Instability of a free-shear layer in the vicinity of a viscosity-stratified layer

Sahu, Kirti Chandra; Govindarajan, Rama

doi:10.1017/jfm.2014.361

Cited by 9 publications

(5 citation statements)

References 47 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It has shown that two types of instability can commonly take place in these flows; the most frequently observed and investigated is Kelvin-Helmholtz instability which has significant role on mixing of the fluids [22]. This instability is well known for its overturning billowing patterns, cats-eye structure, and its ability to mix effectively [1,23]. The chance of Kelvin-Helmholtz instability occurring is when the stratification is weak and the thickness of density transition layer between two layers of different densities is comparable to the shear layer thickness.…”

Section: Introductionmentioning

confidence: 99%

Experimental study on the interfacial instability of particle-laden stratified shear flows

Khavasi

Firoozabadi

2018

J Braz. Soc. Mech. Sci. Eng.

View full text Add to dashboard Cite

Turbidity currents are one of the more frequently observed types of stratified flows. In these currents, the density difference is created as a result of suspended particles. The interfacial instability of turbidity current is studied experimentally in the present research. Both Kelvin-Helmholtz and (asymmetric) Holmboe instabilities are observed during the experiments; the first one was downstream, and the second one was upstream of the obstacle. Kelvin-Helmholtz instability is observed by approximately zero (phase) speed with respect to the mean flow. With the aim of measuring spectral distribution of velocity fluctuations, the effects of some parameters are studied on interfacial waves; Kelvin-Helmholtz waves weaken as the local Richardson number (J), an increase in inlet Froude number (F in) or a reduction in obstacle height (H). The one-sided (asymmetry) Holmboe instability is detected moving to the upstream. This one-sidedness is as a result of asymmetry existence in velocity and density profiles in this research. Train of asymmetric Holmboe waves is observed while ejecting dense fluid into upper layer. The ejecting process happens randomly. Furthermore, secondary circulations behind these waves are perceived. Mentioned parameters (J, F in , H) do not show meaningful effect on Holmboe waves. Phase speed of these waves increases with local Richardson number. The measured average wavelength of these waves is about 17 cm. The wavelength of one-sided Holmboe waves decreases as local Richardson number increases. The unstable region of onesided Holmboe waves is obtained and is compared with linear stability's prediction.

show abstract

Section: Introductionmentioning

confidence: 99%

Experimental study on the interfacial instability of particle-laden stratified shear flows

Khavasi

Firoozabadi

2018

J Braz. Soc. Mech. Sci. Eng.

View full text Add to dashboard Cite

show abstract

“…For example, figure 18 shows a time series of the concentration profile for a case with rad s, and mm. It is known that viscosity stratification in shear flows can lead to instability in certain regimes (Yih 1967; Sahu & Govindarajan 2014). However, the coupled viscosity distribution and velocity profile in the rheometer system are highly nonlinear, and the flow cannot be analysed in terms of simple viscosity-stratified layers of fluid.…”

Section: Discussionmentioning

confidence: 99%

Viscosity measurements of glycerol in a parallel-plate rheometer exposed to atmosphere

et al. 2023

View full text Add to dashboard Cite

Glycerol is a hygroscopic fluid that spontaneously absorbs water vapour from the atmosphere. For applications involving glycerol, care must be taken to avoid exposure to humidity, since its viscosity decreases quickly as water is absorbed. We report experimental measurements of the viscosity of glycerol in a parallel-plate rheometer where the outer interface is exposed to atmosphere. The measurements decrease with time as water is absorbed from the atmosphere and transported throughout the glycerol via diffusion and advection. Measured viscosities drop faster at higher relative humidities, confirming the role of hygroscopicity in the transient viscosities. The rate of viscosity decrease shows a non-monotonic relationship with the rheometer gap height. This behaviour is explained by considering the transition from diffusion-dominated transport in the narrow-gap regime to the large-gap regime where transport is dominated by inertia-driven secondary flows. Numerical simulations of the water absorption and transport confirm this non-monotonic behaviour. The experimental viscosity measurements show unexpectedly fast decreases at very small gap heights, violating the parallel-plate, axisymmetric model. We propose that this drop-off may be due to misalignment in the rheometer that becomes non-negligible for small gaps. Theoretical considerations show that secondary flows in a misaligned rheometer dominate the typical secondary inertial flows in parallel-plate rheometers at small gaps. Finally, simulations in a misaligned parallel-plate system demonstrate the same sharp drop-off in viscosity measurements at small gap heights. This modelling can be used to estimate the gap height where misalignment effects dominate the transient glycerol viscosity measurements.

show abstract

“…It is worth mentioning that a similar analysis was performed by Sahu and Govindarajan [15], in which they have investigated the viscous instability of free shear layer in the vicinity of a viscous stratified mixed layer. Their results show that di↵usivity has no influence on the stability of this class of shear flows but viscosity stratification has a significant role on the stability characteristics.…”

mentioning

confidence: 84%

“…For a vertical wall (✓ = 90 ), in the absence of surface tension (S = 0), we have f = 0. It may be checked that 1 + B + C + D = 0, showing that c = 1 is a root of the cubic equation (15). The other two roots are those of the quadratic equation…”

Section: Vertical Wall No Surface Tensionmentioning

confidence: 99%

See 1 more Smart Citation

Inviscid instability of two-fluid free surface flow down an incline

et al. 2016

Self Cite

View full text Add to dashboard Cite

The inviscid temporal stability analysis of two-fluid parallel shear flow with a free surface, down an incline, is studied. The velocity profiles are chosen as piecewise-linear with two limbs. The analysis reveals the existence of unstable inviscid modes, arising due to wave interaction between the free surface and the shearjump interface. Surface tension decreases the maximum growth rate of the dominant disturbance. Interestingly, in some limits, surface tension destabilises extremely short waves in this flow. This can happen because of the interaction with the shear-jump interface. This flow may be compared with a corresponding viscous twofluid flow. Though viscosity modifies the stability properties of the flow system both qualitatively and quantitatively, there is qualitative agreement between the viscous and inviscid stability analysis when the less viscous fluid is closer to the free surface.

show abstract

Instability of a free-shear layer in the vicinity of a viscosity-stratified layer

Cited by 9 publications

References 47 publications

Experimental study on the interfacial instability of particle-laden stratified shear flows

Experimental study on the interfacial instability of particle-laden stratified shear flows

Viscosity measurements of glycerol in a parallel-plate rheometer exposed to atmosphere

Inviscid instability of two-fluid free surface flow down an incline

Contact Info

Product

Resources

About