Effect of heating on topology of vortex breakdown in Vogel–Escudier flow

Vishnu, R.; Sharma, Manjul; Sameen, A.

doi:10.1063/5.0065134

Cited by 3 publications

(1 citation statement)

References 63 publications

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“…The effect of other flow complexities like variable lid-rotation rates [12], two-fluid system [7,[13][14][15][16][17], thermal stratification [18][19][20][21], roughness in the rotating plate [22,23], axial magnetic field [24,25] etc has been of interest to the community due to its engineering application. Various studies have been performed to control the vortex breakdown bubble [26,27].…”

Section: Introductionmentioning

confidence: 99%

Vortex breakdown in the small Mach number regimes

Dhurandhar,

Sharma,

Mohan

et al. 2024

Phys. Scr.

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The effect of compressibility for flow inside the cylinder with the top rotating lid (Vogel-Escudier flow) is examined. Three-dimensional Navier-Stokes equations for compressible flow in Cartesian coordinates are used to simulate the flow using open-source OpenFOAM software. The Mach number (Ma) of the flow is varied from 0.1 to 0.3, and the Reynolds number (Re) is varied from 1000 to 5000 for a fixed aspect ratio (Γ = 2.5) of the cylinder. The flow is found to have a transition from a steady axisymmetric state to a non-axisymmetric state exhibiting multiple azimuthal waves as the Mach number and the Reynolds number are varied. The flow field changes significantly with an increase in Ma for unsteady flow at higher Re. An increase in Ma increases the side wall azimuthal instability, as found in the perturbation contour plots and time series analysis. Further, we reconstruct phase portraits to show the dynamics of the flow finally becoming chaotic as the Reynolds number is increased to 5000. Finally, we support the argument with Lyapunov exponents for the higher Re samples. The Lyapunov Exponent is found to increase with Ma.

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Section: Introductionmentioning

confidence: 99%

Vortex breakdown in the small Mach number regimes

Dhurandhar,

Sharma,

Mohan

et al. 2024

Phys. Scr.

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The unsteadiness of tip leakage vortex breakdown and its role in rotating instability

Yang,

Wu,

Chen

et al. 2023

Physics of Fluids

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The unsteadiness due to tip leakage vortex (TLV) breakdown was studied using a special experimental test campaign in parallel with numerical simulations. The back flow vortex (BFV), an isolated vortex caused by TLV spiral-type breakdown, was found to play a key role in rotating instability (RI). High-speed pressure transducers were used to measure the unsteady pressure field at the casing end wall of the blade in an isolated subsonic compressor rotor, which identified a low-frequency fluctuation at the near stall condition. A single-passage unsteady Reynolds-averaged Navier–Stokes simulation was used to study the evolution of unsteady flow structures, validated by the experimental measurements. Two distinct kinds of periodically unsteady flow were revealed by the simulations. A high-frequency fluctuation corresponding to 1.0 blade pass frequency (BPF) was caused by the spiral-type breakdown of the TLV. The other low-frequency fluctuation corresponding to 0.5BPF was caused by the feedback interaction between the BFV and the blade loading. The BFV was generated by the TLV breakdown, which was separated from the twisted vortex core of the TLV, and it moved downstream along the pressure side of the adjacent blade. A larger sized BFV reduced the local loading of the adjacent blade. The TLV was weakened as a consequence of the reduced loading, resulting in a smaller sized BFV. The blade tip loading was relatively less affected by the small sized BFV rather than the larger sized BFV. Therefore, the blade loading recovered and the size of the BFV increased, repeating the cycle. This feedback mechanism produced a pressure fluctuation with a frequency equal to 0.5BPF, which was closely related to RI.

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Heat transport enhancement by rotating bottom endwall in a cylindrical Rayleigh–Bénard convection

Yang,

Deng,

2024

Physics of Fluids

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Rotating thermal convection, commonly encountered in natural and industrial environments, is typically influenced by both buoyancy forces and boundary rotation. In this study, we conduct direct numerical simulations to explore the effect of rotating bottom on the flow structure and heat transport of Rayleigh–Bénard convection (RBC) in a cylindrical cavity. This cavity has a radius-to-height ratio of 1 and is filled with an incompressible fluid with a Prandtl number of 0.7. Our results show that the axisymmetric convection pattern, observed in RBC for Ra∈[4000,8000] without rotation, transitions into a double roll structure at low rotating speeds (ω), while for Ra≤4000, the pattern remains axisymmetric, independent of ω. We then focus on the impact of bottom rotation on heat transport in the axisymmetric regime. Based on the variation in the Nusselt number (Nu) with ω, two distinct regimes are identified: a convection-dominated regime at low ω, where Nu closely resembles that of standard RBC, and a rotation-dominated regime at high ω, where strong shear induced by the rotating bottom intensifies the meridional circulation, significantly boosting global heat flux. The critical rotating speed, ω*, marking the transition between these regimes, follows different power-law relations below and above the buoyant convection onset (Rac): ω*∼Ra−0.64 for Ra<Rac and ω*∼Ra0.33 for Ra>Rac. As ω increases, the exponents for Nu∼Raλ and Re∼Raγ evolve before converging to λ≈0.3 and γ=0.5, respectively. Scaling laws for Nu and Re as functions of ω and Ra in the rotation-dominated regime are finally derived: Nu∼Ra0.3ω0.64 and Re∼Ra0.5ω.

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Effect of heating on topology of vortex breakdown in Vogel–Escudier flow

Cited by 3 publications

References 63 publications

Vortex breakdown in the small Mach number regimes

Vortex breakdown in the small Mach number regimes

The unsteadiness of tip leakage vortex breakdown and its role in rotating instability

Heat transport enhancement by rotating bottom endwall in a cylindrical Rayleigh–Bénard convection

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