Linear stability of two-layer Couette flows

2017 ◽  
Vol 826 ◽  
pp. 128-157 ◽  
Author(s):  
Alireza Mohammadi ◽  
Alexander J. Smits
Keyword(s):  
Interfacial Tension ◽  
Viscosity Ratio ◽  
Density Ratio ◽  
Initial Step ◽  
Base Flow ◽  
Neutral Stability ◽  
Low Viscosity ◽  
Tollmien Schlichting ◽  
And Performance ◽  
Interfacial Mode

The stability of two-layer Couette flow is investigated under variations in viscosity ratio, thickness ratio, interfacial tension and density ratio. The effects of the base flow on eigenvalue spectra are explained. A new type of interfacial mode is discovered at low viscosity ratio with properties that are different from Yih’s original interfacial mode (Yih, J. Fluid Mech., vol. 27, 1967, pp. 337–352). No unstable Tollmien–Schlichting waves were found over the range of parameters considered in this work. The results for thin films with different thicknesses can be collapsed onto a single curve if the Reynolds number and wavenumber are suitably defined based on the parameters of the thin layer. Interfacial tension always has a stabilizing effect, but the effects of density ratio cannot be so easily generalized. Neutral stability curves for water–alkane and water–air systems are presented as an initial step towards better understanding the effects of flow stability on the longevity and performance of liquid-infused surfaces and superhydrophobic surfaces.

Starting Flow in a Channel With Two Immiscible Fluids

2017 ◽  
Vol 139 (12) ◽  
Author(s):  
C. Y. Wang
Keyword(s):  
Analytic Solution ◽  
Viscosity Ratio ◽  
Density Ratio ◽  
Immiscible Fluids ◽  
Partial Slip ◽  
Eigenvalues And Eigenfunctions ◽  
Important Conclusion ◽  
Low Viscosity ◽  
Starting Flow ◽  
First Time

The starting flow due to a sudden pressure gradient in a channel containing two layers of different fluids is studied for the first time. The necessary eigenvalues and eigenfunctions, including orthogonality, for the composite regions are developed. Infinite series analytic solution is obtained for the starting transient. The properties of the instantaneous velocity profiles depend on the thickness ratio of the layers, the viscosity ratio, and the density ratio. Starting times are determined for the important cases of air over water and oil over water. The bulk flow is greatly increased when there exists a low-viscosity layer buffeting the channel wall. An important conclusion is that, in general, Navier's partial slip condition cannot be applied to unsteady starting flows.

scholarly journals Stability of the shear-thinning boundary-layer flow over a flat inclined plate

2017 ◽  
Vol 473 (2205) ◽  
pp. 20170350 ◽  
Author(s):  
P. T. Griffiths
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Flow ◽  
Passive Control ◽  
Shear Thinning ◽  
Base Flow ◽  
Neutral Stability ◽  
Inclined Plate ◽  
Shear Thinning Fluids ◽  
Tollmien Schlichting ◽  
Layer Flow

In this study, we consider the boundary-layer flow of an inelastic non-Newtonian fluid over an inclined flat plate. Using two popular generalized Newtonian models, we determine base flow profiles and associated linear stability results for a range shear-thinning fluids. In addition to neutral stability curves, we also present results concerning the linear growth of the Tollmien–Schlichting waves as they propagate downstream. Furthermore, to gain an insight into the underlying physical mechanisms affecting the destabilization of the disturbances, an integral energy equation is derived and energy calculations are presented. Results from all three analyses suggest that the effect of shear-thinning will act to stabilize the boundary-layer flow. Consequently, it can be argued that the addition of shear-thinning agents could act as a passive control mechanism for flows of this nature.

The Hydrodynamic Stability of Two Viscous Incompressible Fluids in Parallel Uniform Shearing Motion

1979 ◽  
Vol 46 (3) ◽  
pp. 499-504 ◽  
Author(s):  
D. T. Tsahalis
Keyword(s):  
Reynolds Number ◽  
Incompressible Fluid ◽  
Viscosity Ratio ◽  
Density Ratio ◽  
Steady Motion ◽  
Wave Number ◽  
Neutral Stability ◽  
The Family ◽  
The Stability ◽  
Shearing Motion

The stability problem of a thin film of a viscous incompressible fluid bounded on one side by another more viscous and less dense incompressible fluid of semi-infinite extent and on the other side by a fixed wall, where both fluids are in steady motion parallel to their interface and each fluid has a linear velocity profile, is solved for large values of the Reynolds number and small values of the viscosity ratio. Neutral stability curves of the Reynolds number versus the wave number are presented, parametrized with either the density ratio or the viscosity ratio as the family parameters.

