal folds is investigated. Although the motivation for this study is speech production, the results are generally applicable to a variety of engineering flows involving pulsatile flow through diffusers. Model glottal divergence angles of 10, 20, and 40° represent various geometries encountered in one phonation cycle. Frequency and amplitude of the flow oscillations are scaled with physiological Reynolds and Strouhal numbers typical of human phonation. Glottal velocity trajectories are measured along the anterior–posterior midline by using phase-averaged particle image velocimetry to acquire 1,000 realizations at ten discrete instances in the phonation cycle. The angular deflection of the glottal jet from the streamwise direction (symmetric configuration) is quantified for each realization. A bimodal flow configuration is observed for divergence angles of 10 and 20°, with the flow eventually skewing and attaching to the vocal fold walls. The deflection of the flow toward the vocal fold walls occurs when the forcing function reaches maximum velocity and zero acceleration. For a divergence angle of 40°, the flow never attaches to the vocal fold walls; however, there is increased variability in the glottal jet after the forcing function reaches maximum velocity and zero acceleration. The variation in the jet trajectory as a function of divergence angle is explained by performance maps of diffuser flow regimes. The smaller angle cases are in the unstable transitory stall regime while the 40° divergent case is in the fully developed two-dimensional stall regime. Very small geometric variations in model size and surface finish significantly affect the flow behavior. The bimodal, or flip-flopping, glottal jet behavior is expected to influence the dipole contribution to sound production.     

Experimental investigation of turbulence modulation in particle-laden coaxial jets by Phase Doppler Anemometry

The effect of solid particles on the flow characteristics of axisymmetric turbulent coaxial jets for two flow conditions was studied. Simultaneous measurements of size and velocity distributions of continuous and dispersed phases in a two-phase flow are presented using a Phase Doppler Anemometry (PDA) technique. Spherical glass particles with a particle diameter range from 102 to 212 μm were used in this two-phase flow, the experimental results indicate a significant influence of the solid particles and the Re on the flow characteristics. The data show that the gas phase has lower mean velocity in the near-injector region and a higher mean velocity at the developed region. Near the injector at low Reynolds number (Re = 2839) the presence of the particles dampens the gas-phase turbulence, while at higher Reynolds number (Re = 11 893) the gas-phase turbulence and the velocity fluctuation of particle-laden jets are increased. The particle velocity at higher Reynolds number (Re = 11 893) and is lower at lower Reynolds number (Re = 2839). The slip velocity between particles and gas phase existed over the flow domain was examined. More importantly, the present experiment results suggest that, consideration of the gas characteristic length scales is insufficient to predict gas-phase turbulence modulation in gas-particle flows.     

Dynamics of disk-like particles in turbulent vertical channel flow

The dynamical behavior of inertial disk-like particles in turbulent vertical channel flow is investigated by an Eulerian–Lagrangian point-particle approach. Gravity effects on distribution, translation, rotation and orientation statistics of non-spherical particles modeled as oblate spheroids have been studied both in an upward and a downward flow and compared with results obtained in the absence of gravity. Altogether 12 different particle classes have been studied, with inertia and shape parameterized by means of Stokes number St and aspect ratio λ ≤ 1. The St = 5 disk-like particles distribute more evenly across the channel in upward than in downward flow. The gravity effect on the particle concentration diminishes with large inertia and the spheroid shape has only a modest influence. Although the gravity significantly affects the streamwise and wall-normal mean slip velocities with increasing inertia, the particle shape rarely has any impact on the translational motion, except for the mean wall-normal velocity. The fluctuations of the velocity of disk-like particles are mainly ascribed to inertia, whereas the gravity and shape only have marginal effects. The presence of gravity is moreover found to have a negligible effect on the particles’ orientation and rotation, in spite of the striking effect of λ on the orientation and rotation seen in the near-wall region. The tendency of the disks to align their symmetry axis orthogonal to the fluid vorticity in the channel center is stronger for particles with modest inertia. In the near-wall region, however, oblate spheroids preferentially align with the fluid vorticity for St >> 1. The observed behavior is believed to be caused by the influence of the gravity force on the turbophoresis; i.e. that inertial particles move towards low-turbulence regions.     

