An Overview of Recent DLR Contributions on Active Flow-Separation Control Studies for High-Lift Configurations


V. Ciobaca , J. Wild (DLR)

This is an overview of flow control experiments and simulations for flow separation control on high-lift configurations performed over the last seven years at the German Aerospace Center within national and European projects. Emphasis is placed on the low speed atmospheric and cryogenic experimental setups using the DLR F15 high-lift airfoil and on the numerical verification and validation of the Reynolds Averaged Navier Stokes (RANS) solver TAU for active flow control (AFC) simulations.

Empirical Model for the Evolution of a Vortex-Pair Introduced into a Boundary Layer


T. Yehoshua, A Seifert (School of Mechanical Engineering, Faculty of Engineering TelAvivUniversity)

A linear, empirical, low-order-model was developed with the aim of describing the evolution of a 2D vortex-pair ejected into a boundary layer from a slot-in-the-wall. The model describes the evolution of a counter-rotating pair of Lamb-Oseen vortices in the proximity of a wall on which a cross-flow Blasius boundary layer exits. Two inputs from experimental measurements are used. First, the initial locations where the vortices form and pinch-off from the excitation slot boundary layers.

Numerical and Experimental Investigations of Flow Control in Axial Compressors


J. Marty, L. Castillon, J.-C. Boniface, (Onera)
S. Burguburu (Snecma)
A. Godard (Ecole Centrale de Lyon)

The increase of the thrust-to-weight ratio of modern gas-turbine engines results in higher loads and a reduced number of blades and stages for the compressor. The designer must ensure the acceptable performance of each compressor stage (efficiency and stable operating range) and control the rising risk of blade boundary layer separation.

Passive Control of Cavity Flows


S. Yamouni, C. Mettot, D. Sipp, L. Jacquin (Onera)

This paper deals with cavity flow physics and its passive control by means of a spanwise cylinder. Two configurations are considered. First, a laminar study of a flow over an unconfined square cavity at a low Reynolds number (7500) is presented. Global stability results are shown, allowing the identification of the driving mechanisms of the cavity flow: the aeroacoustic  feedback mechanism ([18]) and the acoustic resonance mechanism [4].

Closed-Loop Control of Fluid Flow: a Review of Linear Approaches and Tools for the Stabilization of Transitional Flows


D. Sipp (Onera)
P. Schmid (LadHyX Ecole Polytechnique)

Flow control is concerned with the targeted manipulation of intrinsic flow behavior to optimally satisfy prescribed objectives. This article will give an overview of the most common tools for the design of control strategies. We focus on linear control that is aimed at stabilizing fixed points of the Navier-Stokes equations, such as those existing in the case of transitional flows.

NARX Modeling and Extremum-Seeking Control of a Separation


J. Dandois (Onera)
P.-Y. Pamart (Snecma)

A numerical study concerning a SISO active closed-loop separation control on a rounded step is presented. A first study of the synthetic jet frequency effect on the separation shows that the mean separation bubble surface is minimized if the mean pressure of a single wall pressure sensor is maximized. With the aim of designing a closed-loop strategy for the control of the recirculation bubble, a NARX black-box model of the pressure signal is identified using a single unsteady RANS simulation.

Recent Onera Flow Control Research on High-Lift Configurations


V. Brunet, J. Dandois, C. Verbeke (Onera)

This paper concerns the recent and most representative work performed at Onera on the application of flow control technologies to high-lift systems of aircraft wings. Two different objectives are considered. First, keeping present architecture, flow control could either enhance the aerodynamic performance (mainly mean and stall lift coefficients) or simplify the mechanisms (flap gap or size).

Active Flow Control for Helicopters


A. Le Pape, C. Lienard, J. Bailly (Onera)

Several active flow control helicopter applications aimed at improving aerodynamic performance have been studied at Onera and are presented in this paper. The distinction between applications for non-rotating or non-lifting parts and for rotating parts is presented. A first part deals with the application of steady/unsteady blowing to simplified rotor hub and fuselage shapes. The objective is to achieve significant drag reduction by suppressing the flow separation occurring in these areas.

Overview of Onera Actuators for Active Flow Control


F. Ternoy, J. Dandois, F. David, M. Pruvost (Onera)

The purpose of this paper is to present an overview of existing actuators at Onera for active flow control. These actuators are used for various applications in wind tunnel tests, from 2D models to half-wing and helicopter models, for external or internal aerodynamics subjects.
Depending on the available volume in the models and on the aerodynamic requirements in terms of actuation magnitude and bandwidth from subsonic to transonic conditions, various technical solutions have been retained.

Boundary Layer Transition Control using DBD Plasma Actuators


A. Kurz, S. Grundmann, C. Tropea (Technische Universität Darmstadt)
M. Forte, A. Seraudie, O. Vermeersch, D. Arnal (Onera)
N. Goldin, R. King (Technische Universität Berlin)

This paper presents experimental and numerical investigations dealing with 2D boundary-layer transition control on an Onera-D airfoil using Dielectric Barrier Discharge actuators. These actuators generate a non-thermal surface discharge, which induces a momentum addition tangentially and close to the wall. In this case, the ability of this kind of plasma actuators to delay transition has been assessed using both steady and unsteady modes of actuation.