Enhancing Bitumen Liberation by Controlling the Interfacial Tension and Viscosity Ratio through Solvent Addition

2014 ◽  
Vol 28 (12) ◽  
pp. 7403-7410 ◽  
Author(s):  
Lin He ◽  
Feng Lin ◽  
Xingang Li ◽  
Zhenghe Xu ◽  
Hong Sui
Keyword(s):  
Interfacial Tension ◽  
Viscosity Ratio

scholarly journals Analysis of the unstable Tollmien–Schlichting mode on bodies with a rounded leading edge using the parabolized stability equation

2009 ◽  
Vol 623 ◽  
pp. 167-185
Author(s):  
M. R. TURNER ◽  
P. W. HAMMERTON
Keyword(s):  
Asymptotic Theory ◽  
Free Stream ◽  
Leading Edge ◽  
Adverse Pressure Gradient ◽  
Reynolds Numbers ◽  
Neutral Stability ◽  
S Wave ◽  
Stability Equation ◽  
Stability Point ◽  
Tollmien Schlichting

The interaction between free-stream disturbances and the boundary layer on a body with a rounded leading edge is considered in this paper. A method which incorporates calculations using the parabolized stability equation in the Orr–Sommerfeld region, along with an upstream boundary condition derived from asymptotic theory in the vicinity of the leading edge, is generalized to bodies with an inviscid slip velocity which tends to a constant far downstream. We present results for the position of the lower branch neutral stability point and the magnitude of the unstable Tollmien–Schlichting (T-S) mode at this point for both a parabolic body and the Rankine body. For the Rankine body, which has an adverse pressure gradient along its surface far from the nose, we find a double maximum in the T-S wave amplitude for sufficiently large Reynolds numbers.

Stability of Viscoelastic Channel Flow

2007 ◽  
Author(s):  
Nariman Ashrafi
Keyword(s):  
Reynolds Number ◽  
Viscosity Ratio ◽  
Weissenberg Number ◽  
Base Flow ◽  
Galerkin Projection ◽  
Large Reynolds Number ◽  
One Dimensional ◽  
Stress Effects ◽  
The Stability ◽  
The One

The nonlinear stability and bifurcation of the one-dimensional channel (Poiseuille) flow is examined for a Johnson-Segalman fluid. The velocity and stress are represented by orthonormal functions in the transverse direction to the flow. The flow field is obtained from the conservation and constitutive equations using the Galerkin projection method. Both inertia and normal stress effects are included. The stability picture is dramatically influenced by the viscosity ratio. The range of shear rate or Weissenberg number for which the base flow is unstable increases from zero as the fluid deviates from the Newtonian limit as decreases. Typically, two turning points are observed near the critical Weissenberg numbers. The transient response is heavily influenced by the level of inertia. It is found that the flow responds oscillatorily. When the Reynolds number is small, and monotonically at large Reynolds number when elastic effects are dominated by inertia.

On the Impact of Liquid Drops on Immiscible Liquids

2016 ◽  
Author(s):  
Eduardo Castillo-Orozco ◽  
Ashkan Davanlou ◽  
Pretam K. Choudhury ◽  
Ranganathan Kumar
Keyword(s):  
Oil Spills ◽  
Silicone Oil ◽  
Density Ratio ◽  
High Viscosity ◽  
Impact Behavior ◽  
Immiscible Fluid ◽  
Liquid Droplets ◽  
Liquid Drops ◽  
Low Viscosity ◽  
The Impact

The release of liquid hydrocarbons into the water is one of the environmental issues that have attracted more attention after deepwater horizon oil spill in Gulf of Mexico. The understanding of the interaction between liquid droplets impacting on an immiscible fluid is important for cleaning up oil spills as well as the demulsification process. Here we study the impact of low-viscosity liquid drops on high-viscosity liquid pools, e.g. water and ethanol droplets on a silicone oil 10cSt bath. We use an ultrafast camera and image processing to provide a detailed description of the impact phenomenon. Our observations suggest that viscosity and density ratio of the two media play a major role in the post-impact behavior. When the droplet density is larger than that of the pool, additional cavity is generated inside the pool. However, if the density of the droplet is lower than the pool, droplet momentary penetration may be facilitated by high impact velocities. In crown splash regime, the pool properties as well as drop properties play an important role. In addition, the appearance of the central jet is highly affected by the properties of the impacting droplet. In general, the size of generated daughter droplets as well as the thickness of the jet is reduced compared to the impact of droplets with the pool of an identical fluid.

