Increase Of Amplitude Ratio Research Articles

On the origin of streamwise vortices in braid regions for compressible mixing layers

The origin of initial streamwise vortices in braid regions and their relationship with deformed spanwise vortices are numerically studied via direct numerical simulation (DNS) in the compressible mixing layer with a convective Mach number (Mc) of 0.4. Through an analysis of fast Fourier transform on DNS data, two low-rank velocity models (vd and vs) are developed to demonstrate that both deformed spanwise vortices and streamwise vortices are all originated from the linear superposition of a fundamental norm mode [mode (1, 0)], a pair of fundamental oblique modes [modes (1, ±1)], and a mean mode. Further investigations reveal that, downstream of spanwise vortices, the increase in amplitude ratio (Ao/An) between modes (1, ±1) and mode (1, 0) leads to the formation of deformed spanwise vortices in vortex regions. As the amplitude ratio Ao/An further increases, reaching the threshold that the streamwise rotation motion from modes (1, ±1) exceeds the spanwise irrotational deformation from mode (1, 0), streamwise vortices are generated in braid regions. The aforementioned formation path for deformed spanwise vortices and streamwise vortices provides a mechanism support for our flow visualization results that the emergence of deformed spanwise vortices precedes that of streamwise vortices in the flow field.

Impact of Homogeneous/Heterogeneous Reactions and Convective Conditions on Peristaltic Fluid Flow in a Symmetric Channel

Simultaneous impacts of homogeneous and heterogeneous reaction and Joule heating in magnetohydrodynamic (MHD) peristaltic flow of viscous fluid in a symmetric channel are analyzed in this investigation. Attention has been focused on designing and simulating a mathematical model for a viscous fluid in presence of viscous dissipation. Long wavelength approximation in wave frame analysis is implemented. Expressions for the stream function, axial pressure gradient, temperature, heat transfer coefficient and concentration are derived and discussed. In addition, the trapping phenomenon is analyzed. The effects of the physical quantities of concern are viewed with a special focus on homogeneous and heterogeneous reaction and convective conditions for the transfer of heat at the walls. It is observed that the pressure rise first increases and then decreases with an increase in amplitude ratio. Effects of Brinkman and Hartmann numbers on temperature are quite analogous and a temperature rise is observed, however, temperature decays for the increased value of Biot number. Moreover, fluid concentration decreases when the value of the homogeneous reaction parameter is increased.

Influence of elasticity in an inclined annulus of nanofluid with peristaltic transport

AbstractPeristaltic transport of Newtonian nanofluid in an inclined annulus terms of radii regarding peristalsis and elasticity. It is noticed that with an increase in amplitude ratio, flux is getting enhanced in the absence of nanoparticles when compared with viscous fluid with nanoparticles. Our results reduce to the corresponding ones of Rubinow and Keller as a special case for the viscous flow in an elastic tube. The effect of various emerging parameters bounded by two concentric cylinders is studied under the assumption of long wavelength and dominance of viscous effects over inertial effects. The outer cylinder is elastic in nature and has a sinusoidal wave traveling down in its wall, whereas the inner cylinder is rigid. Analytical solutions have been established for velocity, flux, pressure rise, temperature distribution, and nanoparticle concentration. The flux, pressure rise, and frictional forces have been obtained in on the flow characteristic are presented and discussed. Obtained results may be useful in understanding the behavior of peristaltic transport of blood flow in small blood vessels and blood flow through elastic arteries.

On electrohydrodynamic flow of Jeffrey fluid through a heating vibrating cylindrical tube with moving endoscope

This paper deals with the study of the effect of a variable normal electric field on Jeffry flow through a heating vibrating cylindrical tube with moving endoscope. Under the assumption of long wavelength and the use of appropriate non-dimensional quantities, the analytical solutions for axial and radial velocities, stream function, fluid pressure, electrical potential function and temperature distribution are obtained. The results show that the volume of the trapped bolus increases by the increase of amplitude ratio, endoscope radius, Jeffry parameter and electrical Rayleigh number, whereas it has an opposite effect on the increase in the endoscope velocity and temperature parameter. Furthermore, it is observed that the effects of the amplitude ratio and Jeffry parameter on the axial velocity in the presence of electric field are greater and clearer than those in the absence of electric field.

Numerical simulation on the forced oscillation of rigid riser with helical strakes in different section shapes

In order to study the helical strakes' suppression effects on the vibration riser, triangle and circular sections helical strakes are proposed. With the technology of dynamic mesh, forced oscillation in steady flow of the riser with helical strakes in different cross-section shapes at low Reynolds number are numerically simulated. The analysis is focused on the lock-in range, as well as the force status and trailing vortex structure under different values of amplitude (A) and oscillation frequency (fe), and draw comparisons to the bare riser's results. Research shows the lock-in range will increase with the increase of amplitude ratio (A/D), the riser with all three different shaped helical strakes have larger lock-in range than bare riser. Before entering into the lock-in region, riser with different shaped helical strakes all have good effects on suppressing the vibrations of riser. Within and after lock-in region, riser with triangle and circular sections helical strakes have smaller lift force than that with rectangular section, which reduced lift coefficient by 65.83% and 83.53%. The trailing vortex structures of the riser with helical strakes are in strength three-dimensional character. Inside the lock-in region, riser with triangle and circular sections have better suppression effect than that with rectangular section. Outside the lock-in region, riser with triangle section helical strakes has the best vortex suppression effect, of which the influence on the flow field is greatest and the vortex-induced force is least.

