HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Active Flow Control for Helicopters A. Le Pape, C. Lienard, J. Bailly

The tissue type resolving X-ray radiography and tomography can be performed even without contrast agents. The differences between soft tissue types such as kidney, muscles, fat, liver, brain and spleen were measured based on their spectral response. The Timepix based X-ray imaging detector WidePIX2×5 with 300 μm thick silicon sensors was used for most of the measurements presented in this work. These promising results are used for further optimizations of the detector technology and radiographic methods.

The authors were listed incorrectly in the article by Zanotti(1). The authors should have appeared in the following order:G. Gibertini, A. Zanotti, G. Droandi, D. Grassi, G. Campanardi, F. Auteri, A. Aceti and A. Le PapeThe article has now been updated with all authors listed in the correct order. This change has been made to the online and print PDF and HTML copies.

Summary Aims: Vaccination by aerosol inhalation can be used to efficiently deliver antigen against HPV to mucosal tissue, which is particularly useful in developing countries (simplicity of administration, costs, no need for cold chain). For optimal immunological response, vaccine particles should preferentially be delivered to proximal bronchial airways. We aimed at quantifying the deposition of inhaled particles in central airways and peripheral lung, and to assess administration biosafety. Participants, methods: 20 healthy volunteers (13W/7M, aged 24±4y) performed a 10-min free-breathing inhalation of 99mTc-stannous chloride colloid aerosol (450 MBq) in a buffer solution without vaccinal particles using an ultrasonic nebulizer (mass median aerodynamic diameter 4.2 μm) and a double mask inside a biosafety cabinet dedicated to assess environmental particle release. SPECT/CT and whole-body planar scintigraphy were acquired to determine whole-body and regional C/P distribution ratio (central-to-peripheral pulmonary deposition counts). Using a phantom, SPECT sensitivity was calibrated to obtain absolute pulmonary activity deposited by inhalation. Results: All participants successfully performed the inhalation that was well tolerated (no change in pulmonary peak expiratory flow rate, p = 0.9). It was environmentally safe (no activity released in the biosafety filter.) 1.3±0.6% (range 0.4–2.6%) of the total nebulizer activity was deposited in the lungs with a C/P distribution ratio of 0.40±0.20 (range 0.15–1.14). Conclusion: Quantification and regional distribution of inhaled particles in an aerosolized vaccine model is possible using radioactive particles. This will allow optimizing deposition parameters and determining the particles charge for active-particles vaccination.

The numerical simulation of dynamic stall around a 3D finite-span oscillating wing of constant OA209 airfoil section is compared to experimental results obtained in the ONERA F2 wind-tunnel, assuming fully turbulent flow. A deep dynamic stall case is considered for a reduced frequency typical of helicopter problems. A detailed comparison with the experimental data available (unsteady pressure distribution and velocity field) shows that the main flow features are captured by the numerical simulation, more especially the large spanwise flow component induced by separation.

The performance of vortex generators in reducing the helicopter drag was investigated by computational fluid dynamics and wind tunnel tests. Numerical simulations were carried out to define the layout and the position of vortex generators to be tested on a heavy-class helicopter fuselage model. A comprehensive experimental campaign including loads, pressure measurements and stereo particle image velocimetry surveys was then performed to assess the results of the numerical activity. Experiments confirmed the main trends predicted by computations. Tests for an array of vortex generators positioned on the model back-ramp showed a maximum drag reduction of about 5% with respect to the clean geometry. Moreover, the analysis of the velocity field and of the pressure distribution around the backdoor/tail-boom junction enabled to investigate the flow physics related to the effect of vortex generators on the fuselage drag.