An investigation of jet trajectory in flow through scaled vocal fold models with asymmetric glottal passages

Pulsatile two-dimensional flow through asymmetric static divergent models of the human vocal folds is investigated. Included glottal divergence angles are varied between 10° and 30°, with asymmetry angles between the vocal fold pairs ranging from 5° to 15°. The model glottal configurations represent asymmetries that arise during a phonatory cycle due to voice disorders. The flow is scaled to physiological values of Reynolds, Strouhal, and Euler numbers. Data are acquired in the anterior–posterior mid-plane of the vocal fold models using phase-averaged Particle Image Velocimetry (PIV) acquired at ten discrete locations in a phonatory cycle. Glottal jet stability arising from the vocal fold asymmetries is investigated and compared to previously reported work for symmetric vocal fold passages. Jet stability is enhanced with an increase in the included divergence angle, and the glottal asymmetry. Concurrently, the bi-modal jet trajectory and flow unsteadiness diminishes. Consistent with previous findings, the flow attachment due to the Coanda effect occurs when the acceleration of the forcing function is zero.     

Experimental study of the blockage boundary for dense-phase pneumatic conveying of powders through a horizontal slit

The estimation of the blockage boundary for pneumatic conveying through a slit is of significant importance. In this paper, we investigate the characteristics for blockage of powder (48 μm average diameter) through a horizontal slit (1.6 m × 0.05 m × 0.002 m). The results show that the required critical solid mass flow rate increases as the superficial air velocity increases superficial air velocity. The solid loading ratio and superficial air velocity displayed a decreasing power law relationship. This finding agrees with existing theory and experimental results. However, a minimum inlet solid loading ratio exists. When the air velocity is greater than the corresponding air velocity of the minimum solid loading ratio, the solid loading ratio exhibits an increasing trend in power law. We also found that when the inlet conveying pressure increased, the critical solid mass flow rate required for blockage, the inlet solid loading ratio, and the minimum inlet solid loading ratio increased.     

Use of zero-net-mass-flow for separation control in diffusing S-duct

Flow control using zero-net-mass-flow jets in an S-shaped diffusing duct was investigated. Experiments were conducted in a channel flow facility at a Reynolds number, Re = 4.1 × 10⁴ with particle image velocimetry measurements in the symmetry plane of the duct. In the natural configuration, separation of the boundary layer occurs in a region of the duct with an high degree of curvature. A stability analysis of the wall normal base flow at the location of the applied control is presented and estimates the most effective frequency of the actuator. Time-averaged velocity fields show total reattachment of the boundary layer using active flow control.     

CFD based mini- vs. micro-system delineation in elongated bubble flow regime

Delineation of mini- and micro-scale channels with respect to two-phase flow has been the subject of many research papers. There is no consensus on when the small channel can be characterized as a mini-channel or micro-channel. The idea proposed by this paper is to use the normalized bubble nose radius, liquid film thickness top over bottom ratio, and bubble shape contour, which are found under normal gravity conditions in slug flow through a horizontal adiabatic channel, as the delineation criteria. The input parameters are bubble nose radius and bubble nose velocity as the characteristic length scale and characteristic velocity scale respectively. 3D numerical simulation with ANSYS FLUENT was used to obtain the necessary data. Following CFD practice, a mesh independence study and a numerical model validation against published experimental data were both conducted. Analysis of the numerical simulation results showed that channels with D ⩽ 100 μm can be characterized as a micro-system, while channels with D ⩾ 400 μm belong to mini-systems. The region 200 μm ⩽ D ⩽ 300 μm represents a transition from the micro-scale to mini-scale.     

CFD–DEM simulation of the pneumatic conveying of fine particles through a horizontal slit

Fine particles play a significant role in many industrial processes. To study the dynamic behavior of fine particle and their deposition in rock fractures, the pneumatic conveying of fine particles (approximately 100 μm in diameter) through a small-scale horizontal slit (0.41 m × 0.025 m) was studied, which is useful for the sealing technology of underground gas drainage in coal mining production. The CFD–DEM method was adopted to model the gas-particle two-phase flow; the gas phase was treated as a continuum and modeled using computational fluid dynamics (CFD), particle motion and collisions were simulated using the DEM code. Then, the bulk movement of fine particles through a small-scale horizontal slit was explored numerically, and the flow patterns were further investigated by visual inspection. The simulation results indicated that stratified flow or dune flow can be observed at low gas velocities. For intermediate gas velocities, the flow patterns showed pulsation phenomena, and dune flow reappeared in the tail section. Moreover, periodic flow regimes with alternating thick and sparse stream structures were observed at a high gas velocity. The simulation results of the bulk movement of fine particles were in good agreement with the experimental findings, which were obtained by video-imaging experiments. Furthermore, the calculated pressure drop versus gas velocity profile was investigated and compared with relative experimental findings, and the results showed good agreement. Furthermore, the particle velocity vectors and voidage distribution were numerically simulated. Selected stimulation results are presented and provide a reference for the further study of fine particles.     

