Centrifugal-Force-Induced Flow Bifurcations in Turbulent Thermal Convection

Hu, Yun-Bing; Huang, Shi-Di; Xie, Yi-Chao; Xia, Ke‐Qing

doi:10.1103/physrevlett.127.244501

Cited by 11 publications

(32 citation statements)

References 43 publications

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“…The so-obtained Fr c as a function of Ra is shown in figure 3(c), which has a power-law behaviour, Fr c ∼ Ra 0.53±0.04 . For comparison, the onset values from Hu et al (2021) for Ra = 4.4 × 10 9 are also plotted, where Fr c = 0.04 (left-pointing triangle) and 0.05 (right-pointing triangle) were obtained from the global heat transport and local temperature measurements, respectively. It is seen that the results obtained using the different methods and in different experimental configurations are consistent with each other within experimental resolution.…”

Section: The Onset Of the Centrifugal Effectmentioning

confidence: 99%

“…Similarly, if the centrifugal buoyancy time scale τ 0 cb = l 0 /(αΩ 2 RΔT) dominates within a horizontal length scale l 0 , the horizontal motion within l 0 can also be regarded as free fall. Then, the onset Froude number Fr c ∼ l 0 /H can be obtained immediately from the balance τ ff ∼ τ 0 cb (Hu et al 2021). This local balance means that just before the vertically moving hot (cold) fluid parcel arrives at, and is annihilated by, the cold (hot) plate (i.e.…”

Section: The Fr C Scalingmentioning

confidence: 99%

“…Very recently, a novel experiment with the convection cell placed off the rotation axis was conducted by some of the present authors to investigate the centrifugal effect at a fixed Ra = 4.4 × 10 9 (Hu et al 2021). One of the results from that study is that the convective flows start to bifurcate at an onset Froude number Fr c 0.04, which can be understood in terms of a local force balance and is believed to be applicable to the non-off-centred configuration like in the present work.…”

Section: Introductionmentioning

confidence: 99%

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On the centrifugal effect in turbulent rotating thermal convection: onset and heat transport

Xie

Xia

2022

J. Fluid Mech.

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The effect of centrifugal force in turbulent rotating Rayleigh–Bénard convection (RRBC) is studied experimentally in an aspect-ratio $\varGamma =1$ cylindrical convection cell and in the ranges of the Froude number $0.004\leq Fr \leq 0.363$ and the Rayleigh number $2.8\times 10^8 \leq Ra \leq 9.5\times 10^9$ , and with the Prandtl number fixed at $Pr=4.34$ . We use the bulk temperature anomaly to determine the onset Froude number $Fr_c$ , beyond which the centrifugal effects cannot be regarded as insignificant. It is found that $Fr_c$ depends on $Ra$ as $Fr_c\sim Ra^{0.53}$ , which may be understood qualitatively by the idea of local force balance. For $Fr>Fr_c$ , the centrifugal effect is more pronounced for smaller $Ra$ , which is also found for larger constant $1/Ro$ . This implies that the response of the system to the centrifugal force depends on the flow states, which, in RRBC, is mainly determined by the competition between the buoyancy and Coriolis forces. Detailed analysis of the sidewall temperature signal shows results consistent with those obtained from the bulk temperature. Based on the above results, we propose a different division of the $1/Ro$ – $Fr$ phase space than previously suggested. For the heat transport, the results under fixed $1/Ro$ show well-defined $Nu$ – $Ra$ scalings, which can provide a better prediction for the heat transport when extrapolating to the unexplored regions in the phase space.

