Lehrstuhl für Fluidmechanik - Technische Universität München


22 Φεβ 2014 (πριν από 2 χρόνια και 8 μήνες)

74 εμφανίσεις




Seminar für Strömungstechnik

SS 2002


Technische Universität München, Garching, Boltzmannstr. 15

Seminarraum des Lehrstuhls für Fluidmechanik

e 6, 1. Stock, Raum 1639



Dienstag, 16.30 Uhr


30. April 2002

Dr. Patrick Ilg

Institut für Theoretische Physik

TU Berlin

“Reduced description of polymer dy
turbulent flow”


Dr. Anne LeDuc

Fachgebiet Strömungsmechanik

Technische Universität München

“Direct numerical simulation of insta

b楬楴楥猠楮i瑨É⁣ mé牥r獩扬s⁳ Éét

Hiemenz flow”


Prof. Sutanu Sarkar

nical and Aerospace Engineering

University of California at San Diego, U.S.A.

“Turbulent reacting shear flows: DNS
and LES“


18. Juni 2002

Prof. Mohamed Gad

Department of Aerospace and

Mechanical Engineering

University of Notre Dame, U.S.A.

“Compliant coatings: What works and

what doesn’t


Prof. Dr.
Ing. Johannes Janicka

FG Energie

und Kraftwerkstechnik

TU Darmstadt

Combustion Systems”


Dr. Jörg Schumacher

Fachbereich P

Universität Marburg

“Statistical and structural investigations
in homogeneous shear flow“


Prof. Dr. Jean
Luc Reboud

École Nationale d’Ingénieurs de Saint


“Numerical simulat
楯n of⁣ v楴i瑩tg

flow behaviour”


䑩É⁄ zÉn瑥n

Friedrich Laschka Schilling

und wissenschaftlichen Mitarbeiter


Kurzfassungen der Vorträge

Dr. Patrick Ilg:

„Reduced description of polymer dynamics in elongational and in wall turbulent flow“

Present day computer simulations of turbulent drag reduction by polymer additives
rely on simplified constitutive equations. The present study focuses o
n the validity of
the constitutive equation in elongational and in wall turbulent flow. It is found, that the
stretch transition in elongational flow causes serious problems concerning the
validity of the constitutive equation, while these problems se
em to be less severe in
turbulent flow.

Dr. Anne LeDuc:

„Direct numerical simulation of instabilities in the compressible swept Hiemenz flow“

The swept Hiemenz flow is a Navier
Stokes solution of the incompressible flow
impinging on a swept flat plate.

Its linear stability has been analytically investigated
by Hall et al. 1984 in the framework of Görtler
Hämmerlin perturbation modes and
relates to the transition processes on a swept wing. The hydrodynamic stability of its
weakly compressible counterpart

is studied here using a temporal compressible
direct numerical simulation. In the compressible case, the presence of three
perturbation modes (vortical, solely present in the incompressible case, acoustic and
entropic), coupled by the non
uniform base fl
ow, can significantly alter the
perturbation dynamics. We will thus assess the validity of the Görtler
assumption for a moderate Mach number and a supercritical Reynolds number. To
this end, the modes obtained from small stochastic perturbations
initially inserted in
the boundary layer will be presented. The influence of the initial nature and location
of the perturbation as well as the crucial importance of the thermal wall boundary
condition (adiabatic or isothermal) will be discussed.

Sutanu Sarkar:

“Turbulent reacting shear flows: DNS and LES“

DNS of a turbulent methane/air shear layer with large heat release has been recently
performed. This study provides results characterizing aspects of the mixture fraction
field pertinent to the

reaction rate that are not easily available by other means. We
will use the DNS results to illustrate how mixing is influenced by heat release and to
discuss some issues related to modeling turbulent combustion.

A challenge in LES of turbulent combustion

is accurate modeling of the strongly
nonlinear reaction rate term. A one
parameter model, essentially based on providing
additional physical information within the framework of mathematical reconstruction,
has been recently formulated. We will discuss o
ur ongoing evaluation of the model in
LES of a turbulent jet.


Prof. Mohamed Gad

“Compliant coatings: What works and what doesn’t“

Compliant coating research is one of those areas which experienced its fair share of
triumphs and debacles.

For o
ver forty years, the subject has fascinated, frustrated
and occasionally gratified scientists and engineers searching for methods to delay
turbulence transition, to reduce skin
friction drag in turbulent wall
flows, to quell vibrations,
and to suppress flow
induced noise.

