Turbulent flow control using spanwise travelling wave via Lorentz forcing
Lorentz-forcing spanwise travelling wave actuation in the turbulent boundary layer has been studied in a water channel at various experimental conditions (St = 139.2, 186 and 232; T+ = 17, 42 and 82). At the Reynolds number of Reτ = 388, a maximum skin friction drag reduction of 30% is achieved in s...
| Main Author: | |
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| Format: | Thesis (University of Nottingham only) |
| Language: | English |
| Published: |
2009
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| Online Access: | https://eprints.nottingham.ac.uk/10710/ |
| _version_ | 1848791119975940096 |
|---|---|
| author | Xu, Peng |
| author_facet | Xu, Peng |
| author_sort | Xu, Peng |
| building | Nottingham Research Data Repository |
| collection | Online Access |
| description | Lorentz-forcing spanwise travelling wave actuation in the turbulent boundary layer has been studied in a water channel at various experimental conditions (St = 139.2, 186 and 232; T+ = 17, 42 and 82). At the Reynolds number of Reτ = 388, a maximum skin friction drag reduction of 30% is achieved in some cases, while up to 22.8% of viscous drag increase is also observed.
The results of the turbulent boundary layer profiles show that the turbulence intensities for both the drag-reducing and the drag-increasing cases are reduced. The higher moments of turbulence statistics such as the skewness and the kurtosis increase near the wall when T+ = 42, St = 232 in the drag-reducing case. For the drag-increasing case (T+ = 17, St = 232), the skewness and the kurtosis are decreased when very close to the wall (y+ < 6), while they are increased for y+ > 6, similar to the drag-reducing case. The reduction in the turbulent intensities as well as the changes in VITA velocity profiles suggest that the drag changes are due to the modified near-wall activities by the Lorentz forcing.
Flow visualisation shows that the low-speed streaks are twisted into the spanwise directions in both the drag-reducing and the drag-increasing cases. For the drag-reducing case, the low-speed streaks are clustered together to form a wide low-speed region similar to what Du et al (2002) have found. This low-speed region seems to act as the ‘storage’ of low-speed fluid to help reduce the skin friction drag. To achieve the drag reduction, the spanwise displacement of low-speed streaks must be greater than 115 wall units in the present configuration, which compares well with the average spacing of low-speed streaks in the turbulent boundary layer.
When the drag increase occurs, only pseudo-local spanwise oscillation is observed without a formation of a wide low-speed region. The pseudo-local spanwise oscillation appears to produce converging and diverging motions around the forcing-activation area. The induced streamwise vorticity layers are believed to enhance the effect of the sweep motion, which results in the increasing skin-friction drag. |
| first_indexed | 2025-11-14T18:23:27Z |
| format | Thesis (University of Nottingham only) |
| id | nottingham-10710 |
| institution | University of Nottingham Malaysia Campus |
| institution_category | Local University |
| language | English |
| last_indexed | 2025-11-14T18:23:27Z |
| publishDate | 2009 |
| recordtype | eprints |
| repository_type | Digital Repository |
| spelling | nottingham-107102025-02-28T11:09:20Z https://eprints.nottingham.ac.uk/10710/ Turbulent flow control using spanwise travelling wave via Lorentz forcing Xu, Peng Lorentz-forcing spanwise travelling wave actuation in the turbulent boundary layer has been studied in a water channel at various experimental conditions (St = 139.2, 186 and 232; T+ = 17, 42 and 82). At the Reynolds number of Reτ = 388, a maximum skin friction drag reduction of 30% is achieved in some cases, while up to 22.8% of viscous drag increase is also observed. The results of the turbulent boundary layer profiles show that the turbulence intensities for both the drag-reducing and the drag-increasing cases are reduced. The higher moments of turbulence statistics such as the skewness and the kurtosis increase near the wall when T+ = 42, St = 232 in the drag-reducing case. For the drag-increasing case (T+ = 17, St = 232), the skewness and the kurtosis are decreased when very close to the wall (y+ < 6), while they are increased for y+ > 6, similar to the drag-reducing case. The reduction in the turbulent intensities as well as the changes in VITA velocity profiles suggest that the drag changes are due to the modified near-wall activities by the Lorentz forcing. Flow visualisation shows that the low-speed streaks are twisted into the spanwise directions in both the drag-reducing and the drag-increasing cases. For the drag-reducing case, the low-speed streaks are clustered together to form a wide low-speed region similar to what Du et al (2002) have found. This low-speed region seems to act as the ‘storage’ of low-speed fluid to help reduce the skin friction drag. To achieve the drag reduction, the spanwise displacement of low-speed streaks must be greater than 115 wall units in the present configuration, which compares well with the average spacing of low-speed streaks in the turbulent boundary layer. When the drag increase occurs, only pseudo-local spanwise oscillation is observed without a formation of a wide low-speed region. The pseudo-local spanwise oscillation appears to produce converging and diverging motions around the forcing-activation area. The induced streamwise vorticity layers are believed to enhance the effect of the sweep motion, which results in the increasing skin-friction drag. 2009 Thesis (University of Nottingham only) NonPeerReviewed application/pdf en arr https://eprints.nottingham.ac.uk/10710/1/Turbulent_flow_control_using_travelling_wave.pdf Xu, Peng (2009) Turbulent flow control using spanwise travelling wave via Lorentz forcing. PhD thesis, University of Nottingham. |
| spellingShingle | Xu, Peng Turbulent flow control using spanwise travelling wave via Lorentz forcing |
| title | Turbulent flow control using spanwise travelling wave via Lorentz forcing |
| title_full | Turbulent flow control using spanwise travelling wave via Lorentz forcing |
| title_fullStr | Turbulent flow control using spanwise travelling wave via Lorentz forcing |
| title_full_unstemmed | Turbulent flow control using spanwise travelling wave via Lorentz forcing |
| title_short | Turbulent flow control using spanwise travelling wave via Lorentz forcing |
| title_sort | turbulent flow control using spanwise travelling wave via lorentz forcing |
| url | https://eprints.nottingham.ac.uk/10710/ |