Effect of the Variable Viscosity on the Peristaltic Flow of Newtonian Fluid Coated with Magnetic Field: Application of Adomian Decomposition Method for Endoscope

In the present analysis, peristaltic flow was discussed for MHD Newtonian fluid through the gap between two coaxial tubes, where the viscosity of the fluid is treated as variable. In addition, the inner tube was considered to be at rest, while the outer tube had the sinusoidal wave traveling down its motion. Further, the assumptions of long wave length and low Reynolds number were taken into account for the formulation of the problem. A closed form solution is presented for general viscosity using the Adomian decomposition method. Numerical illustrations that show the physical effects and pertinent features were investigated for different physical included phenomenon. It was found that the pressure rise increases with an increase in Hartmann number, and frictional forces for the outer and inner tube decrease with an increase in Hartmann number when the viscosity is constant. It was also observed that the size of the trapping bolus decreases with an increase in Hartmann number, and increases with an increase in amplitude ratio when the viscosity is parameter.

Study of electrokinetic effects for heat transfer in microchannel with sinusoidal thermal boundary conditions

PurposeThe purpose of this study is to obtain the numerical as well as regularity results for the nonlinear elliptic set of equations arising in the study of fluid flow in microchannel induced by the pressure in the presence of interfacial electrokinetic effects.Design/methodology/approachFor the numerical study, the authors implemented traditional FDM approach, and for the regularity results they used the classical energy estimates. The interfacial electrokinetic effects result in an additional source term in classical momentum equation, hence affecting the characteristics of the flow and heat transfer. The sinusoidal temperature variation is assumed on side walls.FindingsThe results were obtained for various combinations of physical parameters appearing in the governing equations. This study concludes that in the presence of electric double layer, the average heat transfer rate reduces along with larger values of Reynolds number. It is observed that the heat transfer increases with the increase in amplitude ratio and phase deviation. The flow behavior and heat transfer rate inside the microchannel are also strongly affected by the presence of κ (kappa).Originality/valueTo the best of the authors’ knowledge, the problem of heat transfer through microchannel in combination with sinusoidal temperature variation at boundary with electric double layer effects has not been considered previously. Hence, this paper focuses on the influence of the sinusoidal boundary temperature distributions on both sidewalls of a rectangular microchannel through parallel plates with electrokinetic effects on the pressure-driven laminar flow. In addition, a detailed mathematical analysis is also to be carried out to verify the regularity of this model with the proposed boundary conditions. The study used the classical energy method to get the regularity results.

Predicting the effect on pulse wave reflection of different endovascular repair techniques in abdominal aortic aneurysm using 1D patient-specific models

Abdominal aortic aneurysm (AAA) is a pathological dilation of the abdominal aorta, generally distal to the renal arteries. In relation to this, minimally invasive endovascular aortic repair has become a common technique, and great efforts have been made to characterize surgical outcome in terms of endograft displacement, leakages, aneurysm sac enlargement or other post-operative complication. Recently, two novel devices (AFX and Nellix sealing device) were developed to surpass these complications, but there is no work accounting for the effects they may have on the pressure waveform. In this study, we address the problem of generating a patient-specific 1D model of an aortic aneurysm, and compute the impact that these devices can have on pressure, in terms of wave reflection. As a result, we found both endovascular repair devices decrease the reflected wave transient time by one order of magnitude, and that the Nellix device shows increased reflected wave amplitude at proximal abdominal aorta and at renal artery level compared to AFX (33 % and 75 % increase in amplitude ratio compared to a non-diseased aorta, respectively). Due to the importance that pressure at renal site and pulse waveform have on the overall cardiovascular physiology, the validity of these results should be carefully studied in order to develop a patient-specific tool for medical planning of interventions.

Mathematical Analysis on Heat Transfer during Peristaltic Pumping of Fractional Second-Grade Fluid through a Nonuniform Permeable Tube

This mathematical study is related to heat transfer under peristaltic flow of fractional second-grade fluid through nonuniform cylindrical tube with permeable walls. The analysis is performed under low Reynolds number and long wavelength approximation. The analytical solution for pressure gradient, friction force, and temperature field is obtained. The effects of appropriate parameters such as Grashof number, nonuniformity of tube, permeability of tube wall, heat source/sink parameter, material constant, fractional time derivative parameter and amplitude ratio on pressure rise, friction force, and temperature distribution are discussed. It is found that an increase in amplitude ratio and material constant causes increase in pressure but increase in nonuniformity of the tube causes decrease in pressure. It is also observed that variation of friction force against flow rate shows opposite behavior to that of pressure. Increase in temperature is also observed due to increase in heat source/sink parameter at inlet as well as downstream.

Observational verification of predicted increase in bedrock-to-surface amplitude transfer during a glacier surge

AbstractThe amplitude ratio between surface and bedrock topography has been predicted to depend strongly on the ratio of deformational velocity to mean basal sliding velocity. Observations made prior to and during a surge of Tungnaárjökull, Vatnajökull ice cap, Iceland, allow this prediction to be tested. During the surge, the ratio of internal deformational velocity and basal sliding (slip ratio) changed from about unity to a few hundred. The amplitude ratio changed from about 0.1 to about 0.7. This increase in amplitude ratio is in good overall agreement with predictions based on an analytical perturbation analysis for a linearly viscous medium which includes the effects of horizontal deviatoric stresses on glacier flow. An increase in amplitude ratio of this magnitude is not predicted by a similarly linearized analysis that employs the commonly used shallow-ice approximation. The strong increase in transfer amplitude observed in the surge of Tungnaárjökull is a clear illustration of the effects of horizontal stress transmission on glacier flow reported here for the first time.