The Inner-Shelf Dynamics Experiment

Current models of phonation exhibit a series of flow phenomena such as an oscillating flow separation point, the Coanda effect, and vortex shedding downstream of the glottis. While accounting for such phenomena significantly increases the computational load and may influence many aspects of phonation, the influence of such airflow features on phonation onset is still unknown. In a two-dimensional continuum model of phonation with a fixed flow separation point, a recent analysis showed that, in the absence of acoustics, the primary physical mechanism of phonation onset was the matching of the flow stiffness (i.e., the intraglottal airflow pressure) with the elastic stiffness of the vocal folds, resembling common observations of human phonation. Thus, the oscillation of the flow separation point may be merely a consequence of the unsteady motion of the vocal folds, with only a minor influence on phonation onset at low frequencies. With a natural frequency much higher than the phonation frequency, flow instabilities such as vortex shedding may also only play a secondary role in determining the conditions of phonation onset (apart from being responsible for flow separation and the transglottal pressure drop), at least for normal phonation. Further experiments are needed to clarify the relative importance of these flow features on phonation onset.

The paper provides experimental data on flow separation from a model of the human vocal folds. Data were measured on a four times scaled physical model, where one vocal fold was fixed and the other oscillated due to fluid–structure interaction. The vocal folds were fabricated from silicone rubber and placed on elastic support in the wall of a transparent wind tunnel. A PIV system was used to visualize the flow fields immediately downstream of the glottis and to measure the velocity fields. From the visualizations, the position of the flow separation point was evaluated using a semiautomatic procedure and plotted for different airflow velocities. The separation point position was quantified relative to the orifice width separately for the left and right vocal folds to account for flow asymmetry. The results indicate that the flow separation point remains close to the narrowest cross-section during most of the vocal fold vibration cycle, but moves significantly further downstream shortly prior to and after glottal closure.

Non-Newtonian fluid flow over a circular cylinder at a sub-critical Reynolds number Re=3900 is investigated with large-eddy simulation. Behaviors of both shear-thinning and shear-thickening fluids are compared with the Newtonian fluid flow at the nominal Re. Carreau fluids are chosen here to study non-Newtonian fluid flow. The shear-dependent viscosity changes flow separation point on the cylinder and laminar-to-turbulent transition in separating shear layer. Apparently, low viscosity in shear-thinning fluid causes early flow separation and turbulent transition, resulting in large pressure drag and flow fluctuation indicated by the lift rms. In contrast, shear-thickening fluid exhibits delayed flow separation and turbulent transition, leading to large viscous drag and reduced flow fluctuation. Such non-Newtonian behaviors are comparable to the Newtonian fluid flow in the sub-critical regime but at different apparent Reynolds numbers. The current non-Newtonian fluids modify the apparent Reynolds number by a factor of about 2–3.5. As the apparent Reynolds numbers still belong to the sub-critical regime, the drag coefficient varies little. A notable difference is observed for the lift rms that varies more than double in the shear-thinning fluid.

Thermal cycling and fluctuations in the protoplanetary nebula

Pantographs are important devices on high‐speed trains. When a train runs at a high speed, concave and convex parts of the train cause serious airflow disturbances and result in flow separation, eddy shedding, and breakdown. A strong fluctuation pressure field will be caused and transformed into aerodynamic noises. When high‐speed trains reach 300 km/h, aerodynamic noises become the main noise source. Aerodynamic noises of pantographs occupy a large proportion in far‐field aerodynamic noises of the whole train. Therefore, the problem of aerodynamic noises for pantographs is outstanding among many aerodynamics problems. This paper applies Detached Eddy Simulation (DES) to conducting numerical simulations of flow fields around pantographs of high‐speed trains which run in the open air. Time‐domain characteristics, frequency‐domain characteristics, and unsteady flow fields of aerodynamic noises for pantographs are obtained. The acoustic boundary element method is used to study noise radiation characteristics of pantographs. Results indicate that eddies with different rotation directions and different scales are in regions such as pantograph heads, hinge joints, bottom frames, and insulators, while larger eddies are on pantograph heads and bottom frames. These eddies affect fluctuation pressures of pantographs to form aerodynamic noise sources. Slide plates, pantograph heads, balance rods, insulators, bottom frames, and push rods are the main aerodynamic noise source of pantographs. Radiated energies of pantographs are mainly in mid‐frequency and high‐frequency bands. In high‐frequency bands, the far‐field aerodynamic noise of pantographs is mainly contributed by the pantograph head. Single‐frequency noises are in the far‐field aerodynamic noise of pantographs, where main frequencies are 293 Hz, 586 Hz, 880 Hz, and 1173 Hz. The farther the observed point is from the noise source, the faster the sound pressure attenuation will be. When the distance of two adjacent observed points is increased by double, the attenuation amplitude of sound pressure levels for pantographs is around 6.6 dB.