Experimental study on local characteristics of oil–water dispersed flow in a vertical pipe

The local flow characteristics of oil–water dispersed flow in a vertical upward pipe were studied experimentally. The inner diameter and length of the test section are 40 mm and 3800 mm, respectively. A double-sensor conductivity probe was used to measure the local interfacial parameters, including interfacial area concentration, oil phase fraction, interfacial velocity, and oil drops Sauter mean diameter. The water flow rates varied from 0.12 m/s to 0.89 m/s, while the oil flow rates ranged from 0.024 m/s to 0.198 m/s. Typical radial profiles of interfacial area concentration, oil phase fraction, interfacial velocity, and oil drops Sauter mean diameter are presented. An interesting phenomenon is that the local and cross-section-averaged interfacial area concentrations display concave change with water flow rate under constant oil flow rate. The physical mechanism of such a variation is discussed in details.     

Flow pattern characterization for R-245fa in minichannels: Optical measurement technique and experimental results

An optical measurement method using image processing for two-phase flow pattern characterization in minichannel is developed. The bubble frequency, the percentage of small bubbles as well as their velocity are measured. A high-speed high-definition video camera is used to measure these parameters and to identify the flow regimes and their transitions. The tests are performed in a 3.0 mm glass channel using saturated R-245fa at 60 °C (4.6 bar). The mass velocity is ranging from 100 to 1500 kg/m² s, the heat flux is varying from 10 to 90 kW/m² and the inlet vapor quality from 0 to 1. Four flow patterns (bubbly flow, bubbly–slug flow, slug flow and annular flow) are recognized. The comparison between the present experimental intermittent/annular transition lines and five transition lines from macroscale and microscale flow pattern maps available in the literature is presented. Finally, the influence of the flow pattern on the heat transfer coefficient is highlighted.     

Laminar flow of power-law fluids past a rotating cylinder

In this work, the continuity and momentum equations have been solved numerically to investigate the flow of power-law fluids over a rotating cylinder. In particular, consideration has been given to the prediction of drag and lift coefficients as functions of the pertinent governing dimensionless parameters, namely, power-law index (1 ≥ n ≥ 0.2), dimensionless rotational velocity (0 ≤ α ≤ 6) and the Reynolds number (0.1 ≤ Re ≤ 40). Over the range of Reynolds number, the flow is known to be steady. Detailed streamline and vorticity contours adjacent to the rotating cylinder and surface pressure profiles provide further insights into the nature of flow. Finally, the paper is concluded by comparing the present numerical results with the scant experimental data on velocity profiles in the vicinity of a rotating cylinder available in the literature. The correspondence is seen to be excellent for Newtonian and inelastic fluids.     

Computational and experimental characterization of a liquid jet plunging into a quiescent pool at shallow inclination

A circular water jet (Re = 1.6 × 10⁵; We = 8.8 × 10³) plunging at shallow angles (θ ≈ 12.5°) into a quiescent pool is investigated computationally and experimentally. A surprising finding from the work is that cavities, of the order of jet diameter, are formed periodically in the impact location, even though the impinging flow is smooth and completely devoid of such a periodicity. Computational prediction of these frequencies was compared with experimental findings, yielding excellent agreement. The region in the vicinity of the impact is characterized by strong churning due to splashing and formation of air cavities. Measured velocity profiles indicate a concentration of momentum beneath the free surface slightly beyond the impact location (X/D_j ≈ 14), with a subsequent shift towards the free surface further downstream of this point (X/D_j ≈ 30). This shift is due primarily to the action of buoyancy on the cavity/bubble population. Comparisons of the mean velocity profile between simulations and experiments are performed, yielding good agreement, with the exception of the relatively small churning flow region. Further downstream (X/D_j ≳ 40), the flow develops mostly due to diffusion and the location of peak velocity coincides with the free surface. In this region, the free surface acts as an adiabatic boundary and restricts momentum diffusion, causing the peak velocity to occur at the free surface.     

