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Prediction of laminar-turbulent transition on helicopter rotors in forward flight using the U/RANS solver TAU with an approximate boundary layer method

Heister, C. C. (2016) Prediction of laminar-turbulent transition on helicopter rotors in forward flight using the U/RANS solver TAU with an approximate boundary layer method. DLR-Interner Bericht. DLR-IB-AS-BS-2016-45, 51 S.

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Abstract

The simulation capabilities of the U/RANS solver TAU of DLR have been successfully extended in order to predict the laminar-turbulent transition onset within unsteady rotor simulations. Therefore the existing TAU-Transition module has been Extended by an interface to an approximate rotor blade transition method (RBT code) for helicopter applications. Transition can be empirically predicted due to Tollmien- Schlichting waves, laminar separation bubbles, crossflow, bypass instabilities and attachment line transition. In order to study the effects of blade-wake/vortexinteractions, the turbulence level encountered by a rotor blade can be detected from the URANS solution. For the laminar flow airfoil NLF(1)-0416 the transition positions could be reproduced in close agreement to the experiment. The experiment of the swept wing element NLF(2)-0415 demonstrates the excitation of crossflow instabilities and could be reproduced in good agreement to the solution of a differential boundary layer code. A laminar-turbulent URANS simulation of a helicopter rotor in forward flight (GOAHEAD ONERA 7AD) was successfully demonstrated using the new TAU-TM/RBT process chain. The transition on the upper side generally occurred due to laminar separation bubbles or Tollmien- Schlichting instabilities. On the lower side of the rotor blade the transition Locations showed a large movement during the rotor revolution due to the collective pitch settings. Crossflow instabilities were predicted in areas with highly yawed flow. Blade-wake/vortex interactions triggered bypass transition and resulted in locally reduced laminar flow. For the present test case the laminar flow at the rotor blades reduced the required rotor power by -4.5% compared to a fully turbulent simulation. The rotor thrust remained practically unaffected.

Item URL in elib:https://elib.dlr.de/103256/
Document Type:Monograph (DLR-Interner Bericht)
Title:Prediction of laminar-turbulent transition on helicopter rotors in forward flight using the U/RANS solver TAU with an approximate boundary layer method
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Heister, C. C.christoph.heister (at) dlr.deUNSPECIFIED
Date:26 February 2016
Refereed publication:No
Open Access:No
Gold Open Access:No
In SCOPUS:No
In ISI Web of Science:No
Number of Pages:51
ISSN:1614-7790
Status:Published
Keywords:helicopter, rotor, blade, boundary layer, code, laminar, turbulent, transition, TAU, CFD, U/RANS
Institution:Deutsches Zentrum für Luft- und Raumfahrt (DLR)
Department:Hubschrauber
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Aeronautics
HGF - Program Themes:rotorcraft
DLR - Research area:Aeronautics
DLR - Program:L RR - Rotorcraft Research
DLR - Research theme (Project):L - The Virtual Aerodynamic Rotorcraft
Location: Braunschweig
Institutes and Institutions:Institute of Aerodynamics and Flow Technology > Helicopters
Deposited By: Heister, Christoph
Deposited On:01 Mar 2016 14:50
Last Modified:23 Dec 2016 11:30

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