Performance Enhancement of Air Conditioning (Split Unit) Using CuO/Oil Nano-Lubricant

2021 ◽  
Vol 1021 ◽  
pp. 97-106
Author(s):  
Mustafa W. Hamdallah ◽  
Omar M. Jumaah ◽  
Zaid A. Shaalan ◽  
Adnan M. Hussein
Keyword(s):  
Air Conditioning ◽  
Mass Fraction ◽  
Performance Enhancement ◽  
Viscosity Ratio ◽  
Density Ratio ◽  
Thermal Characteristics ◽  
Cuo Nanoparticles ◽  
Air Conditioner ◽  
Nano Lubricant ◽  
Electrical Consumption

The aims of this study are to improve thermal characteristics and decrease electrical consumption of air-conditioning as well as, to increase the performance (COP) of cooling cycle. CuO nanoparticles (0.003 mass fraction) have been added to compressor oil of air conditioning (1 ton capacity, split-unit) used Freon gas (R22), and then compared with pure oil compressor of air conditioning under same environmental conditions. The results showed that the increasing of density ratio, COP and viscosity ratio are 3%, 50% and 1.8% respectively while the decreasing of electrical consumption is 51.2%. The experimental data are compared with previous data in the literature to be validated. It can be recommended that the nano-oil is significant utilizing in air conditioner compressors for energy consumption applications.

scholarly journals Numerical simulations of vorticity banding of emulsions in shear flows

Soft Matter ◽  
2020 ◽  
Vol 16 (11) ◽  
pp. 2854-2863 ◽  
Author(s):  
Francesco De Vita ◽  
Marco Edoardo Rosti ◽  
Sergio Caserta ◽  
Luca Brandt
Keyword(s):  
Shear Flow ◽  
Numerical Simulations ◽  
Effective Viscosity ◽  
Shear Flows ◽  
Viscosity Ratio ◽  
Low Viscosity

Emulsion under shear flow can exhibit banded structures at low viscosity ratio. When coalescence is favoured, it can stabilize bands generated by migration of droplets. The reduction of the total surface results in a lower effective viscosity state.

scholarly journals Overcoming Rayleigh–Plateau instabilities: Stabilizing and destabilizing liquid-metal streams via electrochemical oxidation

2020 ◽  
Vol 117 (32) ◽  
pp. 19026-19032 ◽  
Author(s):  
Minyung Song ◽  
Karin Kartawira ◽  
Keith D. Hillaire ◽  
Cheng Li ◽  
Collin B. Eaker ◽  
...  
Keyword(s):  
Liquid Metal ◽  
Interfacial Tension ◽  
Electrochemical Anodization ◽  
Metallic Structures ◽  
Low Viscosity ◽  
Fluid Behavior ◽  
Jet Breakup ◽  
Fluid Velocities ◽  
Long Lifetime ◽  
Low Tension

Liquids typically form droplets when exiting a nozzle. Jets––cylindrical streams of fluid—can form transiently at higher fluid velocities, yet interfacial tension rapidly drives jet breakup into droplets via the Rayleigh–Plateau instability. Liquid metal is an unlikely candidate to form stable jets since it has enormous interfacial tension and low viscosity. We report that electrochemical anodization significantly lowers the effective tension of a stream of metal, transitioning it from droplets to long (long lifetime and length) wires with 100-μm diameters without the need for high velocities. Whereas surface minimization drives Rayleigh–Plateau instabilities, these streams of metal increase in surface area when laid flat upon a surface due to the low tension. The ability to tune interfacial tension over at least three orders of magnitude using modest potential (<1 V) enables new approaches for production of metallic structures at room temperature, on-demand fluid-in-fluid structuring, and new tools for studying and controlling fluid behavior.

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