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Numerical and experimental investigations of pseudo-shock systems in a planar nozzle: impact of bypass mass flow due to narrow gaps

Giglmaier, Marcus and Quaatz, Jan Frederik and Gawehn, Thomas and Gülhan, Ali and Adams, N. A. (2014) Numerical and experimental investigations of pseudo-shock systems in a planar nozzle: impact of bypass mass flow due to narrow gaps. Shock Waves, 24 (2), pp. 139-156. Springer. DOI: 10.1007/s00193-013-0475-2 ISSN 0938-1287

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Official URL: http://dx.doi.org/10.1007/s00193-013-0475-2

Abstract

During previous investigations on pseudo-shock systems, we have observed reproducible differences between measurement and simulations for the pressure distribution as well as for size and shape of the pseudo-shock system. A systematic analysis of the deviations leads to the conclusion that small gaps of Δz=O(10 −4 ) m between quartz glass side walls and metal contour of the test section are responsible for this mismatch. This paper describes a targeted experimental and numerical study of the bypass mass flow within these gaps and its interaction with the main flow. In detail, we analyze how the pressure distribution within the channel as well as the size, shape and oscillation of the pseudo-shock system are affected by the gap size. Numerical simulations are performed to display the flow inside the gaps and to reproduce and explain the experimental results. Numerical and experimental schlieren images of the pseudo-shock system are in good agreement and show that especially the structure of the primary shock is significantly altered by the presence of small gaps. Extensive unsteady flow simulations of the geometry with gaps reveal that the shear layer between subsonic gap flow and supersonic core flow is subject to a Kelvin–Helmholtz instability resulting in small pressure fluctuations. This leads to a shock oscillation with a frequency of f=O(10 5 )s −1 . The corresponding time scale τ (s) is 16 times higher than the characteristic time scale τ δ =δ/U ∞ of the boundary layer given by the ratio of the boundary layer thickness δ directly ahead of the shock and the undisturbed free stream velocity U ∞ . To assess the reliability of our numerical investigations, the paper includes a grid study as well as an extensive comparison of several RANS turbulence models and their impact on the predicted shape of pseudo-shock systems.

Item URL in elib:https://elib.dlr.de/88387/
Document Type:Article
Additional Information:Online erschienen am 19. Oktober 2013
Title:Numerical and experimental investigations of pseudo-shock systems in a planar nozzle: impact of bypass mass flow due to narrow gaps
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Giglmaier, MarcusTU MünchenUNSPECIFIED
Quaatz, Jan FrederikTU MünchenUNSPECIFIED
Gawehn, ThomasAS-HYPUNSPECIFIED
Gülhan, AliAS-HYPUNSPECIFIED
Adams, N. A.TU MünchenUNSPECIFIED
Date:1 March 2014
Journal or Publication Title:Shock Waves
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:24
DOI :10.1007/s00193-013-0475-2
Page Range:pp. 139-156
Publisher:Springer
ISSN:0938-1287
Status:Published
Keywords:Pseudo-shock system Shock oscillation CFD Shock wave–turbulent boundary layer interaction
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Space Transport
DLR - Research area:Raumfahrt
DLR - Program:R RP - Raumtransport
DLR - Research theme (Project):R - Raumfahrzeugsysteme - Numerische Verfahren und Simulation
Location: Köln-Porz
Institutes and Institutions:Institute of Aerodynamics and Flow Technology > Über- und Hyperschalltechnologien
Deposited By: Gawehn, Dr.-Ing. Thomas
Deposited On:25 Mar 2014 08:52
Last Modified:10 Jan 2019 15:50

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