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Experimental analysis of the effect of suction and step height on boundary-layer transition

Dimond, Benjamin and Costantini, Marco and Klein, Christian (2020) Experimental analysis of the effect of suction and step height on boundary-layer transition. In: Ninth IUTAM Symposium on Laminar-Turbulent Transition (pos122). IUTAM Symposium on Laminar-Turbulent Transition, 02.-06. September 2019, London, UK.

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Official URL: https://ssl.linklings.net/conferences/iutam-transition/iutamtransition2019_proceedings/views/includes/files/pos122s1.pdf


Laminar flow on transport aircraft is challenging to maintain in the presence of surface imperfections such as steps and/or gaps, which can occur at structural joints. A substantial delay of laminar-turbulent transition, however, can be achieved by suction. This work focuses on the influence of suction on transition in the presence of forward- and backward-facing steps. Systematic experimental investigations were performed in the low-turbulence Cryogenic Ludwieg-Tube Goettingen for large Reynolds numbers (chord Reynolds numbers up to 16 Million), Mach numbers from 0.35 to 0.77 and various stream-wise pressure gradients. The examined wind-tunnel model was a two-dimensional flat plate, designed to have a large area of uniform pressure gradient on the surface of interest (upper side of the model). The model consisted of two main parts that could be assembled with shims of different thickness to obtain sharp steps at 35% of the model chord length. Alignment pins enabled a streamwise displacement to achieve a gap directly upstream of the steps. Suction was achieved passively by exploiting the pressure difference between upper and lower side of the model, induced by the model’s geometry. Depending on the free stream conditions, suction rates of q = vD/d*U of up to around 1 were obtained with average suction velocity v, gap width D, computed displacement thickness d* and the freestream velocity U. Transition was determined non-intrusively by means of Temperature-Sensitive Paint (TSP). Furthermore, the model was equipped with pressure taps to obtain a streamwise pressure distribution. The average suction velocity v was calculated with the help of additional pressure taps installed along the gap inside of the model. The investigation comprised of a reference configuration (without installed step and gap), a gap configuration without step, two forward-facing steps with step Reynolds numbers up to 4800 and a backward-facing step with step Reynolds numbers up to 2400. Compared to the reference configuration, the implemented surface imperfections caused transition to occur at a more upstream location. With additional suction however, transition was significantly shifted downstream and even overcompensated the adverse effect of step and gap, as transition was detected further downstream than for the reference configuration. Detailed results including additional numerical considerations on linear stability analysis will be provided and discussed in the final version of this contribution.

Item URL in elib:https://elib.dlr.de/129301/
Document Type:Conference or Workshop Item (Poster)
Additional Information:Proceedings: Following the theme of previous IUTAM Transition symposia, papers will publish in a peer-reviewed conference proceedings. The IUTAM Transition 2019 proceedings will be published by Springer. Poster Proceedings online - Abstract online E2 https://ssl.linklings.net/conferences/iutam-transition/iutamtransition2019_proceedings/views/by_sub_type.html
Title:Experimental analysis of the effect of suction and step height on boundary-layer transition
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Dimond, Benjaminbenjamin.dimond (at) dlr.deUNSPECIFIED
Costantini, Marcomarco.costantini (at) dlr.dehttps://orcid.org/0000-0003-0642-0199
Klein, Christianchristian.klein (at) dlr.dehttps://orcid.org/0000-0001-7592-6922
Journal or Publication Title:Ninth IUTAM Symposium on Laminar-Turbulent Transition
Refereed publication:Yes
Open Access:Yes
Gold Open Access:No
In ISI Web of Science:No
Keywords:Laminar-Turbulent Transition, Suction, Surface Imperfections, Temperature-Sensitive Paint
Event Title:IUTAM Symposium on Laminar-Turbulent Transition
Event Location:London, UK
Event Type:international Conference
Event Dates:02.-06. September 2019
Organizer:Imperial College London
Institution:Deutsches Zentrum für Luft- und Raumfahrt e.V.
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 - Simulation and Validation
Location: Göttingen
Institutes and Institutions:Institute for Aerodynamics and Flow Technology > Experimental Methods, GO
Deposited By: Micknaus, Ilka
Deposited On:11 Oct 2019 13:38
Last Modified:10 Jun 2020 19:23

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