| 1. |
- Örlü, Ramis, 1977-, et al.
(författare)
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Towards canonical adverse-pressure-gradient turbulent boundary layers
- 2017
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Ingår i: 10th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2017. - : International Symposium on Turbulence and Shear Flow Phenomena, TSFP10. - 9780000000002
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Konferensbidrag (refereegranskat)abstract
- The present investigation focuses on the concerted investigation of pressure gradient and streamwise curvature effects on turbulent boundary layers. In particular, a number of direct and large-eddy simulations covering a wide range of pressure gradient parameters and streamwise histories on flat and curved surfaces is performed and will be compared with wind-tunnel experiments utilising hot-wire anemometry and particle image velocimetry that overlap and extend the Reynolds number range. Results are aimed at isolating the effects of pressure gradients, streamwise curvature and streamwise (pressure gradient) histories as well as Reynolds number, which have traditionally inhibited to draw firm conclusions from the available data.
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| 2. |
- Sanmiguel Vila, C., et al.
(författare)
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Identifying well-behaved turbulent boundary layers
- 2017
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Ingår i: Progress in Turbulence VII. - Cham : Springer Science+Business Media B.V.. - 9783319579337 ; , s. 67-72
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Konferensbidrag (refereegranskat)abstract
- This paper presents a study focused on the development of zero-pressure-gradient turbulent boundary layers (ZPG TBL) towards well-behaved conditions in the low Reynolds-number range. A new method to assess the length required for the ZPG TBL to exhibit well-behaved conditions is proposed. The proposed method is based on the diagnostic-plot concept (Alfredsson et al., Phys. Fluids, 23:041702, 2011), which only requires mean and turbulence intensity measurements in the outer region of the boundary layer. In contrast to the existing methods which rely on empirical skin-friction curves, shape-factor or wake-parameter, the quantities required by this method are generally much easier to measure. To test the method, the evolution of six different tripping configurations, including weak, late and strong overtripping, are studied in a wind-tunnel experiment to assess the convergence of ZPG TBLs towards well-behaved conditions in the momentum-thickness based Reynolds-number range 500 < Reθ < 4000.
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| 3. |
- Sanmiguel Vila, C., et al.
(författare)
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On the identification of well-behaved turbulent boundary layers
- 2017
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Ingår i: Journal of Fluid Mechanics. - : Cambridge University Press. - 0022-1120 .- 1469-7645. ; 822, s. 109-138
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Tidskriftsartikel (refereegranskat)abstract
- This paper introduces a new method based on the diagnostic plot (Alfredsson et al., Phys. Fluids, vol. 23, 2011, 041702) to assess the convergence towards a well-behaved zero-pressure-gradient (ZPG) turbulent boundary layer (TBL). The most popular and well-understood methods to assess the convergence towards a well-behaved state rely on empirical skin-friction curves (requiring accurate skin-friction measurements), shape-factor curves (requiring full velocity profile measurements with an accurate wall position determination) or wake-parameter curves (requiring both of the previous quantities). On the other hand, the proposed diagnostic-plot method only needs measurements of mean and fluctuating velocities in the outer region of the boundary layer at arbitrary wall-normal positions. To test the method, six tripping configurations, including optimal set-ups as well as both under- and overtripped cases, are used to quantify the convergence of ZPG TBLs towards well-behaved conditions in the Reynolds-number range covered by recent high-fidelity direct numerical simulation data up to a Reynolds number based on the momentum thickness and free-stream velocity of approximately 4000 (corresponding to 2.5 m from the leading edge) in a wind-tunnel experiment. Additionally, recent high-Reynolds-number data sets have been employed to validate the method. The results show that weak tripping configurations lead to deviations in the mean flow and the velocity fluctuations within the logarithmic region with respect to optimally tripped boundary layers. On the other hand, a strong trip leads to a more energized outer region, manifested in the emergence of an outer peak in the velocity-fluctuation profile and in a more prominent wake region. While established criteria based on skin-friction and shape-factor correlations yield generally equivalent results with the diagnostic-plot method in terms of convergence towards a well-behaved state, the proposed method has the advantage of being a practical surrogate that is a more efficient tool when designing the set-up for TBL experiments, since it diagnoses the state of the boundary layer without the need to perform extensive velocity profile measurements.
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