A model study of circulation and cross-shelf exchange on the west Antarctic Peninsula continental shelf

A time-dependent numerical simulation is performed to examine the flow separation control with the action of a hybrid jet (the combination of synthetic and continuous jets) over a NACA23012 airfoil. The unsteady Reynolds-averaged Navier–Stokes (URANS) simulation is performed with Spalart-Allmaras (SA) turbulence model to simulate the flow field around the airfoil to analyse the effect of the hybrid jet. A combined jet is placed at the point of flow separation on the upper surface of the airfoil which is located at the 12% of the chord length from the leading edge of the airfoil for a given flow configuration. Flow simulations are performed at a chord-based Reynolds number of 2.19 × 106 for the hybrid jet oscillating frequency of 0.159 at a blowing ratio of 3.0. The contribution of the continuous jet in the hybrid jet is evident by the flow control. Variation in the continuous jet velocity is studied, which improved the aerodynamic characteristics of the airfoil. The maximum improvement in lift to drag ratio is observed from 11.19 to 22.14 at an angle of attack of 22 degree. The stall angle also shows an enhancement from 18 degree to 20 degree.

Take-off and landing are the critical phases of an aircraft flight where there is a high demand of lift force at the lowest stalling speed of aircraft. Use of different techniques to increase the lift force during these phases of flight is one of the prime objectives in the design of an aircraft wing. Delaying and eliminating flow separation using boundary layer control (BLC) techniques will improve the aerodynamic characteristics of a wing. This work presents an experimental study on the effect of BLC on the aerodynamic characteristics of NACA 0021 aerofoil. Both the techniques of blowing and suction has been considered in this study. Model was built using composites and tested in a subsonic wind tunnel integrated with a compressor/vacuum pump setting for to control the boundary layer on the aerofoil. Firstly, the model with 20 pressure tappings was tested without BLC and the point of flow separation was noted. Later, the suction and blowing holes were made suitably in the model and equipped with a compressor/vacuum pump to control the boundary layer and study the effects of it on the performance of NACA 0021 aerofoil. As expected, the BLC by both the techniques show improvement in the maximum lift coefficient.

Unsteady flow separation in rotationally augmented flow fields plays a significant role in the aerodynamic performance of industrial rotors, including wind turbines. Current computational models underestimate the aerodynamic loads due to the inaccurate prediction of the emergence and severity of unsteady flow separation, especially in response to a sudden change in the effective angle of attack. Through the use of time-resolved particle image velocimetry (PIV), coherent structure formation during the unsteady separation over an experimental wind turbine blade is examined. Time-dependent empirical mode decomposition results during a dynamic pitching cycle give insight into the spatio-temporal scales that influence the transition from attached to separated flow. Empirical mode decomposition (EMD) modes are represented as two-dimensional fields and are analyzed together with Lagrangian coherent structures, the spatial distribution of vortices, the location of the separation point, and velocity contours focusing on the role of vortex shedding and shear-layer perturbation in unsteady flow separation, stall, and reattachment. The combination of these analytical techniques provides experimental evidence that the location of the separation point and the stability of the shear layer are directly influenced by the presence of vortices. Within this paper, each of the scales represented by the EMD are directly connected to the size of the vortices present, from the smallest representing a vortex radius to the largest reaching to two full vortex diameters. The velocity scales and spatial scales provided by the EMD modes are also found to supply valuable inputs into the identification of Lagrangian coherent structures within each of the PIV snapshots. This indicates that the scales captured by the EMD can be used to extract important turbulent scales present at the point of flow separation where the vortices are created, providing relenvant insight into the separation dynamics of the airfoil.

