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Institut für Aerodynamik und Gasdynamik

Arbeitsgruppe Transition und Turbulenz

Die Arbeitsgruppe Transition und Turbulenz führt numerische Grundlagenuntersuchungen zu Strömungsvorgängen hauptsächlich in 3D- und Überschall-Grenzschichten durch.

An jedem umströmten Körper bildet sich an der Körperoberfläche eine Grenzschicht aus, innerhalb der sich die Geschwindigkeit des strömenden Mediums aufgrund Reibung an die Geschwindigkeit der Körperoberfläche angleicht. Diese Grenzschicht verursacht im laminaren (schichtenartigen, ruhigen) Zustand einen erheblich geringeren Reibungswiderstand als im turbulenten (unruhigen, vermischenden) Zustand. In der Aerodynamik ist bei gepfeilten Flügeln die laminare Grenzschichtströmung schon dreidimensional, und die laminar-turbulente Transition läuft anders ab als in 2D-Grenzschichten. Bei Überschall­geschwindigkeit kommt aufgrund der großen Reibungswärme die Temperaturgrenzschicht hinzu. Die Instabilitätsvorgänge, die turbulente Strömung und Einflüsse/Kontrollmaßnahmen, z.B. Rauigkeit, Wandtemperatur, Druckgradient, Einblasen, Absaugen, Aufprägen nützlicher Längswirbel, Plasmaaktuatorik, werden durch direkte numerische Simulationen (DNS) mit einem eigenen Forschungscode auf Supercomputern untersucht.

Forschungsprojekte

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Control of 3-d boundary-layer transition

The basic mechanism in laminar-turbulent transition of 3-d boundary layers like on a swept wing or wind-turbine blades is crossflow instability. It leads to growing steady or travelling crossflow vortices that trigger turbulence by secondary instability. Control of instability and receptivity is investigated by application of spanwise rows of roughness, suction, or plasma actuators, the latter exerting a localized volume force on the flow.

 

Further reading:

VENKATA, S.Y., HEHNER, M.T., SERPIERI, J., BENARD, N., DÖRR, P.C., KLOKER, M.J., KOTSONIS, M. (2018) Experimental control of swept-wing transition through baseflow modification by plasma actuators. J. Fluid Mech. 844 R2-1-11, http://dx.doi.org/10.1017/jfm.2018.268.

DOERR, P.C., GUO, Z., PETER, J.M.F., KLOKER , M.J. (2018) Control of traveling crossflow vortices using plasma actuators. In: High Performance Computing in Science and Engineering ´17 (eds. W.E. Nagel, D.B. Kröner, M.M. Resch), Transactions (peer-reviewed) of the HLRS 2017, 289-306, Springer ; DOI 10.1007/978-3-319-68394-2_18.

DOERR, P.C., KLOKER, M.J. (2018) Numerical Investigations on Tollmien-Schlichting-Wave Attenuation Using Plasma Actuator Vortex Generators. AIAA Journal; 56: 1305-1309, 10.2514/1.J056779.

DOERR, P.C., KLOKER, M.J., HANIFI, A. (2017) Effect of Upstream Flow Deformation Using Plasma Actuators on Crossflow Transition Induced by Unsteady Vortical Free-Stream Disturbances. AIAA-2017-3114.

DOERR, P.C., KLOKER, M.J. (2017) Crossflow transition control by upstream flow deformation using plasma actuators. J. Appl. Phys. 121, 063303 (2017), http://dx.doi.org/10.1063/1.4975791.

DOERR, P.C., KLOKER, M.J. (2016) Transition control in a three-dimensional boundary layer by direct attenuation of nonlinear crossflow vortices using plasma actuators. Int. J. Heat Fluid Flow 61 (B), 449-465; 10.1016/j.ijheatfluidflow.2016.06.005.

DOERR, P.C., KLOKER, M.J. (2015) Numerical investigation of plasma actuator force-term estimations from flow experiments. J. Phys D: Appl. Phys. 48 (2015) 395203.

DOERR, P.C., KLOKER, M.J. (2015) Stabilisation of a three-dimensional boundary layer by base-flow manipulation using plasma actuators.  J. Phys D: Appl. Phys. 48 (2015) 285205.

