Stable stratification enhances transient growth in streaky shear flows
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arXiv
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| Format: | Preprint |
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2025
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| _version_ | 1866909847512940544 |
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| author | Oxley, Will Kerswell, Rich |
| author_facet | Oxley, Will Kerswell, Rich |
| contents | Recent work has found that the well-known `lift-up' mechanism is not important for, and may even inhibit, the transient growth possible on streaky wall-bounded shear flows which is believed an important process in the near-wall cycle for turbulent flows. Moreover, artificially removing the wall-normal velocity has been found to unleash 3 orders of magnitude more perturbation energy growth in an unbounded streaky flow model. Motivated by this, we examine the effect of introducing stable stratification which naturally suppresses wall-normal velocities (the `vertical' shear case) and find it permits the hugely enhanced linear energy growth predicted by simply removing the wall-normal velocity. Alternatively, imposing stable stratification such that the spanwise velocities are suppressed (`horizontal shear') not surprisingly inhibits transient growth by weakening the active `push over' mechanism. A formula for the critical stratification strength to completely suppress the preferred growth mechanism is determined which proves a useful predictor for what is seen in the full numerical solutions of the model. Implications for a stratified near-wall cycle are briefly discussed. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2510_13336 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Stable stratification enhances transient growth in streaky shear flows Oxley, Will Kerswell, Rich Fluid Dynamics Recent work has found that the well-known `lift-up' mechanism is not important for, and may even inhibit, the transient growth possible on streaky wall-bounded shear flows which is believed an important process in the near-wall cycle for turbulent flows. Moreover, artificially removing the wall-normal velocity has been found to unleash 3 orders of magnitude more perturbation energy growth in an unbounded streaky flow model. Motivated by this, we examine the effect of introducing stable stratification which naturally suppresses wall-normal velocities (the `vertical' shear case) and find it permits the hugely enhanced linear energy growth predicted by simply removing the wall-normal velocity. Alternatively, imposing stable stratification such that the spanwise velocities are suppressed (`horizontal shear') not surprisingly inhibits transient growth by weakening the active `push over' mechanism. A formula for the critical stratification strength to completely suppress the preferred growth mechanism is determined which proves a useful predictor for what is seen in the full numerical solutions of the model. Implications for a stratified near-wall cycle are briefly discussed. |
| title | Stable stratification enhances transient growth in streaky shear flows |
| topic | Fluid Dynamics |
| url | https://arxiv.org/abs/2510.13336 |