---
_id: '10820'
abstract:
- lang: eng
  text: Streaky structures in the boundary layers are often generated by surface roughness
    elements and/or free-stream turbulence, and are known to have significant effects
    on boundary-layer instability. In this paper, we investigate the impact of two
    forms of streaks on the instability of supersonic boundary layers. The first concerns
    the streaks generated by an array of spanwise periodic and streamwise elongated
    surface roughness elements, and our interest is how these streaks influence the
    lower-branch viscous first modes, whose characteristic wavelength and frequency
    are on the classical triple-deck scales. By adapting the triple-deck theory in
    the incompressible regime to the supersonic one, we first derived a simplified
    system which allows for efficient calculation of the streaks. The asymptotic analysis
    simplifies a bi-global eigenvalue problem to a one-dimensional problem in the
    spanwise direction, showing that the instability is controlled at leading order
    solely by the spanwise-dependent wall shear. In the fundamental configuration,
    the streaks stabilize first modes at low frequencies but destabilize the high-frequency
    ones. In the subharmonic configuration, the streaks generally destabilize the
    first mode across the entire frequency band. Importantly, the spanwise even modes
    are of radiating nature, i.e. they emit acoustic waves spontaneously to the far
    field. Streaks of the second form are generated by low-frequency vortical disturbances
    representing free-stream turbulence. They alter the flow in the entire layer and
    their effects on instability are investigated by solving the inviscid bi-global
    eigenvalue problem. Different from the incompressible case, a multitude of compressible
    instability modes exists, of which the dominant mode is an inviscid instability
    associated with the spanwise shear. In addition, there exists a separate branch
    of instability modes that have smaller growth rates but are spontaneously radiating.
acknowledgement: The work is supported by the National Key Research and Development
  Program of China (No. 2016YFA0401200), the National Natural Science Foundation of
  China (Grant Nos. 91952202 and 11402167).
article_processing_charge: No
author:
- first_name: Jianxin
  full_name: Liu, Jianxin
  last_name: Liu
- first_name: Elena
  full_name: Marensi, Elena
  id: 0BE7553A-1004-11EA-B805-18983DDC885E
  last_name: Marensi
- first_name: Xuesong
  full_name: Wu, Xuesong
  last_name: Wu
citation:
  ama: 'Liu J, Marensi E, Wu X. Effects of streaky structures on the instability of
    supersonic boundary layers. In: Sherwin S, Schmid P, Wu X, eds. <i>IUTAM Laminar-Turbulent
    Transition</i>. Vol 38. 1st ed. IUTAM Bookseries. Cham: Springer Nature; 2022:587-598.
    doi:<a href="https://doi.org/10.1007/978-3-030-67902-6_51">10.1007/978-3-030-67902-6_51</a>'
  apa: 'Liu, J., Marensi, E., &#38; Wu, X. (2022). Effects of streaky structures on
    the instability of supersonic boundary layers. In S. Sherwin, P. Schmid, &#38;
    X. Wu (Eds.), <i>IUTAM Laminar-Turbulent Transition</i> (1st ed., Vol. 38, pp.
    587–598). Cham: Springer Nature. <a href="https://doi.org/10.1007/978-3-030-67902-6_51">https://doi.org/10.1007/978-3-030-67902-6_51</a>'
  chicago: 'Liu, Jianxin, Elena Marensi, and Xuesong Wu. “Effects of Streaky Structures
    on the Instability of Supersonic Boundary Layers.” In <i>IUTAM Laminar-Turbulent
    Transition</i>, edited by Spencer Sherwin, Peter Schmid, and Xuesong Wu, 1st ed.,
    38:587–98. IUTAM Bookseries. Cham: Springer Nature, 2022. <a href="https://doi.org/10.1007/978-3-030-67902-6_51">https://doi.org/10.1007/978-3-030-67902-6_51</a>.'
  ieee: 'J. Liu, E. Marensi, and X. Wu, “Effects of streaky structures on the instability
    of supersonic boundary layers,” in <i>IUTAM Laminar-Turbulent Transition</i>,
    1st ed., vol. 38, S. Sherwin, P. Schmid, and X. Wu, Eds. Cham: Springer Nature,
    2022, pp. 587–598.'
  ista: 'Liu J, Marensi E, Wu X. 2022.Effects of streaky structures on the instability
    of supersonic boundary layers. In: IUTAM Laminar-Turbulent Transition. vol. 38,
    587–598.'
  mla: Liu, Jianxin, et al. “Effects of Streaky Structures on the Instability of Supersonic
    Boundary Layers.” <i>IUTAM Laminar-Turbulent Transition</i>, edited by Spencer
    Sherwin et al., 1st ed., vol. 38, Springer Nature, 2022, pp. 587–98, doi:<a href="https://doi.org/10.1007/978-3-030-67902-6_51">10.1007/978-3-030-67902-6_51</a>.
  short: J. Liu, E. Marensi, X. Wu, in:, S. Sherwin, P. Schmid, X. Wu (Eds.), IUTAM
    Laminar-Turbulent Transition, 1st ed., Springer Nature, Cham, 2022, pp. 587–598.
conference:
  end_date: 2019-09-06
  location: London, United Kingdom
  name: IUTAM Symposium
  start_date: 2019-09-02
date_created: 2022-03-04T09:14:34Z
date_published: 2022-01-01T00:00:00Z
date_updated: 2023-08-03T12:54:59Z
day: '01'
department:
- _id: BjHo
doi: 10.1007/978-3-030-67902-6_51
edition: '1'
editor:
- first_name: Spencer
  full_name: Sherwin, Spencer
  last_name: Sherwin
- first_name: Peter
  full_name: Schmid, Peter
  last_name: Schmid
- first_name: Xuesong
  full_name: Wu, Xuesong
  last_name: Wu
external_id:
  isi:
  - '000709087600051'
intvolume: '        38'
isi: 1
language:
- iso: eng
month: '01'
oa_version: None
page: 587-598
place: Cham
publication: IUTAM Laminar-Turbulent Transition
publication_identifier:
  eisbn:
  - '9783030679026'
  eissn:
  - 1875-3493
  isbn:
  - '9783030679019'
  issn:
  - 1875-3507
publication_status: published
publisher: Springer Nature
quality_controlled: '1'
scopus_import: '1'
series_title: IUTAM Bookseries
status: public
title: Effects of streaky structures on the instability of supersonic boundary layers
type: book_chapter
user_id: 4359f0d1-fa6c-11eb-b949-802e58b17ae8
volume: 38
year: '2022'
...