The SCALEX facility – an apparatus for scaled fluid dynamical experiments

Ghazijahani, Mohammad Sharifi; Kästner, Christian; Valori, Valentina; Thieme, Alexander; Täschner, Kerstin; Schumacher, Jörg; Cierpka, Christian

doi:10.1515/teme-2022-0121

Cited by 5 publications

(8 citation statements)

References 30 publications

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“…Therefore, experiments in pressurized fluids are necessary in order to reach high Rayleigh numbers. In this regard, the Scaled Convective Airflow Laboratory Experiment (SCALEX) at Technische Universität Ilmenau was designed to conduct experiments for pressurized gases 30 . The pressure vessel is cylindrical and has a diameter of 1100 mm and a length of 2200 mm.…”

Section: Methodsmentioning

confidence: 99%

“…Compared to air, SF 6 has the advantage of providing higher Rayleigh numbers (roughly 10 times more) in the same pressure ranges while maintaining the desired low Prandtl numbers the same as the air (0.7 < Pr < 1.3). For a further detailed explanation of the SCALEX facility, please see 30 .…”

Section: Methodsmentioning

confidence: 99%

“…The non-transparent cooling plate is made from aluminum, and a recirculating cooler (Medingen C20 KB10) moderates its temperature. While the transparent heating plate 30 is made from a glass pane with a thin layer of coated Indium Tin Oxide (ITO) in its outer surface to provide Ohmic heating using an electric current that is applied by copper flat bands pushed on the ITO surface. The side walls are made from 4 mm thick polycarbonate, and considering the temperature difference range of ∆T ≈ 7K for the current experiments, they can be assumed adiabatic.…”

Section: Methodsmentioning

confidence: 99%

“…The Stokes number (St = d p ρ p u f /18µg) for the particles in the current experiment is calculated to be St < 0.1, and thus the particles are assumed to follow the flow faithfully. Then the generated particles were settled in a settling chamber and pushed to the RBCell via a fan gently from six inlets (three on the left and three on the right of the figures for the current study) 30 . Due to the momentum addition during the seeding particle injection to the RBCell, all experiments are conducted at least 15 minutes after the particle injection.…”

Section: Methodsmentioning

confidence: 99%

“…Therefore, it is necessary to provide similar experimental measurements for the gases like air or, in the case of this study, SF 6 . In this regard, the SCALEX facility at Technische Universität Ilmenau was designed to investigate RBC in pressurized air and SF 6 at high Rayleigh numbers [30][31][32] . Recently, initial SPIV experiments in the SCALEX over an RBC with Γ = 10 were conducted by Valori et al 33 .…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

On the role of vortices in turbulent Rayleigh-Bénard convection

Ghazijahani,

Cierpka

2024

Preprint

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Understanding turbulent thermal convection is essential for modeling many natural phenomena. This study investigates the spatio-temporal dynamics of the vortical structures in the mid-plane of turbulent Rayleigh-Bénard convection in SF6 via experiments. For this, a Rayleigh-Bénard cell of aspect ratio 10 is placed inside a pressure vessel and pressurized up to 1, 1.5, and 2.5 bar in order to reach Rayleigh numbers of Ra = 9.4×105,2.0×106 and 5.5×106. For all three cases, the Prandtl number is Pr = 0.79 and ΔT ≈ 7K. Then, stereoscopic particle image velocimetry is conducted to measure the three velocity components in the horizontal mid-plane for 5.78×103 free-fall times. For the given aspect ratio the flow is no longer dominated by the side walls of the cell and turbulent superstructures that show a 2D repetitive organization form. These superstructures show diverse shapes with faster dissipation rates as Ra increases. Out-of-plane vortices are the main feature of the flow. As Ra increases, the number of these vortices also increases, and their size shrinks. However, their total number is almost constant for each Ra through the measurement period. Furthermore, their occurrence is random and does not depend on whether the flow is upward-heated, downward-cooled, or horizontally-directed. Vortex tracking was applied to measure life time, displacement, and traveled distance of these structures. The relation between life time and traveled distance is rather linear. Interestingly, in the vortex centers, the out-of-plane momentum transport is larger in comparison to the bulk flow. Therefore, these vortices will play a major role in the heat transport in such flows.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

