Multi-scale interactions in a compressible boundary layer

ABSTRACT

The properties of spectral subranges of scales in a boundary layer at Mach=2.3 and friction Reynolds number Reτ = 570 are investigated by analysing DNS data. One major aim is to examine whether footprinting and modulation of small-scale near-wall motions by outer large structures, observed at high Reynolds numbers, also pertain to this low-Reynolds-number case, or whether the logarithmic layer simply contains a continuous hierarchy of motions without specific outer scales playing a distinctive role. To this end, the spectrum of scales is decomposed into modes by application of the “Empirical Mode Decomposition”. The properties of different scales are then investigated by means of spectra, maps of isotropy/anisotropy parameters, the premultiplied derivative of the second-order structure function, correlation coefficients and joint probability density function (PDF), the last constructed from conditionally sampled data for the small-scale motions within the large-scale footprints. A clear commonality is identified between interactions in high-Reynolds-number channel flow and the present low-Reynolds-number boundary layer.

KEYWORD:

• Turbulent boundary layers

Acknowledgements

L. Agostini, J. Poggie and N. Bisek appreciate the sponsorship of the Air Force Office of Scientific Research (Monitor: Dr. I. Leyva). D. Gaitonde is partly supported by the Collaborative Center for Aeronautical Sciences. Large scale simulations have been performed with grants on the DOD HPCMP machines at AFRL, ERDC and NAVO. Post-processing work has been performed at the Ohio Supercomputer Center.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Air Force Office of Scientific Research; Collaborative Center for Aeronautical Sciences; AFRL, ERDC and NAVO.