Combining time-resolved multi-point and spatially-resolved measurements for the recovering of very-large-scale motions in high Reynolds number turbulent boundary layer
Résumé
A methodology to recover very-large-scale motions based on the combination of time-resolved multi-point measurements and spatially-resolved full field information is here presented and applied to a high Reynolds number turbulent boundary layer flow developing over a flat plate. These very-large-scale motions are characterised by a large degree of persistence, both in time and space, and are believed to play an active role in the development of turbulence in the near-wall region (Bandyopadhyay and Hussain, 1984; Chung and McKeon, 2010; Hutchins and Marusic, 2007; Marusic et al., 2010). Due to the very large streamwise extent of these structures and of their meandering nature, point-measurement techniques or low time-resolved full field techniques such as Particle Image Velocimetry (PIV) offer a limited view when used alone. In the present paper, a time-resolved estimate of the full velocity vector field in a spanswise/wall-normal plane is obtained by combining low-repetition two-dimensional stereo-PIV measurements and a two-dimensional rake of 143 single hot-wire probes sampled at 30 kHz. The latter is used to animate the PIV data at a high sampling rate by implementing an extended version of the complementary technique (Bonnet et al., 1994) which combines Proper Orthogonal Decomposition (POD) and multi-time Linear Stochastic Estimation (mLSE) (Kerhervé, 2012). The results show the potential of the methodology to extract large-scale motions in turbulent boundary layer. This paves the way for further advanced time-resolved description of the spatially developing very-large-scale structures populating the logarithmic region. In addition, the main characteristics of the structures observed are found to be well consistent with that described in literature, validating the methodology and the time-resolved data-set built.