Instability control of spanwise coherent vortical structures in the separating transitional boundary-layer

Das räumlich zeitliche Ablöseverhalten der transitionellen Grenzschicht des querangeströmten Kreiszylinders wird experimentell im subkritischen bis transkritischen Reynoldszahlbereich untersucht. Für die Erfassung des räumlichen Ablöseverhaltens werden Wanddruckmessungen durchgeführt und Anstrichbilder angefertigt. Das zeitliche Ablöseverhalten wird aus Kraftmessungen mit Hilfe einer piezoelektrischen Waage ermittelt. Als Ergebnis wird detaillierte Beschreibung der räumlichen und zeitlichen Skalen von kohärenten Ablösestrukturen und deren Wirkung auf Widerstand, Auftrieb und Strouhalzahl gegeben. Die beobachteten Wirbelstrukturen können durch passive bis aktiv-dynamische Verfahren in ihrer Entwicklung beeinflusst werden. Durch spannweitig periodisch aufgeprägte stationäre Störungen werden die Wirbelstrukturen in ihrer spannweitigen Entwicklung maßgeblich bestimmt, was allerdings zu keiner Widerstandsreduktion führt. Hingegen erweisen sich spannweitig und zeitlich periodisch eingebrachte Störungen in die ablösende Grenzschicht als effektive Instrumente zur Widerstandsreduktion insbesondere im subkritischen Reynoldszahlbereich

Active Flow Separation Control on a High-Lift Wing-Body Configuration - Part 1: Baseline Flow and Constant Blowing

This paper describes the influence of grid resolution and turbulence modeling for a 3D transport aircraft in high lift configuration with massive flap separation. The flap is equipped with spanwise slotted active flow control (AFC) devices to allow studies on active separation control. The effects of constant slotted blowing on the high lift performance are highlighted. Oil flow pictures from a mid-scale experiment in the low speed wind tunnel of Airbus in Bremen (B-LSWT) serve as a validation database for the baseline CFD results. RANS calculations are carried out with and without constant blowing boundary conditions. The baseline flow is also investigated with a time-accurate URANS approach. One of the major outcomes of the AFC study is the demonstration of the feasibility to simulate AFC concepts on a 3D configuration. Constant blowing shows the beneficial effect that separation can largely be suppressed because of the energy added to the flow on the suction side of the flap. This study serves as a preceding validation for the subsequent pulsed blowing approach treated in Part 2

Active Flow Separation Control on a High-Lift Wing-Body Configuration. Part 2: The Pulsed Blowing Application.

This contribution discusses the implementation of active flow separation control for a 3D high-lift wing-body configuration under atmospheric low-speed wind tunnel conditions. The slot-actuators are applied on the suction side of the trailing edge flap to prevent local flow separation. It is the consequent progression of the work presented in Part 1 of this paper. The active flow control (AFC) method of choice is now the pulsed blowing. The experimental results indicate that this AFC technique is feasible for such applications with a global performance enhancement. Here, the wind tunnel findings are briefly discussed while the emphasis is given on the numerical investigations. The verification of the URANS approach points out that the global enhancement through AFC may easily be overestimated by insufficient numerical convergence. Thus, high computational requirements are needed for a consistent numerical evaluation. The computational results highlight the ability of pulsed blowing at moderate blowing momentum coefficients to suppress the flow separation on the trailing edge flap and support the global aerodynamic enhancement. The numerical results show an acceptable agreement with the experimental results for this AFC application

Active Flow-Separation Control on a High-Lift Wing-Body Configuration

This contribution discusses the implementation of active flow-separation control for a three-dimensional high-lift wing-body configuration under atmospheric low-speed wind-tunnel conditions. The slot actuators are applied on the suction side of the trailing-edge flap to prevent local flow separation. The experimental results indicate that the pulsed blowing flow control technique is effective on the present configuration with a global performance enhancement. Numerical investigations are the focus of this article. The baseline case is characterized by substantial portions of separated flow. Thus, the influence of grid resolution and turbulence modeling is investigated. Based on this an intermediate mesh in combination with the Shear Stress Transport model gives the best compromise between quality and computational turnaround times. The steady Reynolds Averaged Navier Stokes (RANS) calculations carried out with constant blowing demonstrate the feasibility to simulate active flow control concepts. The key flow control method is the pulsed blowing. The verification of the unsteady RANS approach with active flow control shows that high computational resources are required for consistent numerical evaluations. The computational results highlight the ability of pulsed blowing at moderate blowing momentum coefficients to suppress the flow separation on the trailing-edge flap. The numerical results show an acceptable agreement with the experiments

Dynamic Flow Control Experiments for Innovative High-Lift Configurations on IHK/M-FLY Programs

Meaningful analysis of the performance potentials of dynamic flow actuators for increasing the lift is presently not possible without detailed wind-tunnel experiments on realistic airfoil shapes. The approach of the present work consists of combining advanced flow actuation approaches to delay flow separation on both the high-lift flap and the leading edge of the main wing of a state-of-the-art, two-element airfoil section and performing high-quality flow measurements at chord Reynolds numbers between 2 and 3 Million. The project objective is to demonstrate technology potentials to increase the maximum lift coefficient as well as the maximum angle of attack, and to identify possible interactions between the different flow actuation approaches along with guidelines for future aerodynamic design improvements and needs for further testing