Vlad Ciobaca

LAGOON: further analysis of aerodynamic experiments and early aeroacoustics results

This paper presents early results of an experimental aeroacoustic program recently performed in ONERA’s open-jet anechoic windtunnel CEPRA19 with a generic landing gear configuration. This program is the continuation of steady/unsteady flow measurements achieved in 2007 in ONERA’s F2 aerodynamic windtunnel (closed test section). Both experiments constitute the experimental phase of the LAGOON program (LA nding Gear NOise database for CAA validatiON ), currently supported by Airbus and involving ONERA and DLR (the French and German national aerospace research centres) and Southampton University, with the general purpose of evaluate up-to-date CFD/CAA techniques for airframe noise simulation, validated against an extensive experimental aerodynamic/acoustic database. The first point addressed in the present paper is the flow identification between both facilities, relying on limited aerodynamic measurements performed with a 5-hole probe and with onboard static pressure taps and unsteady pressure transducers. This flow identification was supported by a CFD study of the 3D flows in both windtunnels, performed by DLR. It is shown that there exist tiny differences between both flows. The second addressed point is the “signal-to-noise” ratio, or the ratio of the aerodynamic noise radiated by the model, to the background noise measured in the windtunnel without the model. It is shown that this ratio is globally satisfying, especially since this landing gear model with smooth shape is expected to be more silent than an actual landing gear with the same scale.

Active Flow Control for an Outer Wing Model of a Take-off Transport Aircraft Configuration - A Numerical Study

This contribution discusses the implementation of fluidic actuators that produce a pulsed outlet flow on a three dimensional model of the outer wing of a long-range transport aircraft at take-off, by high-fidelity numerical simulations. The leading-edge high-lift unprotected wing extension, including a wingtip device, designed for high performance at cruise flight, is subject to local flow separation at high angles of attack and low speed flight conditions. Active flow control (AFC) applied at the outer wing can prevent the formation of large turbulent flow separation and increase the aircraft lift to drag ratio (L/D), decrease the drag (D), and increase the angle of attack (AoA) for maximum lift (CLmax). The performed unsteady Reynolds-averaged Navier-Stokes (URANS) simulations prove the flow changes by the local AFC application and include a variation of the actuator’s geometrical setup. The results suggest a successful implementation on a transport aircraft and with an acceptable blowing momentum coefficient.

Separation Control on a High-Lift Airfoil using Vortex Generator Jets at High Reynolds numbers

This paper describes an active flow control wind tunnel experiment with a 2D two element high-lift airfoil at high Reynolds numbers of up to Re = 12:2 10 6 and for a corresponding Mach number of M = 0:2. Additional test cases with variations of the Reynolds and Mach number were also conducted. The measurements allow to study Reynolds and Mach number scaling effects. The wind tunnel experiments were performed in the cryogenic test facility DNW-KKK at Cologne, Germany. The main wing is equipped with vortex generator jets which are located close to the leading edge on the pressure side. The objective of the active flow control system is to suppress or delay a turbulent leading edge stall. The experiments clearly show that the active flow control system can prevent stall but the increase of the maximum lift coefficient decreases the higher the Reynolds number is. The benefits primarily depend on the flow rate. In most cases dynamic blowing is superior to static blowing. The actuation frequency seems to be more efficient with higher value. In range of the tested active flow control parameters the Mach number has a small influence.

Numerical Studies of Active Flow Control applied at the Engine-Wing Junction

This paper presents a numerical study of active flow control applied at the engine-wing junction to increase the high-lift performance of a generic full scale wind tunnel model representing a landing configuration of conventional airliners with engines mounted under backward swept wings. The use of UHBR (Ultra High Bypass Ratio) engines is currently one of the most promising approaches to further increase the efficiency of transport aircraft. However their large engine diameter prevents the mounting of leading edge devices at the engine-wing junction. This leads to a local flow separation on the wing suction side in the wake of the nacelle which may trigger the total wing stall and hence compromises the high-lift performance and therefore the total aircraft efficiency. At DLR (German Aerospace Center) numerical simulations of AFC (active flow control) at the engine-wing junction were conducted to study the capability of suppressing this local flow separation. The effects of steady and pulsed jet blowing with the same actuator geometry are compared. The results show that the steady blowing reduces the size of the nacelle-wake separation. However the pulsed blowing of the analyzed setup shows a low effect on the size of the nacelle-wake separation.

