Experimental and theoretical investigation of the nonmodal growth of steady streaks in a flat plate boundary layer

By J. Fransson, Luca Brandt, A. Talamelli, C. Cossu. 2004

218 citations recorded by the source corpus.

An experimental and theoretical investigation aimed at describing the nonmodal growth of steady and spanwise periodic streamwise streaks in a flat plate boundary layer is presented. Stable laminar streaks are experimentally generated by means of a spanwise periodic array of small cylindrical roughness elements fixed on the plate. The streamwise evolution of the streaks is measured and it is proved that, except in a small region near the roughness elements, they obey the boundary layer scalings. The maximum achievable amplitude is mainly determined by the relative height of the roughness elements. Results are compared with numerical simulations of optimal and suboptimal boundary layer streaks. The theory is able to elucidate some of the discrepancies recently noticed between experimentally realizable nonmodal growth and optimal perturbation theory. The key factor is found to be the wall normal location and the extension of the laminar standing streamwise vortices inducing the streaks. The differences among previous experimental works can be explained by different dominating streak generation mechanisms which can be linked to the geometry and to the ratio between the roughness height and the boundary layer scale.

Subfields: Computational Mechanics, Environmental Engineering, Global and Planetary Change

View Paper: https://www.semanticscholar.org/paper/4bcd315b75034eec12b7f3ad19fa554543e2334d

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Computational Mechanics

1. Y. Hwang
2. C. Cossu
3. Luca Brandt
4. J. Fransson
5. G. Pujals
6. S. Depardon
7. B. McKeon
8. P. Henrik Alfredsson

In Environmental Engineering

1. Y. Hwang
2. C. Cossu
3. G. Pujals
4. P. Henrik Alfredsson
5. J. Fransson
6. S. Depardon
7. B. McKeon
8. Luca Brandt

In Global and Planetary Change

1. Y. Hwang
2. C. Cossu
3. B. McKeon
4. G. Pujals
5. P. Henrik Alfredsson
6. J. Fransson
7. M. Matsubara
8. S. Depardon

Citations in the corpus

• Linear non-normal energy amplification of harmonic and stochastic forcing in the turbulent channel flow (2010, methodology): “In the experiments of Fransson et al. (2004), finite-amplitude streamwise streaks with the optimal spanwise wavelength predicted by the linear optimal spatial transient growth analysis of Andersson, Berggren & Henningson (1999) have been artificially forced in the laminar Blasius boundary layer.”
• Optimal transient growth and very large–scale structures in turbulent boundary layers (2008, background): “In passive control applications (e.g. Fransson et al. 2004, 2006) vortices are forced downstream at an already large Reδ∗ , and in this case the parallel flow theories should give even more accurate predictions.”
• Transition induced by free-stream turbulence (2005, background): “Fransson et al. (2004) investigated stationary and steady streaks, generated by means of an array of roughness elements in the spanwise direction.”