On the role of vortices in turbulent Rayleigh-Bénard convection

Ghazijahani,

Cierpka

2024

Preprint

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Spatial prediction of the turbulent unsteady von Kármán vortex street using echo state networks

Sharifi Ghazijahani,

Heyder,

Schumacher

et al. 2023

Physics of Fluids

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The spatial prediction of the turbulent flow of the unsteady von Kármán vortex street behind a cylinder at Re = 1000 is studied. For this, an echo state network (ESN) with 6000 neurons was trained on the raw, low-spatial resolution data from particle image velocimetry. During prediction, the ESN is provided one half of the spatial domain of the fluid flow. The task is to infer the missing other half. Four different decompositions termed forward, backward, forward–backward, and vertical were examined to show whether there exists a favorable region of the flow for which the ESN performs best. Also, it was checked whether the flow direction has an influence on the network's performance. In order to measure the quality of the predictions, we choose the vertical velocity prediction of direction (VVPD). Furthermore, the ESN's two main hyperparameters, leaking rate (LR) and spectral radius (SR), were optimized according to the VVPD values of the corresponding network output. Moreover, each hyperparameter combination was run for 24 random reservoir realizations. Our results show that VVPD values are highest for LR ≈ 0.6, and quite independent of SR values for all four prediction approaches. Furthermore, maximum VVPD values of ≈0.83 were achieved for backward, forward–backward, and vertical predictions while for the forward case VVPDmax=0.74 was achieved. We found that the predicted vertical velocity fields predominantly align with their respective ground truth. The best overall accordance was found for backward and forward–backward scenarios. In summary, we conclude that the stable quality of the reconstructed fields over a long period of time, along with the simplicity of the machine learning algorithm (ESN), which relied on coarse experimental data only, demonstrates the viability of spatial prediction as a suitable method for machine learning application in turbulence.

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Spatio-temporal dynamics of superstructures and vortices in turbulent Rayleigh–Bénard convection

Sharifi Ghazijahani,

Cierpka

2024

Physics of Fluids

View full text Add to dashboard Cite

Understanding turbulent thermal convection is essential for modeling many natural phenomena. This study investigates the spatiotemporal dynamics of the vortical structures in the mid-plane of turbulent Rayleigh–Bénard convection in SF6 via experiments. For this, a Rayleigh–Bénard cell of aspect ratio 10 is placed inside a pressure vessel and pressurized up to 1, 1.5, and 2.5 bar in order to reach Rayleigh numbers of Ra = 9.4×105,2.0×106, and 5.5×106, respectively. For all three cases, the Prandtl number is Pr =0.79 and ΔT≈7 K. Then, stereoscopic particle image velocimetry is conducted to measure the three velocity components in the horizontal-mid-plane for 5.78×103 free fall times. For the given aspect ratio, the flow is no longer dominated by the side walls of the cell and turbulent superstructures that show a two-dimensional repetitive organization form. These superstructures show diverse shapes with faster dissipation rates as Ra increases. Out-of-plane vortices are the main feature of the flow. As Ra increases, the number of these vortices also increases, and their size shrinks. However, their total number is almost constant for each Ra through the measurement period. Furthermore, their occurrence is random and does not depend on whether the flow is upward-heated, downward-cooled, or horizontally directed. Vortex tracking was applied to measure lifetime, displacement, and traveled distance of these structures. The relation between lifetime and traveled distance is rather linear. Interestingly, in the vortex centers, the out-of-plane momentum transport is larger in comparison to the bulk flow. Therefore, these vortices will play a major role in the heat transport in such flows.

show abstract

The SCALEX facility – an apparatus for scaled fluid dynamical experiments

Cited by 5 publications

References 30 publications

On the role of vortices in turbulent Rayleigh-Bénard convection

On the role of vortices in turbulent Rayleigh-Bénard convection

Spatial prediction of the turbulent unsteady von Kármán vortex street using echo state networks

Spatio-temporal dynamics of superstructures and vortices in turbulent Rayleigh–Bénard convection

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