Interaction of noise disturbances and streamwise streaks

Abstract

Disturbance evolution in a boundary layer with streamwise streaks and random two-and three-dimensional noise of various amplitudes is studied via numerical simulations. The aim of the present work is to determine the impact of the interaction on the arising flow structures and, eventually, on the location and details of the breakdown to turbulence. It is shown that largescale 2D noise can be controlled via streaks, whereas the more general 3D noise configuration is prone to premature transition due to increased instability of the introduced streaks. It is interesting to note that the latter transition scenario closely resembles the flow structures found in bypass transition.A recent theoretical and numerical study by Cossu and Brandt [2] has shown that a substantial stabilisation of a boundary layer subject to essentially two-dimensional disturbances (i.e. Tollmien-Schlichting (TS) waves) can be achieved by a spanwise modulation of the mean flow, i.e. via superimposed streamwise streaks on the laminar Blasius flow. In particular, it has been shown both experimentally via finite-amplitude roughness [3] and later via large-eddy simulation (LES, [5]) that transition to turbulence can effectively by moved to a more downstream position via this essentially passive control mechanism. However, the disturbances considered in the mentioned studies have all had their maximum energy in two-dimensional (spanwise invariant) modes. It is therefore interesting to examine the interaction of streamwise streaks with disturbences of a more general nature, i.e. 2D and 3D random noise at various frequencies and (spanwise) wavenumbers.The present study uses a spectral numerical method [1] together with LES based on high-order filtering (ADM-RT model [6]), in a similar setup as presented in Ref. [5]. In particular, the computational domain starts at Re x = 32000 extending up to Re x = 590000. The streaks are introduced at the inlet as optimal disturbances computed from PSE (parabolised stability equations), subsequently evolving nonlinearly inside the domain. Conversely, the noise is forced within the computational domain at Re x = 60000 by a volume force close to the wall. Two frequency spectra of the noise are shown in Fig.

Bypass transition delay using oscillations of spanwise wall velocity

“…The setup is the same as the one used in Ref. [45] to study the interaction of noise in the boundary layer with streamwise streaks. An identical setup is used in Ref.…”

Prediction of Streaks in Rectangular Jets

“…For instance, the shear layer characteristics dictate the formation of the Kelvin-Helmholtz wavepackets shown to be important in jet noise [1]. Elongated streamwise velocity perturbations called streaks are also present within shear layers and provide promising research avenues to achieve control of this jet noise [2].…”