Monoclonal antibodies (mAbs) are usually delivered systemically, but only a small proportion of the drug reaches the lung after intravenous injection. The inhalation route is an attractive alternative for the local delivery of mAbs to treat lung diseases, potentially improving tissue concentration and exposure to the drug while limiting passage into the bloodstream and adverse effects. Several studies have shown that the delivery of mAbs or mAb-derived biopharmaceuticals via the airways is feasible and efficient, but little is known about the fate of inhaled mAbs after the deposition of aerosolized particles in the respiratory system. We used cetuximab, an anti-EGFR antibody, as our study model and showed that, after its delivery via the airways, this mAb accumulated rapidly in normal and cancerous tissues in the lung, at concentrations twice those achieved after intravenous delivery, for early time points. The spatial distribution of cetuximab within the tumor was heterogeneous, as reported after i.v. injection. Pharmacokinetic (PK) analyses were carried out in both mice and macaques and showed aerosolized cetuximab bioavailability to be lower and elimination times shorter in macaques than in mice. Using transgenic mice, we showed that FcRn, a key receptor involved in mAb distribution and PK, was likely to make a greater contribution to cetuximab recycling than to the transcytosis of this mAb in the airways. Our results indicate that the inhalation route is potentially useful for the treatment of both acute and chronic lung diseases, to boost and ensure the sustained accumulation of mAbs within the lungs, while limiting their passage into the bloodstream.

This paper presents a Zonal Detached Eddy Simulation (ZDES) of a leading-edge stall airfoil in post-stall conditions. Different DES-type methodologies are first evaluated and discussed. The results obtained with the selected approach are presented and compared to detailed experimental results including unsteady pressure measurements and unsteady velocity flow field measurements obtained using Time-Resolved PIV (TR-PIV) and Laser Doppler Velocimetry (LDV). Important features of the flow are correctly captured by the computation and good agreements are observed with experiment on pressure distribution, separation location and aerodynamic forces. Unsteady content of the numerical simulation is also confronted with unsteady measurements showing that the St=0.2 frequency corresponding to the vortex separation shedding is correctly predicted in the computation. Detailed analysis of the mixing-layer and the wake properties highlights some deficiency of the computations that are fully analysed. The detailed comparisons of the ZDES result with the experimental data allow general requirements to be drawn for further improvements.

An OA209 airfoil equipped with an innovative deployable vortex generator device is investigated through static stall numerical simulations. Computations are performed by solving the Reynolds Averaged Navier-Stokes equations with the elsA code, which is developed by the Office National d'Etudes et de Recherche Aerospatiale-the French Aerospace Lab. Deployable vortex generator computations are compared to a wide set of experimental data, and the actuator effect on the airfoil boundary layer is highlighted. Detailed flow analysis provides an understanding of the vortex generation mechanisms, and the influence of initial vortex interactions and merging over the control effect is shown. The influence of the deployable vortex generator thickness on static stall control efficiency is finally investigated through simulations featuring a deployable vortex generator of reduced thickness.

The development of the Plasma Gun, generating Pulsed Atmospheric-pressure Plasma Streams inside long and small diameter tubes flushed with low gas flow rates, is reported with a special emphasis on the first demonstration and perspectives for in vivo endoscopic applications. The safe delivery and antitumor action of plasma have been achieved for in vivo colorectal and pancreatic cancers. Plasma delivery and plasma triggered inflammation inside mouse lungs were performed through an endoscopic protocol. The study of plasma splitting or transfer across metallic sections or dielectric barriers is documented and open up opportunities for self guided and low invasive plasma endoscopy.

The flow over an OA209 airfoil subjected to a sinusoidal pitching motion under dynamic stall conditions and equipped with an innovative deployable vortex generator actuator inducing stall control is experimentally and numerically investigated. Pressure and time-resolved particle image velocimetry measurements allow a detailed comparison to be performed between clean and controlled cases, including separation point detection and proper orthogonal decomposition analysis. Along with wind tunnel testing, numerical simulations are performed by solving the unsteady Reynolds-averaged Navier–Stokes equations with the ONERA elsA code. Computations are successfully compared to the experimental reference and bring further understanding of the deployable vortex generator actuation.

Compared to fixed wing aircraft, the helicopter is still a challenging configuration in terms of drag evaluation and understanding. In order to reduce and optimize the drag, the interactions between all components of fuselage and rotor head have to be analyzed. Thanks to the computational resources increase, the CFD becomes an efficient tool, complementary to the wind tunnel testing, to investigate different geometries and flow conditions. In the frame of the JTI CleanSky European project, the work presented in this paper is a preliminary task before the optimization and the drag reduction. It deals with the drag prediction of the fuselage and its main rotor head by CFD. The approach used here relies on a partitioning of the computational domain into near-body structured grids and off-body Cartesian grids, based on the Chimera method. The current work includes analysis of solutions for the isolated fuselage, the isolated rotor head and the complete configuration.