Computational and experimental results in the open test section of the aeroacoustic windtunnel Braunschweig

This paper discusses results of numerical simulations for low speed open tunnel test section in connection to wind tunnel experiments aiming to assess the computational accuracy. The investigations are performed for the aeroacoustic wind tunnel Braunschweig with and without a mounted experimental model. RANS simulations are performed within a CFD procedure developed to simulate open test sections. In the empty tunnel, measurements of the free shear layers and of the flow fields downstream the nozzle show a good agreement with the predicted flows. The jet core size and its position, as well as the velocity gradients in the mixing layer are simulated mostly accurate. Afterwards, the in-tunnel simulations with a 2D-high lift model are discussed. These reproduce very well the measured global lift force and local flow pressure distributions at moderate angles of attack but show discrepancies at maximum lift. In overall a good agreement of the numerical results compared to the experiments is achieved.

Wind Tunnel Experiments with Active Flow Control for an Outer Wing Model

This contribution discusses the implementation of fluidic slit-actuators as well as fluidic vortex generators on a three dimensional model of the outer wing of a long-range transport aircraft at take-off, by low speed wind tunnel experiments in the large test facility of DNW-NWB. The leading-edge high-lift unprotected wing extension, including a wingtip device, designed for high performance at cruise flight, is subject to local flow separation at high angles of attack and low speed flight conditions. Active flow control (AFC) applied at the outer wing can prevent the formation of large turbulent flow separation and increase the aircraft lift to drag ratio (L/D), decrease the drag (D), and increase the angle of attack (AoA) for maximum lift (CLmax). The recently performed experiments show the improvement in the aerodynamic coefficients by the local AFC applications. The drag coefficient decreases of up to 40% at fixed large AoA, while the maximum AoA is proved to increase in the order of 2°. The results suggest a successful implementation on a transport aircraft and with an acceptable blowing momentum coefficient.

Experimental and numerical studies of the low speed wind tunnel DNW-NWB’s open test section towards an aeroacoustic facility

This paper presents results of experimental and numerical investigations performed in the open-jet of the low speed atmospheric wind tunnel DNW-NWB prior the revision to accommodate a high-performance aeroacoustic test section. The investigations aim to assess the accuracy of the computations for open tunnel test sections and include a basic study of the empty tunnel as well as a study of a complex flow topology, the full 3D high-lift model of Do728 in landing configuration. The basic study addresses aerodynamic measurements of the open-jet flow in the empty tunnel which include pressure distributions along the tunnel axis and in cut planes downstream the rectangular nozzle as well as limited hot-wire measurements for the shear layers. The steady RANS simulations have a computational domain restricted to settling chamber, nozzle, test section and collecting system and are in very good agreement with the experimental findings. The pressure along the tunnel axis which has a bath-tube-shape-like with gradients after the nozzle and before the collector has still place for aerodynamic improvements. The investigations with the 3D high-lift Do728 model are devoted to cross-comparisons with the aerodynamic closed test section setup and to a better understanding of the flow deviations of the open-jet at high angles of attack and high lift force. It is shown that the flow is still well captured by the collecting system and that the numerics predict well the flow physics prior to maximum lift. The implications of this work are discussed related to the latter modification of the DNW-NWB facility to allow accurate aerocoustic testing as well as towards the optimization of the collecting system. First results of the ongoing work to optimize the collector’s geometry are presented.

Investigation of Active Flow Control Using a Differential Reynolds Stress Model

In the present work the predictive capabilities of different turbulence models for active flow control applications by means of vortex generator jets are evaluated by comparing numerical predictions with experimental data.With suitable turbulence model, the influence of orientation of actuator and jet velocity ratio are studied for a round jet actuator on a flat plate with zero pressure gradient. Finally, a two-element high-lift airfoil with a pair of vortex generator jets on the leading-edge of the main wing is studied with an emphasis on the interaction of longitudinal vortices with boundary layer under adverse pressure gradient.