Flow around a hemisphere-cylinder at high angle of attack and low Reynolds number. Part II: POD and DMD applied to reduced domains

Le Clainche Martinez, Soledad and Rodriguez, Daniel and Theofilis, Vassilis and Soria, Julio (2015). Flow around a hemisphere-cylinder at high angle of attack and low Reynolds number. Part II: POD and DMD applied to reduced domains. "Aerospace Science and Technology", v. 44 ; pp. 88-100. ISSN 1270-9638. https://doi.org/10.1016/j.ast.2014.10.009.

Description

Title: Flow around a hemisphere-cylinder at high angle of attack and low Reynolds number. Part II: POD and DMD applied to reduced domains
Author/s:
  • Le Clainche Martinez, Soledad
  • Rodriguez, Daniel
  • Theofilis, Vassilis
  • Soria, Julio
Item Type: Article
Título de Revista/Publicación: Aerospace Science and Technology
Date: July 2015
ISSN: 1270-9638
Volume: 44
Subjects:
Faculty: E.T.S. de Ingeniería Aeronáutica y del Espacio (UPM)
Department: Matemática Aplicada a la Ingeniería Aeroespacial
Creative Commons Licenses: Recognition - No derivative works - Non commercial

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Abstract

Three-dimensional direct numerical simulations (DNS) have been performed on a finite-size hemispherecylinder model at angle of attack AoA = 20◦ and Reynolds numbers Re = 350 and 1000. Under these conditions, massive separation exists on the nose and lee-side of the cylinder, and at both Reynolds numbers the flow is found to be unsteady. Proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) are employed in order to study the primary instability that triggers unsteadiness at Re = 350. The dominant coherent flow structures identified at the lower Reynolds number are also found to exist at Re = 1000; the question is then posed whether the flow oscillations and structures found at the two Reynolds numbers are related. POD and DMD computations are performed using different subdomains of the DNS computational domain. Besides reducing the computational cost of the analyses, this also permits to isolate spatially localized oscillatory structures from other, more energetic structures present in the flow. It is found that POD and DMD are in general sensitive to domain truncation and noneducated choices of the subdomain may lead to inconsistent results. Analyses at Re = 350 show that the primary instability is related to the counter rotating vortex pair conforming the three-dimensional afterbody wake, and characterized by the frequency St ≈ 0.11, in line with results in the literature. At Re = 1000, vortex-shedding is present in the wake with an associated broadband spectrum centered around the same frequency. The horn/leeward vortices at the cylinder lee-side, upstream of the cylinder base, also present finite amplitude oscillations at the higher Reynolds number. The spatial structure of these oscillations, described by the POD modes, is easily differentiated from that of the wake oscillations. Additionally, the frequency spectra associated with the lee-side vortices presents well defined peaks, corresponding to St ≈ 0.11 and its few harmonics, as opposed to the broadband spectrum found at the wake.

Funding Projects

TypeCodeAcronymLeaderTitle
FP7247651ICOMASEFUnspecifiedInstability and Control of Massively Separated Flows
Government of SpainTRA2012-34148UnspecifiedUnspecifiedMejoras del rendimiento aerodinámico de alas mediante control demecanismos de inestabilidad global

More information

Item ID: 40896
DC Identifier: http://oa.upm.es/40896/
OAI Identifier: oai:oa.upm.es:40896
DOI: 10.1016/j.ast.2014.10.009
Official URL: http://www.sciencedirect.com/science/article/pii/S1270963814002077
Deposited by: Memoria Investigacion
Deposited on: 29 Sep 2016 11:22
Last Modified: 05 Jun 2019 16:46
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