The instability of non-Newtonian boundary-layer flows over rough rotating disks

Alqarni, A.A; Alveroğlu, Burhan; Griffiths, Paul; Garrett, S. D.

doi:10.1016/j.jnnfm.2019.104174

Cited by 21 publications

(9 citation statements)

References 22 publications

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“…In summary, our results are in a good agreement with previous studies investigating the effects of surface roughness on the instability of the boundary-layer flow over rotating disks. 23,[30][31][32]…”

Section: B Steady Mean Flow Solutionsmentioning

confidence: 99%

“…An exponential map of the Gauss-Lobatto grid points is adopted for the Chebyshev polynomials at a number of points into the physical domain: 100 points are sufficient to achieve accurate results such as results of previous studies, which are validated by confirming 100 points distributed between the geometry surface z = 0 and the top of the domain η max = 20 using the spectral method based on Chebyshev polynomials such as. 5,[30][31][32] Our simulations were run with a variable number of collocation points e.g. 110 or 120 and also η max was varied e.g.…”

Section: A Formulationmentioning

confidence: 99%

“…There is a number of recent studies concerned with investigating the effects of surface roughness on the boundary-layer flows over rotating disks such as Cooper et al, 23 Alveroglu et al, 30 and Alqarni et al 31 All these contributions agreed that the concentrically-grooved disks increase the stability of the type I mode for the von Kármán system. Al-Malki et al 32 confirmed the previous results of the effects of roughness types on the boundary-layer flow over a rotating disk in an enforced axial flow.…”

Section: Introductionmentioning

confidence: 99%

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Competing roughness effects on the non-stationary crossflow instability of the boundary-layer over a rotating broad cone

2022

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There are two primary aims of this paper: The first aim is to investigate the effects of the roughness types of the Miklavcic and Wang (MW) model on stationary disturbances of the boundary-layer flow over a broad cone . The second aim is to examine similar effects of surface roughness, but on non-stationary modes. This study begins with the formulations of the mean-flow system based on the cone geometry. These equations are solved using a spectral numerical method based on Chebyshev polynomials, and then used to formulate the linear stability system, which are computed for obtaining neutral curves of the unsteady flows. For the stationary modes, our results indicate that the inviscid instability is more stable while the viscous instability (type II mode) entirely eliminates, as concentric grooves or isotropic roughness and the cone half-angle increases. In contrast, streamwise grooves have a slight stabilizing effect on the type I mode and a significant destabilizing effect on the viscous instability. Another finding indicates that decreasing the half-angle leads to a greater stabilizing effect of isotropic roughness on the type I modes. Our outcomes are also confirmed by the growth rate and the energy analysis, which shows a large reduction of the total energy balance as a result of increasing concentric grooves or isotropic roughness for the crossflow mode. For non-stationary modes, similar effects are observed in that increasing all levels of roughness stabilizes the type I branch (with concentric grooves and isotropic roughness having a much stronger effect than streamwise grooves).

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Section: B Steady Mean Flow Solutionsmentioning

confidence: 99%

Section: A Formulationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Competing roughness effects on the non-stationary crossflow instability of the boundary-layer over a rotating broad cone

2022

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“…The study of non-Newtonian fluids on rotating disk has always been a hot research topic due to the complexity of its research and the wide range of applications. Alqarni et al [39] used Carreau model to study the instability of non-Newtonian boundary layer flow on a rough rotating disk. Researchers' enthusiasm for studying power-law fluids has not diminished in the studies of many non-Newtonian fluids.…”

Section: Introductionmentioning

confidence: 99%

Coupled flow and heat transfer of power-law nanofluids on non-isothermal rough rotary disk subjected to magnetic field

Pei¹,

Zhang²,

Zheng³

et al. 2022

Chinese Phys. B

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In this paper, we study coupled flow and heat transfer of power-law nanofluids on a non-isothermal rough rotating disk subject to a magnetic field. The problem is formulated in terms of specified curvilinear orthogonal coordinate system. An improved BVP4C algorithm is proposed and numerical solutions are obtained. The influence of volume fraction, types and shapes of nanoparticles, magnetic field and power-law index on the flow and heat transfer behavior are discussed.<br/>Results show that the power-law exponents (PLE), nanoparticle volume fraction (NVF) and magnetic field inclination angle (MFIA) are almost no effects on velocities in wave surface direction, but have small or significant effects on azimuth direction. NVF have remarkable influence on local Nusselt number (LNN) and friction coefficients (FC) in radial and azimuth directions (AD). LNN increases with NVF while FC in AD decrease. The types of nanoparticles, magnetic field strength and inclination have small effects on LNN, but they have remarkable effects on the friction coefficients with positively correlated while the inclination is negatively correlated with heat transfer rate. The size of the nanoparticle shape factor is positively correlated with LNN.

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“…Results were comparable with the case of partial-slip considered by Cooper et al 1 for the inviscid crossflow modes, with differences found for the viscous instability modes. More recently, these studies have been extended to consider the effect of surface roughness on the non-Newtonian flow due to a rotating disc 10 . Here partial-slip boundary conditions appropriate for the non-Newtonian viscosity model were imposed with the results revealing a stabilisation of local convective instabilities for isotropic roughness and also for radial grooves (azimuthally anisotropic roughness).…”

Section: Introductionmentioning

confidence: 99%

Effects of partial slip on the local-global linear stability of the infinite rotating disk boundary layer

2020

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A numerical investigation is undertaken on the effect of small-scale surface roughness on the local absolute and global stability of the flow due to a rotating disc. Surface roughness is modeled via the imposition of the partial-slip wall boundary condition, with radial and concentric anisotropic roughnesses and isotropic roughness considered. The effect of the partial-slip parameters on the neutral characteristics for absolute instability is presented, while the azimuthal mode numbers required for global linear instability to occur are determined for the genuine inhomogeneous base flow. Predictions for the threshold values for the azimuthal mode numbers needed for globally unstable behavior are also computed by coupling solutions of the Ginzburg-Landau equation with the local linear stability properties obtained using the homogeneous flow approximation. These are found to be in excellent agreement with the exact values realised from the numerical simulations. In general, surface roughness is demonstrated to stabilise the absolute instability as well as the global linear instabilities.

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The instability of non-Newtonian boundary-layer flows over rough rotating disks

Cited by 21 publications

References 22 publications

Competing roughness effects on the non-stationary crossflow instability of the boundary-layer over a rotating broad cone

Competing roughness effects on the non-stationary crossflow instability of the boundary-layer over a rotating broad cone

Coupled flow and heat transfer of power-law nanofluids on non-isothermal rough rotary disk subjected to magnetic field

Effects of partial slip on the local-global linear stability of the infinite rotating disk boundary layer

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