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Section: The Onset Of the Centrifugal Effectmentioning

confidence: 99%

Section: The Fr C Scalingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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On the centrifugal effect in turbulent rotating thermal convection: onset and heat transport

Xie

Xia

2022

J. Fluid Mech.

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“…Moreover, the effect of has been investigated in the present study, which shows that the joint action of and results in a symmetry breaking in the centrifugal effect for the hot and cold fluid parcels; whereas only the effect of was studied in Hu et al. (2021).…”

Section: Introductionmentioning

confidence: 74%

“…In a recent paper (Hu et al. 2021), it has been reported that the symmetry of the system is broken by this directed centrifugal force, resulting in a flow bifurcation. Specifically, the hot and cold fluid parcels are separated by and condensed, respectively, near the nearest and farthest points to the rotation axis.…”

Section: Introductionmentioning

confidence: 99%

An experimental study of off-centred rotating thermal convection: a laboratory model for the tidal effects

Xia

2023

J. Fluid Mech.

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A novel experiment was performed in rotating Rayleigh–Bénard convection (RRBC), wherein the convection cell with radius $R$ was shifted away from the rotation axis by a distance $d$ . In this case, the centrifugal force felt by a fluid parcel (characterized by the Froude number $Fr$ ) can be decomposed into an axisymmetrical part $Fr_R$ and a directed one $Fr_d$ . It has been reported that the global heat transport enhances at $Fr_{d,c}$ and then reaches an optimal state at $Fr_{d,max}$ (Hu et al., Phys. Rev. Lett., vol. 127, 2021, 244501). In this paper, the local properties after the offset effects set in are investigated further, which show different features before and after $Fr_{d,max}$ . The local temperature measurements at the cell centre reveal that the bulk flow turns from a turbulent state into a laminar state at $Fr_{d,max}$ , which is consistent with the particle image velocimetry results. This transition can be qualitatively understood by an equivalent tilted RRBC system. As for the hot and cold coherent structures near the sidewall, their vertical temperature variations reach a minimum at $Fr_{d,max}$ , implying that these structures are mostly uniform in the vertical direction at $Fr_{d,max}$ . Their temperature contrasts show a linear dependence on $Fr_d$ and start to deviate from this linear behaviour when $Fr_d>Fr_{d,max}$ . Besides the dominant effects of $Fr_d$ , the secondary effects of $Fr_R$ are also investigated. Due to the positive effect of $+Fr_R$ on the cold structure and the negative effect of $-Fr_R$ on the hot one, the cold structure is more coherent than the hot one, but its size is smaller. The shift of the cold cluster centre from the farthest point is also larger than the shift of the hot one from the nearest point.

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Meta‐Lens Particle Image Velocimetry

Liu,

Zhao,

et al. 2023

Advanced Materials

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Fluid flow behavior is visualized through particle image velocimetry (PIV) for understanding and studying experimental fluid dynamics. However, traditional PIV methods require multiple cameras and conventional lens systems for image acquisition to resolve multi‐dimensional velocity fields. In turn, it introduces complexity to the entire system. Meta‐lenses are advanced flat optical devices composed of artificial nanoantenna arrays. It can manipulate the wavefront of light with the advantages of ultrathin, compact, and no spherical aberration. Meta‐lenses offer novel functionalities and promise to replace traditional optical imaging systems. Here, a binocular meta‐lens PIV technique is proposed, where a pair of GaN meta‐lenses are fabricated on one substrate and integrated with a imaging sensor to form a compact binocular PIV system. The meta‐lens weigh only 116 mg, much lighter than commercial lenses. The 3D velocity field can be obtained by the binocular disparity and particle image displacement information of fluid flow. The measurement error of vortex‐ring diameter is ≈1.25% experimentally validates via a Reynolds‐number (Re) 2000 vortex‐ring. This work demonstrates a new development trend for the PIV technique for rejuvenating traditional flow diagnostic tools toward a more compact, easy‐to‐deploy technique. It enables further miniaturization and low‐power systems for portable, field‐use, and space‐constrained PIV applications.

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Centrifugal-Force-Induced Flow Bifurcations in Turbulent Thermal Convection

Cited by 11 publications

References 43 publications

On the centrifugal effect in turbulent rotating thermal convection: onset and heat transport

On the centrifugal effect in turbulent rotating thermal convection: onset and heat transport

An experimental study of off-centred rotating thermal convection: a laboratory model for the tidal effects

Meta‐Lens Particle Image Velocimetry

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