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

Content Provider	Springer Nature Link
Author	Giglmaier, M. Quaatz, J. F. Gawehn, T. Gülhan, A. Adams, N. A.
Copyright Year	2013
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 $$\Delta z=O(10^{-4})$$ 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 $$f= O(10^5) \hbox {s}^{-1}$$ . The corresponding time scale $$\tau $$ (s) is 16 times higher than the characteristic time scale $$\tau _\delta =\delta /U_\infty $$ of the boundary layer given by the ratio of the boundary layer thickness $$\delta $$ directly ahead of the shock and the undisturbed free stream velocity $$U_\infty $$ . 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.
Starting Page	139
Ending Page	156
Page Count	18
File Format	PDF
ISSN	09381287
Journal	Shock Waves
Volume Number	24
Issue Number	2
e-ISSN	14322153
Language	English
Publisher	Springer Berlin Heidelberg
Publisher Date	2013-10-19
Publisher Place	Berlin, Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Pseudo-shock system Shock oscillation CFD Shock wave–turbulent boundary layer interaction Engineering Thermodynamics, Heat and Mass Transfer Fluid- and Aerodynamics Engineering Fluid Dynamics Thermodynamics Acoustics Condensed Matter Physics
Content Type	Text
Resource Type	Article
Subject	Physics and Astronomy Mechanical Engineering

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