8/11/2019 Engi 0851 ILLI Sebastian
1/1
Transonic Tail Buffet Simulations on a Passenger Aircraft
Sebastian Illi, Thorsten Lutz and Ewald Krmer
Institute for Aerodynamics and Gas Dynamics, University of
Stuttgart, Pfaffenwaldring 21, 70569 Stuttgart
Introduction
The effect of the three-dimensional nature of the flow over
anaircraft wing in the transonic regime during shock induced
stallconditions is relatively poorly understood. The focus of
theinvestigations, which have been conducted at the EPCCduring the
HPC Europa 2 call in 2012, lay in the simulation ofthis phenomenon
of a common passenger aircraft using theDLR TAU code [1]. The
horizontal and vertical tail planes aswell as the wing and fuselage
of the aircraft were included inthis simulation, allowing to
simulate the interaction betweenthe turbulent separated structures
originating from the mainwing and the horizontal tail plane (HTP).
The interaction leadsto a phenomenon known as tail buffet, and is
thought to beable to generate significant load fluctuations on the
HTP which
can be safety critical.
Mesh generation
A hybrid mesh has been built by the German AerospaceCenter DLR
using the mesh generator Centaur. At the Instituteof Aerodynamics
and Gas Dynamics (University of Stuttgart) ablock suitable for
Delayed Detached Eddy Simulation (DDES)[2] was generated in Gridgen
around the expected separatedarea on the wing. Both meshes were
merged via the Chimaeraapproach. To reduce the mesh size and
therefore thecomputational resources that are required, only a
half-modelof the airplane was simulated. The large turbulent
structuresthat are created in the vicinity of the shock separation
of thewing need to be propagated successfully downstream to theHTP.
To achieve this, a highly resolved Cartesian block in the
area of the wake was included in the mesh.
Performance
For optimal performance the graph partitioner Chaco waslinked to
TAU to guarantee a proper partitioning. To performscaling test the
mesh was split into a large number of domainsranging from 128 up to
8192. Because of the relatively lowmemory per node and the big mesh
size (42 million points)128 domains was the smallest amount of
processors asimulation was able to run on the CRAY XE 6 HECToR.
TheTAU-Code performs well in a range of 128 to 2048 showing
ascaling performance of over 90% based on the results for 128cores.
Beyond this amount of cores the scaling efficiency isstill
acceptable showing 85% for 4096 and around 70% for8192 cores but
due to limited resources the production job
was run on 2048 cores.
Results
The simulations show a separation of the flow followed by ashock
movement in the outer section of the wing. The globalforce
coefficients also indicate this behavior oscillating at thesame
frequency. The results of the Detached Eddy Simulationand the
Spalart Allmaras turbulence model show goodaccordance. But a clear
change in the topology of theturbulent structures can be seen due
to the rapid drop in eddyviscosity in the LES area in the wake.
While the RANSmethod preserves large vortices originating in the
detachedarea and influencing the flow in the wake, the DES
showssmall turbulent structures propagating through the wake to
theHTP. The effect of these structures can also be seen in
thespectra monitored in the wake and on the surface of the
HTP.While the RANS model shows only a little bump in the
lowfrequency domain which is followed by very low amplitudes forthe
middle and high frequencies, the DDES preserves the
spectrum up to its cutoff wave length. Therefore the tail
buffeteffect in the DES can also be seen more clearly in
thevariances of the surface pressure distribution on the HTP.
Acknowledgement
The work was carried out under the HPC-EUROPA2 project(project
number: 228398) with the support of the EuropeanCommission -
Capacities Area - Research Infrastructures.This work made use of
the facilities of HECToR, the UK'snational high-performance
computing service, which isprovided by UoE HPCx Ltd at the
University of Edinburgh,Cray Inc and NAG Ltd, and funded by the
Office of Scienceand Technology through EPSRC's High End
ComputingProgramme.
References
[1] Gerhold, T., Overview of the Hybrid RANS Code TAU,Notes on
Numerical Fluid Mechanics and MultidisciplinaryDesign, Vol 89,
81-92, Kroll, N. and Fassbende, J. K., 2005
[2] Spalart, P. R. et al., A new version of
detached-eddysimulation, resistant to ambiguous grid densities,
TheoreticalComputational Fluid Dynamics, 20, 181-195, 2006
Figure 1:Scaling of the DLR-TAU code on HECToR
Figure 2:Turbulence visualizatzion using 2-iso-surfacesin the
wake