FRIEDERICH, T., KLOKER, M.J. (2012) Control of the secondary crossflow instability using localized suction. J. Fluid Mech. 706, 470-495.

MESSING, R., KLOKER, M.J. (2010) Investigation of suction for laminar flow control of three-dimensional boundary layers. J. Fluid Mech. 658, 117-147.

WASSERMANN, P., KLOKER, M.J. (2002) Mechanisms and passive control of crossflow-vortex-induced transition in a three-dimensional boundary layer. J. Fluid Mech. 456, 49-84.

Receptivity of the boundary layer on a swept wing at low and high Re number

The fundamental receptivity to wall roughness and external disturbances is investigated in the boundary layer on a swept wing subject to crossflow instability. The knowledge of the maximum allowable roughness to not cause sudden transition to turbulence is a prerequisite for laminar flow control on a swept wing. Oncoming external disturbances are squeezed near the attachment line and the process which parts are taken up by the crossflow boundary layer is complex. The DNS strive to clarify these points at low and high Re number, including compressibility effects.

 

Further reading:

DOERR, P.C., KLOKER, M.J., HANIFI, A. (2017) Effect of Upstream Flow Deformation Using Plasma Actuators on Crossflow Transition Induced by Unsteady Vortical Free-Stream Disturbances. AIAA-2017-3114.

KURZ, H.B.E., KLOKER, M.J. (2016) Mechanisms of flow tripping by discrete roughness elements in a swept-wing boundary layer. J. Fluid Mech. 796, 158-194.

KURZ, H.B.E., KLOKER, M.J. (2016) Receptivity of a swept-wing boundary layer to steady vortical free-stream disturbances. In: New Results in Numerical and

Experimental Fluid Dynamics X (eds. A. Dillmann et al.), NNFM 132, peer-reviewed contributions to the 19. STAB/DGLR-Symposium, Munich, Nov. 2014, 227-236, Springer.

KURZ, H.B.E., KLOKER, M.J. (2015) Swept-wing boundary-layer receptivity to steady free-stream disturbances. AIAA-2015-3079.

KURZ, H.B.E., KLOKER, M.J. (2015) Discrete-roughness effects in a 3-d boundary layer on an airfoil investigated by DNS. Procedia IUTAM 14, IUTAM ABCM Symposium on Laminar Turbulent Transition, Rio de Janeiro, Brazil, Sept. 2014, 163-172, Elsevier.

KURZ, H.B.E., KLOKER, M.J. (2014) Receptivity of a swept-wing boundary layer to micron-sized discrete roughness elements. J. Fluid Mech. 755, 62-82.

Film cooling in supersonic boundary layers

Modern rocket nozzle extensions have to be actively cooled in addition to cooling channels below the wall. A cooling gas is injected normally or tangentially into the supersonic flow, in the latter case also with supersonic velocity. The resulting shear-flow field and the wall heat-load protection can be very complex depending on many parameters like the axial pressure gradient, the hot, main-gas boundary-layer state – laminar or turbulent –, the injection slot height, the step height, the cooling gas type, over- or underexpanded cooling jet.

 

Further reading:

WENZEL, C., SELENT, B., KLOKER, M.J., RIST, U. (2018)
DNS of compressible turbulent boundary layers and assessment of data-/scaling-law quality. J. Fluid Mech. 842, 428-468, http://dx.doi.org/10.1017/jfm.2018.179.

PETER, J.M.F., KLOKER, M.J. (2017) Preliminary work for DNS of rocket-nozzle film cooling. DLRK-2017-450178, urn:nbn:de:101:1-201710202849

KELLER, M., KLOKER, M.J. (2016) Direct numerical simulation of foreign-gas film cooling in supersonic boundary-layer flow. AIAA Journal 55, no. 1, 99-111; http://arc.aiaa.org/doi/abs/10.2514/1.J055115. 

KELLER, M., KLOKER, M.J., OLIVIER, H. (2015) Influence of cooling-gas properties on film-cooling effectiveness in supersonic flow. J. Spacecraft and Rockets 52, no. 5, 1443-1455; http://arc.aiaa.org/doi/abs/10.2514/1.A33203.

