Instantaneous convective heat transfer at the wall: a depiction of turbulent boundary layer structures
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arXiv
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| Autori principali: | , , , |
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| Natura: | Preprint |
| Pubblicazione: |
2025
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| _version_ | 1866912217412141056 |
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| author | Foroozan, Firoozeh Ianiro, Andrea Discetti, Stefano Baars, Woutijn J. |
| author_facet | Foroozan, Firoozeh Ianiro, Andrea Discetti, Stefano Baars, Woutijn J. |
| contents | We demonstrate the ability to experimentally measure fluctuations of the convective heat transfer coefficient at the wall in a turbulent boundary layer. For this, we measure two-dimensional fields of wall-temperature fluctuations beneath a zero-pressure-gradient turbulent boundary layer, at two moderate friction Reynolds numbers ($Re_τ\approx 990$ and $Re_τ\approx 1800$). Spatiotemporal data of wall-temperature are acquired by means of a heated-thin-foil sensor as sensing hardware, and an infrared camera as temperature detector. At low $Re_τ$ conditions, the fields of the Nusselt number fluctuations are populated by elongated structures comprising streamwise and spanwise length scales comparable to those of near-wall streaks. At higher $Re_τ$ conditions, the effective width and length of the coherent $Nu$ fluctuations increases. These findings are based on two-point correlations, as well as streamwise-spanwise energy spectra of $Nu$ fluctuations. The convective velocities of the $Nu$ fluctuations are also computed with the available time resolution from the measurements. This allows for resolving the multi-scale nature of convective footprints of wall-bounded turbulence: our experimental data reflect that larger streaks in the footprint convect at velocities in the order of the free-stream velocity, while the more energetic smaller-scale features move at velocities in the order of $10u_τ$. Measurements of the kind presented here offer a promising method for sensing, as they can be used as input to flow control systems. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2502_01494 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Instantaneous convective heat transfer at the wall: a depiction of turbulent boundary layer structures Foroozan, Firoozeh Ianiro, Andrea Discetti, Stefano Baars, Woutijn J. Fluid Dynamics We demonstrate the ability to experimentally measure fluctuations of the convective heat transfer coefficient at the wall in a turbulent boundary layer. For this, we measure two-dimensional fields of wall-temperature fluctuations beneath a zero-pressure-gradient turbulent boundary layer, at two moderate friction Reynolds numbers ($Re_τ\approx 990$ and $Re_τ\approx 1800$). Spatiotemporal data of wall-temperature are acquired by means of a heated-thin-foil sensor as sensing hardware, and an infrared camera as temperature detector. At low $Re_τ$ conditions, the fields of the Nusselt number fluctuations are populated by elongated structures comprising streamwise and spanwise length scales comparable to those of near-wall streaks. At higher $Re_τ$ conditions, the effective width and length of the coherent $Nu$ fluctuations increases. These findings are based on two-point correlations, as well as streamwise-spanwise energy spectra of $Nu$ fluctuations. The convective velocities of the $Nu$ fluctuations are also computed with the available time resolution from the measurements. This allows for resolving the multi-scale nature of convective footprints of wall-bounded turbulence: our experimental data reflect that larger streaks in the footprint convect at velocities in the order of the free-stream velocity, while the more energetic smaller-scale features move at velocities in the order of $10u_τ$. Measurements of the kind presented here offer a promising method for sensing, as they can be used as input to flow control systems. |
| title | Instantaneous convective heat transfer at the wall: a depiction of turbulent boundary layer structures |
| topic | Fluid Dynamics |
| url | https://arxiv.org/abs/2502.01494 |