A new concept of active dynamic stall control is proposed, designed and experimentally tested on a OA209 airfoil model. The active control principle is based on leading-edge vortex generation in order to alleviate the dynamic stall vortex formed and convected at the leading-edge of an airfoil operating at a helicopter blade in fast forward flight. The active device aims to be used only during retreating blade side for dynamic stall flight conditions in order to avoid drag penalties on the advancing blade side. The designed actuator is a row of deployable vortex generators (DVGs) located at the leading-edge of the airfoil that fit the airfoil shape when retracted. Deployment is possible for different heights as well as different phases and frequencies with respect to the airfoil oscillation. The paper addresses the validation of the effectiveness of the devices to delay static stall and alleviate dynamic stall penalties. Results show a delay in static stall angle of attack of 3 deg and a reduction of negative pitching moment peak up to 60% for dynamic stall. The analysis of the experimental database indicates that different compromises between lift and pitching-moment can be achieved depending on the phase actuation of the DVGs.

A comprehensive experimental investigation of helicopter blunt fuselage drag reduction using active flow control is being carried out within the Clean Sky project. The objective is to demonstrate the capability of several active technologies to decrease fuselage drag by alleviating the flow separation occurring in the backdoor area of some helicopters (with pronounced ramp for backdoor loading). The work is performed on a simplified blunt fuselage at model scale. Several active flow control actuators are considered for evaluation: steady blowing, unsteady blowing (or pulsed jets), and zero-net-mass-flux blowing (or synthetic jets). Laboratory tests of each individual actuator are first performed to assess their performance and properties. The fuselage model is then equipped with these actuators distributed in eight slots forming a U-shape on the fuselage backdoor. This paper addresses the promising results obtained during the wind tunnel campaign, since significant drag reductions are achieved for a wide range of fuselage angles of attack. Moreover, a flow control strategy depending on the fuselage attitude is proposed. The link between the best actuation scheme for this attitude and the corresponding flow topology of the backdoor separation is also discussed.

The unsteady turbulent flow around a three-dimensional finite-span wing at stall is investigated by means of a zonal detached-eddy simulation. The computation captures a nondelayed development of unsteady structures at the beginning of the separation and accurately resolves the energy cascade in the fully turbulent mixing layer over a large frequency range. A comparison with the experimental data shows that the zonal detached-eddy simulation approach clearly improves the prediction of the mean flow, whereas classical Reynolds-averaged Navier–Stokes methods usually fail. A spectral analysis of pressure signals highlights the origin and the characteristics of the various unsteady mechanisms involved in this complex flow.

A joint comprehensive validation activity on the structured numerical method elsA and the hybrid numerical method TAU was conducted with respect to dynamic stall applications. To improve two-dimensional prediction, the influence of several factors on the dynamic stall prediction was investigated. The validation was performed for three deep dynamic stall test cases of the rotor blade airfoil OA209 against experimental data from two-dimensional pitching airfoil experiments, covering low-speed and high-speed conditions. The requirements for spatial discretization and for temporal resolution in elsA and TAU are shown. The impact of turbulence modeling is discussed for a variety of turbulence models ranging from one-equation Spalart–Allmaras-type models to state-of-the-art, seven-equation Reynolds stress models. The influence of the prediction of laminar/turbulent boundary layer transition on the numerical dynamic stall simulation is described. Results of both numerical methods are compared to allow conclusions to be drawn with respect to an improved prediction of dynamic stall.

A gradient-based method using a discrete adjoint of the Reynolds-averaged Navier-Stokes (RANS) equations is applied to the problem of helicopter blade shape optimization in hover. First, the RANS equations expressed in a specific coordinate system, adapted to the problem of a hovering rotor, are introduced. Then the numerical scheme used to solve the flow equations and the discrete adjoint equation is presented. They are then used within a gradient-based optimizer to perform rotor shape optimizations. The method is applied to the planform optimization of two different rotor blades: a classical rectangular blade and an innovative double swept blade planform. Design variables define the twist, chord, anhedral, and sweep distributions over the blade span, and the objective of the optimization is to improve the rotor figure of merit. The method demonstrated its efficiency in terms of central processing unit time and memory requirement and succeeded in providing interesting rotor blade shapes. The main interest of the present method is its ability to perform local optimization of isolated rotor in hover using an accurate computational fluid dynamics model and accounting for a large number of shape parameters.