Particle Dry Deposition to Water Surfaces: Processes and Consequences

To determine the causes and history of atherosclerosis it is necessary to understand the hemodynamic parameters of blood circulation. Hemodynamic parameters play an important role in the formation of atherosclerotic plaques, especially near bends and bifurcations where the flow separates from the wall. Here the flow is laminar and non-axial with eddies, secondary flow, flow separation and stagnation points. Stenoses are found predominantly in flow separation areas. Therefore, it is important to separately study the following flow parameters: steady and pulsatile flow, wall elasticity and non-Newtonian flow behavior of blood. A simplified silicon elastic y-model simulating the human carotid artery was used for the analysis of these parameters. This model can be used for numerical studies as well. Flow was visualized at steady flow using dyes and at pulsatile flow with a photoelastic apparatus and a birefringent solution. The local axial velocity at steady and pulsatile flow was determined with a one-component Laser-Doppler-Anemometer (LDA). Pulsatile flow was generated by a piston membrane pump. A glycerin-water solution was used to simulate the Newtonian flow behavior of blood. A DMSO-Separan water solution was used to simulate the non-Newtonian flow behavior. Pulsatile flow creates higher and lower shear rates so called oscillating shear rate compare to steady flow depending on the velocity amplitude. The non-Newtonian fluid showed a markedly different flow behavior than the Newtonian fluid especially in areas of flow separation. Shear gradients were calculated from these velocity measurements using a bicubic spline interpolation. Shear stresses were calculated from these velocity shear gradients and the viscosity of the non-Newtonian fluid at these shear gradients. At special areas, high shear stresses > 10 Pa were found. The elasticity of the model wall also influences the flow behavior. The measurements showed that the characteristics of pulsatile flow and the elasticity of the model wall should be observed concomitantly. This paper presents the steady and pulsatile flow with a Newtonian and non-Newtonian fluid in an elastic model.

A thermal non-equilibrium perspective on mixed convection in a vertical channel

Oscillation of the vocal folds makes a sound source of the human voiced sound. Understanding of the oscillation mechanism, which is a complex flow-structure interaction problem in the airway, is crucial for considering clinical diagnosis of voice disorders. However, details of the oscillation mechanism are still unclear partly because, from a fluid mechanical viewpoint, the effect of oscillation of the vocal fold wall during the phonation on airflow behaviors remains elusive. In the present study, flow characteristics in a sinusoidally-oscillating constriction mimicking the vocal fold were investigated by numerical and experimental approaches. The numerical analyses focused in particular on the effect of constriction oscillation on flow separation demonstrated that the flow separation point moves continuously and periodically in a frequency-dependent manner. In the experimental study, an apparatus was newly designed, with a view to detect the oscillation-induced movement of the flow separation point, to enable detailed measurement of pressure distribution along the constriction with an interval of 2 mm that is synchronized with measurement of constriction displacement. Although movement of the separation point as seen in the numerical analyses was not detected by this limiting resolution of the apparatus, we obtained pressure-width relations that is partly contrary to the numerical results but is presumably dependent on the inlet boundary condition. These findings indicate that appropriate evaluations of separation point and inlet boundary conditions are key factors to characterize the flow in oscillating constriction, which is crucial for better understanding of the vocal fold mechanics.

This research article explains the Joule heating and inclined magnetic field effects on Ti6Al4V-MWCNT/[Formula: see text] hybrid nanofluids toward an exponentially shrinking surface. The system of flow governing equations, which is a coupled system of non-linear PDE’s, are transformed into a system of non-dimensional ODE’s by using suitable similarity transformations. The shooting method along with a fourth order Runge-Kutta approach is used to solve the system of resultant ODE’s. As a result, the dual solutions are identified for this problem. By utilizing the least eigenvalue approach, the first solution is found to be realistic and stable whereas the second solution is not stable. In order to verify the accuracy of outcomes, it is compared with the previously published results, and it is found that the present analysis is accurate upto four decimal places. Further, the streamline profiles are also provided in addition to the least eigenvalue profiles to understand the flow patterns. Finally, the flow separation point is identified. The velocity profiles improves in the case of first solution but it declines in the case of second solution with a rise in the shrinking strength parameter, however the temperature profiles behave in opposite manner. The skin friction coefficient and heat transfer rate of Ti6Al4V-MWCNT/[Formula: see text] based hybrid nanofluids are found to be better with higher values of inclined MHD [Formula: see text] and incline angle [Formula: see text].

Ecosystem coupling: A unifying framework to understand the functioning and recovery of ecosystems