KELLER, M., KLOKER, M.J. (2014/15) Effusion cooling and flow tripping in a laminar supersonic boundary-layer flow. AIAA Journal 53, no. 4, 902-919; http://arc.aiaa.org/doi/abs/10.2514/1.J053251.

KELLER, M., KLOKER, M.J., KIRILOVSKIY, S., POLIVANOV, P., SIDORENKO, A., MASLOV, A. (2014) Study of Flow Control by Localized Volume Heating in Hypersonic Boundary Layers. CEAS Space Journal 6, Issue 3, p. 119-132.

KELLER, M.; KLOKER, M.J. (2013) Direct Numerical Simulations of Film Cooling in a Supersonic Boundary-Layer Flow on Massively-Parallel Supercomputers. In: Sustained Simulation Performance 2013 (eds. M.M. Resch, W. Bez, E. Focht, H. Kobayashi, Y. Kovalenko), 107-128, Springer.

KELLER, M., KLOKER, M.J. (2011) Influence of a favorable streamwise pressure gradient on laminar film cooling at Mach 2.67, Proc. 4th European Conference for Aerospace Sciences (EUCASS 2011), 10 pages, http://eucass.ru/cs/index.php/eu/2011, see ResearchGate.

Transition in hypersonic flow

In hypersonic flow, with the Mach number larger than 4, wall heating is a critical issue. The flow tends to be longer laminar in terms of the transition Reynolds number. However, surface roughness and a special disturbance mode, caused by a relative supersonic region near the wall where the disturbances travel faster than the fast sound wave, can lead to early turbulence. Understanding, avoiding or controlling hypersonic transition enables not to overdesign the thermal protection necessary due to safety reasons, and the payload ratio can then be larger.

 

Further reading:

GROSKOPF, G., KLOKER, M.J. (2016) Instability and transition mechanisms induced by skewed roughness elements in a high-speed boundary-layer. J. Fluid Mech. 805, 262-302, http://dx.doi.org/10.1017/jfm.2016.563.

GROSKOPF, G., KLOKER, M.J. (2012) Stability analysis of three-dimensional hypersonic boundary-layer flows with discrete surface roughness, NATO-RTO-MP-AVT-200-30:1-19.

GROSKOPF, G., KLOKER, M.J., STEPHANI, K.A. (2011)Temperature / rarefaction effects in hypersonic boundary-layer flow with an oblique roughness element, AIAA-2011-3251.

LINN, J., KLOKER, M.J. (2010) Investigation of thermal nonequilibrium on hypersonic boundary-layer transition by DNS. In: Laminar-Turbulent Transition (eds. P. Schlatter, D. Henningson), 7th IUTAM-Symposium, Stockholm, Sweden (2009), 521-524, Springer.

FEZER, A., KLOKER, M.J. (2003) DNS of transition mechanisms at Mach 6.8 – flat plate vs. sharp cone. In: West East High Speed Flow Fields 2002 (eds. D.E. Zeitoun, J. Periaux, J.A. Desideri, M. Marini), Proc. W.E.H.S.F.F. conference, Marseille, France, April 22-26, 2002, 434-441,CIMNE (Barcelona, Spain).

Einblasen von kühlem Stickstoff (Mach 1.8) durch eine rückspringende Stufe in eine heiße turbulente Grenzschichtströmung von gasförmigem Wasser (Mach=3.3), Anströmung von links. Oberfläche nach der Stufe: Konturen der momentanen Temperatur - rot: heiß, blau: kalt; Querschnitt: Stickstoffmassenanteil - weiß: 1, rot: null; Längsschnitt: Dichte - blau: klein, rot: hoch. (J.M.F. Peter, M.J. Kloker 2018). (c)
Einblasen von kühlem Stickstoff (Mach 1.8) durch eine rückspringende Stufe in eine heiße turbulente Grenzschichtströmung von gasförmigem Wasser (Mach=3.3), Anströmung von links. Oberfläche nach der Stufe: Konturen der momentanen Temperatur - rot: heiß, blau: kalt; Querschnitt: Stickstoffmassenanteil - weiß: 1, rot: null; Längsschnitt: Dichte - blau: klein, rot: hoch. (J.M.F. Peter, M.J. Kloker 2018).

Dr.-Ing. Markus J. Kloker

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Dr.-Ing.

Markus J. Kloker

Leiter Transition und Turbulenz