Instantaneous flow field above the free end of finite-height cylinders and prisms

The flow above the free ends of surface-mounted finite-height circular cylinders and square prisms was studied experimentally using particle image velocimetry (PIV). Cylinders and prisms with aspect ratios of AR = 9, 7, 5, and 3 were tested at a Reynolds number of Re = 4.2 × 10⁴. The bodies were mounted normal to a ground plane and were partially immersed in a turbulent zero-pressure-gradient boundary layer, where the boundary layer thickness relative to the body width was δ/D = 1.6. PIV measurements were made above the free ends of the bodies in a vertical plane aligned with the flow centreline. The present PIV results provide insight into the effects of aspect ratio and body shape on the instantaneous flow field. The recirculation zone under the separated shear layer is larger for the square prism of AR = 3 compared to the more slender prism of AR = 9. Also, for a square prism with low aspect ratio (AR = 3), the influence of the reverse flow over the free end surface becomes more significant compared to that for a higher aspect ratio (AR = 9). For the circular cylinder, a cross-stream vortex forms within the recirculation zone. As the aspect ratio of the cylinder decreases, the reattachment point of the separated flow on the free end surface moves closer to the trailing edge. For both the square prism and circular cylinder cases, the instantaneous velocity vector field and associated in-plane vorticity field revealed small-scale structures mostly generated by the separated shear layer.     

An investigation of asymmetric flow features in a scaled-up driven model of the human vocal folds

Flow through a driven, 7.5 times life-size vocal fold model was investigated at corresponding life-size flow rates of Q _mean  = 89.1 ml/s, 159.4 ml/s, and 253.0 ml/s. The flow was scaled to match physiological values for Reynolds, Strouhal, and Euler numbers. The models were driven at a life-size frequency of 94 Hz. Particle image velocimetry (PIV) data were acquired in the anterior–posterior midplane of the glottis, and the unsteady transglottal pressure drop across the vocal folds was simultaneously measured. Flow and pressure data were obtained at four discrete instances during the closing phases of the phonatory cycle for which t/T _open  = 0.60, 0.70, 0.80, and 0.90. The glottal jet trajectory exhibited a bimodal distribution of flow attachment between the two medial surfaces of the glottis. Vortex shedding at the trailing edge separation point generated instabilities in the shear layer, which caused large oscillations in the glottal jet orientation downstream of the glottal exit. The development of the Coanda effect during the glottal cycle was found to have minimal impact on the transglottal pressure drop, suggesting that flow orientation does not directly influence the dipole sound source. The change in transglottal pressure drop as a result of jet trajectory was less than 2% for all three investigated flow rates.     

Flow of mono-dispersed particles through horizontal bend

Pipeline slurry flow of mono-dispersed particles through horizontal bend is numerically simulated by implementing Eulerian two-phase model in FLUENT software. A hexagonal shape and Cooper type non-uniform three-dimensional grid is chosen to discretize the entire computational domain, and a control volume finite difference method is used to solve the governing equations. The modeling results are compared with the experimental data collected in 53.0 mm diameter horizontal bend with radius of 148.4 mm for concentration profiles and pressure drops. Experiments are performed on narrow-sized silica sand with mean diameter of 450 μm and for flow velocity up to 3.56 m/s (namely, 1.78, 2.67 and 3.56 m/s) and four efflux concentrations up to 16.28% (namely, 0%, 3.94%, 8.82% and 16.28%) by volume for each velocity. Eulerian model gives fairly accurate predictions for both the pressure drop and concentration profiles at all efflux concentrations and flow velocities.     

UDV measurements of single bubble rising in a liquid metal Galinstan with a transverse magnetic field

Liquid metal is an important type of energy transport carrier in nuclear reactors, such as in accelerator-driven sub-critical systems, fusion reactors and spallation neutron source devices. It is necessary to conduct research for bubbles rising in a liquid metal under different magnetic field intensities. The Perspex container is positioned concentrically inside a transverse magnetic field, which provides a homogeneous DC longitudinal magnetic field that passes through the fluid district. The coils are supplied with maximum field strength of 1.97 T. The equivalent diameter of the bubble is 3.1–5.6 mm. The Ultrasonic Doppler Velocimetry (UDV) method is used to evaluate the internal flow velocity of opaque liquid metals. Research shows that the influence of the Lorenz force on the bubble ascension velocity is not simply positive or negative. The magnetic field inhibits the ascension velocity of small bubbles with diameters of 3.1 mm and 3.4 mm. The terminal velocity for large bubbles with diameters of 4.57 mm, 5.15 mm and 5.6 mm is higher under a weak magnetic field than without a magnetic field. The positive effect happens under strong magnetic intensity. The target is to obtain the hydro-dynamical relationships between the terminal velocity, drag coefficient, the Eötvös number, Reynolds number, and Stuart number in a strong magnetic field using a multiple regression method to reveal that the mechanism of the induced current's restraining influence determines the ascension velocity of the bubble in viscous electric liquids with a strong magnetic field.     

