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Experimental investigation on the influence of rotation on thermal convection

dc.contributor.advisorWeiss, Stephan Dr.
dc.contributor.authorWedi, Marcel Frederik
dc.titleExperimental investigation on the influence of rotation on thermal convectionde
dc.contributor.refereeDreizler, Stefan Prof. Dr.
dc.subject.gokPhysik (PPN621336750)de
dc.description.abstractengWe report on experimental measurements of rotating Rayleigh-Bénard convection to study the influence of the Coriolis force on the heat transport and the flow structure. Two experimental setups were used. The first is a 2.24 m tall cylindrical cell with an aspect ratio between its diameter (D) and its height H, Γ = D/H = 0.5. It is filled with either nitrogen or pressurized gaseous sulfur hexafluoride to achieve Rayleigh numbers 7.5 × 10^9 ≤ Ra ≤ 7.5 × 10^14, while the Prandtl number Pr remained fairly constant at 0.72 ≤ Pr ≤ 0.96. We performed heat flux measurements (i.e. the Nusselt number Nu) and obtain scaling relations as function of Ra and the rotation rate in form of the inverse Rossby number 1/Ro. We find Nu_0 ∝ Ra^0.315 for the non-rotating and a collapse of Nu/Nu_0(1/Ro) for the rotating case. For sufficiently large 1/Ro, we find Nu/Nu_0 ∝ 1/Ro^-0.42. Three regimes were determined, with increasing influence of rotation. Their transitional values 1/Ro^*_1 = 0.8 and 1/Ro^*_1 = 4 could be found in numerous quantities throughout the analysis, where we relied on point-wise temperature measurements distributed throughout the cell. 1/Ro^*_1 was found as the onset of a travelling temperature wave around the circumference close to the sidewall, referred to as boundary zonal flow (BZF). This structure with wave number k_BZF = 1 drifts in counter-rotating direction with a frequency ω/Ω ∝ 1/Ro^-3/4. In the smaller, optically accessible setup, we performed particle image velocimetry (PIV). It consists of a H = 0.196 m, Γ = 1, transparent setup made out of acrylic glass. With mixtures of water and glycerol at different mass concentrations we achieved 6.55 ≤ Pr ≤ 76 at various combinations of Ra and the dimensionless rotation rate (Ekman number - Ek ). We focussed on an horizontal layer at half-height, where we investigated the BZF in the velocity field. We found a thickness scaling relation δ_0 ∝ Ek^1/2, while the distance from the sidewall to the maximum azimuthal velocity was found to scale as δ^max_φ ∝ Ek^3/2Ra^1/2Pr^
dc.contributor.coRefereeShishkina, Olga PD Dr.
dc.subject.engrotating flowsde
dc.subject.engrotating turbulencede
dc.affiliation.instituteFakultät für Physikde
dc.notes.confirmationsentConfirmation sent 2022-10-18T12:15:01de

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