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Experimental Investigation of Spanwise Periodic Surface Heating for Control of Crossflow-Dominated Laminar-Turbulent Transition

Barth, Hans Peter and Hein, Stefan (2019) Experimental Investigation of Spanwise Periodic Surface Heating for Control of Crossflow-Dominated Laminar-Turbulent Transition. In: Ninth IUTAM Symposium on Laminar-Turbulent Transition. IUTAM Symposium on Laminar-Turbulent Transition 2019, 2.-6. Sept. 2019, London, Großbritannien.

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Official URL: http://www.iutamtransition2019.org/

Abstract

Research into laminar-turbulent transition delay in three-dimensional boundary layers is motivated by the possible drag reduction of aircraft with swept wings. Saric et al. discovered a nonlinear transition-delaying mechanism which is now known as "Upstream Flow Deformation" (UFD). Because the effect can be triggered by artificially exciting an exponentially amplified instability mode, it has the potential to be used as an energetically very efficient method for boundary-layer stabilization compared to approaches such as distributed suction and other actuation concepts aimed at reducing the crossflow component of the laminar boundary layer. Saric et al. used discrete roughness elements to artificially excite a stationary instability mode as control mode. Naturally, the stabilizing nonlinear effects strongly depend on initial conditions which motivates the research into actuation concepts better suited for controlling them. Therefore, different actuation methods with a controllable excitation amplitude have already been investigated, such as discrete pneumatic and plasma actuation. In the case of pneumatic actuation, the UFD effect has been successfully employed for transition delay, while no such successful attempt with a plasma actuator is known to the authors. In the present work, an alternative actuation concept based on spanwise periodic surface heating and its effect on the boundary-layer flow field were investigated using the redesigned DLR swept-flat plate experiment at a Reynolds number of Re=1.6*10^6 in the 1MG wind tunnel in Göttingen. An actuator has been developed which can create a spanwise periodic wall-temperature distribution at 8 different chordwise positions to introduce an initial disturbance into the boundary-layer flow field. Hot-wire anemometry in the boundary layer downstream has shown the successful excitation of the control mode and quantified its amplitude depending on the actuation position and the amplitude of the surface-temperature periodicity. For a selected combination of actuation position and amplitude, the impact on the boundary layer downstream of the actuator was investigated in detail. The unsteady boundary-layer flow field was sampled at 14 chordwise, 60 spanwise and 30 wallnormally distributed positions for a duration of 4 seconds each with a sampling rate of 32 kHz. This allows for the quantitative characterization of the relevant stationary and non-stationary phenomena across the complete transition scenario, including the onset of secondary instabilities and subsequent transition itself. Particular attention is paid in the presentation to the development of travelling crossflow instabilities because their inadvertent elevation by other actuation methods has been known to cause the UFD method to fail.

Item URL in elib:https://elib.dlr.de/126127/
Document Type:Conference or Workshop Item (Speech)
Title:Experimental Investigation of Spanwise Periodic Surface Heating for Control of Crossflow-Dominated Laminar-Turbulent Transition
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Barth, Hans PeterPeter.Barth (at) dlr.dehttps://orcid.org/0000-0002-4513-5684
Hein, StefanStefan.Hein (at) dlr.deUNSPECIFIED
Date:3 September 2019
Journal or Publication Title:Ninth IUTAM Symposium on Laminar-Turbulent Transition
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In SCOPUS:No
In ISI Web of Science:No
Status:Published
Keywords:Laminar-turbulent Transition, Crossflow, Upstream Flow Deformation, Transition control, Surface heating, Actuation
Event Title:IUTAM Symposium on Laminar-Turbulent Transition 2019
Event Location:London, Großbritannien
Event Type:international Conference
Event Dates:2.-6. Sept. 2019
Organizer:International Union of Theoretical and Applied Mechanics
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Aeronautics
HGF - Program Themes:fixed-wing aircraft
DLR - Research area:Aeronautics
DLR - Program:L AR - Aircraft Research
DLR - Research theme (Project):L - Flight Physics
Location: Göttingen
Institutes and Institutions:Institute for Aerodynamics and Flow Technology > High Speed Configurations, GO
Deposited By: Barth, Hans Peter
Deposited On:17 Sep 2019 16:19
Last Modified:17 Sep 2019 16:19

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