Rheology of liquid metals and alloys

The flow behavior and viscosity of liquid Zn, Sn, Cd, Bi-42 wt%Sn, Zn-7 wt%Al, and Sn-3 wt%Ag-0.5 wt%Cu were characterized and quantified with rotational rheometry experiments. Evidences from this study shows these liquid systems uniquely exhibit a shear thinning and time-independent (non-thixotropic) flow behavior in all the evaluated shear rate regimes. We have attempted to offer a physical explanation from prior-art for the observed unique flow behavior of the liquid metal systems. The strong short range atomic order in these metals significantly contribute to their flow behavior and at any shear rate the viscosity obeys the standard Arrhenius energy equation for temperature dependence.     

Electroviscous effect on non-Newtonian fluid flow in microchannels

Understanding non-Newtonian flow in microchannels is of both fundamental and practical significance for various microfluidic devices. A numerical study of non-Newtonian flow in microchannels combined with electroviscous effect has been conducted. The electric potential in the electroviscous force term is calculated by solving a lattice Boltzmann equation. And another lattice Boltzmann equation without derivations of the velocity when calculating the shear is employed to obtain flow field. The simulation of commonly used power-law non-Newtonian flow shows that the electroviscous effect on the flow depends significantly on the fluid rheological behavior. For the shear thinning fluid of the power-law exponent n < 1, the fluid viscosity near the wall is smaller and the electroviscous effect plays a more important role. And its effect on the flow increases as the ratio of the Debye length to the channel height increases and the exponent n decreases. While the shear thickening fluid of n > 1 is less affected by the electroviscous force, it can be neglected in practical applications.     

Simulation of a valveless pump with an elastic tube

A valveless pump consisting of a pumping chamber with an elastic tube was simulated using an immersed boundary (IB) method. The interaction between the motion of the elastic tube and the pumping chamber generated a net flow toward the outlet throughout a full cycle of the pump. The net flow rate of the valveless pump was examined by varying the stretching coefficient (ϕ), bending coefficient (γ), the aspect ratio (l/d) of the elastic tube, and the frequency (f) of the pumping chamber. As the stretching and bending coefficients of the elastic tube increased, the net flow through the valveless pump decreased. Elastic tubes with aspect ratios in the range of 2 ⩽ l/d ⩽ 3 generated a higher flow rate than that generated for tubes with aspect rations of l/d = 1 or 4. As the frequency of the pumping chamber increased, the net flow rate of the pump for l/d = 2 increased. However, the net flow rate for l/d = 3 was nonlinearly related to the pumping frequency due to the complexity of the wave motions. Snapshots of the fluid velocity vectors and the wave motions of the elastic tube were examined over one cycle of the pump to gain a better understanding of the mechanism underlying the valveless pump. The relationship between the average gap in the elastic tube and the average flow rate of the pump was analyzed. A smaller gap in the elastic tube during the expansion mode and a wider gap in the elastic tube during the contraction mode played a dominant role in generating a high average flow rate in the pump, regardless of the stretching coefficient (ϕ), the aspect ratio (l/d) of the elastic tube, or the pumping frequency of the pumping chamber (f).     

Numerical simulation of the fountain flow instability in injection molding

For the first time, the viscoelastic flow front instability is studied in the full non-linear regime by numerical simulation. A two-component viscoelastic numerical model is developed which can predict fountain flow behavior in a two-dimensional cavity. The eXtended Pom-Pom (XPP) viscoelastic model is used. The levelset method is used for modeling the two-component flow of polymer and gas. The difficulties arising from the three-phase contact point modeling are addressed, and solved by treating the wall as an interface and the gas as a compressible fluid with a low viscosity. The resulting set of equations is solved in a decoupled way using a finite element formulation. Since the model for the polymer does not contain a solvent viscosity, the time discretized evolution equation for the conformation tensor is substituted into the momentum balance in order to obtain a Stokes like equation for computing the velocity and pressure at the new time level. Weissenberg numbers range from 0.1 to 10. The simulations reveal a symmetric fountain flow for Wi = 0.1–5. For Wi = 10 however, an oscillating motion of the fountain flow is found with a spatial period of three times the channel height, which corresponds to experimental observations.