In its simplest form, the
technique is passive, relatively easy to apply to an existing vehicle or device, and
perhaps not too expensive.

Through the years, however, claims for substantial drag
and noise reductions were
made, only to be later refuted when the results were more
critically examined.

There are several important issues with regard to the reliability of
available analytical, numerical and experimental results.

In this presentation, some of
these issues will be

addressed with the objective of elucidating the potential pitfalls to
newcomers to the field. Problem formulation with proper boundary conditions and
limitations of existing numerical simulations will be elaborated.

The effects of
background turbulence in

a wind or water tunnel, accurate drag measurements,
compliant wall motion, and the geometry and properties of the coating used will be
among the outstanding experimental issues discussed.

Attempts will be made to
explain some of the seemingly contradictor
y results available in the open literature.

Prof. Jean
Luc Reboud:

„Numerical simulation of cavitating flows in turbomachinery: Prediction of head
breakdown and unsteady flow behaviour”

The Turbomachinery and Cavitation team of LEGI (Grenoble) develops

models to take into account the cavitation phenomenon in turbomachinery for more
than 10 years, in collaboration with the French space agency CNES and the rocket
engine division of SNECMA
Moteurs. The final objective is to provide assistance to
the design and prevision of operating range of rocket engine turbopumps, taking into
account the steady state and unsteady effects of cavitation.

A single fluid model is used to describe the liquid
vapour mixture, with a mixture

varying in the f
low field between the vapour density and the liquid density
with respect to the local static pressure. A 2D numerical model of unsteady cavitation
was first developed at LEGI and was applied to cavitating flows around hydrofoils or
in Venturi type ducts. R
ecent applications to 2D inducer blade cascades predict the
unsteady behaviour of sheet cavities attached to the blades: under certain conditions
a rotating cavitation phenomenon is obtained, in good agreement with experimental
observations [PHD Courtot, 2
000]. A 3D numerical model is now developed from the
3DNS commercial code FINE/TURBO
. Cavitating flows in axial and centrifugal
pumps are calculated and the quasi
steady cavitating behaviours are compared with
experimental results [PHD Coutier

Prof. Dr.
Ing. Johannes Janicka:

Eddy Simulation of Combustion Systems“


Trotz wachsender Bemühungen um den Ausbau regenerativer Energiequellen wird
auch in den kommenden Jahrzehnten der überwiegende Teil der Energieerzeugung
durch fossil
e Energieträger gedeckt werden. Bei der notwendigen und unstrittigen
Entwicklung innovativer Energieerzeugungsverfahren ist die numerische Simulation
das zentrale Entwicklungswerkzeug.

Im Unterschied zu den bisher überwiegend verwendeten RANS
Modellen bi
etet die
Grobstruktursimulation (LES) im Grundsatz das Potenzial einer (nahezu)
allgemeingültigen Vorhersage von Ver

In dem Vortrag wird auf Stand und Perspektive der Verbrennungs
LES sowohl für
Diffusionsflammen als auch für Vormisch
flammen einge
gangen. Von besonderer
Bedeutung sind dabei die Effekte der Flammenstabilisierung und sog. „finite
chemistry effects“, die für die Schadstoffbildungsvorhersage bedeutsam sind.
Eingegangen wird weiterhin auf Fragen der Randbedingungen und auf
Behandlung von komplexen Geometrien mit der LES. Der Vortrag schließt mit einer
Einschätzung der zukünftigen Entwicklung der LES zur Vorhersage von

Dr. Jörg Schumacher:

“Statistical and structural investigations in homogeneous

shear flow”

A statistically stationary and nearly homogeneous turbulent shear flow is established
by an additional volume forcing in combination with stress
free boundary conditions
in the shear direction. Both turbulent energy and enstrophy are station
ary to a much
better approximation than in previous simulations that use remeshing. Energy
spectra show that local isotropy is satisfactorily obeyed at the level of second
moments. However, transverse derivative moments of the streamwise turbulent
velocity up to order of seven yield increasing values for the range of Taylor Reynolds
numbers between 59 and 99. Additionally, first results on passive scalar fields with
constant mean gradient forcing in the homogeneous shear flow are presented for
idt numbers larger than unity. It is found that scalar derivative moments
decrease for increasing Schmidt number. Coherent structures of the scalar field are
identified that are related to its persistent derivative skewness.