Evaluation and validation of incompressible flow simulations of an

Reliability of 2D and 3D simulations for incompressible flows in
OpenFOAM
Evaluation and validation of incompressible flow simulations of an airfoil with a droop nose
leading-edge device combined with an internally-blown Coanda flap using OpenFOAM
R. Radespiel, R. Seeman, Institut für Strö- model was shown to perform poorly for massively
mungsmechanik, TU Braunschweig
separated cases. For partially and fully attached
flows, the SA model yielded good physical results
that compared well with other more complex modIn Short
els.Figure 1 shows the flow behavior obtained for
• Evaluation of OpenFOAM against the existing TAU an actuated case at Mach number (Ma = 0.15) ussimulations in air to establish confidence.
ing Spalart-Allmaras turbulence model with jet momentum coefficient Cµ = 0.0379 and angle of attack,
• Assessment of different turbulence models for var- α = 5◦ . As the figure shows, these simulations reied Mach and Reynolds number.
sult in a quasi-steady flow, where the vortex over the
• Validation of the numerical approach against water- flap remains attached. Such behavior is not physical,
tunnel experiments. This involves, on the numer- and a highly unsteady flow should be expected, as
ical side, 3D RANS simulations that include the observed in the water tunnel experiments. Figure 2
tunnel walls. The test condition will be, in this way, shows a snapshot of the wakeflow where the shed
entirely reproduced in order to accurately compare vortices are clearly visible. This is only achieved under very low jet momentum coefficient, Cµ = 0.015
the results obtained by the two approaches.
and very high angle of attack, α = 17◦ .
Following the validation of OpenFOAM, this tool
This project is part of the Collaborative Research will be used for assessing different turbulence modCenter 880 (SFB 880), where the primary objec- els so that best suited model for the range of postive is the improvement of the flight performance of sible conditions can be determined. The numerical
commercial aircraft during take-off and landing. The approach involves 2D and 3D simulations of an airwing high-lift configuration is composed of an active foil. The computations will be based on the solution
internally-blown trailing-edge flap and a droop-nose of the Reynolds Averaged Navier Stokes equations
leading-edge device. The efficiency of the trailing- (RANS) in conjunction with the Spalart-Allmaras and
edge system has been assessed by numerous 2D Menter-SST turbulence model. In order to assess
and 3D RANS simulations, as well as wind-tunnel the performance of OpenFOAM againt TAU, 2D simexperiments. However, the high circulation gener- ulation of the airfoil with farfield conditions using
ated by the active flap makes compulsory the use Spalart-Allmaras(SA) turbulence model and air as a
of a leading-edge stall protection device in order to medium will be first performed. In the next step, 3D
bring the stall angle of attack to a suitable operative simulation will be performed with the water experirange. For this purpose a droop-nose leading-edge ment conditions.
device was developed by means of 2D RANS simulations. These simulations were performed using
TAU-code developed by DLR [1], which computes Need for computing resources:
the 3 dimensional compressible Reynolds-average
Navier-Stokes equations on either unstructured or For the simulations to be performed in OpenFOAM,
hybrid grids. The TAU-code performs well for com- large grid size along with very small time steps
−6
pressible flows but is unsuitable for incompressible (∼ 10 s) is going to be used. This increases the
flows. Some of these incompressibility issues can be computation cost since with decreased time step
remedied with preconditioning,however, it is usually high number of grid points are required for the satisassociated with a certain level of uncertainty. Open- faction of grid resolution requirements. The compuFOAM is a good alternative which is suitable for tations required for the present project exceed the
both compressible as well as incompressible flows. internal capacity of the institute, because of the large
Therefore, the first objective of the present work number of points needed to simulate the complex
is the evaluation of OpenFOAM against the exiting geometries and HLRN resources are required for
TAU simulations results. Another critical component the feasibility of the current project.
affecting the accuracy of numerical simulations is
the turbulence model. Various turbulence models WWW
have been already tested during the project. The SA http://www.tu-brauncshweig.de/ism
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Figure 2: 3D simulation of the actuated case: Ma= 0.15, Cµ = 0.015, α = 17◦
More Information
[1] Schwamborn, Dieter and Gerhold, Thomas
and Heinrich, Ralf, The DLR TAU-code: Recent
applications in research and industry 132,
ECCOMAS (2006).
Project Partners
Institut für Adaptronik und Funktionsintegration,
Braunschweig; Institut für Aerodynamik und Strömungstechnik, Braunschweig; Institut für Aerodynamik und Strömungstechnik, Göttingen; Institut für Aeroelastik, Göttingen; Institut für Antriebssysteme und Leistungselektronik, Hannover; InFigure 1: Numerical simulation of the actuated case: Ma= 0.15,
stitut für Faserverbundleichtbau und Adaptronik, Cµ = 0.0379, α = 5◦ .
Braunschweig; Institut für Flugantriebe und Strömungsmaschinen, Braunschweig; Institut für Flugexperimente, Weßling; Institut für Flugführung(IFF)
Braunschweig; Institut für Flugführung (FL), Braunschweig; Institut für Gasanalytik und Zustandsverhalten(F3.2), Braunschweig; Institut für Konstruktionstechnik, Braunschweig; Institut für Luft- und Raumfahrtsysteme, Braunschweig; Institut für Mikrotechnik, Braunschweig; Institut für Niedersächsisches
Forschungszentrum für Luftfahrt, Braunschweig; Institut für Oberflächentechnik, Braunschweig; iRMB,
Braunschweig; Institut für Statik, Braunschweig; Institut für Statik und Dynamik, Hannover; Institut für
Strömungsmechanik, Braunschweig; Institut für Turbomaschinen und Fluid-Dynamik, Hannover; Institut für Werkstoffe, Braunschweig; Institut für Wissenschaftliches Rechnen, Braunschweig
Funding
Sonderforschungsbereich 880
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